Search

Live attenuated HIV vaccines offer a means to introduce exogenous sequences into the viral genome to target the virus elimination in vivo. Foreign genes inserted into the nef region of HIV-1 NL4-3 were found to be rapidly deleted following virus infection and/or replication, in a size dependent manner, in the human fetal Thymus/Liver implants of severe combined immunodeficient mouse (SCID-hu) model. When the murine heat stable antigen (HSA) of 283 bp was substituted into HIV-1 nef region, the viral loads in vivo were comparable to the negative control nef attenuated HIV-1, and the reporter HSA gene was not deleted upon infection. However, the murine Thy1.2 gene (505 bp) substituted into the nef attenuated HIV-1, upon infection and replication, deleted 441 bp in vitro and 437 bp in vivo, of the inserted Thy1.2 gene. When the enhanced green fluorescence protein (eGFP) gene (720 bp) was substituted for nef, virus replication was aborted in vivo in the Thy/Liv implants, as seen by the background levels of viral loads, comparable to mock infected implants, and the eGFP gene was deleted. When the herpes simplex virus thymidine kinase gene, HSV-TK (1.15 kbp), or HSA gene, was substituted into the viral vpr gene, TK but not HSA gene was deleted, upon infection in vitro. Moreover, NL-TKI reporter virus with both intact nef and vpr genes shows deletion of TK gene both in vitro and in vivo. Excision of foreign genes occurred within the exogenous segments but not in the viral own regions. These results suggest that larger "suicide" genes introduced via HIV-1 can be deleted upon infection. However, smaller size nucleotide sequences or genes (approximately 300 bp) inserted in place of viral nef or vpr gene may be used to target the virus or its components, for attack and elimination in vivo, and thus have implications for the development of live attenuated HIV vaccines.

Hematopoietic abnormalities including anemia, cytopenias, and alterations of the stem cell plasticity in the bone marrow microenvironment commonly occur in HIV infected patients. These observations suggest that HIV-1 infection may affect processes important during early stages of hematopoiesis or stem cell differentiation. Hematopoietic abnormalities may be caused by altered stem cell differentiation possibly due to abnormal lineage specific expression of certain cellular genes such as cytokines relevant to hematopoiesis. These cytokines could affect regulatory signals important in hematopoiesis. However, in HIV infected individuals, it is not only the virus but also the highly active antiretroviral therapy (HAART) that both contribute to persistent hematopoietic suppression and ensuing cytopenias. Even if a lowering of HIV replication by HAART were to occur in infected individuals, prolonged HAART by itself and/or appearance of drug resistant mutants can contribute to hematopoietic suppression and resulting cytopenias. However, confounding factors such as opportunistic infections, immune mediated effects, or the consequences of prolonged physiological stress, which could contribute to decreased hematopoiesis in patients or other individuals, make the causative role of HIV in vivo, uncertain. The severe combined immunodeficient mouse transplanted with human fetal thymus and liver tissues (SCID-hu) is a small animal model which mimics HIV infection in humans, and is useful to determine the mechanisms of HIV-1 induced hematopoietic inhibition and development of drug therapies for interventions of stem cell differentiation. Further, SCID mouse serves as a useful small animal recipient of human progenitor cells and also allows us to study the differentiation of these cells in vivo. Results from our studies are expected to provide relief for HIV infected individuals from hematopoietic inhibition and ensuing cytopenias.