Despite the known limitations of xeno-transplant models (38, 43, 49), this polyclonal engraftment in infected hosts is noteworthy given the numerous previous reports on the direct and indirect effects of HIV infection on BM niche cells, including HSPC (15), stromal cells (16), and possibly, CD4+ T cells that reside in the niche (17). This evidence concerns the gene CD4 and HIV infectious disease.