Enhancing Cancer Chemo‐Immunotherapy: Innovative Approaches for Overcoming Immunosuppression by Functional Nanomaterials

Chemotherapy is a critical modality in cancer therapy to combat malignant cell proliferation by directly attacking cancer cells and inducing immunogenic cell death, serving as a vital component of multi‐modal treatment strategies for enhanced therapeutic outcomes. However, chemotherapy may inadvertently contribute to the immunosuppression of the tumor microenvironment (TME), inducing the suppression of antitumor immune responses, which can ultimately affect therapeutic efficacy. Chemo‐immunotherapy, combining chemotherapy and immunotherapy in cancer treatment, has emerged as a ground‐breaking approach to target and eliminate malignant tumors and revolutionize the treatment landscape, offering promising, durable responses for various malignancies. Notably, functional nanomaterials have substantially contributed to chemo‐immunotherapy by co‐delivering chemo‐immunotherapeutic agents and modulating TME. In this review, recent advancements in chemo‐immunotherapy are thus summarized to enhance treatment effectiveness, achieved by reversing the immunosuppressive TME (ITME) through the exploitation of immunotherapeutic drugs, or immunoregulatory nanomaterials. The effects of two‐way immunomodulation and the causes of immunoaugmentation and suppression during chemotherapy are illustrated. The current strategies of chemo‐immunotherapy to surmount the ITME and the functional materials to target and regulate the ITME are discussed and compared. The perspective on tumor immunosuppression reversal strategy is finally proposed.


Introduction
Chemotherapy, a principal approach in cancer management, employs a wide range of pharmacological agents to combat malignant cell proliferation, serving as a vital component of DOI: 10.1002/smtd.202301005multi-modal treatment strategies for enhanced treatment outcomes.Several chemotherapeutic agents, including paclitaxel (PTX), doxorubicin (Dox), methotrexate (MTX), cisplatin, and 5fluorouracil (5-Fu), have been broadly applied as first-line drugs to treat various cancers owing to their effectiveness and potential of inducing immunogenic cancer cell death (ICD) specific immune responses. [1,2]However, chemotherapy faces critical challenges, including off-target systemic toxicities, [3] multi-drug resistance (MDR), [4] and immunosuppression, [5] which negatively impact the patient's prognosis and survival (Table 1).Such challenges are principally caused by the disruption of the tumor microenvironment (TME) during the process of chemotherapy.
Cancer, a disease induced by genetic mutation, is characterized by aberrant vasculature and hypoxic circumstances.The TME is a complex system comprising various cells (cancer, immune, endothelial, fibroblasts, and stromal cells), vasculature, extracellular matrix, and soluble components (cytokines, growth factors, chemokines, and interferons), collectively contributing to cancer growth and progression. [6]Notably, chemotherapy drugs can attack the immune cells, and restrict tumor infiltration of lymphocytes, producing immune resistance. [7]Moreover, chemotherapy can lead to desmoplasia that remodels the extracellular matrix, creating physical barriers to restrict drug penetration by formatting dense fibrotic tissues in TME, resulting in poor chemotherapy response. [8]In most cases, the subsequent low immunogenicity in TME results in the inability to establish long-term immuno-surveillance for monitoring and eliminating metastatic and recurrent tumors.
Cancer immunotherapy has demonstrated promising clinical responses due to anti-tumor immunity stimulation and enhancement.Immunotherapy has found extensive application in clinical settings for treating a range of cancer types, such as lung cancer, acute myeloid leukemia, colon cancer, and melanoma. [14]In particular, FDA-approved immune checkpoint inhibitors (ICIs) and chimeric antigen receptor T cell therapy (CAR-T) provide patients with prolonged survival and improved quality of life. [9,10]able 1.The advantages and disadvantages of chemotherapy and immunotherapy.
Low anti-tumoral immunity [11] ; High selectivity for tumor types [12] ; Slow process of immune responses [13] ; Immune resistance. [11]wever, low immune response rate, [11] slow process, [13] and high selectivity for tumor types [12] dramatically restrict the advance of immunotherapy in cancer patients (Table 1).Very interestingly, the advantages and disadvantages of chemotherapy and immnotherapy seem to complement each other to some extent.To be specific, immunotherapy demonstrates the potential to decrease the systematic toxicity and overcome the MDR of chemotherapy through reducing the chemo-drug dosages. [15]urthermore, immunotherapy has the remarkable capability to reverse tumor immunosuppression induced by chemotherapy, leading to long-lasting immunity for metastatic tumor surveillance and eradication.Complementally, rapid ICD induction by chemotherapy can potentially expedite the immune response process, whereas the resulting release of ICD-specific antigens can be harnessed as an in situ vaccine to improve the specific anti-tumoral immunity.Decreasing the immunization dose and priming duration to a large extent benefits immune resistance alleviation.Traditionally, combining chemotherapy and immunotherapy drugs (chemo-immunotherapy) has demonstrated significant advances in promoting antigen presentation and enhancing the immune response.In the last decade, bioactive materials with adjuvant-like activities and tumor immunosuppression reversal capacities have shown great success in enhancing anti-tumor immunity.Thus, the incorporation of novel immunomodulation strategies using immunomodulatory materials has emerged as a promising cancer chemo-immunotherapy, leading to the restoration of immunity for tumor surveillance and the reduction of MDR development. [16,17]Cancer chemoimmunotherapy cannot only improve the preponderance but also address the drawbacks of both modalities, offering tremendous potential for cancer treatment.
Several strategies have been developed to reverse tumor immunosuppression to improve chemo-immunotherapeutic outcomes.The combination of chemotherapy with immune checkpoint blockade (ICB) is the most appealing strategy to treat malignancies by directly blocking inhibitory checkpoint molecules, reversing tumor immunosuppression, and reviving adoptive T cells. [18]Similarly, tumor-associated macrophages (TAMs) reprogramming in combination with chemotherapy has demonstrated enhanced treatment efficacy attributed to the interruption of the immunoinhibitory network. [19]Cancer vaccination and multimodal therapy-mediated immunoaugmentation are also in combination with chemotherapy to achieve enormous synergies via remodeling the immunosuppressive tumor microenvironment (ITME) for eliciting robust immune responses. [20,21]he burgeoning development of nanotechnology has advanced cancer combinational immunotherapy to a new era as novel nanomaterials cannot only afford personalized targeting ac-cumulation of the therapeutics in the tumor tissues, [22] but also provide improved biocompatibility to overcome systemic toxicity. [23]Intriguingly, many functional nanomaterials have shown immune activation properties by promoting dendritic cells (DCs) maturation and antigen cross-presentation to attenuate tumor immunoinhibition and awaken the anticancer immune response, such as extracellular vehicles, [24,25] layered double hydroxides (LDHs), [26] dendrimers, [27] silica nanoparticles, polymeric nanoparticles, gold nanoparticles, [28] and so on. [29]Facilitation of loading immunostimulatory molecules (e.g., antibodies, antigens, and cytokines) into such nanoparticles further benefits the modulation of ITME to boost tumor immunogenicity.
In this review, we have summarized the recent strategies to modulate the ITME for boosting chemo-immunotherapy, which primarily involves ICB, macrophage repolarization, cancer vaccine, and multi-ICD (Figure 1).First, we introduce the critical factors that influence the intrinsic ITME and how chemotherapy exacerbates the immunosuppression in TME.Then, recent approaches to retract the immunosuppression are outlined for synergizing with chemotherapy, either by downregulating the suppressive genes with ICB, such as PD-L1, CXCR4, and NLG919, [30][31][32] or reprogramming the ITME by targeting and repolarizing TAMs.The combination of chemotherapy with other immune activators is also encompassed in this review, such as cancer vaccines, [33][34][35] and multi-modal therapeutics as ICD inducers. [36]We subsequently discuss the most recent advanced nanomaterials for enhanced chemo-immunotherapy and the constraints of current immunosuppressive alleviation strategies.Finally, we provide our perspectives on how to improve chemoimmunotherapy.

Two-Way Immunomodulation during Chemotherapy
The crosstalk between immune cells and tumor cells during immunotherapy is a dynamic and evolutionary process, especially in combination with chemotherapy.At the early stage, some chemotherapeutic treatments can potentially induce ICD to ignite immune responses. [37]Similarly, the chemotherapeutic agents are demonstrated to activate the stimulator of the interferon genes (STING) pathway and benefit the innate immunity, which is recognized as the first-line of host defense. [38]n the contrary, chemotherapy mostly targets rapidly dividing cells, including cancer, immune, and healthy cells, resulting in immune cell attack and immunosuppression, especially at the late stage of treatment, due to the inherent cytotoxic nature of chemotherapeutic drugs. [39]The immunosuppressive effects tremendously counteract the ICD-mediated immune responses, leading to insufficient immunity and poor prognosis.Thus, strategies that amplify the immunogenic effects while mitigating the immunosuppressive effects will be the option for effective chemo-immunotherapy.

ICD-Based Immunoaugmentation
[42] The molecules released during the ICD process are critical parameters for immune induction.The production of HMGB1 can enormously induce proinflammatory responses by signaling the crosstalk between immune cells and nonimmune cells via the receptors on the cell surface.In particular, the interaction of HMGB1 and TLR4 can stimulate monocytes and macrophages to release proinflam-matory cytokines to fight cancer cells. [43]More importantly, the exposure of ATP and CRT on the surface of dying cells is recognized as "find me" and "eat me" signals for antigen presentation cells (APC) to present anti-tumor antigens, and promote DC maturation, cytotoxic T lymphocyte activation and cytokine release (Figure 2). [44,45]These immune "danger signals" promote the phagocytosis of APC toward dying tumor cells.Tumor-specific antigens on the surface of dying cells inherit endogenous "vaccine-like" properties to provoke antigen cross-presentation between DC and T cells in the lymphoid organs (lymph nodes and spleen) and tumors. [46]The underlying mechanism of ICD induction by chemotherapeutic drugs is that chemotherapeutic agents can cause lysosomal alkalization, autophagy flux interference, and endoplasmic reticulum stress, which further mediate ICD-specific immune responses. [47]Intriguingly, chemotherapy-mediated ICD could further stimulate innate and adaptive immune responses to enhance anti-tumoral immunity against malignant tumors. [48]Copyright 2018 Elsevier.

Activation of STING Pathway
The stimulator of interferon genes (STING) pathway is closely related to innate immunity and STING activation can facilitate the stimulation of tumor-infiltrating lymphocytes, and remodel the TAM to immunostimulatory phenotype. [49]Dying tumor cells during chemotherapy can activate STING signaling, contributing to the production of type I interferon (IFN-I), which promotes the maturation and trafficking of innate immune cells, such as DC and NK cells.The activation of the STING pathway can also elicit innate and adaptive immunity by inducing the secretion of the immunoregulatory cytokines. [50]Many studies have elucidated the engagement of the STING pathway in improving cancer chemo-immunotherapy efficiency.Yu et al. demonstrated synergistic chemo-immunotherapy effects by polymeric phenanthriplatin drug-mediated DNA damage, activation of the STING pathway, and stimulation of innate and adaptive immune responses.Particularly, long-term surveillance was established for both primary and distant tumor elimination when PD-1 was incorporated owning to the immunogenic TME. [51]ikewise, a polymeric drug delivery system carrying chemotherapy agent SN38 and STING agonist DMXAA was fabricated to convert "cold" to "hot" tumors by activating the STING pathway and promoting cancer chemo-immunotherapy.When this system was further combined with anti-PD-1 therapy, a synergistic treatment efficiency for primary and lung metastatic tumors and prolonged survival rate were observed in melanoma and breast cancer tumor models. [52]These findings demonstrate that the tumor phenotype can be reshaped into the immunogenic state by STING activation, which can further enhance the immune responses.

Immunosuppression by Chemotherapy
The intrinsic ITME network comprises regulatory T lymphocytes (Tregs), myeloid-derived suppressor cells (MDSCs), and M2-type TAMs, collectively hindering infiltration of antigen-presenting cells (APCs) and T cells and counteracting the anti-tumor immunity. [53]The immunosuppressive effects can be aggravated by chemotherapy as the chemotherapeutic drugs can paralyze the immune cells and handicap the immune-stimulation process.Proverbially, chemotherapeutic drugs can inadvertently attack the bone marrow and depress the host immune system, leading to inadequate immune responses in cancer patients. [54]n the other hand, the proportion of pro-tumorigenic M2-TAM increases substantially following chemotherapy, accelerating immunosuppression and chemoresistance. [55]The condensed extracellular matrix can be also formed during chemotherapy, which hampers infiltration of APCs and T cells, causing chemoresistance and immune escape. [56]When chemotherapy reaches a plateau, the tumor builds an immunosuppressive niche to avoid immunosurveillance by adaptively producing a large amount of programmed death-1 ligand 1 (PD-L1) to counteract the immune checkpoint receptor programmed death-1 (PD-1). [57,58]This kind of chemotherapy thus inevitably exacerbates the ITME and recedes the anti-cancer immune responses.
The tumor immunosuppression during chemotherapy can vary depending on the specific drug, dosage, treatment schedule, and individual patient conditions.The ITME network ceases antigen cross-presentation and T-cell infiltration in the tumor tissues, leading to limited immune responses against malignancies. [59,60]Some specific classes of chemotherapeutic agents known to cause TME immunosuppression are listed below (Table 2): 1) Alkylating agents (e.g., cyclophosphamide (CTX), OXA, and cisplatin).These drugs work by inducing intra-strand DNA crosslink to damage the DNA of cancer cells and produce reactive oxygen species (ROS), but they can also affect healthy immune cells in a similar way. [61]Specifically, patients receiving a high dose of CTX reduced lymphocytes, attributed to myelosuppression. [62]Upregulation of PD-L1 has been discovered in patients with the standard cisplatin treatment, causing significant immune resistance. [63]Moreover, cisplatin has been validated to induce the differentiation of TAMs from immunogenic M1 phenotype to immunosuppressive M2 phenotype, leading to severe immunosuppression and poor prognosis. [64]) Anti-metabolite drugs (e.g., MTX, 5-Fu, and gemcitabine).
These agents disrupt the synthesis of essential cellular components, such as nucleotides or amino acids, leading to the inhibition of cell replication.However, they may also affect immune cells and other rapidly dividing cells in the body. [65]or example, they cannot only attack bone marrow but also facilitate the differentiation of monocytes into immunosuppressive MDSCs, depressing immune cell activities. [66]In the triple-negative breast model, 5-Fu is reported to increase the expression of immunosuppressive genes, such as PD-L1 and CD47, and deplete CD8 + T lymphocytes, which is similar to the immunosuppression mechanism of gemcitabine, Dox, and PTX. [67,68]Furthermore, gemcitabine has been demonstrated to foster the ITME by encouraging the growth and infiltration of M2-polarized macrophages in tumor tissues. [69]) Anti-tumor antibiotics (e.g., Dox, daunorubicin, and bleomycin).These drugs promote ROS production and interfere with DNA/RNA synthesis or replication, which can damage both immune cells and cancer cells. [70]Several antibiotics can induce the up-regulation of PD-L1 and M2-polarized TAMs, resulting in chemoresistance and the formation of ITME. [64]) Topoisomerase inhibitors (e.g., topotecan, irinotecan, and etoposide).These agents inhibit topoisomerase I and II enzymes, which play a crucial role in DNA replication and transcription. [71]As a result, they can inadvertently impact healthy immune cells.Furthermore, topoisomerase inhibitors display similar immunosuppressive effects by promoting PD-L1 expression. [72]) Mitotic inhibitors (e.g., PTX, docetaxel (DTX), and vincristine).These drugs target the process of cell division (mitosis) by disrupting the formation of the mitotic spindle.They can affect both cancer cells and healthy immune cells.

Reversal of Immunosuppression for Boosting Cancer Chemo-Immunotherapy
Several strategies have been exploited to overcome tumor immunosuppression and revive T cells by chemotherapy-based combination therapies, such as with ICB, TAM reprogramming, and immunostimulants.[75] By contrast, immunostimulants can activate the immune system and transform the tumor from an immunosuppressed "cold" state into an immunogenic "hot" state, inducing infiltration of cytotoxic CD8 + T lymphocytes in tumor tissues. [76,77]Accordingly, the anti-tumoral platform should be meticulously designed to improve chemo-immunotherapy effectiveness.In this section, we initially summarize the strategies that employ ICB and TAM repolarization to boost the immune response by compromising chemotherapy-mediated tumor immune-inhibition.Further, we discuss the combination of chemotherapy with multiple immune activators to reverse the ITME, primarily including cancer vaccines and multi-modal ICD-induced therapies (Table 3).

Chemotherapy with ICB
Numerous investigations have demonstrated that various tumors confront an inadequate immune response toward ICB therapy due to overexpressed immunosuppressive genes and constricted T-cell infiltration in tumors. [78,79]For example, combination with chemotherapy can significantly enhance the immunological response toward ICB, especially for ICBmonotherapy non-responsible cancer types. [62]Thanks to the prospective translation potential, ICB has been broadly explored to remit chemotherapy-mediated tumor immunosuppression for reinvigorating cytotoxic T lymphocytes.The combination of chemotherapy with several ICB antibodies (such as -PD1, PD-L1, -CXCR4, and -CD47) has demonstrated better treatment outcomes, such as efficiently inhibiting the primary tumor growth and pulmonary metastasis, and establishing long-lasting memory. [80]In particular, chemotherapeutic drugs and ICB antibodies selected for chemo-immunotherapy combination have been approved by the FDA for several cancer types, such as triplenegative breast cancer and non-small cell lung cancer, [81,82] implicating the high potential for clinical applications to elicit robust immunity.

PD-1/PD-L1
Evidence indicates that the PD-1/PD-L1 axis anticipates the differentiation of the immunosuppressive Tregs, contributing to tu-moral immunity arrest, host immunosurveillance suspension, and hampered immune responses. [83]The antibodies that inhibit the PD-1/PD-L1 checkpoint could restore tumor immunosurveillance and rejuvenate T cell activity, especially when it is combined with chemotherapy. [84]For instance, Zhang et al. devised a TME-responsive Dox controllable release nanoparticle as an ICD trigger and subsequently combined it with PD-1 antibody (PD-1) to revive ICD-mediated specific T cell activity, leading to inhibiting aggressive 4T1 tumor (Figure 3A). [85]Similarly, a hypoxia-responsive chemotherapy prodrug tirapazamine (TPZ)incorporated porphyrinic-MOF was engineered to activate the hypoxic tumor and prime the immune system for ablating the primary tumor.Combination with PD-L1 completely inhibited the growth of untreated distant tumors, ascribed to activating specific T cells. [86]Altogether, chemo-immunotherapy containing chemotherapeutic drugs and PD-1/PD-L1 inhibitors could effectively mitigate tumor immunosuppression and trigger T-cell immunity against cancers.Notably, combined immune stimulation by chemotherapyinduced ICD and ICB can successfully convert immunoinhibitory "cold" to immunostimulatory "hot" TME, which facilitates the cross-presentation of TAA to DC and T lymphocyte infiltration and improves immunotherapy outcomes. [87]Inspired by this observation, a two-wave strategy has been proposed to transfer "cold" through "warm" to "hot" by chemotherapy-ICD priming and checkpoint blockade boosting to stimulate anti-tumoral T cell immunity (Figure 3B).In another example, epirubicin conjugated polymer KT-1 was exploited for immunogenic chemotherapy, and PD-L1 antagonists MPPA were employed for checkpoint blockade immunotherapy to eradicate the primary tumor and prevent metastatic tumor. [88]Such a combined immunoaugmen-Figure 3. ICB-mediated alleviation of the ITME following chemotherapy for cancer chemo-immunotherapy.A) Schematic illustration of a pH-responsive drug delivery system to incorporate Dox-mediated ICD and PD-1 for eliciting tumor immunogenicity.Reproduced with permission. [85]Copyright 2021, American Chemical Society.B) Conversion of "cold" tumor to "hot" tumor by chemotherapy-ICD priming and PD-L1 antagonist boosting to improve the immune responses.Reproduced with permission. [88]Copyright 2020, Wiley-VCH.C,D) Schematic illustration of the combination of chemotherapy with PD-L1 silence.Reproduced with permission. [89]Copyright 2021, American Chemical Society.
tation strategy that employed chemo-ICD priming and was then followed by ICB boosting has validated its effectiveness for tumor eradication and immunosurveillance.
An alternative strategy for blocking the immune checkpoint to counteract the immune suppressive microenvironment is to silence the PD-1/PD-L1 gene by utilizing small interfering RNA.For example, Chen et al. designed a nanomedicine composed of arginine self-assembled nanofibers, chemotherapeutic prodrug camptothecin (CPT), and pshPD-L1/pSpam1 plasmids for improving immune cell infiltration into tumor tissues (Figure 3C).Plasmid pshPD-L1 attenuates the overexpression of PD-L1 for the alteration of T cells from the dormant state to the tumor-reactive state, whereas pSpam1 causes extracellular matrix degradation by generating hyaluronidase, contributing to T cell deep penetration within the tumor tissue.Double enhancement of antitumor immunity enabled by pshPD-L1/pSpam1 plasmids synergistically improved CPT-mediated chemo-immunotherapy efficiency (Figure 3D). [89]In addition, various chemotherapeutic drugs, such as DTX [90] and OXA, [91] were reported to combine with PD-1/PD-L1 to boost anticancer immunogenicity against different types of malignancies.

CXC Chemokine Receptor 4 (CXCR4)
Previous studies have demonstrated that CXC chemokine receptor 4 (CXCR4) is a crucial immunosuppressive signal that cannot only intervene in Tregs traffic and repress T cell response but also enhance the migration and invasion of cancer cells. [92,93]To reverse tumor suppression, a Dox-conjugated CXCR4 inhibitor-incorporated polymer nanoparticle was fabricated for the combination of chemotherapy and checkpoint blockade therapy against triple-negative breast cancer.The combination of Dox-ICD and CXCR4 inhibitor synergistically revitalized T-cell response by boosting CD8 + T-cell infiltration in tumor tissues, resulting in the complete elimination of orthotopic tumors and effective inhibition of metastatic tumors. [94]CXCR4 blockage has been testified to its efficaciousness in the inversion of tumor suppression for boosting chemotherapy-ICD mediated antigen-specific immune responses.

CD47
[97] Accordingly, CD47 antagonist (CD47) was employed to intensify the chemotherapy-ICD immune response triggered by OXA/photosensitizer prodrug incorporated tumoral enzymatic-responsive vesicle for chemo-immunotherapy.The OXA/photosensitizer could be released from the prodrug vesicle in the tumor tissues as an immunogenic primer upon encountering matrix metalloproteinase-2 for ICD induction.Then, ICD-mediated tumor immunity was augmented by CD47 blockade, which enabled effector memory T-cell production for primary tumor elimination and recurrence tumor prevention. [98]Silence of CD47 is an alternative approach to downregulate CD47 overexpression and intensify APC phagocytosis of apoptotic tumor cells for eliciting antitumor immune responses.Inspired by this idea, a PLGA-assembled nanomedicine was devised for the co-delivery of mitoxantrone (MTO) and CD47-targeted siRNA (siCD47).Chemotherapeutic drug MTO benefited "eat me" signal CRT expression during chemotherapy-ICD, whereas siCD47 restricted "don't eat me" signal CD47 expression, leading to robust antigen presentation and activation of APCs for the suppression of aggressive melanoma and colon cancer. [99]

IDO Inhibition
Excess expression of immunosuppressive checkpoint indoleamine 2,3-dioxygenase (IDO) is a principal factor for tumor immunosuppression and an indicator of poor prognosis in cancer patients as IDO can converse tryptophan to immunosuppressive kynurenine. [100]Recently, combining IDO inhibitors with chemotherapy has shown advanced benefits in improving therapeutic efficiency. [101]ang et al. constructed a pH-redox responsive size/charge changeable micelle co-loading IDO-inhibitor NLG919 and drug curcumin (Cur) to avoid immune escape and elevate tumor immunogenicity.The dual size/charge changeable property of the delivery system bestowed the loaded chemicals with prolonged blood circulation, deep tumor penetration, and optimized tumor endocytosis efficiency.In the acidic TME, released NLG919 prevented IDO-induced immune resistance, activated the effector T cell responses, and improved Cur treatment efficiency.Notably, the tumor recurrence rate of the nanomedicine (Cur)-treated group reduced to 37.5% compared to that (87.5-100%) of the control group, clarifying that long-term immunosurveillance was built for preventing tumor recurrence. [102]Similarly, Liu et al. constructed liposomal nanomedicine with high drug loading capacity and prolonged blood circulation by self-assembly of OXA and IDO inhibitor NLG919.The released OXA killed cancer cells directly, and NLG919 counteracted the ITME for improving colorectal cancer chemo-immunotherapeutic efficiency. [103]hese examples indicate that the blockage of IDO checkpoint is a promising approach to alleviate the ITME for overcoming chemotherapy-induced immunoinhibition.

Chemotherapy with TAM Repolarization
As is well known, TAM plays a significant role in TME as an indispensable part of tumor-infiltrating leukocytes.TAM-targeted immunomodulation [104] and TAM repolarization from the protumor M2 phenotype to the immune-promoting M1 phenotype show prosperous outcomes in cancer immunotherapy. [105,106]or instance, immunomodulator imiquimod (R837), an FDAapproved TLR agonist, can activate the TAM, elicit the adaptive immune response, and reverse ITME. [107]Hence, two types of micelle-based nanomedicines were fabricated for the delivery of chemotherapy drug Dox (intratumoral injection)/immunoadjuvant R837 (intravenous injection) to attack cancer cells and simultaneously stimulate TAM reprogramming to mitigate the immunosuppressive effects and enhance the adaptive immune responses.Micelle modification conferred Dox/R837 with favorable solubility, active targeting property, and colloid stability, leading to improved drug accumulation in TAM and enhanced T cell response for tumor inhibition. [108] the other hand, lactate depletion can induce TAM polarization and remodel ITME.Cai et al. developed camptothecin (CPT)/siMCT-4 co-loaded mesoporous organosilica nanoplatform for boosting tumor chemo-immunotherapy (Figure 4A).MCT-4 silencing enabled the accumulation of intracellular lactate for strengthening CPT-mediated tumor apoptosis and reduction of extracellular lactate for inducing M2 type to M1 type polarization (Figure 4B), leading to activated CD8 + T cells for lung metastasis inhibition (Figure 4C). [17]Collectively, reshaping TAM from M2 to M1 phenotype displays a prospective blueprint in cancer chemo-immunotherapy by restoring anti-tumor immunity.

Chemotherapy with Cancer Vaccine
Immunization with anticancer vaccine holds great advances in the stimulation of tumor-specific immunity and establishment of long-term memory for monitoring tumor recurrence and metastasis.The duration and level of immune responses differ under various immunization modalities, in which subcutaneous injection of vaccine is a slow, long-term process with strong immune responses in the lymphoid organs.In contrast, intravenous injection is a rapid, short-term induction method with comparatively weak immune responses. [13]In comparison, ICD-induced immune response is quite weak and can only maintain a very short period (appropriately one week). [109]By sharp contrast, a cancer vaccine comprised of specific antigens and adjuvants can potentially enhance tumor-specific immune responses and prolong the immune response for years.Therefore, the combination of ICD with cancer vaccine under the optimized immunization approach can elicit ICD-based rapid induction and maintain vaccine-mediated durable immune responses.
Wang et al. demonstrated a nanomedicine/nano-vaccine colocalized delivery strategy to simultaneously initiate tumor immunogenicity by chemotherapy-ICD and boost the postoperative immune responses by adjuvants (Figure 5A).A Curloaded heat-responsive hydrogel was designed to completely cover the tumor surgical bed and eliminate the residual cells by chemotherapy-ICD (Figure 5B).The CpG/antigen peptide was co-encapsulated in the hydrogel to trigger DC maturation and vaccine-specific T-cell responses (Figure 5C).As a consequence, the nanomedicine/nano-vaccine co-localized delivery strategy enabled the amplification of CD8 + T lymphocyte infiltration and the prevention of pulmonary metastasis (Figure 5D). [110]he chemo-immunotherapy efficiency of chemotherapy-ICD with vaccine through different immunization approaches has been also investigated.It is well known that CTX is a broadly used chemotherapy agent with ICD-inducing capability and the released TAA from the apoptotic cells acts as a specific vaccine to cause an antigen-specific immune response.A PLEL hydrogel-based platform was established by combining CTX-ICD and an immune-stimulation vaccine for amplifying cancer chemo-immunotherapy in a "prime-boost" manner.Thermalsensitive CTX-loaded PLEL hydrogel (CTX@PLEL) was designed as an ICD inducer for tumor immunity priming, whereas CpG-loaded hydrogel (CpG&TL@PLEL) was prepared as a vaccine for boosting to elicit robust antitumor immune responses (Figure 6A,B).Copyright 2021, Elsevier.
the "prime-boost" (CTX@PLEL + CpG&TL@PLEL) group, attributed to the systemic immunity induced in the "prime-boost" strategy (Figure 6C,D).Moreover, the chemotherapy-ICD priming plus vaccine boosting strategy alleviated CTX-induced systemic toxicity and enhanced memory CD8 + T cell response to prolong survival and prevent recurrence (Figure 6E). [111]The results indicate that the cancer vaccine significantly boosts the immune responses primed by chemotherapy-ICD, leading to effective treatment of primary and distant tumors and long-term surveillance.
Another example has implemented a double enhancement strategy to overcome tumor immunosuppression by intravenous injection of the cancer cell membrane (CCM)-cloaked Dox (Dox@PM) and intratumoral injection of DC recruiter composed of lymphotactin (XCL-1) incorporated alginate (XCL-1@ALG).On the one hand, CCM encapsulation promoted tumor targeting, which strengthened Dox-mediated chemotherapy-ICD effects and tumor-specific antigen release.On the other hand, XCL-1 guaranteed the recruitment of XCL-1 + DC cells to the tumor tissue, which benefited the antigen cross-presentation and T-cell activation.A higher CD11c antibody signal was observed in the tumors treated with XCL-1@ALG, demonstrating rapid in situ DC recruiting.In vivo results showed that DC recruitment in the Dox@PM+XCL-1@ALG group was 1.9-fold higher than that of the Dox+XCL-1 group, clarifying that the combination therapy intensified the immune response for tumor inhibition. [112]The data indicate that the cancer vaccine facilitated DC recruitment and engulfed tumor-specific antigens produced by chemotherapy-ICD, leading to enhanced chemoimmunotherapy efficiency.

Multi-Modal Therapy for ICD Induction
Owning to low delivery efficiency and immunosuppressive microenvironment, ICD induction by chemotherapy alone only stimulates weak or moderate immune responses, leading to inadequate therapeutic outcomes, especially for distant tumors. [115]herefore, approaches to amplify tumor immunogenicity have been developed for cancer immunotherapy.To improve immunogenicity, multi-modal therapies are incorporated as ICD inducers for strengthening anti-tumoral immune responses, such as radiotherapy, phototherapy, [116,117] and sonodynamic therapy (SDT). [118]For example, ICG/PTX co-loaded nanomedicine was developed as an ICD inducer for triple-negative breast cancer chemo-photo-immunotherapy. Upon laser irradiation, ICG/PTX co-induced ICD by inducing ROS-mediated ER stress and overcame ITME via suppressing Treg expression and boosting cell death receptor Fas (Figure 7A). [113]The dual drugloaded nanomedicine exhibited unexpected targeting delivery properties and facilitated CRT translocation and HMGB1 release in vitro and in vivo (Figure 7B), causing higher DC maturation and enhancing intratumoral CTL infiltration (Figure 7C,D).
In recent years, SDT has become an emerging treatment with deep tissue penetration and caused tumor cell death by endoplasmic reticulum (ER) stress, reactive oxygen species  [113] Copyright 2020, Wiley-VCH.
(ROS) production, and the subsequent ICD responses. [119]hang et al. engineered chemotherapy/SDT/phototherapy ICDinducing nanoparticles by encapsulating oxygen carrier (OXP) and ICG in PLGA for combined activation of ICD to fight primary and distant ovarian cancer in a bilateral mouse model. [114]These studies demonstrate that the multi-ICD induction approach significantly improves anti-tumoral immunity against tumors.
In summary, the tumor immunosuppression during chemotherapy can be evidently counteracted by ICB antibodies, and the decline of immunosuppressive cells, such as MDSCs and M2-phenotype TAMs, to enhance the immunogenicity.Other immune amplification strategies have demonstrated high effectiveness in stimulating robust immune response, including multi-modal therapies and the combination of chemotherapy with immune-modulating cancer vaccines.More significantly, the involvement of nanomaterials to some extent facilitates the ITME reversal process, achieved either by augmenting tumor accumulation of therapeutic drugs through passive targeting or by leveraging the immunostimulatory effects of the functional components (Table 3).In the next session, we will particularly depict the advantages, disadvantages, and biomedical applications of the functional materials in cancer chemo-immunotherapy (Table 4).

Advanced Functional Materials for Enhanced Chemo-Immunotherapy
Advanced functional materials empower the therapeutic drugs with advantages to regulate the ITME and enhance cancer chemo-immunotherapy efficiency, [120,121] including 1) multiple payloads with high loading efficiency; 2) improved colloidal sta-bility and biocompatibility; 3) controlled release and prolonged blood circulation; 4) targeting property by specific ligands and enhanced permeability and retention (EPR) effect; [122] and 5) tumor imaging capability with contrast agents. [123]In addition, a variety of nanoparticles inherit certain adjuvant activities for immune stimulation, which could potentially benefit cancer immunotherapy, such as cell membranes, layered double hydroxides, and other nanomaterials (Table 4).

Cell Membrane
[128] Cell membrane endows the chemo-immunotherapy nanomedicines with favorable functions, including homologous targeting, antigen-specific immunity (cancer cell membrane), and colloidal stability.A variety of cell membrane types is exploited for biomedical applications, such as cancer cell membrane (CCM), [129] red blood cell membrane (RBC), [130] and immune cell membrane. [131]Despite these advantages, the limited productivity of cell membranes to a large extent restricts their potential for clinical application and translation.More importantly, it is crucial to address safety concerns associated with cell membrane vesicles, as incomplete removal of genetic components could potentially lead to tumorigenesis and other adverse effects.
Cell membrane encapsulation is considered a potent approach for intensifying the treatment efficiency by combining chemotherapeutic chemicals with immunomodulators, such as IL-2 and PD-L1. [132]Zhang's group constructed a CCM-encapsulated interleukin-2 (IL-2)/PTX co-loaded nanogel for targeted chemo-immunotherapy.Due to the homologous targeting effects of CCM, the CCM-coated delivery system exhibited 1.59-fold drug accumulation in the tumor tissue in comparison with the control group, which benefited PTX-mediated chemotherapy and ICD.The ICD-induced immune response was further enhanced by IL-2 (2.77-fold) via enhancing T cell activation and proliferation, contributing to the eradication of primary tumor and lung metastasis. [133]Zhou et al. employed RBC to carry Dox and hemoglobin (Hb) for reversing the suppressive TME and improving chemo-immunotherapy against lung metastasis.Following Hb-mediated TAM targeting via the CD163 receptor, the released O 2 alleviated TME hypoxia, leading to M2-TAM depletion, natural killer cell/T cell activation, and PD-L1 downregulation. [134]side from the tumor-targeting property provided by the tumor cell membrane, hybrid [135] or engineered cell membranes [136] with affixed functions have been proposed for amplifying cancer chemo-immunotherapy.It is well known that glycolysis within cancer-associated fibroblasts plays a significant role in tumor progression, and the blockage of the glycolysis process not only retards tumor growth, but also mitigates ITME by eliminating lactate.Thus, the 4T1-3T3 hybrid cell membrane was prepared by the integration of breast cancer cell (4T1) and activated fibroblast (3T3) membranes, demonstrating dual-targeting ability toward tumor cells and cancer-associated fibroblasts.To further modulate the immune TME, PTX and glycolysis inhibitor PFK15 were co-load on the hybrid cell membrane for targeted lactate reduction and TAM reprogramming, resulting in elevated chemo-immunotherapy. [137] Folate engineering on cell membranes enhances specific TAM targeting via folate receptor-mediated endocytosis, offering tremendous potential for cancer immunotherapy by decreasing M2-TAM.A TAM-targeting nanoparticle was engineered by decorating folate on RBC to deliver PTX/NLG919 to triply augment the immune responses.Upon arrival at TME, PTX-induced ICD and TAM were depleted whereas NLG919 facilitated the reversion of ITME, collectively contributing to effector T cell activation for enhanced melanoma chemo-immunotherapy. [138] Moreover, engineered cell membranes can harbor APCs for membrane-specific antigen delivery and immune activation to improve immunotherapy outcomes.As an example, CRToverexpressed CCM was isolated from cancer cells treated with Dox for inducing ICD-mediated CRT exposure in vitro.Such CRT-rich CCM can deliver adjuvant R837 to DC cells, and promote antigen presentation, leading to enhanced immune responses.The drug-free CRT-CCM nanovaccine not only reduces the systematic toxicity caused by chemotherapy in vivo, but also boosts antigen-specific immune response, shedding light on the prospects of cancer chemo-immunotherapy. [139]

Layered Double Hydroxide (LDH)
LDHs are brucite-like compounds with a general formulation of , where M 2+ and M 3+ represent divalent and trivalent metal cations and A n− an nvalent interlayer anion.LDH has shown prosperous biomedical applications owing to their large surface area, intercalation and ion exchange for drug loading, and low cytotoxicity. [140]LDH nanoparticles are not only a carrier for delivering agents for chemotherapy, phototherapy, [141] and gene therapy, [142] but also efficient adjuvants for the stimulation of immune responses. [143]DH provokes immune functions by 1) neutralization of acidic TME, 2) obstruction of tumor cell autophagy, and 3) elicitation of long-term immune responses by forming depots and inducing unremitting antigen stimulation. [144,145]Hence, LDH nanoparticles demonstrate promising potential in cancer Figure 8. LDH nanoparticles for cancer chemo-immunotherapy.A) Schematic illustration of LDH deacidification mediated TAM repolarization for tumor growth inhibition.B) Flow cytometry analysis of M1 phenotype (F4/80 + CD86 + ), and M2 phenotype (F4/80 + CD206 + ) TAM. Reproduced with permission. [146]Copyright 2023, Elsevier.C) Antigens released by LDH-mediated photo-chemotherapy act as in situ vaccines to stimulate CD8 + T cells for preventing tumor lung metastasis.D,E) The growth curve of the primary and distant tumor with different treatments.F) Representative images of the dissected lung in different groups.Reproduced with permission. [147]Copyright 2019, American Chemical Society.
immunotherapy through immune stimulation and modulation of the ITME.
To attenuate the ITME, Liu et al. introduced Dox-loaded NiFe-LDH nanosheets for chemodynamic immunotherapy.The NiFe-LDH nanosheets exhibited excellent deacidification ability to transfer acidic to neutral TME, leading to M2-to-M1 TAM repolarization.The released Fe 3+ during the deacidification process further facilitated Dox-mediated chemodynamic therapy through the Fenton reactions (Figure 8A).As a consequence, the expression of M1 TAM marker CD86 was increased whereas M2 TAM marker CD206 was reduced significantly, indicating TAM was reprogrammed, which further induced CD8 + T cell activation (Figure 8B). [146]Our group also demonstrated a three-inone LDH nano-vaccine integrated with Dox/ICG/CpG for cancer chemo-phototherapy (Dox/ICG) and antitumor immunity activation (CpG) (Figure 8C). [147]The multifunctional LDH nanovaccine effectively eliminated the primary tumor and retarded distant tumor growth by strengthening the in-situ immunity (Figure 8D,E).More remarkably, negligible tumor metastasis in the lung was observed whereas many tumor nodules appeared in the lung for the control group of mice, demonstrating the immune adjuvant CpG significantly enhanced the immune responses (Figure 8F).

Mesoporous Silica
Owing to the inherently high surface area, tailorable surface property, and preferable biocompatibility, mesoporous silica nanoparticles are ideal candidates for drug delivery and cancer chemo-immunotherapy. [148,149] The combination of immunogenic chemotherapeutics with ICIs in mesoporous silica nanoparticles has exhibited a strong immune stimulation capacity for cancer chemo-immunotherapy through simultaneously Reproduced with permission. [155]Copyright 2023, Wiley-VCH.
increasing ICD and reversing the tumor immunosuppressive microenvironment. [150,151]However, the approval of mesoporous silica nanoparticles by the FDA has been suspended due to their unknown biodistribution, limited biodegradation, and obscure clearance. [152]It is imperative to make effects on the investigation of clearance mechanisms to advance their clinical trials in the future.
A ROS/thermal responsive mesoporous silica nanoparticle with controllable size and transformable charge was designed for deep tumor penetration, prolonged blood circulation, and facilitated Dox/ICG release under NIR laser irradiation for inducing ICD in the tumor tissues.By further incorporating with PD-1, the immune response was significantly enhanced for preventing pulmonary tumor metastasis. [153]Similarly, cisplatin-loaded mesoporous silica with a lipid bilayer coating was validated to effectively target orthotopic pancreatic cancer and induce ICDspecific immune responses, which was further boosted by PD-1 combination, resulting in prolonged survival outcomes. [154]esoporous silica has also been reported to integrate TAM repolarization components to attenuate the ITME and stimulate anti-tumoral immunity by transforming macrophages from immunosuppressive M2 to immunostimulatory M1 phenotype.For example, Chen et al. fabricated thiolated mesoporous sil-ica with mitomycin C (MMC) loaded as an immunoadjuvant to benefit the chemo-immunotherapy outcomes via enhancing mucoadhesive effect, opening tight junction, and further switching M2-to-M1 type macrophages (Figure 9A). [155]The redistribution of claudin-4 implicated that thiolated mesoporous silica can induce the opening of tight junctions and enhance permeation (Figure 9B).Remarkably, mesoporous silica nanoparticles treated cells showed a significant increase in M1-TAM markers compared to the control group, suggesting great potential for amplifying tumor immunity (Figure 9C,D).In addition, silica-based nanoparticles have been demonstrated to reshape the ITME and improve the chemo-immunotherapy efficacy by delivering immunomodulators, such as TLR agonists, [156] and T cell growth factor IL-2. [157]

Lipid
Lipid nanoparticles are FDA-approved carriers for the delivery of drugs, small and large molecules in the clinic, including anticancer drugs and COVID-19 mRNAs. [158]Lipid nanoparticles exhibit unexceptionable properties, including high drug loading, prolonged blood circulation, preferable biocompatibility,  [163] Copyright 2021, American Chemical Society.
and targeted delivery through enhanced permeability and retention (EPR) effect. [159]Hence, lipid nanoparticles have attracted intensive attention for the delivery of immunomodulators to regulate the ITME and strengthen chemo-immunotherapy outcomes.For example, Peer et al. demonstrated a PD-L1 modified lipid nanoparticle for dual-targeting cancer cells/myeloid tumor cells and delivering Dox and heme oxygenase-1 (HO1) silencing RNA, contributing to simultaneous chemo-ICD-boost and immune-boost against melanoma.Silencing HO1 not only enhanced chemotherapy-ICD efficiency but also reprogrammed TAM into immunogenic subtype, co-stimulating CD8 + T lymphocytes and resulting in primary tumor elimination and lung metastasis prevention. [160]Nevertheless, lipid nanoparticles exhibit poor stability in vivo and high sensitivity to temperature and pH, which may hinder their medical and commercial translation.

Metal-Organic Framework (MOF)
Metal-organic framework (MOF), an emerging class of organicinorganic hybrid porous materials, comprises metal-containing nodes and organic ligands and is widely applied for biosensing, drug delivery, imaging, and cancer therapy due to their unique advantages, including high surface area, tunable pore scale, excellent thermal stability, and easy surface functionalization. [161]n particular, porphyrinic MOF nanoparticles are heralded as the next generation of photodynamic therapy agents and effective ICD inducers to increase cancer immunotherapy efficiency.When combined with chemotherapy, the porphyrinic MOF platform demonstrates the potential to substantially decrease the dosage of chemotherapeutic drugs and mitigate systematic cytotoxicity. [162]o enhance the immunogenicity, the Tian group devised a photo-responsive ICD-inducible MOF nanomedicine loaded with chemotherapeutics MTO and combined it with PTT for double enhancement of ICD-mediated immune response.Meanwhile, an immunosuppression modulator anti-OX40 antibody (OX40) was incorporated to downregulate Tregs, MDCSs, and M2 macrophages while improving the proportion of DCs, T cells, and the secretion of cytokines for boosting immunotherapy efficacy (Figure 10A). [163]As a result, ICD was evidently enhanced to counteract the suppressive effects of immunosuppressive cells, and the anti-tumoral immunity was further elevated by OX40mediated ITME reversal (Figure 10B,C).As expected, the photochemo-immunotherapy mediated by MOF nanomedicine contributed to primary tumor eradiation, abscopal tumor inhibition, and lung metastasis tumor prevention (Figure 10D).All these studies demonstrate the promising potent of MOF in eliciting anti-cancer immune responses.

Others
Other functional nanomaterials, including hydrogels, polymer, and iron oxides, have exhibited notable efficacy in cancer chemoimmunotherapy, attributable to their distinct characteristics. [164]he hydrogels are 3D frameworks comprised of hydrophilic polymers, showing high drug loading, controllable drug release, and excellent biocompatibility and biodegradability. [165]For instance, a hydrogel-based nanoplatform was demonstrated to achieve programmed delivery of Dox and CpG in the tumor tissues for regulating the ITME and boosting chemotherapy-mediated ICD immune responses.As a result, a reduction of the immunosuppressive cells, including MDSCs and M2-TAMs, and an increase of CD8 + T lymphocytes was discovered, indicating beneficial therapeutic responses. [166]olymer nanoparticles have attracted increasing attention in biomedical applications due to their profitable merits, including controllable drug release, easy modification with functional components, excellent biocompatibility and biodegradability, and prolonged blood circulation. [167]As an example, three-in-one polymer nanoparticles were designed for the combination of chemotherapy with immune checkpoint inhibition for potent chemo-immunotherapy.The polymeric nanoparticles were comprised of two different chemotherapy drugs (OXA/gemcitabine) for chemotherapy and subsequent induction of ICD, and a small molecular inhibitor (CQ) for targeting PD-L1, repressing Pglycoprotein to reduce multidrug resistance and finally boosting OXA/gemcitabine mediated ICD. [168]Such a polymer-based drug delivery system effectively elicited a robust immune response by simultaneously inducing ICD and reversing the tumor suppression via inhibiting PD-L1 expression.
Iron oxide nanoparticles are also approved by the FDA for clinical uses, such as in iron deficiency treatment and as magnetic resonance imaging contrast agents. [169]An efficient drug delivery system was also constructed by loading Dox and a TLR3 agonist on endoglin-binding peptide-modified iron oxide for tumor and DC dual-targeting to boost the immune responses.The iron oxide nanoparticles could multiply improve chemo-immunotherapy through the endoglin-binding peptide-mediated dual targeting, Dox-induced DNA topoisomerase II inhibition, TLR3 activation, and the stimulation of innate and adaptive immunity. [170]

Conclusion and Perspectives
To overcome the systemic toxicity and MDR of chemotherapy, efforts have been made to alter the ITME and intensify the antitumoral immunogenicity for chemo-immunotherapy.We have presented current approaches for the rescission of tumor immunosuppression, either by regulating the ITME with ICB and TAM repolarization or eliciting the immune system through immune activators, such as cancer vaccines and multi-modal therapies as ICD inducers.The advent of nanotechnologies further renders the anticancer agents with targeting delivery function, exhilarating biocompatibility, and adjuvant-like immunostimulation properties, leading to prolonged blood circulation and improved tumor accumulation for cancer chemo-immunotherapy.Despite tremendous achievements in improving chemo-immunotherapy outcomes via remodeling the ITME, there are still several challenges in further research prior to the translation into the clinic, as follows.

Immunomodulation Profile of Chemotherapeutic Drugs
ICD-induced chemotherapeutic drugs can function as a doubleedged sword in regulating antitumor immune responses.They can promote strong immune responses through inducing ICD or activating STING, but also severely refrains the host defense system and/or accelerate the proliferation of immunosuppressive cells, such as Tregs, MDSCs, and M2-TAMs.[173] The function of these agents on immune cells is a dynamic and evolutionary process, making it difficult to understand the final effects of chemotherapeutic agents on the immune system.Thus, a comprehensive understanding of the dynamic immunomodulatory profile of the chemotherapeutic drugs would provide significant clinical guidance in cancer chemo-immunotherapy.

Potential Strategies for Tumor Immunosuppression Reversal
The progress in combining chemotherapy with strategies for tumor suppression reversal has led to significant advancements in initiating robust immune responses.However, establishing durable and robust immune responses to completely prevent tumor recurrence and metastasis remains a major challenge for chemo-immunotherapy.Recent research has shown that the timing, sequence, and method of administering primers and boosters can greatly influence the level and duration of immune responses. [13,174]Subcutaneous injection of the immunomodulators is recognized as a slow, long-term process through the depot effect whereas intravenous injection is reckoned as quick induction via systemic blood circulation to the target spleen.On the other hand, the choice of vaccination timeframe and modalities can have a distinct influence on anticancer immunity, especially using various injection methods, including intravenous, intratumoral, intramuscular, and subcutaneous injections.These combination strategies could probably elicit stronger immune responses for effective cancer chemoimmunotherapy.

Immune Response Mechanism
In this review, tumor immunosuppression reversal strategies, such as ICB and TAM reprogramming, have shown enormous effects in stimulating long-lasting immunosurveillance against orthotopic and abscopal tumors.On the other hand, weak antitumor immunity induced by chemotherapy-ICD can be enormously magnified by cancer vaccines, or other types of ICD inducers, including radiotherapy, phototherapy, and sonotherapy.However, whether there are synergistic effects between chemotherapy-mediated ICD as well as other therapies and ITME reversal strategy has not been thoroughly investigated.The immune-stimulation effects of these combinations and the underlying mechanism are still elusive.

Rational Design of Functional Nanomaterials
Various nanomaterials have been exploited as carriers of chemotherapeutic agents and immunomodulators to counteract the ITME for synergistic chemoimmunotherapy.[177] For example, future studies could incorporate cell membranes derived from immune cells (including DCs, macrophages, leukocytes, and NK cells) and genetically engineered cells to render the nano-platform with immunogenic antigens, functional peptides, and recognition receptors to facilitate vaccine delivery and antigen presentation for cancer chemo-immunotherapy.Similarly, immunostimulatory LDH nanoparticles can be used to possibly attenuate the ITME by inducing robust immune responses.Particularly, Mn 2+ incorporated LDH nanoparticles have been validated to promote DC maturation, modulate the ITME, and induce cytotoxic T cell responses for enhancing cancer combination immunotherapy. [178]he remission of the disadvantages of functional materials (Table 4) represents another research direction to advance the clinical translation by improving the stability and biodegradation and mitigating the side effects.Revelation and rational design of the potential immunomodulatory function of nanomaterials provide new insights into alleviating immunosuppression and activating robust immune responses.

Biosafety Profile
Off-target systemic toxicity of chemotherapeutics is recognized as an insurmountable challenge that rigorously hampers the chemotherapy outcomes and negatively affects the treatment prognosis of the patients.Despite enhanced tumor accumulation of the drugs through EPR effects and actively targeting enabled by targeting ligands modified nanoparticles, a large proportion of the drugs was found to be accumulated in the liver and kidney, which probably leads to undesired adverse effects. [179,180]Our previous study revealed that even with the assistance of passive targeting enabled by LDH nanosheets, only 1.66% of the chemicals accumulated in the tumor under intravenous injection, which is still comparatively low. [147]Even worsely, biodistribution analysis results have demonstrated that the accumulation of the anticancer agents in the liver was appropriately 6-7 times that in the tumor tissues using MOF nanoparticles. [181]The long-term biosafety of nanotechnology-mediated drug delivery is not fully understood and should be carefully evaluated prior to clinic use.
In summary, emerging strategies have been developed to debilitate the tumor immunosuppression induced by chemotherapy to amplify cancer chemo-immunotherapy efficiency.The combination of chemotherapy with ICIs, TAM reprograming, cancer vaccines, and multi-modal therapies has attracted increasing attention in the mitigation of tumor immunosuppression and improvement of therapeutic performance.In future, efforts can be devoted to the investigation of novel strategies to further boost anticancer immunity for tumor recurrence remission as well as approaches to improve the biosafety of the nanoplatforms to reduce therapeutic toxicity.Once the challenges are addressed, cancer chemo-immunotherapy by combining chemotherapy with ITME reversal strategy would become a powerful weapon for cancer management.

Figure 4 .
Figure 4. TAM repolarization to counteract the tumor suppression for boosting cancer chemo-immunotherapy effectiveness.A) The combination of chemotherapy with TAM reprogramming.B) Flow cytometry analysis of TAM repolarization.C) The metastatic nodules in the lung metastatic tumor model.Reproduced with permission.[17]Copyright 2020, American Chemical Society.

Figure 5 .
Figure 5. Co-localization of the nanoparticles for simultaneous ICD induction and vaccine boosting.A) Schematic illustration of the co-immunostimulation enabled by a nanomedicine/nano-vaccine platform for cancer chemo-immunotherapy.The synthesis of B) the chemotherapy-ICD inducer and C) the vaccine.D) Tumor lung metastasis prevention in mice.Reproduced with permission.[110]Copyright 2020, Elsevier.

Figure 6 .
Figure 6.Cancer chemo-immunotherapy by combining chemotherapy-ICD with cancer vaccine in a "prime-boost" manner.A) Preparation of CTX-based ICD inducer and CpG-loaded vaccine hydrogel.B) Schematic illustration of the "prime-boost" procedure to stimulate T-cell response.C) The in vivo treatment timeline.D) Representative tumor images collected from the mice after treatments.E) Memory T cell proportion after treatments.Reproduced with permission.[111]Copyright 2021, Elsevier.

Figure 7 .
Figure 7. Dual ICD induction for improving cancer chemo-immunotherapy.A) Schematic illustration of the dual ICD induction enabled by chemotherapy and phototherapy.B) The production of HMGB1 in cells treated with ISPN+L.C) Evaluation of the DC maturation and D) T cell activation in dual ICDtreated mice model.Reproduced with permission.[113]Copyright 2020, Wiley-VCH.

Figure 9 .
Figure 9. Mesoporous silica nanoparticles as an immunoadjuvant for bladder cancer chemo-immunotherapy.A) Schematic illustration of thiolated mesoporous silica nanoparticles for mucoadhesion, tight junction opening, and TAM repolarization.B) Claudin-4 expression level during tight junction opening when treated with mesoporous silica nanoparticles.C,D) RT-qPCR analysis of macrophage polarization by mesoporous silica nanoparticles.Reproduced with permission.[155]Copyright 2023, Wiley-VCH.

Figure 10 .
Figure 10.MOF nanoparticles modulate the immune TME for enhancing cancer chemo-immunotherapy.A) Schematic illustration of the preparation of MOF nanomedicine, and ITME modulation mechanism.B,C) The expression of ICD markers CRT, and HMGB1 in tumor tissues treated with MOF nanomedicine.D) H&E staining of lung metastasis after the treatment.Reproduced with permission.[163]Copyright 2021, American Chemical Society.

Li
Li is a senior research fellow at the Australian Institute for Bioengineering and Nanotechnology (AIBN), The University of Queensland (UQ).She received her Ph.D. in chemical engineering from the China University of Petroleum in 2007.Her research focuses on engineering nanocomposites in biomedical applications and animal healthcare, including precision medicine for cancer, combinedcancer immunotherapy, oral vaccines, and nanosupplements for animal health.Her research performance has been recognized with the award of the Churchill Fellowship, QLD International Fellowship, and ATSE Early Career Fellowship.Zhi Ping Xu received his Ph.D. from the National University of Singapore in 2001.Then, he performed his postdoctoral research at the University of North Texas from 2001 to 2003 and at the University of Queensland from 2003 to 2007.He worked at The University of Queensland as an associate professor and professor from 2007 to 2022.Currently, he is a senior principal investigator and professor at the Institute of Biomedical Health Technology and Engineering, Shenzhen Bay Laboratory as well as at the Australian Institute for Bioengineering and Nanotechnology, the University of Queensland.His research focuses on control preparation of layered double hydroxide nanomaterials, calcium phosphate nanoparticles, nanoemulsions, quantum dots, chemosensors, and nanosensors, and their applications in biomedicine and agriculture.

Table 2 .
Immunosuppression mechanism of various types of chemotherapy drugs.

Table 3 .
Summary of the combination of chemotherapy with immunotherapy.
P: Primary tumor elimination; D: Distant tumor elimination; L: Lung metastatic tumor prevention; M: Long-term memory.

Table 4 .
Summary of the combination of chemotherapy with immunotherapy.
P: Primary tumor elimination; D: Distant tumor elimination; L: Lung metastatic tumor prevention; M: Long-term memory.