Preserved Mucosal-Associated Invariant T-Cell Numbers and Function in Idiopathic CD4 Lymphocytopenia

Abstract

Background: Mucosal-associated invariant T (MAIT) cells constitute a subset of unconventional, MR1-restricted T cells involved in antimicrobial responses as well as inflammatory, allergic, and autoimmune diseases. Chronic infection and inflammatory disorders as well as immunodeficiencies are often associated with decline and/or dysfunction of MAIT cells.

Methods: We investigated the MAIT cells in patients with idiopathic CD4+ lymphocytopenia (ICL), a syndrome characterized by consistently low CD4 T-cell counts (<300 cell/µL) in the absence of HIV infection or other known immunodeficiency, and by susceptibility to certain opportunistic infections.

Results: The numbers, phenotype, and function of MAIT cells in peripheral blood were preserved in ICL patients compared to healthy controls. Administration of interleukin-7 (IL-7) to ICL patients expanded the CD8+ MAIT-cell subset, with maintained responsiveness and effector functions after IL-7 treatment.

Conclusions: ICL patients maintain normal levels and function of MAIT cells, preserving some antibacterial responses despite the deficiency in CD4+ T cells.

Clinical trials registration: NCT00867269.

Keywords: IL-7; MAIT cells; idiopathic CD4+ lymphocytopenia.

Figure 1.

Levels of MAIT cells are preserved in peripheral blood of ICL patients compared to HCs at steady state. A, Flow cytometry gating strategy to identify total MAIT cells in peripheral blood of study participants. B–D, Frequency of total MAIT cells identified by CD161 and Vα7.2 markers (B) or MR1 tetramer (C), and total number of MAIT cells (D) in peripheral blood of tested participants. E–G, Frequency of MAIT subpopulations CD4⁺ (E), CD8⁺ (F), and CD4⁻CD8⁻ (G) in peripheral blood of study participants. Scatter plots show median ± IQR. ICL, n = 30; HCs, n = 14. Identity numbers on the plots indicate patients falling outside the IQR. Data tested by Mann-Whitney U tests to detect differences across multiple samples. Abbreviations: HC, healthy control; ICL, idiopathic CD4⁺ lymphocytopenia; IQR, interquartile range; MAIT cell, mucosal-associated invariant T cell; MR1, MHC class I-related protein 1; TCR, T-cell receptor.

Figure 2.

Immunophenotype of MAIT cells in peripheral blood of ICL patients and HCs at steady state. A, Expression of activation markers on MAIT cells (CD57, HLA-DR, CD25, CD127, CD56, and CD38). B, Expression of inhibitory markers on MAIT cells (Ki-67, Prf, and GrzB). C, Expression of markers indicating cytotoxic capacity and proliferation (PD-1, TIM-3, and LAG-3). Scatter plots show median ± IQR. ICL, n = 30; HCs, n = 14. Data tested by Mann-Whitney U tests to detect differences across multiple samples. Identity numbers on the plots indicate patients falling outside the IQR. Abbreviations: gMFI, geometric mean fluorescence intensity; GrzB, granzyme B; HC, healthy control; ICL, idiopathic CD4⁺ lymphocytopenia; LAG-3, lymphocyte-activation gene 3; MAIT cell, mucosal-associated invariant T cell; PD-1, programmed cell death 1; Prf, perforin; TIM-3, T-cell immunoglobulin mucin 3.

Figure 3.

Function of MAIT cells tested in PBMCs from peripheral blood of ICL patients and HCs. A–C, MAIT-cell expression of CD69 IFN-γ, TNF-α, GrzB, and Prf in PBMCs stimulated with Escherichia coli (A), Pseudomonas aeruginosa (B), or IL-12 combined with IL-18 for 24 hours. Scatter plots show median ± interquartile range. ICL, n = 30; HCs, n = 14. Data tested by Mann-Whitney U tests to detect differences across multiple samples. Abbreviations: gMFI, geometric mean fluorescence intensity; GrzB, granzyme B; HC, healthy control; ICL, idiopathic CD4⁺ lymphocytopenia; IFN-γ, interferon-γ; IL, interleukin; MAIT cell, mucosal-associated invariant T cell; PBMC, peripheral blood mononuclear cell; Prf, perforin; TNF-α, tumor necrosis factor-α.

Figure 4.

Effect of IL-7 treatment on levels of MAIT cells in peripheral blood of ICL patients. A and B, Frequency and absolute numbers of MAIT cells following 12 weeks of treatment with IL-7 in ICL patients. C–E, Absolute numbers of CD8⁺ (C), CD4⁺ (D), and CD4⁻CD8⁻ (E) MAIT subpopulations following 12 weeks of treatment with IL-7 in ICL patients. Before-after plots show median; n = 6 ICL patients. Data tested by Wilcoxon signed-rank tests. * P < .05. Abbreviations: ICL, idiopathic CD4⁺ lymphocytopenia; IL-7, interleukin-7; MAIT cell, mucosal-associated invariant T cell.

Figure 5.

Phenotype and cytotoxic capacity of MAIT cells following IL-7 treatment in ICL patients. A–C, Frequencies of MAIT cells expressing activation markers and CD127. D and E, Frequencies of MAIT cells expressing markers indicating cytotoxic capacity. F, Frequencies of cycling MAIT cells. Before-after plots show median; n = 6 ICL patients. Data tested by Wilcoxon signed-rank tests. * P value < .05. Abbreviations: GrzB, granzyme B; ICL, idiopathic CD4⁺ lymphocytopenia; IL-7, interleukin-7; MAIT cell, mucosal-associated invariant T cell; Prf, perforin.