Inhibition of CDK4/6 Promotes CD8 T-cell Memory Formation

CDK4/6 inhibitors are approved to treat breast cancer and are in trials for other malignancies. We examined CDK4/6 inhibition in mouse and human CD8 T cells during early stages of activation. Mice receiving tumor-specific CD8 T cells treated with CDK4/6 inhibitors displayed increased T cell persistence and immunologic memory. CDK4/6 inhibition upregulated Mxd4, a negative regulator of Myc, in both mouse and human CD8 T cells. Silencing of Mxd4 or Myc in mouse CD8 T cells demonstrated the importance of this axis for memory formation. We used single cell transcriptional profiling and TCR clonotype tracking to evaluate recently activated human CD8 T cells in breast cancer patients before and during treatment with either palbociclib or abemaciclib. CDK4/6 inhibitor therapy in humans increases the frequency of CD8 memory precursors and downregulates their expression of MYC target genes, suggesting that CDK4/6 inhibitors in cancer patients may augment long-term protective immunity.