Tumor infiltrating lymphocytes (TIL) is a heterogeneous population with potential anti-tumor reactivity. TIL recognition and reactivity with autologous tumor is associated with increased secretion of IFN-γ, a key cytokine involved in T cell recognition and activation. Despite the encouraging results obtained from the use of adoptive cell transfer, in stage IV metastatic melanoma patients, and despite extensive research efforts, little is known about the cellular interactions that determine TIL reactivity. In previous work, we demonstrated that by extensive phenotypic analysis of Selected-TIL cultures combined with computational tools we generated a set of rules (a decision tree algorithm) that accurately predict the degree of TIL reactivity in terms of its subpopulation constituents. Our current studies are focused on understanding the molecular basis that enables the control and prediction of this complex immune cell population. Analyzing pre-REP young TIL cultures, we found significant correlation between reactivity and non-reactivity, and subpopulation signatures. The subpopulation signatures of reactive vs. non-reactive TIL cultures are distinctive. Importantly, we revealed that pre-REP Young and Selected TIL cultures share similar signatures for reactivity vs. non-reactivity. Further analysis of Pre-REP vs. post-REP Young TIL cultures revealed the unexpected finding that they possess similar signature for non-reactivity, but differ in the signatures for tumor reactivity. Moreover, expansion of TIL cultures induces alternations in subpopulation composition and thus, changes TIL reactivity and TIL subpopulation signatures. We aim to determine the biological processes that govern TIL reactivity during TIL expansion and the relationships between the various subpopulations and TIL functions using systems biology approaches. Our studies may shed light on the molecular mechanism that control TIL reactivity combined with controlling the long-term reactivity of these populations and improve the clinical efficacy of TIL cultures. It will also set the foundations to study other types of heterogeneous cell populations (e.g. stem cells).
