Abstract:
Human immunodeficiency virus (HIV-1) infection remains a significant global public health concern, particularly in sub-Saharan Africa where the majority of HIV infections are concentrated. HIV-1 is known to target the host immune system. However, HIV-infected patients also often present with haematological abnormalities such as cytopenias. Haematopoietic stem/progenitor cells (HSPCs) give rise to all blood cell types and are crucial for maintaining continuous production of blood cells throughout life via the process of haematopoiesis. HSPCs have been investigated in the context of HIV-1 infection with HIV-1 being suggested to negatively affect the functioning of HSPCs through various mechanisms. This leads to impaired haematopoiesis resulting in the manifestation of HIV-associated cytopenias. While not the primary targets of HIV-1, the direct infection of HSPCs is proposed as one of the direct mechanisms by which HIV-1 interacts with HSPCs thereby disrupting optimal haematopoiesis. Uncertainty surrounds whether HSPCs are susceptible to direct infection by HIV-1 as no consensus has been reached regarding this topic. Moreover, the phenotype of HSPCs that may be prone to HIV-1 infection has not been elucidated. The direct infection of bone marrow (BM)-derived HSPCs was investigated in this project by determining if HSPCs from HIV-infected patients harbour HIV-1 proteins. The phenotypic profile of HSPCs that harboured HIV-1 proteins was also established. Firstly, the HIV-associated receptors, namely cluster of differentiation 4 (CD4), C-X-C motif chemokine receptor 4 (CXCR4) and C-C motif chemokine receptor 5 (CCR5) of BM-derived HSPCs from HIV-positive and HIV-negative controls was investigated as an indicator of their susceptibility to HIV-1 infection. CD4 was expressed by HSPCs that were maturing into haematopoietic progenitors with these cells also co-expressing at least one of the co-receptors (CXCR4 or CCR5) required for viral entry. Secondly, the intracellular HIV-1 p24 expression of BM-derived HSPCs was determined. This was done by performing the HIV-flow assay on HSPCs from the BM aspirates of HIV-positive patients. Intracellular p24 was detected in a subset of haematopoietic progenitors. Findings thus indicated that haematopoietic progenitors, of both the lymphoid and myeloid lineage, are prone to direct HIV-1 infection. In addition, the absolute count and sub-population distribution of HSPCs in the BM aspirates of HIV-positive and HIV-negative patients was also investigated. BM aspirates of HIV-positive patients were observed to have elevated HSPCs counts with a myeloid-bias HSPC sub-population distribution. In conclusion, the present study provides evidence of a plausible mechanism involved in the development of HIV-associated cytopenias. It also sheds light on the HIV-induced changes to HSPCs sub-population distribution in the BM compartment of HIV-infected individuals.
