Cancer testis autoantigens as germ cell autoantigens continuously egress from normal testes and maintain Treg-dependent tolerance

Abstract

Abstract We investigated tolerance for: 1) testis antigens (mitotic germ cells and somatic cells) located external to the blood-testis barrier (BTB) and 2) testis antigens (sperm and meiotic germ cells) located internal to the BTB. Transiently Treg-depleted B6AF1-DEREG mice produced autoantibodies to mitotic germ cells known to express NY-ESO-1 and MAGE-A (target cancer testis antigens (CTA) in cancer vaccine trials) and to Leydig cells. Unexpectedly, Treg-depleted mice also produced autoantibodies to sperm antigens. These plasma membrane and cytoplasmic sperm antigens continuously egressed from normal seminiferous tubules via the residual bodies. They were recognized by infused circulating antibodies to form local immune complexes outside the BTB and were sensed by antigen-specific T cells in regional lymph nodes. In contrast, sequestered sperm antigens, excluded from residual bodies, were not tolerogenic. Therefore, we provided direct evidence against the “complete testis antigen sequestration” dogma and established Tregs as a critical physiological tolerance mechanism for non-sequestered testis autoantigens. These findings are germane to both autoimmunity and tumor immunity. We found that vasectomized mice responded to sequestered sperm antigens, whereas Treg-depleted mice with autoimmune orchitis responded to non-sequestered sperm antigens. We also detected both tolerogenic and non-tolerogenic sperm antigens as CTA in many types of human cancer. We posit that the existence of two sets of CTA as normal germ cells antigens with distinct tolerogenic properties will impact the outcome of anti-tumor immunity in male patients and will influence the selection of optimal immunogens in cancer vaccine development.