HIV infection impairs HPCs. A combination of colony-forming and viral detection assays were used on in vitro– and in vivo–infected HPCs to demonstrate hematological abnormalities. Marked viral-induced suppression was seen on intermediate progenitor cells. (A) For in vivo studies, a humanized BM, liver, and thymus mouse model that supports human hematopoiesis and is susceptible to HIV infection was used. Sixty days postinfection, HPCs were examined for the presence of viral protein expression by flow cytometry and viral DNA by PCR. (B) Viral protein expression was detected in the GMP and the MEP cells. Colony assays showed HPC impairment. HIV-1 infection was detected in multiple populations of intermediate HPCs and their progeny from BM-derived cells of HIV-1–exposed mice. HIV genomes were detected in a granulocyte, macrophage, and erythroid colonies. Viral protein/DNA detection is indicated in colored boxes. CFU-E, colony-forming unit erythroid; CFU-GM, colony-forming unit granulocyte macrophage; CFU-Mk, colony-forming unit megakaryocyte. Professional illustration by Debra T. Dartez.