Lelliott et al. showed that the CDK4/6 inhibitor trilaciclib enhanced the metabolic fitness of and cytotoxicity by human CD19 CAR-T cells while reducing their proliferation in vitro. In mice with RB-proficient, trilaciclib-sensitive, CD19+ leukemia, trilaciclib plus CD19 CAR-T cell therapy was more efficacious than monotherapies. In mouse models of solid (breast, ovarian) tumors, even tumors poorly sensitive to trilaciclib alone responded better to tumor antigen-directed CAR-T cells plus trilaciclib than to the single therapies. Trilaciclib reduced suppressive Treg numbers and boosted CAR-T cell persistence, tumor trafficking, and cytotoxic function per cell in solid tumors.
Contributed by Paula Hochman
ABSTRACT: CDK4/6 inhibitors promote anti-tumor immunity through diverse mechanisms, positioning them as promising adjuvants to cancer immunotherapies. While CDK4/6 inhibitors have demonstrated strong synergy with immune checkpoint inhibitors across numerous preclinical cancer models, their combination with CAR-T cell therapy remains unexplored. In this study, we examined the efficacy of combined CDK4/6 inhibition (trilaciclib) and CAR-T therapy across a range of preclinical blood and solid cancer models. In vitro, trilaciclib enhanced human CAR-T cell cytotoxicity and metabolic fitness while reducing expansion. In vivo, the combination outperformed single agents against retinoblastoma protein (RB)-proficient, trilaciclib-sensitive CD19+ leukemia. However, in an equivalent RB-deficient model, the combination therapy was no more effective than CAR-T cells alone, suggesting that enhanced CAR-T cell function may be offset by reduced expansion. In contrast, in solid cancer models the combination was consistently more efficacious than either monotherapy. Notably, combination effects were most pronounced in immunocompetent mouse models, including a model with poor sensitivity to trilaciclib as a monotherapy. Mechanistically, CDK4/6 inhibition reduced tumor-infiltrating T-regulatory cells while enhancing CD8+ CAR-T cell persistence, tumor trafficking, and cytotoxic function within the tumor. Together, these findings suggest that trilaciclib and CAR-T cell therapy may be an effective combinatorial treatment for solid cancers.
