Cytotoxic CD4+ T cells eliminate senescent cells by targeting cytomegalovirus antigen.

Senescent cell accumulation has been implicated in the pathogenesis of aging-associated diseases, including cancer. The mechanism that prevents the accumulation of senescent cells in aging human organs is unclear. Here, we demonstrate that a virus-immune axis controls the senescent fibroblast accumulation in the human skin. Senescent fibroblasts increased in old skin compared with young skin. However, they did not increase with advancing age in the elderly. Increased CXCL9 and cytotoxic CD4+ T cells (CD4 CTLs) recruitment were significantly associated with reduced senescent fibroblasts in the old skin. Senescent fibroblasts expressed human leukocyte antigen class II (HLA-II) and human cytomegalovirus glycoprotein B (HCMV-gB), becoming direct CD4 CTL targets. Skin-resident CD4 CTLs eliminated HCMV-gB+ senescent fibroblasts in an HLA-II-dependent manner, and HCMV-gB activated CD4 CTLs from the human skin. Collectively, our findings demonstrate HCMV reactivation in senescent cells, which CD4 CTLs can directly eliminate through the recognition of the HCMV-gB antigen.