CDK4/6 inhibition sensitizes breast cancer to NK cell therapy by inducing immune-interactive surface proteins

CDK4/6 inhibitors are standard-of-care for metastatic estrogen receptor-positive (ER+) breast cancer, yet the development of resistance remains a significant clinical hurdle. While CDK4/6 inhibitors are primarily recognized for their ability to induce cytostasis, their role in modulating innate immune responses remains poorly defined. Here, we demonstrated that CDK4/6i treatment remodels the tumor cell surface to favor recognition and elimination by Natural Killer (NK) cells. Using a diverse biobank of patient-derived organoids (PDOs), we found that CDK4/6 inhibition robustly upregulated the adhesion molecule ICAM-1 and the NKG2D stress ligands (ULBP2/5/6 and MICA/B). This NK-engaging cell surface phenotype was driven by a bifurcated signaling network: NF-{kappa}B signaling orchestrated ICAM-1 induction, while the PI3K/mTOR pathway regulated the expression of stress ligands. Functional assays confirmed that these ligands were indispensable for NK cell-mediated elimination of breast cancer cells. In vivo studies using ER+ PDX models revealed that a brief seven-day primer treatment with the CDK4/6 inhibitor abemaciclib was sufficient to sensitize tumors to NK cell therapy, significantly inhibiting tumor growth and prolonging survival. We also observed efficacy with a concurrent dosing strategy that delayed the onset of acquired resistance. These findings provide a mechanistic rationale for combining CDK4/6 inhibitors with NK cell therapy. This "prime and kill" approach offers a promising strategy to overcome therapeutic resistance and improve outcomes for patients with metastatic ER+ breast cancer.