Human cytomegalovirus latent infection modulates HIV restriction factors in CD34+ hematopoietic stem cells

Abstract

BACKGROUND: Individuals pre-exposed to human cytomegalovirus (HCMV) are more prone to HIV/AIDS disease progression but the reasons remain elusive. HCMV is a ubiquitous DNA virus that establishes natural lifelong latent infection in CD34+ progenitor cells, where latency-specific viral genes modulate the host cell environment. Myeloid-lineage cells are known to resist replicative HIV-1 infection but recent studies provided evidence that latent reservoir may be established in CD34+ myeloid progenitors. Therefore, an intricate relationship between HCMV and HIV-1 may occur in these cells. METHODS: CD34+ cells isolated from healthy PBMCs were cultured in specialized media for ~30 days to allow expansion. Phenotype of CD34-subsets were assessed by flow cytometry before infection by HCMV. Establishment of HCMV latency and modulation of cellular responses were assessed using real-time PCR and plaque assay. X4/R5-HIV-1 was used to infect CD34+ cells harboring latent HCMV and successful HIV-1 infection was examined for proviral DNA by digital PCR. RESULTS: Peripheral blood-derived (PB-)CD34+ cells expanded up to 50-fold after 30 days in culture and retained early progenitor phenotype. The success of the establishment of HCMV latency was assessed by the detection of latency-specific transcripts UL111.5A, LUNA and UL138, lack of infectious virions, and the ability to reactivate upon co-culture with permissive cells. Importantly, latent HCMV infection downregulated the HIV-1 restriction factors SAMHD1, APOBEC3A/G, tetherin and Mx2 in PB-CD34+ cells, which led to higher HIV-1 transcriptional activity and proviral DNA. Interestingly, these cells retained HCMV-induced downmodulation of MHC class II molecules and did not show differentiation tendency. Furthermore, we demonstrated that the expression of CXCR4 and CCR5 on CD34+ cells were not altered by HCMV latent infection, but HIV-1 infection can be inhibited by antiretrovirals. Lastly, using a dual-reporter pseudovirus, infection of latent HCMV PB-CD34+ cells resulted in increased active infection compared to mock cells. CONCLUSIONS: This study describes an in vitro CD34+ cell expansion culture model to study the establishment of HCMV and HIV-1 infections. Furthermore, we demonstrated that interplay exists between latent HCMV and HIV-1 infection in CD34+ progenitor cells. These findings provide insights into the importance of pre-existing latent HCMV that affects HIV-1 infection outcome.