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Pancreatic cancer is an aggressive cancer with poor prognosis. Little is known about the immune response in the tumor microenvironment after chemotherapy for initially unresectable tumor. The purpose of this study was to investigate the immunological effects of chemoradiation therapy in the tumor microenvironment of pancreatic adenocarcinoma. Seventeen patients with pancreatic adenocarcinoma with and without preoperative chemoradiation therapy were retrospectively analyzed using immunohistochemical methods for HLA class I heavy chain, CD4+, CD8+, CD45RO+ and Foxp3+ T cell infiltrations. Seven of the 17 study patients received preoperative chemoradiation therapy. There were no statistically significant differences in the number of CD4+ and CD8+ T cell infiltrations in the tumor microenvironment. However, the number of Foxp3+ T cell infiltrations was significantly lower in the neoadjuvant chemoradiation therapy group. The HLA class I expression status was the same between the two groups. In conclusion, preoperative chemoradiation therapy in pancreatic adenocarcinoma is useful for reducing regulatory T cell levels in combination with its direct cytotoxic effects.
Pancreatic carcinoma is a malignant disease with poor prognosis. It is the fourth leading cause of death worldwide. Surgery is the only curative treatment for localized pancreatic carcinoma;[2, 3] however, clinical symptoms do not appear until the disease is in the advanced stage. Therefore, two-thirds of all patients with pancreatic carcinoma have unresectable disease.
Recently, some new anti-cancer agents have been developed that are effective against pancreatic cancer. Administration of intensive neoadjuvant chemoradiation therapy with these drugs has sometimes enabled initially unresectable tumors (which were metastatic or abutted major arterial vessels) to become operable. We have been performing extensive surgery for patients with initially unresectable pancreatic disease; these patients have had good prognosis compared with the patients who underwent up-front surgery first, before chemoradiation therapy.
It has been confirmed that some anti-cancer agents and irradiation have immunomodulatory effects in addition to their own cytotoxic effects.[6, 7] The basic mechanisms underlying these immunomodulatory effects are mainly an increase in tumor antigenicity and control of regulatory T cells (Treg), myeloid-derived suppressor cells (MDSC) and tumor associated macrophages (TAM).[8-10] However, the immunomodulatory effects of chemoradiation therapy vary between types of cancer, and also sometimes depend on the host immune responses.
The aim of the present study was to investigate the immunological effects of chemoradiation therapy in the tumor microenvironment of pancreatic adenocarcinoma. We compared surgical specimens between the patients who underwent surgery before receiving chemoradiation therapy and those who received neoadjuvant chemoradiation therapy.
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- Materials and Methods
- Disclosure Statement
There have been growing evidences that chemotherapy can modulate the host immune response in a variety of cancers. Several types of evidence underlying this process have been proposed besides the cytotoxic effects of chemotherapy. First, is the association of calreticulin, one of the antigen-processing components for HLA class I. It has been suggested that calreticulin increases the antigenicity of tumor antigens by releasing an “eat me” signal with the antigen-presenting cells. Second, is the inhibitory effect of anti-cancer agents on the immune suppressor cells, including Treg, MDSC and TAM.[8-10] The last type of evidence is antigen spreading by tumor shrinkage and the formation of antigen antibody immune complex, stimulating activation of the complement pathway and inducing antibody-dependent cellular cytotoxicity. Irradiation also mediates many immunological effects including upregulation of HLA class I molecules, tumor associated antigens, and adhesion molecules by endothelial cells, thereby boosting cytotoxic T-cell activity.
In the present study, we evaluated the effects of preoperative chemoradiation therapy on the tumor microenvironment of pancreatic carcinoma and analyzed whether the microenvironment became immunologically modified. In our previous study series, we demonstrated that CD8+ tumor-infiltrating lymphocytes, together with CD4+ tumor-infiltrating lymphocytes, improve the prognosis of patients with pancreatic adenocarcinoma, esophageal carcinoma and lung carcinoma. Furthermore, we indicated that neoadjuvant chemotherapy effectively induced CD4+ and CD8+ lymphocyte infiltration into the cancer microenvironment, together with HLA class I upregulation. However, the present data suggest that preoperative chemoradiation therapy did not induce CD4+ nor CD8+ lymphocyte infiltration compared with the specimens without preoperative therapy. This might be because of differences in the types and combinations of anti-cancer agents or the dose intensities used in the preoperative clinical setting. Brode et al. reported that cyclophosphamide could modulate the host immune response, depending on the dose and timing of administration. Muranski et al. also suggested in their adoptive immunotherapy strategy for the metastatic melanoma that the host's immune system needs to be properly conditioned by lymphodepletion, in order to create an appropriate ‘lymphoid space’ that is devoid of regulatory mechanisms. Taken together with this evidence, our present data might be interpreted as the summed results of the balance of various factors including the type of reagents, cycles of chemotherapy, the depletion and the proliferation of the lymphocytes.
It is of interest that the numbers of CD4+ and CD8+ T cells were equal between the SF group and the AS group despite the number of preoperative lymphocytes becoming significantly decreased in the AS group. The reduction in the number of peripheral lymphocytes during the preoperative period might be the result of the bone marrow suppression. The correlation between the amount of bone marrow suppression and preoperative chemotherapy, duration of chemotherapy, number of tumor-infiltrating lymphocytes (TIL), and patient survival rates should be investigated in a future prospective study. It might be possible that anti-cancer agents improve the microenvironment, thereby inducing CD4 and CD8 T cell infiltration and also reducing the number of local Treg. In addition, bone marrow suppression during chemoradiation therapy might possibly boost proliferation in the host microenvironment, similar to the pretreatment regimen in adoptive immunotherapy. Regarding the clinical implication of the reduced regulatory T cells in the AS group, it might be contributing to the patients prognosis, because the overall survival of the AS group, which were initially considered unresectable disease, was equal to that of the SF group, which were all resectable.
In terms of the memory cells, it is of interest that CD45RO+ T cell infiltration was significantly lower in the AS group. Galon et al. reported that increased CD45RO infiltration was associated with good prognosis in human colorectal tumors. Although in Galon et al.'s study, increased CD45RO infiltration was associated with good prognosis in stage I–III according to the UICC-TNM classification, there were no significant differences regarding CD45RO infiltration in stage IV. In agreement with these data, the patients in the AS group in our study initially had far advanced carcinoma, and there might be little contribution of the CD45RO infiltration to the patients survival in the AS group. Although we do not have data regarding the subgroup characteristics of the memory T cells, further fundamental study is warranted to investigate the possibility that the effecter memory T cell population decreases in the tumor microenvironment after chemotherapy.
The present study was limited by the retrospective nature of this investigation, the small number of the patients included and also the fact that lymphocyte infiltration was increased mainly by non-specific inflammation induced by the chemotherapy; therefore, future prospective studies are needed to evaluate infiltrated lymphocytes for tumor specificity or antigen specificity. Further study is also needed in terms of the infiltration of other local immune cells, such as dendritic cells, TAM, MDSC and tumor-specific lymphocytes. The purpose would be to clarify whether chemotherapeutic agents might help educate the immune system by destroying tumor cells, resulting in the release of internal tumor-associated antigens, thereby inducing the formation of immune complexes and inducing specific immunity in combination with direct cytotoxic effects of the chemotherapy. The results of the present study help understand the complicated balance of immunological responses between the host and the tumor.
In conclusion, preoperative chemoradiation therapy in pancreatic adenocarcinoma is useful for reducing regulatory T cell levels in combination with the direct cytotoxic effects of the chemotherapeutic agents and radiation.