Inhibition of p300 impairs Foxp3+ T-regulatory cell function and promotes anti-tumor immunity. Mus musculus

Foxp3+ T-regulatory (Treg) cells maintain immune homeostasis and limit autoimmunity, but can also curtail host responses to cancers. Tregs are therefore promising targets to enhance anti-tumor immunity. Histone/protein acetyltransferases (HATs) promote chromatin accessibility, gene transcription and the function of multiple transcription factors and non-histone proteins. We found that conditional deletion or pharmacologic inhibition of one specific HAT, p300, in Foxp3+ Tregs, increased TCR-induced apoptosis in Tregs, impaired Treg suppressive function and iTreg peripheral conversion, and limited tumor growth in immunocompetent, but not in immunodeficient, hosts. Our data demonstrate that p300 is important for Foxp3+ Treg function and homeostasis in vivo and in vitro, and identify a novel mechanism to diminish Treg function without overtly impairing effector Tcell responses or inducing autoimmunity. Collectively, these data suggest a new approach for cancer immunotherapy. Overall design: RNA from three independent samples from magnetically separated CD4+CD25+ Treg of fl-p300/Foxp3cre mice, compared to wild type (Foxp3cre) control (all C57Bl/6 background).