Peripheral Blood Immunophenotypic Characterization of Breast Cancer

Breast cancer treatment involves a combination of surgery, chemotherapy, and radiation, which may be complemented by targeted therapy and immunotherapy. Mounting evidence suggests that treatment efficacy is influenced by the presence of an active antitumor immune response, and conversely that treatment can trigger changes in immune cells. Furthermore, breast tumors display a heterogeneous tumor immune microenvironment which results in different clinical outcomes and treatment responses. In this study, we assessed the frequency and phenotypes of circulating immune cells in patients with different breast cancer subtypes. Peripheral blood mononuclear cells were isolated from healthy controls (HC, n=20), breast cancer (BC) patients with hormone receptor positive-Her2 positive tumours (HR+HER2+, n=26), HR+HER2- tumours (n=35), HER2-enriched tumours (HER2+, n=9), and triple negative breast cancer (TNBC, n=12). Immune cell profiling was achieved using four polychromatic flow cytometry panels to identify T cell subsets, myeloid derived suppressor cells and assess immune checkpoint expression. Overall, BC patients displayed a lower number of CD4+ and CD8+ naïve T cells and an increased proportion of CD4+ and CD8+ T effector and effector memory cells. The frequency of CD4+CD25+FoxP3+ T regulatory cells is significantly higher in breast cancer compared to healthy controls.

Furthermore, we found a significant increase in the frequency of PD-1+, CTLA4+, and TIGIT+ CD8+ T cells in hormone receptor positive patients (HR+HER2- and HR+HER2+) in comparison to HC and HER2+ or TNBC patients. Our findings suggest that although BC patients exhibited higher levels of circulating CD4+ and CD8+ T effector and effector memory T cells, they may have reduced cytotoxic anti-tumor activity resulting from a higher regulatory T cell (Tregs) frequency and inhibitory checkpoint molecules expression compared to healthy controls.