TCRγδ+ and CD161+ Thymocytes Express HIV-1 in the SCID-hu Mouse, Potentially Contributing to Immune Dysfunction in HIV Infection

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Abstract
The vast diversity of the T cell repertoire renders the adaptive immune response capable of recognizing a broad spectrum of potential antigenic peptides. However, certain T cell rearrangements are conserved for recognition of specific pathogens, as is the case for TCRγδ cells. In addition, an immunoregulatory class of T cells expressing the NK receptor protein 1A (CD161) responds to nonpeptide Ags presented on the MHC-like CD1d molecule. The effect of HIV-1 infection on these specialized T cells in the thymus was studied using the SCID-hu mouse model. We were able to identify CD161-expressing CD3+ cells but not the CD1d-restricted invariant Vα24/Vβ11/CD161+ NK T cells in the thymus. A subset of TCRγδ cells and CD161-expressing thymocytes express CD4, CXCR4, and CCR5 during development in the thymus and are susceptible to HIV-1 infection. TCRγδ thymocytes were productively infectable by both X4 and R5 virus, and thymic HIV-1 infection induced depletion of CD4+ TCRγδ cells. Similarly, CD4+CD161+ thymocytes were depleted by thymic HIV-1 infection, leading to enrichment of CD4−CD161+ thymocytes. Furthermore, compared with the general CD4-negative thymocyte population, CD4−CD161+ NK T thymocytes exhibited as much as a 27-fold lower frequency of virus-expressing cells. We conclude that HIV-1 infection and/or disruption of cells important in both innate and acquired immunity may contribute to the overall immune dysfunction seen in HIV-1 disease.