Tat(28-35)SL8-specific CD8+ T lymphocytes are more effective than Gag(181-189)CM9-specific CD8+ T lymphocytes at suppressing simian immunodeficiency virus replication in a functional in vitro assay

Abstract

Epitope-specific CD8+ T lymphocytes may play an important role in controlling human immunodeficiency virus (HIV)/simian immunodeficiency virus replication. Unfortunately, standard cellular assays do not measure the antiviral efficacy (the ability to suppress virus replication) of CD8+ T lymphocytes. Certain epitope-specific CD8+ T lymphocytes may be better than others at suppressing viral replication. We compared the antiviral efficacy of two immunodominant CD8+ T lymphocyte responses--Tat(28-35)SL8 and Gag(181-189)CM9--by using a functional in vitro assay. Viral suppression by Tat-specific CD8+ T lymphocytes was consistently greater than that of Gag-specific CD8+ T lymphocytes. Such differences in antigen-specific CD8+-T-lymphocyte efficacy may be important for selecting CD8+ T lymphocyte epitopes for inclusion in future HIV vaccines.

FIG. 1.

VSA schematic. (A) Target cells are freshly isolated PBMC, depleted of CD8⁺ cells, and activated with phytohemagglutinin (PHA). (B) Effector cells are SIV-specific in vitro-stimulated CD8⁺ T cells that are sorted to high specificity. (C) After a 4-h incubation of the target cells with SIV_mac239, we combined target and effector cells at E:T ratios of 1:10, and 1:20. The cocultures were maintained for 8 to 11 days. 0.5 ml of supernatant was taken every 2 days for vRNA quantification. MOI, multiplicity of infection.

FIG. 2.

Day 8 intracellular Gag p27 staining of representative VSA results with Tat_28-35SL8- and Gag_181-189CM9-specific CD8⁺ T-lymphocytes from a single macaque (animal 2125). Results for MHC class I-matched effector and target cells (A) and MHC-mismatched effector (Mamu-A*01⁺) and target (Mamu-A*01⁻) cells (B) at an E:T of 1:10 are shown. Viral suppression only occurred in an MHC class I-restricted fashion.

FIG. 3.

Quantitative PCR of representative VSA results with Tat_28-35SL8- and Gag_181-189CM9-specific CD8⁺ T lymphocytes from macaque 2125. Results for MHC class I-matched effector and target cells (A) MHC-mismatched effector (Mamu-A*01⁺) and target (Mamu-A*01⁻) cells (B) at an E:T of 1:10 are shown. Viral suppression only occurred in an MHC class I-restricted fashion.

FIG. 4.

Day 8 viral suppression by Tat_28-35SL8- and Gag_181-189CM9-specific CD8⁺ T lymphocytes derived from several SIV-infected macaques (animal identification number shown below bars) at an E:T ratio of 1:10 as measured by fold reduction of intracellular Gag p27 (A) and fold reduction of vRNA copies/ml (B). Bars: ▪, Tat-specific cells; □, Gag-specific cells.