A CARMIL2 gain-of-function mutation suffices to trigger most CD28 costimulatory functions in vivo

• DOI: 10.1084/jem.20250339
• Publication Date: 2025-05-22T13:49:23Z
• Authors: Fanghui Zhang; Javier Celis-Guti...; Lichen Zhang; Valentin Mellado; Léna Gelard; Sophie Panigot; Daiki Mori; Liaoxun Lu; Guillaume Voisinne; Carine Vilarnau W...; Marielle Mello; Odile Burlet-Schiltz; Anne Gonzalez de ...; Frédéric Fiore; Romain Roncagalli; Yinming Liang; Marie Malissen; Bernard Malissen

Naive T cell activation requires both TCR and CD28 signals. The CARMIL2 cytosolic protein enables CD28-dependent activation of the NF-κB transcription factor via its ability to link CD28 to the CARD11 adaptor protein. Here, we developed mice expressing a mutation named Carmil2QE and mimicking a mutation found in human T cell malignancies. Naive T cells from Carmil2QE mice contained preformed CARMIL2QE-CARD11 complexes in numbers comparable to those assembling in wild-type T cells after CD28 engagement. Such ready-made CARMIL2QE-CARD11 complexes also formed in CD28-deficient mice where they unexpectedly induced most of the functions that normally result from CD28 engagement in a manner that remains antigen-dependent. In turn, tumor-specific T cells expressing Carmil2QE do not require CD28 engagement and thereby escape to both PD-1 and CTLA-4 inhibition. In conclusion, we uncovered the overarching role played by CARMIL2-CARD11 signals among those triggered by CD28 and exploited them to induce potent solid tumor–specific T cell responses in the absence of CD28 ligands and immune checkpoint inhibitors.