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Journal of Virology, May 2004, p. 4541-4551, Vol. 78, No. 9
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.9.4541-4551.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Apoptosis of Bystander T Cells Induced by Human Immunodeficiency Virus Type 1 with Increased Envelope/Receptor Affinity and Coreceptor Binding Site Exposure

Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115,¹ Department of Pathology,² Neurology, Harvard Medical School, Boston, Massachusetts 02115,⁵ Laboratory of Retrovirus Research, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892,³ Laboratory of Experimental Chemotherapy, Rega Institute for Medical Research, Katholieke Universiteit Leuven, Leuven, Belgium⁴

Received 6 November 2003/ Accepted 22 December 2003

Apoptosis of uninfected bystander CD4⁺ T cells contributes to T-cell depletion during human immunodeficiency virus type 1 (HIV-1) pathogenesis. The viral and host mechanisms that lead to bystander apoptosis are not well understood. To investigate properties of the viral envelope glycoproteins (Env proteins) that influence the ability of HIV-1 to induce bystander apoptosis, we used molecularly cloned viruses that differ only in specific amino acids in Env. The ability of these strains to induce bystander apoptosis was tested in herpesvirus saimiri-immortalized primary CD4⁺ T cells (CD4/HVS), which resemble activated primary T cells. Changes in Env that increase affinity for CD4 or CCR5 or increase coreceptor binding site exposure enhanced the capacity of HIV-1 to induce bystander apoptosis following viral infection or exposure to nonreplicating virions. Apoptosis induced by HIV-1 virions was inhibited by CD4, CXCR4, and CCR5 antibodies or by the CXCR4 inhibitor AMD3100, but not the fusion inhibitor T20. HIV-1 virions with mutant Envs that bind CXCR4 but are defective for CD4 binding or membrane fusion induced apoptosis, whereas CXCR4 binding-defective mutants did not. These results demonstrate that HIV-1 virions induce apoptosis through a CXCR4- or CCR5-dependent pathway that does not require Env/CD4 signaling or membrane fusion and suggest that HIV-1 variants with increased envelope/receptor affinity or coreceptor binding site exposure may promote T-cell depletion in vivo by accelerating bystander cell death.

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