Cytotoxic CD8⁺ T cells play a critical role in controlling herpes simplex virus (HSV) infection and reactivation. However, little is known about the spatiotemporal dynamics of CD8⁺ T cells during HSV lesion evolution or about their involvement in immune surveillance after lesion resolution. Using quantum dot–conjugated peptide–major histocompatibility complex multimers, we investigated the in vivo localization of HSV-2–specific CD8⁺ T cells in sequential biopsies of human genital skin during acute, resolving, and healed stages of HSV-2 reactivation. Our studies revealed that functionally active CD8⁺ T cells selectively infiltrated to the site of viral reactivation. After lesion healing in concert with complete reepithelialization and loss of HSV DNA from skin biopsies, HSV-2–specific CD8⁺ T cells persisted for more than two months at the dermal–epidermal junction, adjacent to peripheral nerve endings. In two out of the six sequentially studied individuals, HSV-2 DNA reappeared in clinically and histologically normal–appearing skin. Detection of viral DNA was accompanied by increased numbers of both HSV-specific and total CD8⁺ T cells in the dermis. These findings indicate that the frequency and clinical course of HSV-2 reactivation in humans is influenced by virus-specific CD8⁺ T cells that persist in peripheral mucosa and genital skin after resolution of herpes lesions.

HLA-B*4402 and B*4403 are naturally occurring MHC class I alleles that are both found at a high frequency in all human populations, and yet they only differ by one residue on the α2 helix (B*4402 Asp156→B*4403 Leu156). CTLs discriminate between HLA-B*4402 and B*4403, and these allotypes stimulate strong mutual allogeneic responses reflecting their known barrier to hemopoeitic stem cell transplantation. Although HLA-B*4402 and B*4403 share >95% of their peptide repertoire, B*4403 presents more unique peptides than B*4402, consistent with the stronger T cell alloreactivity observed toward B*4403 compared with B*4402. Crystal structures of B*4402 and B*4403 show how the polymorphism at position 156 is completely buried and yet alters both the peptide and the heavy chain conformation, relaxing ligand selection by B*4403 compared with B*4402. Thus, the polymorphism between HLA-B*4402 and B*4403 modifies both peptide repertoire and T cell recognition, and is reflected in the paradoxically powerful alloreactivity that occurs across this “minimal” mismatch. The findings suggest that these closely related class I genes are maintained in diverse human populations through their differential impact on the selection of peptide ligands and the T cell repertoire.