Substitutions in a major histocompatibility complex class II-restricted human immunodeficiency virus type 1 gp120 epitope can affect CD4+ T-helper-cell function

Abstract

It has been suggested that the inability of the immune response to control human immunodeficiency virus type 1 (HIV-1) replication may be due, at least in part, to the capacity of this virus to escape from immune recognition through mutation. While there is increasing evidence for the importance of HIV-1-specific CD4+ T cells in containing HIV-1 spread in the infected individual, little is known about the consequences of HIV-1 mutation on virus-specific CD() T-cell function. The impact of HIV-1 sequence variation on CD4+ T-helper (Th)- cell function was assessed with a rhesus monkey model for immune recognition of the HIV-1 envelope (Env) glycoprotein. A series of HIV-1 Env(484-496) variant peptides were shown to retain the ability to bind to the appropriate rhesus monkey major histocompatibility complex class II DR molecule. Peptides bearing substitutions at position 490, however, failed to drive the proliferation or cytokine secretion of two well-characterized HXBc2 Env-specific rhesus monkey CD4+ Th-cell lines. Exogenous costimulation was ineffective in complementing the ability of the nonstimulatory peptides to induce [3H]thymidine incorporation by these cells. Finally, HIV-1 Env(484-496) variant peptides with substitutions at position 490 antagonized the HXBc2 Env peptide-induced proliferative response of the CD4+ Th-cell lines. Thus, HIV-1 variants appear to have the capacity to neutralize the function of virus-specific CD4+ T lymphocytes.

FIG. 1

Peptides corresponding to naturally occurring variants of the CD4⁺ Th- cell epitope Env (484-496) compete with the Env (171-192) peptide for binding to Mamu-DR*W201 molecules expressed by RM3-transfected antigen-presenting cells. Mamu-DR*W201-expressing RM3 cells were plated at 2 × 10⁴ cells/ well in 96-well flat-bottom microtiter plates and incubated for 2 h with 25 μg of the Env (484-496) variant peptides or an irrelevant Env (241-262) peptide per ml. Approximately 2 × 10⁴ 431.08 CD4⁺ Th cells were then added to each well along with 0.5 μg of the Env (171-192) peptide per ml. Cultures were pulsed with 1 μCi of [³H]thymidine per well after 2 days and harvested on day 3.

FIG. 2

Peptides corresponding to naturally occurring variants of the CD4⁺ Th- cell epitope Env (484-496) bearing substitutions at amino acid position 490 fail to stimulate cytokine secretion by two CD4⁺ Th- cell lines. Approximately 10⁶ CD4⁺ Th cells were cultured in the presence of an equivalent number of autologous B-LCL in 1 ml of medium in the presence or absence of Env (484-496) variant peptides. After 2 days, supernatants were harvested and frozen. Cytokine content was later measured with commercially available ELISA kits.

FIG. 3

HIV-1 Env (484-496) variant peptides with substitutions at position 490 antagonize the recognition of wild-type Env (484-496) as measured in a proliferation assay. Autologous B-LCL were prepulsed with 0.5 μg of the index HXBc2 Env (484-496) peptide per ml for 2 h to stimulate the CD4⁺ Th- cell lines to the levels indicated by the horizontal broken lines. Prepulsed B-LCL were then pulsed for an additional 2 h with the indicated concentrations of the index peptide, the Env (484-496) variant peptides, or the nonstimulatory, Mamu-DR*W201-binding Env (172-191) peptide p15. Results are expressed as [³H]thymidine incorporation in counts per minute. In the absence of peptides, the background proliferation of both Th- cell lines was less than 400 cpm.