Skeletal muscle antagonizes antiviral CD8⁺ T cell exhaustion.

Abstract

CD8⁺ T cells become functionally impaired or "exhausted" in chronic infections, accompanied by unwanted body weight reduction and muscle mass loss. Whether muscle regulates T cell exhaustion remains incompletely understood. We report that mouse skeletal muscle increased interleukin (IL)-15 production during LCMV clone 13 chronic infection. Muscle-specific ablation of <i>Il15</i> enhanced the CD8⁺ T cell exhaustion phenotype. Muscle-derived IL-15 was required to maintain a population of CD8⁺CD103⁺ muscle-infiltrating lymphocytes (MILs). MILs resided in a less inflamed microenvironment, expressed more T cell factor 1 (Tcf1), and had higher proliferative potential than splenic T cells. MILs differentiated into functional effector T cells after reentering lymphoid tissues. Increasing muscle mass via muscle-specific inhibition of TGFβ signaling enhanced IL-15 production and antiviral CD8⁺ T cell responses. We conclude that skeletal muscle antagonizes T cell exhaustion by protecting T cell proliferative potential from inflammation and replenishing the effector T cell progeny pool in lymphoid organs.