The kinetics of gene expression of human immunodeficiency virus type 1 (HIV-1) following release from latency

The ability of HIV to establish a latent infection has rendered any current regimen of antiretroviral drug therapy ineffective at achieving the complete eradication of the virus. Hence, infected individuals must remain on HAART indefinitely, with often insidious and debilitating consequences. Finding a strategy to eliminate the latent reservoir has thus become one of the primary focuses of HIV research. We have sought to characterize the environment in which viral latency can develop and reside. Our model of HIV latency, based on the SCID-hu mouse, entails the direct infection of human thymocytes, which enables the generation of a population of latently infected cells that may be studied ex vivo. Experimental evidence revealed that the activation state of the host cell significantly impacts the nature of HIV infection. Activated cells allow productive infections to occur, while quiescent cells enable the virus to enter a latent state. We examined how differences in the activation state of host cells affected the viral gene expression. Up-regulation of multiply spliced Tat-Rev and unspliced genomic RNA in latently infected cells occurred very soon after stimulation, within two hours. In primary cells activated prior to de novo infection, viral RNA was not seen until at least twelve hours post-infection, and in quiescent cells stimulated post-infection, not until at least thirty-six hours. This hierarchy also held true for Gag protein production. In all cases, increases in both unspliced and multiply spliced viral RNA occurred simultaneously. Interestingly, there was little difference in the timing of viral RNA expression between thymocytes latently infected with wild-type virus and those infected with a nef-deleted mutant. Protein released by cells infected with the nef-deleted mutant, however, occurred approximately twenty-four hours later than by cells infected with wild-type virus. Thus, altering the activation state of the host cell dramatically changes the progression and outcome of the infection. Taken together, these results should help in the design of therapies targeting latent infection.