AEGiS-9CROI: Apoptosis of Uninfected Bystander T Cells Induced by HIV-1 Viruses with Enhanced Affinity for CD4 and Increased Exposure of the Co-Receptor Binding Site

9th Conference on Retroviruses and Opportunistic Infections

Seattle, Washington - February 24 -February 28, 2002

Apoptosis of Uninfected Bystander T Cells Induced by HIV-1 Viruses with Enhanced Affinity for CD4 and Increased Exposure of the Co-Receptor Binding Site

Conf Retroviruses Opportunistic Infect 2002 Feb 24-28;9:abstract no. 29
Holm G, Zhang C, Gabuzda D; Dana-Farber Cancer Inst., Boston, MA

BACKGROUND: During HIV-1 infection, both infected and uninfected CD4⁺ T cells undergo apoptosis, contributing to T-cell depletion. We investigated the ability of HIV-1 to induce apoptosis in uninfected bystander CD4⁺ and CD8+ T cells, and determinants of the viral envelope that influence indirect cytopathic effects.

METHODS: HVS-immortalized T cells (CD4/HVS) and primary T cells were infected with CXCR4-tropic viruses SG3, ELI-1, ELI-4, and ELI-6. ELI-1 is a primary isolate that was passaged to derive ELI-4 and ELI-6, which exhibit increased CD4 affinity and fusogenicity. FACS analysis of infected cultures stained with 7AAD, anti-p24-PE and TUNEL-FITC was performed on days 7 and 14. In other experiments, CD4/HVS cells or primary T cells were incubated with non-replicating HIV-1 virions.

RESULTS: On day 14 of infection with SG3, ELI-4, and ELI-6, 10-30% of CD4/HVS cells were TUNEL+ and p24-. Non-replicating virions induced apoptosis 3- to 4-fold over background (p<.05). ELI-4 and ELI-6 induced higher levels of apoptosis in uninfected cells than ELI-1, indicating that increased CD4 affinity and/or fusogenicity is associated with enhanced cytopathicity. CD4⁺ T cell apoptosis induced by non-replicating virions was blocked by anti-CD4, anti-CXCR4, and anti-gp120 antibodies, and by AMD3100. The CD4-independent viruses 8x-NL4-3 and 8xV3BaL-NL4-3, which have increased exposure of the coreceptor binding site and enhanced fusogenicity compared to the CD4-dependent parental controls, induced higher levels of apoptosis than the control viruses. Virions produced in 293T cells did not induce apoptosis. However, the ability of 293T-produced virions to induce apoptosis could be restored by co-transfecting MHC class II molecules. Finally, uninfected primary CD4⁺ and CD8+ T cells were shown to undergo apoptosis in ELI-6-infected cultures, and when incubated with non-replicating virions.

CONCLUSIONS: HIV-1 virions induce bystander cell apoptosis in CD4/HVS and primary CD4⁺ and CD8+ T cells. The ability of virions to induce bystander apoptosis is enhanced by viral envelope glycoproteins with increased affinity for CD4 and/or increased exposure of the coreceptor binding site, and is influenced by cell surface molecules that are incorporated into the viral membrane. These findings suggest that reduced CD4 dependence and enhanced fusogenicity are properties of the viral envelope glycoproteins which enhance indirect cytopathic effects of HIV-1.

Keywords: Antigens, CD4, HIV-1, Apoptosis, T-Lymphocytes, CD4-Positive T-Lymphocytes, HIV Infections, Virion, Antigens, CD8, Membrane Glycoproteins, Antigens, CD, Greece, CD9 antigen, virology, immunology

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Copyright © 2002 - Foundation for Retrovirology and Human Health. Reproduction of this abstract (other than one copy for personal reference) must be cleared through the Foundation for Retrovirology and Human Health. Licensed (AIDSLINE) from National Library of Medicine.