Levels of human immunodeficiency virus type 1-specific cytotoxic T-lymphocyte effector and memory responses decline after suppression of viremia with highly active antiretroviral therapy

Abstract

Therapeutic suppression of human immunodeficiency virus type 1 (HIV-1) replication may help elucidate interactions between the host cellular immune responses and HIV-1 infection. We performed a detailed longitudinal evaluation of two subjects before and after the start of highly active antiretroviral therapy (HAART). Both subjects had evidence of in vivo-activated and memory cytotoxic T-lymphocyte precursor (CTLp) activity against multiple HIV-1 gene products. After the start of therapy, both subjects had declines in the levels of in vivo-activated HIV-1-specific CTLs and had immediate increases in circulating HIV-1-specific CTL memory cells. With continued therapy, and continued suppression of viral load, levels of memory CTLps declined. HLA A*0201 peptide tetramer staining demonstrated that declining levels of in vivo-activated CTL activity were associated with a decrease in the expression of the CD38(+) activation marker. Transient increases in viral load during continued therapy were associated with increases in the levels of virus-specific CTLps in both individuals. The results were confirmed by measuring CTL responses to discrete optimal epitopes. These studies illustrate the dynamic equilibrium between the host immune response and levels of viral antigen burden and suggest that efforts to augment HIV-1-specific immune responses in subjects on HAART may decrease the incidence of virologic relapse.

FIG. 1

Longitudinal plasma HIV-1 RNA levels in subjects 115i (a) and 221l (b). All assays were performed on plasma with the Amplicor assay (Roche).

FIG. 2

Longitudinal CD4 cell numbers in subjects 115i (a) and 221l (b).

FIG. 3

Longitudinal in vivo-activated CTL lysis of vaccinia virus-expressed HIV-1 proteins or peptides representing optimal HLA class I-restricted CTL epitopes by subject 115i. Freshly isolated PBMC were incubated with vaccinia virus-infected autologous B-LCL or peptide-pulsed B-LCL at an E/T ratio of 100:1. Background lysis against NYCBH vaccinia virus-infected target cells was <12% at all time points except on day 20 after the start of therapy, when it was 24%. In each case background lysis was subtracted. Background lysis against unpulsed B-LCL targets was always <5%. The targets used were Vac-Gag (a), Vac-RT (b), Vac-Env (c), Vac-Nef (d), SLYNTVATL (HLA A2 restricted) (e), and ERYLKDQQL (HLA B14 restricted) (f).

FIG. 4

Longitudinal direct CTL lysis of vaccinia virus-expressed HIV-1 proteins by subject 221l. The mean background lysis against NYCBH-infected target cells was 19% (range 2.3 to 42%) and was subtracted. The targets used were Vac-Gag (a), Vac-RT (b), Vac-Env (c), and Vac-Nef (d).

FIG. 5

Longitudinal CTLp frequency in subject 115i. The targets used were Vac-Gag (a), Vac-RT (b), Vac-Env (c), and Vac-Nef (d).

FIG. 6

Longitudinal CTLp frequency in subject 221l. The targets used were Vac-Gag (a), Vac-RT (b), Vac-Env (c), and Vac-Nef (d).

FIG. 7

Longitudinal flow cytometric visualization of A*0201-restricted, SLYNTVATL-specific CTL in subjects 115i and 221l. PBMC were stained with HLA-A*0201/SLYNTVATL tetramers and monoclonal antibodies specific for CD8 and CD38. The limit of detection was 0.02% of CD8⁺ T cells, and the lowest value obtained in either subject was 0.1%. (a) Percentage of tet⁺ CD8⁺ T cells in subject 115i. (b) Percentage of CD38⁺ tet⁺ cells in subject 115i. (c) Percentage of tet⁺ CD8⁺ T cells in subject 221l. (d) Percentage of CD38⁺ tet⁺ cells in subject 221l.