699 Similarities and Differences in the Fate of HIV-1 Infection in Human Astrocytes and Neural Progenitor Cells D. Lawrence*, L. Durham, E. Major Natl Inst of Neurological Disorders and Stroke, NIH, Bethesda, MD
Background: Although monocytic cells are the predominant source of HIV-1 in the brain, little is understood about HIV-1 replication in astrocytes or other critical cells in the CNS, including neural stem and progenitor cells abundant in the immature brain. The goal of this study was to compare the susceptibility and fate of HIV-1 infection in human neural progenitor cells and astrocytes.
Methods: Undifferentiated nestin+ progenitor cells were isolated from human fetal brain tissue under selective growth conditions and either grown as attached cell layers or differentiated into highly purified GFAP+ astrocyte populations. Astrocytes and progenitors transfected with the infectious HIV-1 clone, pNL4-3, were tested for viral production by p24 ELISA. Infectivity of the supernatant virus was confirmed using the H938 LTR-CAT indicator T-cell line (NIH AIDS Reagent Program). Immunohistochemical staining of p24 viral antigen was also performed.
Results: pNL4-3 transfection of both progenitor cultures and progenitor-derived astrocytes resulted in a productive infection for 2-6 days, but diminished to low but detectable levels (50-200 pg of p24/106 cells) by 8 days post-transfection. Immunohistochemical analysis also showed evidence of intracellular virus in a small subset of both progenitors and astrocytes; cell-free supernatants from these cultures (3-4 days post-transfection) were infectious to T-cells. The peak production at 3 days post-transfection was 5-fold higher in astrocytes (27 ng of p24/106 cells) compared to progenitors (5 ng of p24/106 cells). Viral antigen production was still detectable after 3 wks in astrocytes and after 5 weeks in progenitor cells, indicating a persistent infection in both cell types. Treatment of either phenotype with 50 ng/ml TNF-alpha after 3, 4, or 5 wks post-transfection increased p24 production at least 2- to 3-fold within 48 h, even when astrocyte virus production was normally undetectable. Finally, when infected progenitors were differentiated to astrocytes, HIV-1 p24 production immediately increased, providing further evidence that 1) progenitor cells can harbor virus that can be activated, and 2) HIV-1 regulatory factors differ in astrocytes and progenitor cells.
Conclusions: These results suggest that both astrocytes and undifferentiated neural progenitor cells are permissive for HIV-1, and may support latent or persistent infection that can be activated by TNF-alpha or differentiation pathways.