Human endogenous retrovirus K (HERV-K) is distinctive among the retroviruses that comprise about 8% of the human genome in that multiple HERV-K proviruses encode full-length viral proteins, and many HERV-K proviruses formed during recent human evolution. HERV-K gag proteins are found in the cytoplasm of primary tumor cells of patients with seminoma. We identified HERV-K-specific T cells in patients with a past history of seminoma using the interferon-gamma ELISPOT assay and an MHC-HERV-K peptide-specific tetramer. A minority of apparently healthy subjects without evident germ cell tumors also made HERV-Kspecific T cell responses. In summary, we detected T cell reactivity to HERV-K peptides in both past seminoma patients and a minority of apparently healthy controls.

CD4+ T cells are thought to be critical in the maintenance of virus-specific CD8+ cytotoxic T-cell (CTL) responses. In human immunodeficiency virus type 1 (HIV-1) infection, a selective decline in HIV-1-specific CTL as the CD4+ T-cell count decreases has been reported. Using HLA-peptide tetrameric complexes, we show the presence at high frequency of HIV-1- and cytomegalovirus-specific CD8+ T cells when the peripheral CD4+ T-cell count was low or zero in three HIV-1-infected patients. No direct virus-specific CD8+-mediated effector activity was seen in these subjects, suggesting antigen unresponsiveness, although tetramer-sorted cells could be expanded in vitro in the presence of interleukin-2 into responsive effector cells. Thus, virus-specific CD8+ T cells can be maintained in the peripheral circulation at high frequency in the absence of circulating peripheral CD4+ T cells, but these cells may lack direct …