Activation, exhaustion, and persistent decline of the antimicrobial MR1-restricted MAIT-cell population in chronic HIV-1 infection

Abstract

Mucosal-associated invariant T (MAIT) cells are an evolutionarily conserved antimicrobial MR1-restricted T-cell subset. MAIT cells are CD161(+), express a V7.2 TCR, are primarily CD8(+) and numerous in blood and mucosal tissues. However, their role in HIV-1 infection is unknown. In this study, we found levels of MAIT cells to be severely reduced in circulation in patients with chronic HIV-1 infection. Residual MAIT cells were highly activated and functionally exhausted. Their decline was associated with time since diagnosis, activation levels, and the concomitant expansion of a subset of functionally impaired CD161(+) V7.2(+) T cells. Such cells were generated in vitro by exposure of MAIT cells to Escherichia coli. Notably, whereas the function of residual MAIT cells was at least partly restored by effective antiretroviral therapy, levels of MAIT cells in peripheral blood were not restored. Interestingly, MAIT cells in rectal mucosa were relatively preserved, although some of the changes seen in blood were recapitulated in the mucosa. These findings are consistent with a model in which the MAIT-cell compartment, possibly as a result of persistent exposure to microbial material, is engaged, activated, exhausted, and progressively and persistently depleted during chronic HIV-1 infection.

Figure 1

MAIT cells are depleted in the peripheral blood of chronically HIV-infected patients. (A) Identification of peripheral blood MAIT cells in uninfected and HIV-infected individuals. The frequency of total MAIT cells (B), and DN, CD4, and CD8 subsets (C) was determined in 34 HIV-1–uninfected individuals and 33 patients with chronic untreated HIV-infection. (D) The relationship between MAIT-cell frequency and time since HIV diagnosis was assessed using Spearman rank correlation. The numbers (E) and frequency (F) of MAIT cells, and CD4 T-cell counts (G) were compared in 22 HIV-infected patients before and after commencing cART. Box and whisker plots show median, IQR and the 10th to 90th percentile. Tx indicates therapy.

Figure 2

MAIT cells are functionally impaired in chronically HIV-infected patients. (A) The gating strategy for fixed Escherichia coli–activated MAIT cells in blood from HIV-1–uninfected and HIV-infected individuals. Gray dots represent unstimulated controls from the same donors. CD69, IFNγ, TNF, and IL-17 expression were determined in 10 uninfected and untreated HIV-infected individuals after an overnight stimulation with fixed E coli (B) and a 6 hour PMA/ionomycin stimulation (C). MAIT-cell activation and cytokine production from these HIV-infected patients were then assessed using an overnight bacterial stimulation after commencing cART (D). Box and whisker plots show median, IQR, and the 10th to 90th percentile. Tx indicates therapy.

Figure 3

MAIT cells express activation phenotypes in chronically HIV-infected patients. (A) The gating strategy for CD38^hi, HLA-DR, TIM-3, CD27, CD57, and CD127 expression on MAIT cells in HIV-1–uninfected and HIV-infected individuals. The expression of these markers was determined in 33 uninfected and 29 untreated HIV-infected individuals (B), and in 20 HIV-infected individuals before and after commencing cART (C). Spearman rank correlation between CD38^hi-expressing MAIT cells (D) and total CD8 T cells (E) with the frequency of MAIT cells in the peripheral blood of 29 untreated HIV-infected individuals. Box and whisker plots show median, IQR and the 10th and 90th percentile. Tx indicates therapy.

Figure 4

Accumulation of CD161⁻ Vα7.2⁺ T cells in the peripheral blood of chronically HIV-infected patients. (A) Identification and frequency of CD161⁻ Vα7.2⁺ T cells in 34 HIV-1–uninfected and 33 untreated HIV-infected individuals. The frequency of total Vα7.2⁺ T cells is shown in subpanel iii. (B) Peripheral blood MAIT cells that were defined as IL-18R⁺ Vα7.2⁺ T cells (Bi left), and the proportion of IL-18R⁺ Vα7.2⁺ MAIT cells that did not express CD161 (Bi right) was determined in HIV-1 uninfected and HIV-1 infected individuals (iii). The frequency of CD161⁻ IL-18R⁺ Vα7.2⁺ MAIT cells as a percentage of CD3⁺ T cells is shown in subpanel iv. The relationship between proportion of IL-18R⁺ Vα7.2⁺ MAIT cells that did not express CD161 and time since HIV diagnosis was assessed using Spearman rank correlation (v). (C) The frequency of Vβ2/Vβ13.1/Vβ13.2/Vβ13.6⁺ CD161⁺ Vα7.2⁺ MAIT cells and CD161⁻ Vα7.2⁺ T cells in 13 uninfected controls and 12 HIV-infected patients (i-ii). The CD4 and CD8 distribution of CD161⁻ Vα7.2⁺ T cells in a representative uninfected control, a viremic, and an elite controller HIV-infected patient (iii). (D) A representative figure of the transcription factor PLZF expression in CD161⁺ Vα7.2⁺ MAIT (Di left) and CD161⁻ Vα7.2⁺ T cells (Di right). Black lines denote uninfected control and gray lines untreated HIV-infected patient. Light gray lines denote FMO controls. The PLZF mean fluorescence intensity (MFI) from 12 uninfected controls and 19 HIV-infected patients is shown in subpanel ii. Box and whisker plots show median, IQR and the 10th to 90th percentile. VL indicates viral load; and Tx, therapy.

Figure 5

CD161⁻ Vα7.2⁺ T cells in chronic HIV-1 patients are highly activated and can be generated by stimulation with E coli. (A) Representative CD38, HLA-DR and CD57 staining on MAIT (gray line) and CD161⁻ Vα7.2⁺ T cells (black line) from the same HIV-1 patient. (B) The expression of these markers was determined in 29 untreated HIV-infected individuals. (C) Vα7.2⁺ cells were purified by MACS-sorting and cocultured for 3 days with autologous unstimulated or fixed E coli–fed monocytes at indicated MOI (i). Ki67 expression was determined in CD161⁻ Vα7.2⁺ T cells (ii). Gray lines represent unstimulated and black lines represent fixed E coli–fed cultures. A representative figure from 3 independent HIV-1–uninfected donors is shown.

Figure 6

MAIT cells and CD161⁻ Vα7.2⁺ T cells in rectal mucosa of uninfected and HIV-infected individuals. Identification, frequency, and distribution of CD4 and CD8 subsets of rectal MAIT cells in 9 HIV-1–uninfected and 11 HIV-infected individuals (A-C). Spearman correlation between peripheral blood and rectal MAIT cells with time since HIV diagnosis (D), and a simple linear regression analysis of the relationship between frequency of blood MAIT cells and rectal MAIT cells (both are log₁₀-transformed) in uninfected and infected individuals (E). The frequency of CD161⁻ Vα7.2⁺ T cells (F) and IL-18R⁺ Vα7.2⁺ MAIT cells that did not express CD161 (G) in blood and rectal mucosa of HIV-1 infected and uninfected individuals. (H) Spearman correlation between the proportion of IL-18R⁺ Vα7.2⁺ MAIT cells that did not express CD161 and time since HIV diagnosis. (I) Frequency of CD4 T cells in the rectal mucosa. Open circles represent peripheral blood and closed circles represent rectal mucosa. Box and whisker plots show median, IQR and the 10th to 90th percentile.