Immune effects of CDK4/6 inhibitors in patients with HR+/HER2− metastatic breast cancer: Relief from immunosuppression is associated with clinical response
Fabio Scirocchi, Simone Scagnoli, Andrea Botticelli, Alessandra Di Filippo, Chiara Napoletano, Ilaria Grazia Zizzari, Lidia Strigari, Federica Tomao, Enrico Cortesi, Aurelia Rughetti, Paolo Marchetti, Marianna Nuti
Abstract
BackgroundCyclin-dependent kinase 4/6 inhibitors (CDK4/6i) are innovative small target molecules that, in combination with endocrine therapy, have recently been employed in the treatment of patients with HR+/HER2− metastatic breast cancer (mBC). In this prospective study, we investigate the impact of CDK4/6i on the immune profile of patients with HR+/HER2− mBC.MethodsImmune cell subsets were analysed using flow cytometry of peripheral blood mononuclear cells (PBMCs) isolated from patients with HR+/HER2− mBC, both before and during treatment. Regulatory T cells (Tregs) were identified using the markers CD4, CD25, CTLA4, CD45RA, and intracellular FOXP3. Monocytic and polymorphonuclear myeloid-derived suppressor cells (M-MDSCs and PMN-MDSCs) and other immune populations were analysed using CD45, CD14, CD66b, CD11c, HLA-DR, CD3, CD8, CD28, CD137, PD1, CD45RA, CCR7, and Ki67.FindingsThe percentage of circulating Tregs and M/PMN-MDSCs was significantly downregulated from baseline during CDK4/6i-treatment (p<0.0001 and p<0.05, respectively). In particular, the effector Treg subset (CD4+CD25+FOXP3highCD45RA−) was strongly reduced (p<0.0001). The decrease in Treg levels was significantly greater in responder patients than in non-responder patients. Conversely, CDK4/6i treatment was associated with increased levels of CD4+ T cells and anti-tumour CD137+CD8+ T cells (p<0.05).InterpretationCDK4/6i treatment results in downregulation of Tregs, M-MDSCs, and PMN-MDSCs, thus weakening tumour immunosuppression. This decrease is associated with response to treatment, highlighting the importance of unleashing immunity in cancer treatment efficacy. These results suggest a novel mechanism of immunomodulation in mBC and provide valuable information for the future design of novel treatments combining CDK4/6i with immunotherapy in other cancer settings.FundingSapienza University of Rome.