Embryonic Fibroblasts Promote Antitumor Cytotoxic Effects of CD8+ T Cells

Rejuvenating Effector/Exhausted CAR T Cells to Stem Cell Memory-Like CAR T Cells By Resting Them in the Presence of CXCL12 and the NOTCH Ligand

T cells with a stem cell memory (T_SCM) phenotype provide long-term and potent antitumor effects for T-cell transfer therapies. Although various methods for the induction of T_SCM-like cells in vitro have been reported, few methods generate T_SCM-like cells from effector/exhausted T cells. We have reported that coculture with the Notch ligand-expressing OP9 stromal cells induces T_SCM-like (iT_SCM) cells. Here, we established a feeder-free culture system to improve iT_SCM cell generation from expanded chimeric antigen receptor (CAR)-expressing T cells; culturing CAR T cells in the presence of IL7, CXCL12, IGF-I, and the Notch ligand, hDLL1. Feeder-free CAR-iT_SCM cells showed the expression of cell surface markers and genes similar to that of OP9-hDLL1 feeder cell-induced CAR-iT_SCM cells, including the elevated expression of SCM-associated genes, TCF7, LEF1, and BCL6, and reduced expression of exhaustion-associated genes like LAG3, TOX, and NR4A1. Feeder-free CAR-iT_SCM cells showed higher proliferative capacity depending on oxidative phosphorylation and exhibited higher IL2 production and stronger antitumor activity in vivo than feeder cell-induced CAR-iT_SCM cells. Our feeder-free culture system represents a way to rejuvenate effector/exhausted CAR T cells to SCM-like CAR T cells.

SIGNIFICANCE

Resting CAR T cells with our defined factors reprograms exhausted state to SCM-like state and enables development of improved CAR T-cell therapy.

NIH3T3 Directs Memory-Fated CTL Programming and Represses High Expression of PD-1 on Antitumor CTLs

Memory CD8⁺ T cells have long been considered a promising population for adoptive cell therapy (ACT) due to their long-term persistence and robust re-stimulatory response. NIH3T3 is an immortalized mouse embryonic fibroblast cell line. We report that NIH3T3-conditioned medium (CM) can augment effector functions of CTLs following antigen priming and confer phenotypic and transcriptional properties of central memory cells. After NIH3T3-CM-educated CTLs were infused into naïve mice, they predominantly developed to central memory cells. A large number of NIH3T3-CM-educated CTLs with high functionality persisted and infiltrated to tumor mass. In addition, NIH3T3-CM inhibited CTLs expression of PD-1 in vitro and repressed their high expression of PD-1 in tumor microenvironment after adoptive transfer. Consequently, established tumor models showed that infusion of NIH3T3-CM-educated CTLs dramatically improved CTL mediated-antitumor immunity. Furthermore, NIH3T3-CM also promoted human CD8⁺ T cells differentiation into memory cells. These results suggest that NIH3T3-CM-programmed CTLs are good candidates for adoptive transfer in tumor therapy.