Empowering the Potential of CAR-T Cell Immunotherapies by Epigenetic Reprogramming

T-cell-based, personalized immunotherapy can nowadays be considered the mainstream treatment for certain blood cancers, with a high potential for expanding indications. Chimeric antigen receptor T cells (CAR-Ts), an ex vivo genetically modified T-cell therapy product redirected to target an antigen of interest, have achieved unforeseen successes in patients with B-cell hematologic malignancies. Frequently, however, CAR-T cell therapies fail to provide durable responses while they have met with only limited success in treating solid cancers because unique, unaddressed challenges, including poor persistence, impaired trafficking to the tumor, and site penetration through a hostile microenvironment, impede their efficacy. Increasing evidence suggests that CAR-Ts' in vivo performance is associated with T-cell intrinsic features that may be epigenetically altered or dysregulated. In this review, we focus on the impact of epigenetic regulation on T-cell differentiation, exhaustion, and tumor infiltration and discuss how epigenetic reprogramming may enhance CAR-Ts' memory phenotype, trafficking, and fitness, contributing to the development of a new generation of potent CAR-T immunotherapies.

Tethered IL-15 augments antitumor activity and promotes a stem-cell memory subset in tumor-specific T cells

Adoptive immunotherapy retargeting T cells to CD19 via a chimeric antigen receptor (CAR) is an investigational treatment capable of inducing complete tumor regression of B-cell malignancies when there is sustained survival of infused cells. T-memory stem cells (T_SCM) retain superior potential for long-lived persistence, but challenges exist in manufacturing this T-cell subset because they are rare among circulating lymphocytes. We report a clinically relevant approach to generating CAR⁺ T cells with preserved T_SCM potential using the Sleeping Beauty platform. Because IL-15 is fundamental to T-cell memory, we incorporated its costimulatory properties by coexpressing CAR with a membrane-bound chimeric IL-15 (mbIL15). The mbIL15-CAR T cells signaled through signal transducer and activator of transcription 5 to yield improved T-cell persistence independent of CAR signaling, without apparent autonomous growth or transformation, and achieved potent rejection of CD19⁺ leukemia. Long-lived T cells were CD45RO^negCCR7⁺CD95⁺, phenotypically most similar to T_SCM, and possessed a memory-like transcriptional profile. Overall, these results demonstrate that CAR⁺ T cells can develop long-term persistence with a memory stem-cell phenotype sustained by signaling through mbIL15. This observation warrants evaluation in clinical trials.