Humanized FLT3 mice display enhanced tissue engraftment and support HIV‑1 persistence and rebound

Despite advances in antiretroviral therapy (ART), HIV-1 cure efforts remain hindered by viral persistence in long-lived myeloid cells and immune-privileged tissues that are poorly accessible and therefore unlikely to be assessed in human clinical trials. Consequently, robust research platforms, such as immune-cell humanized mice, are needed to bridge preclinical and clinical HIV research. However, previously described humanized mouse models often show incomplete hematopoietic development, particularly showing low levels of NK or myeloid cells. Herein, we evaluate a humanized FLT3 mouse model that develops NK cells, myeloid progenitors, monocytes, and both conventional (cDCs) and plasmacytoid dendritic cells (pDCs), and assessed its capacity to support HIV-1 infection, persistence, and viral rebound. Human cord blood derived CD34⁺ hematopoietic stem cells (HSC) were engrafted in FLT3 (Hu-FLT3) and NSG (Hu-NSG) mouse strains for comparison. While Hu-NSG and Hu-FLT3 mice showed comparable human lymphocyte levels, the proportion of myeloid-enriched populations, including monocytes, pDCs and cDCs, was three-fold higher in Hu-FLT3 mice (16.2%) than in Hu-NSG mice (5.6%), and the proportion of NK cells was six-fold higher (12.8% vs. 1.9%). Both strains supported HIV-1 infection, maintained viral replication for 17 weeks in untreated animals, and had detectable proviral DNA in peripheral blood, bone marrow and spleen. Oral ART reduced plasma HIV-1 RNA to undetectable levels within four weeks in both strains. After treatment discontinuation, viral rebound occurred within three weeks and approached pre-ART levels, consistent with rebound kinetics observed after treatment interruption in people living with HIV (PLWH). Human immune cells and HIV-1 RNA were more abundant in tissues from Hu-FLT3 mice than in Hu-NSG mice. This study establishes Hu‑FLT3 mice as a novel, robust and accessible in vivo platform to investigate potential HIV cure and persistence‑targeting interventions with translational relevance to human therapeutic development thanks to the improved and more complete human immune repertoire in Hu-FLT3.