Impaired negative regulation of homeostatically proliferating T cells.

Acute lymphopenia-induced homeostatic proliferation (HP) of T cells promotes antitumor immunity, but the mechanism is unclear. We hypothesized that this is due to a lack of inhibitory signals that allows activation of T cells with low affinity for self-antigens. Tumors resist immunity in part by expressing inhibitory molecules such as PD-1 ligand 1 (PD-L1), B7-H4, and TGF-beta.