Which cell type inhibits T cell function in tumors as part of immune suppression?

• A. Dendritic cells
• B. Myeloid-derived suppressor cells
• C. B cells
• D. NK cells

Answer: (B)

Immune evasion in tumors often hinges on cells that dampen T cell responses within the tumor microenvironment. The primary cell type that inhibits T cell function in tumors is myeloid-derived suppressor cells. These immature myeloid cells accumulate in cancer and become potent suppressors of T cells through several coordinated mechanisms. They deplete nutrients essential for T cell activity, notably L-arginine, by producing arginase-1, which disrupts T cell receptor signaling. They also generate reactive oxygen and nitrogen species that impair T cell function and modify T cell receptors, and they express inhibitory signals like PD-L1. In addition, MDSCs secrete immunosuppressive cytokines such as IL-10 and TGF-β and can promote regulatory T cells, collectively blunting T cell proliferation, cytokine production, and cytotoxic activity.

Dendritic cells, by contrast, are typically antigen-presenting cells that activate T cells, though some tumor-associated DCs can be tolerogenic. B cells and NK cells are not the main suppressors of T cell function in tumors; NK cells are more associated with direct anti-tumor killing, and B cells can have varied roles but do not primarily drive the suppression of T cell activity like MDSCs do.