Lin et al. studied the mechanism of improved antitumor efficacy of IL-12-pretreated, adoptively transferred (ADT) CD8+ T cells. IL-12 exposure before ADT of Pmel-transgenic CD8+ T cells enhanced persistence and IFNγ production within the B16F10 TME and dampened PD-1 and IFNγR2 expression. In human melanoma CD8+ TILs, IL-12 treatment in vitro reduced PD-1 and enhanced IFNγ levels. Pmel IFNγR1-/- CD8+ T cells, lacking IFNγ signaling, showed improved expansion, reduced apoptosis, and enhanced survival, suggesting that IL-12 suppression of the IFNγ receptor reduces responsiveness to IFNγ and its downstream negative regulatory effects.
Optimal ex vivo expansion protocols for adoptive cell therapy (ACT) must yield T cells able to effectively home to tumors and survive the inhospitable conditions of the tumor microenvironment (TME), while simultaneously exerting persistent anti-tumor effector functions. Our previous work has shown that ex vivo activation in the presence of IL-12 can induce optimal expansion of murine CD8(+) T cells, thus resulting in significant tumor regression after ACT mostly via sustained secretion of IFN-gamma. In this report, we further elucidate the mechanism of this potency, showing that IL-12 additionally counteracts the negative regulatory effects of autocrine IFN-gamma. IL-12 not only downregulates PD-1 expression by T cells, thus minimizing the effects of IFN-gamma-induced PD-L1 upregulation by tumor stromal cells, but also inhibits IFNgammaR2 expression, thereby protecting T cells from IFN-gamma-induced cell death. Thus, the enhanced anti-tumor activity of CD8(+) T cells expanded ex vivo in the presence of IL-12 is due not only to the ability of IL-12-stimulated cells to secrete sustained levels of IFN-gamma, but also to the additional capacity of IL-12 to counter the negative regulatory effects of autocrine IFN-gamma.