What is the primary role of myeloid-derived suppressor cells (MDSCs) in cancer?

• A. They activate T cells to attack tumors.
• B. They suppress T cell responses, promoting tumor growth.
• C. They differentiate into cytotoxic T cells.
• D. They produce antibodies.

Answer: (B)

In cancer, myeloid-derived suppressor cells are immunosuppressive players that dampen the immune response rather than attack the tumor. Their primary role is to suppress T cell responses, which weakens the body's ability to kill cancer cells and thus promotes tumor growth and progression. They do this through multiple well-established mechanisms: depleting nutrients needed by T cells (such as L-arginine) via arginase activity, producing reactive oxygen species and nitric oxide that impair T cell signaling, secreting suppressive cytokines like IL-10 and TGF-beta, and upregulating inhibitory molecules such as PD-L1. They can also foster regulatory T cell development, all of which collaborate to blunt the cytotoxic activity that would otherwise control the tumor. They don’t activate T cells or turn into cytotoxic T cells, and they don’t produce antibodies—roles filled by other immune cells like B cells and plasma cells.