Tumor infiltrating lymphocytes (TIL) have demonstrated therapeutic effects in adoptive cell therapy of melanoma, and there is great interest in optimizing this response. However, the role of lymphocytes during tumor initiation and progression is complex and evolves over time. We have identified two distinct subsets of TIL that have divergent effector vs. regulatory function in murine tumor models. These subsets can be efficiently segregated in vitro based on differential expression of L-selectin (CD62L). Although initially present in small numbers, they can be activated in vitro with anti-CD3 mAb and expanded with a combination of IL-2 and IL-7 to provide sufficient numbers for adoptive transfer into secondary hosts with advanced tumors. Our initial studies demonstrated that the TIL CD62L-low subset is a mixture of CD4 and CD8 cells that individually or in combination mediate tumor-specific regression. By contrast, the CD62L-high subset, which is exclusively CD8+, does not have therapeutic efficacy. Moreover, when CD62Lhigh TIL are co-transferred with CD62L-low effector cells they abrogate their therapeutic efficacy, thus they have suppressor function. Because L-selectin is involved in lymphocyte homing to secondary lymphoid tissues, we hypothesized that the CD62L-high TIL cells might preferentially re-circulate into lymph nodes and inhibit primary sensitization of naìˆve T cells to tumor antigens. Tumor cells were inoculated subcutaneously, alone or with either CD62L-high TIL or CD62L-low TIL. The CD62L-high TIL actually enhanced the growth of subcutaneous tumors whereas the CD62L-low cells prevented tumor growth. More importantly, tumor-draining lymph nodes were harvested twelve days later and activated in vitro with anti-CD3 and IL-2/IL-7 for adoptive cell transfer to secondary tumor-bearing hosts. The presence of TIL suppressor cells during sensitization of tumor-draining lymph node cells partially inhibited the development of tumor-reactive effector cells. This inhibition was not tumor-antigen specific because TIL suppressor cells derived from the MCA205 fibrosarcoma were able to inhibit sensitization of B16/F10 draining lymph node effector cells. These data suggest that tumors acquire a population of CD8 CD62L-high T cells that can inhibit other effector T cells. The suppressor TIL cells also appear to modulate the tumor stroma to promote tumor growth and modulate antigen-presenting cells that migrate to draining lymph nodes thereby dampening the development of effector cells. Studies are ongoing to determine the mechanism of suppressor function.

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