Expansion of Inefficient HIV-Specific CD8 T Cells during Acute Infection

Abstract

Attrition within the CD4(+)T cell compartment, high viremia, and a cytokine storm characterize the early days after HIV infection. When the first emerging HIV-specific CD8(+)T cell responses gain control over viral replication it is incomplete, and clearance of HIV infection is not achieved even in the rare cases of individuals who spontaneously control viral replication to nearly immeasurably low levels. Thus, despite their partial ability to control viremia, HIV-specific CD8(+)T cell responses are insufficient to clear HIV infection. Studying individuals in the first few days of acute HIV infection, we detected the emergence of a unique population of CD38(+)CD27(-)CD8(+)T cells characterized by the low expression of the CD8 receptor (CD8(dim)). Interestingly, while high frequencies of HIV-specific CD8(+)T cell responses occur within the CD38(+)CD27(-)CD8(dim)T cell population, the minority populations of CD8(bright)T cells are significantly more effective in inhibiting HIV replication. Furthermore, the frequency of CD8(dim)T cells directly correlates with viral load and clinical predictors of more rapid disease progression. We found that a canonical burst of proliferative cytokines coincides with the emergence of CD8(dim)T cells, and the size of this population inversely correlates with the acute loss of CD4(+)T cells. These data indicate, for the first time, that early CD4(+)T cell loss coincides with the expansion of a functionally impaired HIV-specific CD8(dim)T cell population less efficient in controlling HIV viremia.

Importance: A distinct population of activated CD8(+)T cells appears during acute HIV infection with diminished capacity to inhibit HIV replication and is predictive of viral set point, offering the first immunologic evidence of CD8(+)T cell dysfunction during acute infection.

FIG 1

Longitudinal changes in HIV-1 load and CD4 and CD8 T cell absolute counts. (A) Average absolute CD4 T cell count (blue box), absolute CD8 T cell count (black box), and viral load (red circle) are presented for 24 individuals identified during acute HIV infection. (B) Aggregate CD8 T cell absolute counts are displayed for all 24 individuals during acute HIV infection.

FIG 2

Bulk CD8 T cell receptor changes through acute HIV-1 infection. Changes of individual markers on CD8 T cells for all patients during acute HIV infection. The relative frequency of CD8 T cells expressing α4β7 (A), CCR5 (B), CD27 (C), CD28 (D), CD38 (E), CD45RA (F), CD45RO (G), CD57 (H), CD95 (I), CD127 (J), CXCR3 (K), HLA-DR (L), and PD-1 (M) is shown. Color-coding across panels indicates each subject, and day 0 indicates the day of the first reactive HIV-1 Aptima nucleic acid test.

FIG 3

Longitudinal changes of surface maker expression on CD8⁺ T cells during acute HIV infection. (A) Relative changes (Z-score) of surface markers on CD8⁺ T cells during acute HIV infection. Average viral loads are depicted as red-segmented lines from the first RNA-positive HIV nucleic acid test. (B) Color intensity map of the most dramatic shifts within the CD8⁺ T cell populations during acute HIV infection. Populations are shown as a median frequency of CD8⁺ T cells based on specific combinations of receptors from green (no expression) to red (∼40% expression). (C) Successive pseudocolor plots from CD8⁺ T cells, demonstrating CD38 against CD27 longitudinally, through acute HIV-1 infection and the emergence of a CD38⁺ CD27⁻ population in a representative donor. (D) Expansion of cells in association with viral loads. (E) Concatenated polychromatic plot of CD8 over time depicts the emergence of the CD38⁺ CD27⁻ population as a CD8^dim subset.

FIG 4

Temporal dynamics of CD4⁺ T cell count, HIV-1 viral load, CD38⁺ CD27⁻ CD8^dim T cell population, and plasma cytokine levels during acute HIV infection (n = 22). Two study participants were considered to have missing set point viral loads and were excluded. (A and B) Correlation of acute CD4 count nadir and HIV-1 viral load (A) and frequency of CD38⁺ CD27⁻ CD8^dim T cells an average 7 days after peak viral load (B). (C) Smoothed curve of means showing trends in 22 HIV-1-infected individuals of CD4 absolute counts (green) and CD38⁺ CD27⁻ CD8^dim T cell frequency (blue). (D) Scaled proportional group means of IL-2 (red), IL-7 (green), IL-15 (gray), and IL-21 (orange) relative to plasma baseline levels for each analyte. Mean fold difference from the background is presented for CD38⁺ CD27⁻ CD8^dim T cell frequency.

FIG 5

HIV-1-specific CD8⁺ T cells within the CD8^bright and CD8^dim population. PBMC from three donors were chosen an average 8, 19, 53, and 93 days after the 1st RNA-positive HIV nucleic acid test. (A) Shown are the kinetics of total HIV-specific CD8⁺ T cell responses (CD107a, IFN-γ, and/or IL-2) in each individual measured by flow cytometry. (B) The majority of HIV-specific CD8⁺ T cell responses emerge from the CD8^dim (red) T population. (C) Representative donor demonstrating the effector phenotype of the HIV-specific CD8⁺ T cell responses (in red) overlaying the total CD8 compartment (contour plot, in gray). (D) Pie charts showing average frequency of HIV-specific CD8^bright and CD8^dim T cells with combinatorial expression of 5 phenotypic markers assessed. Arcs show individual expression levels of each phenotypic marker. (E) Box-and-whisker plots show the relative expression of phenotypic markers between HIV-specific CD8^bright and CD8^dim T cells 39 days after peak viremia. Different donor responses are indicated by different colors for various peptide pools. Nonparametric comparisons were performed using the Wilcoxon method, and nonsignificant relationships are denoted as NS.

FIG 6

CD8^dim CD38⁺ CD27⁻ T cell population demonstrates a less efficient ability to inhibit viral replication in vitro and is associated with higher viral loads in vivo. (A) Sorting strategy for CD8^bright and CD8^dim cells. (B) Differences in viral inhibition between CD8^bright and CD8^dim T cells. (C) CD8^dim CD38⁺ CD27⁻ T cell frequency correlates positively with contemporaneous viral loads an average of 7 days after peak viral load and (D) negatively correlates with contemporaneous CD4⁺ T cell count. (E) Maximum CD8^dim CD38⁺ CD27⁻ T cell frequency was predictive of HIV set point using linear regression after the removal of two potential outliers. (F) CD8^dim CD38⁺ CD27⁻ T cell frequency an average of 7 days after peak viral load correlates directly with set point activation of CD4⁺ T cells (CD38⁺ HLADR⁺).