Abstract 2685: Irradiation and reconstitution with in vitro-expanded polyclonal T cells from naïve mice augments antitumor response

Transfer of naïve T cells into lymphopenic tumor-bearing hosts induces antitumor effector T cells effectively and inhibits tumor progression. Although the exact mechanism underlying this augmentation of antitumor immune responses remains unclear, possible explanations have been proposed; depletion of suppressor cells, improvement of tumor-antigen presentation, and elimination of lymphocytes competing activation cytokines. Thus, the combination of lymphodepletion by cytotoxic regimens, such as chemotherapy or radiotherapy, and transfer of naïve T cells seems to be an attractive approach. Because of difficulty to acquire enough number of naïve T cells from cancer patients, it is necessary to establish a method for obtaining the large number of naïve T cells. The current study seeks to determine whether lymphodepletion and transfer of in vitro expanded T cells enhances antitumor immunity. We stimulated CD4+ and CD8+ T cells from naïve C57/BL6 mice with homeostatic cytokines. At day9 of culture, their number increased 4 to 10-fold. FACS analysis demonstrated TCR diversity of stimulated T cells. Resulted cells were injected into mice harboring MCA205 fibrosarcoma after sublethal irradiation (500 rad). As well as transfer of fresh naïve T cells, transfer of stimulated T cells strongly inhibited tumor-progression. To confirm whether in vitro stimulated T cells become antitumor effector T cells and retarded tumor growth, GFP+ T cells were expanded in vitro and transferred into irradiated wild mice. On the same day, mice were inoculated s.c. with tumor cells. Twelve days later, tumor-draining LNs were harvested and cells were stimulated with the anti-CD3/IL-2 method. Activated tumor-draining LN cells were analyzed for secretion of IFN-γ after specific tumor stimulation. Intracellular IFN-γ staining revealed that the majority of effector T cells were GFP+ donor cells. We next examined whether dendritic cell vaccination enhances antitumor immune responses of in vitro stimulated T cells. Bone marrow dendritic cells were co-cultured with irradiated tumor cells and were injected into mice reconstituted with in vitro stimulated T cells. Compared with transfer of T cells alone, the combination of vaccination and transfer of T cells significantly delayed tumor progression. We report in this study that even after nonspecific stimulation, naïve T cells retain their ability to respond to tumor-antigens when they are transferred into lymphopenic hosts. Irradiation and r