The present study shows that a high number of tumor-infiltrating FOXP3+ T cells is associated with a higher CR rate and prolonged PFS in patients with OAML, and this association is evident in patients who received combination chemotherapy as a front-line treatment. Patients with a high number of FOXP3+ T cells in the initial tumor tissue had a CR rate of 71% and a median PFS of 67 months.
Because the relationship between the extent of immune cell infiltration and prognosis was first identified in 1949 in cases of breast cancer, several studies have demonstrated the role of tumor-infiltrating T cells in antitumor immune surveillance and the role of Tregs in immune escape in patients with solid tumors.(3–5,7,19) A high number of tumor-infiltrating T cells has been related to prolonged survival whereas a high number of tumor-infiltrating Tregs has been associated with reduced survival in melanoma, colorectal and ovarian cancer.(3–5,7,19) However, the role of the T cells is more complex for lymphoma. Autoimmunity, chronic infection, antigenic stimulation and T cells play a pivotal role in the pathogenesis of some lymphomas.(20–22) Lymphomas that arise according to this model commonly originate from marginal zone B cells.(21,23) Furthermore, in vitro studies on gastric MALT lymphoma support the interaction between T cells and lymphoma cells. Hussell et al.(18) showed that the neoplastic B cells of gastric MALT lymphoma are not immunoresponsive to H. pylori, but that their proliferation is dependent on cognate help from H. pylori-specific T cells. In addition, one study revealed that Tregs can direct the differentiation of conventional CD4-positive helper T cells toward an additional population of Tregs that inhibit the activation of conventional, freshly isolated CD4-positive helper T cells.(24) This suppressive activity is partially mediated by soluble transforming growth factor-β. It has also been shown that Tregs potently suppress follicular helper T cells and follicular helper T-cell-mediated B-cell functions such as immunoglobulin production and B-cell survival.(25,26) Thus, we hypothesized that Tregs would have antitumor activity in OAML by suppressing antigen-stimulated T cells. Consequently, it was found that the number of FOXP3+ T cells was significantly associated with clinical outcomes, whereas the number of CD3-, CD4- and CD8-positive T cells was not associated with either the number of FOXP3+ T cells or clinical outcome. The literature provides an explanation for the direct relationship between FOXP3+ T cells and B cells. Lim et al.(27) revealed that Tregs can directly suppress and even kill B cells. In this study, FOXP3+ T cells are present in B-cell areas where T–B cell interaction and humoral immune responses are believed to occur and can directly suppress the B-cell immunoglobulin response without having to suppress helper T cells. Zhao et al.(28) also reported that preactivated Tregs suppress B-cell proliferation and induce B-cell apoptosis in a cell-contact-dependent but cytokine-independent manner. Taken together, it might be considered that the lack of a significant effect of CD4- or CD8-positive T cells on clinical outcome is a result of the direct suppressive effect of FOXP3+ T cells on neoplastic B cells. Tregs have been consistently associated with improved overall survival in patients with several types of lymphomas such as follicular lymphoma (FL), diffuse large B-cell lymphoma (DLBCL), Hodgkin lymphoma, T-cell and natural killer-cell lymphoma.(10,11,13,14,29) Carreras et al.(13) demonstrated that high numbers of FOXP3+ Treg improve the 5-year overall survival in FL patients. Similarly, Lee et al.(29) showed that FOXP3+ cells in a perifollicular location are more frequently found in FL patients with long-term survival. In addition, Alvaro et al.(14) demonstrated that a small number of FOXP3+ cells and a high proportion of TIA-1+ cells independently reduce event-free survival and disease-free survival in classic Hodgkin lymphoma. Recently, Tzankov et al.(11) performed a large-scale analysis using tissue microarray in 1019 patients with various types of lymphomas. High numbers of intratumoral FOXP3+ Treg correlates with improved survival in germinal center B cell like DLBCL, FL and classical Hodgkin lymphoma. Higher numbers of FOXP3+ T cells are associated with longer overall survival in patients with DLBCL.(30) Accordingly, our results produced a conclusion that corresponded with the literature on other types of lymphoma. In the current study, the association between the number of tumor-infiltrating FOXP3+ T cells and clinical outcome was more significant in patients treated with chemotherapy. This result might have meaning despite the small sample size. Replenishment of Tregs by conversion and proliferation has been extensively reviewed in the literature.(31) Although cyclophosphamide might target proliferation of Treg, replenishment by conversion would result in expansion of Tregs. Hypothetically, cyclophosphamide-containing chemotherapy used in the present study might selectively affect lymphoma cells, providing a way for Tregs to repopulate the tumor microenvironment. However, caution is warranted in interpreting these results due to the admixture of FOXP3+ effector T cells or Tregs as well as activated or resting Tregs. Furthermore, the unknown results of tumor-infiltrating FOXP3+ T cells after chemotherapy might weaken the repopulation hypothesis.
Although translocations that involve the MALT1 gene in chromosome 18 are the most frequent abnormality in OAML, t(11;18) and t(14;18) are very low in OAML (0–10% and 0–25%, respectively).(32,33) Similarly, none harbored MALT1 translocation in the present study.
Patients with OAML generally have a favorable prognosis and follow an indolent clinical course. Several retrospective studies have identified clinical prognostic factors such as the primary site, stage, nodal involvement, age, presence of B symptoms, serum LDH levels and histopathological factors such as CD5, CD43, p53 and BCL-6 in ocular adnexal lymphoma.(34) However, the results of these studies are difficult to generalize due to the heterogeneity of pathological diagnosis, treatment protocols and primary objectives. Various effective treatment modalities are available for OAML patients such as excision, radiotherapy, single-agent or combination chemotherapy, immunotherapy, Chlamydia psittaci eradicating antibiotics and even observation.(34) Most of these strategies are well tolerated, and re-treatment with the same regimens is an option. Although the present study is limited by its retrospective nature and small cohort size, it is noteworthy that it demonstrates significant prognostic discrimination on PFS in a homogeneous subgroup of OAML patients who underwent chemotherapy. In the present study, PFS after front-line treatment was assessed to exclude possible biases.
In conclusion, a high number of tumor-infiltrating FOXP3+ T cells is associated with a favorable clinical outcome in patients with OAML. Future efforts should be directed towards finding a network between the tumor microenvironment and tumor cells in extranodal marginal zone B-cell lymphoma of MALT type.