HIV-1 Nef disrupts maturation of CD4+ T cells through CD4/Lck modulation

The HIV-1 Nef protein is a major determinant of HIV-1 pathogenicity. It has been found to induce thymocyte depletion, but the mechanisms involved are not completely understood. Also, nothing is known about its effects on thymocyte selection. We used the CD4C/HIV(Nef) transgenic (Tg) mice, which develop a profound CD4(+) T cell lymphopenia, to study their thymic development. We report that HIV-1 Nef causes depletion of double-positive thymocytes and impairs selection and lineage commitment of CD4(+) single-positive thymocytes. This latter defect could be relieved by increasing the affinity of the TCR-MHC interaction or by allowing CD4(+) T cell maturation to proceed in absence of the CD4 tail, in double-Tg (Nef × CD4(tailless)) mice or in the presence of constitutively active Tg Lck(Y505F). These rescue strategies also resulted in reversal of peripheral CD4(+) T cell lymphopenia. Our data indicate that impairment of Lck-mediated CD4 coreceptor signaling by Nef is an important in vivo mechanism of HIV-1 pathogenesis.