Adoptive transfer of chimeric antigen receptor (CAR)-T cells, comprising an increased proportion of memory-T cells, results in increased expansion, persistence, and better disease control in patients. Human memory T cells include stem-like-CD8+-memory-T cell progenitors which have distinct fates, either functional (TSTEM) or dysfunctional and exhausted (TPEX). Indeed, we demonstrated this TSTEM compartment was decreased in the infused CAR-T cells for our Lewis Y-CAR-T cell trial (NCT03851146), and the infused CAR-T cells displayed poor persistence in patients.
To address this issue, we developed a novel production protocol to generate TSTEM-like CAR-T cells, a CAR-T cell product enriched with a cell population exhibiting a stem cell-like memory-phenotype and a distinct gene expression profile enriched for cell self-renewal pathways. Compared with conventional-CAR-T cells, TSTEM-like CAR-T cells had increased cytokine secretion, significantly enhanced proliferative capacity following short-term CAR stimulation or after chronic CAR stimulation in vitro. These responses were dependent on the presence of CD4+ T cells during TSTEM-like CAR-T cell production. Adoptive transfer of TSTEM-like CAR-T cells induced better control of established tumors in two pre-clinical NSG mice models, and this was associated with increased systemic persistence of TSTEM-like CAR-T cells and an increased memory-T cell pool. The mice with tumor clearance also showed resistance to tumor re-challenge. Finally, TSTEM-like CAR-T cells and anti-PD-1 treatment completely eradicated established tumors, and this was associated with increased percentage of tumor infiltrating CD8+IFN-g+ CAR-T cells.
In conclusion, our novel CAR-T cell protocol generated TSTEM-like CAR-T cells with enhanced therapeutic efficacy, which correlated with increased proliferative capacity and persistence in vivo. Successful translation of this protocol into the clinic will have significant potential to improve the current treatment outcomes of CAR-T therapy.