The complex role of regulatory cells in breast cancer: implication for immunopathogenesis and immunotherapy

Breast cancers (BCs) are frequently linked to an immunosuppressive microenvironment that facilitates tumor evasion of anti-cancer immunity. The cells that suppress the immune system such as regulatory B cells (Bregs), regulatory T cells (Tregs), tumor-associated macrophages (TAMs), tumor-associated neutrophils (TANs), myeloid-derived suppressor cells (MDSCs), play a crucial role in immune resistance. Also, tumor progression and immune evasion of cancers are facilitated by cytokines and factors released by tumor cells or immunosuppressive cells. Targeting these regulatory cells therapeutically, whether through elimination, inactivation, or reprogramming, has resulted in hopeful anti-tumor reactions. Yet, the substantial diversity and adaptability of these cells, both in terms of appearance and function, as well as their variation over time and depending on where they are in the body, have posed significant challenges for using them as reliable biomarkers and creating focused therapies that could target their creation, growth, and various tumor-promoting roles. The immunotherapy approaches in BC and their effectiveness in treating certain subtypes are still in their initial phases. In this review, we thoroughly outlined the characteristics, roles, and possible treatment options for these immune-suppressing cells in the tumor environment.