Humanized Bone Marrow-Liver-Thymus Mice for Studying HIV-1 Persistence in Liver and Lung CD4+ T and Myeloid Cell Subsets during Antiretroviral Therapy
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Background
While the role of CD4 + T-cells in HIV-1 reservoir persistence during antiretroviral therapy (ART) is well-established, studies on tissue-resident macrophages (MΦ) in people with HIV-1 (PWH) are restricted by difficulties in accessing deep tissue samples. Investigations in myeloid-only humanized mouse models demonstrated the contribution of MΦ to viral rebound upon ART interruption. Two distinct MΦ subsets exist in mice and humans: one of embryonic origin and self-renewal capacity generating long-lived tissue-resident MΦ (LL-TRM), and another one of short-lived MΦ (SL-MΦ), constantly replenished by bone marrow monocytes. The relative contribution of LL-TRM versus SL-MΦ to tissue HIV-1 reservoir persistence during ART remains understudied. Here, we used a humanized BM-liver-thymus (hu-BLT) mouse model to quantify integrative HIV-1 infection in liver/lung MΦ versus CD4 + T-cells before/after ART and document their expression of LL-TRM/SL-MΦ markers.
Results
Lung/liver immune cells were extracted from ART-naive (ART-) and ART-treated (ART+) HIV-infected (HIV+) hu-BLT mice, as well as HIV-uninfected mice (HIV-). MΦ were identified as cells expressing the myeloid markers CD33/HLA-DR and/or CD68 and flow-cytometry sorted based on their differential expression of CD14 and/or CCR2. Matched CD3 + CD4 + T-cells were sorted in parallel and used as controls. HIV-DNA integration was measured by nested real-time PCR. In contrast to CD4 + T-cells that carried the highest levels of proviral HIV-DNA before and after ART, integrative infection in liver/lung MΦ was detected before ART, but was drastically reduced in HIV+ART+ hu-BLT mice, regardless of CD14 or CCR2 expression on MΦ. Markers of LL-TRM (CD163/CX3CR1/Ki67/c-Kit) were expressed on a small fraction of liver but not lung MΦ, indicative of a deficient LL-TRM development in this hu-BLT model.
Conclusions
Together our results demonstrate that lung/liver MΦ in hu-BLT mice support integrative HIV-1 infection in vivo , but their contribution to viral reservoir persistence during ART is minor when compared to CD4 + T-cells. This is consistent with the deficient development of LL-TRM we observed in hu-BLT mice. However, HIV-1 permissive MΦ present in this model likely contribute to viral rebound upon ART interruption. Therefore, HIV-1 cure interventions that are tested in such preclinical models should consider targeting HIV-1 replication in both MΦ and CD4 + T-cells.
