Latent human cytomegalovirus enhances HIV-1 infection in CD34+ progenitor cells

Individuals who have been preinfected by human cytomegalovirus (HCMV) are more prone to AIDS disease progression after subsequent HIV-1 infection but the underlying mechanism remains elusive. HCMV is a ubiquitous DNA virus that commonly establishes lifelong latent infection in CD34(+) progenitor cells, where latency-specific HCMV genes may modulate host restriction to HIV-1 infection. To test this hypothesis, we studied progenitor cells that are known to resist replicative HIV-1 infection because of the intrinsic expression of host restriction factors. Interestingly, in primary CD34(+) cells undergoing latent HCMV infection, an enhanced level of HIV-1 proviral DNA and replication was observed as measured by digital polymerase chain reaction, quantitative polymerase chain reaction, and Gag expression, and confirmed using dual-reporter pseudovirus encoding X4- or R5-tropic envelope and T-cell transfer. This phenomenon may be partially explained by the upregulation of HIV-1 entry coreceptors, including chemokine receptors CXCR4 and CCR5, but not of the primary receptor CD4. Furthermore, latent HCMV infection downregulated the expression of HIV-1 restriction factors SAMHD1, APOBEC3G, tetherin, and Mx2 in CD34(+) progenitor cells, which may confer to enhanced HIV-1 infection. However, this enhancement was abrogated when ultraviolet-inactivated HCMV was used for comparison, suggesting that expression of latent HCMV genes is essential for this effect. Importantly, HCMV gB and HIV-1 p24 can be detected in the same cell by immunofluorescence and flow cytometry; therefore, the establishment of HCMV latency in CD34(+) cells likely leads to host cell gene modulation that favors HIV-1 infection.