Enhanced Lymphodepletion Is Insufficient to Replace Exogenous IL2 or IL15 Therapy in Augmenting the Efficacy of Adoptively Transferred Effector CD8 T Cells.

Effector CD8 T cells conditioned with IL12 during activation mediate enhanced antitumor efficacy after adoptive transfer into lymphodepleted hosts; this is due in part to improved IL7 responsiveness. Therefore, we hypothesized that increasing the intensity or type of lymphodepletion would deplete more IL7-consuming host cells and improve the persistence and antitumor activity of IL12-conditioned CD8 T cells. Using cyclophosphamide, fludarabine, and total body irradiation (TBI, 6 Gy) either individually or in combination, we found that combined lymphodepletion best enhanced T-cell engraftment in mice. This improvement was strongly related to the extent of leukopenia, as posttransfer levels of donor T cells inversely correlated to host cell counts after lymphodepletion. Despite the improvement in engraftment seen with combination lymphodepletion, dual-agent lymphodepletion did not augment the antitumor efficacy of donor T cells compared with TBI alone. Similarly, IL7 supplementation after TBI and transfer of tumor-reactive T cells failed to improve persistence or antitumor immunity. However, IL15 or IL2 supplementation greatly augmented the persistence and antitumor efficacy of donor tumor-reactive T cells. Our results indicate that the amount of host IL7 induced after single agent lymphodepletion is sufficient to potentiate the expansion and antitumor activity of donor T cells, and that the efficacy of future regimens may be improved by providing posttransfer support with IL2 or IL15. The relationship between lymphodepletion and cytokine support plays a critical role in determining donor T-cell engraftment and antitumor efficacy. .