Immune checkpoint blockade improves the activation and function of circulating mucosal-associated invariant T (MAIT) cells in patients with non-small cell lung cancer

Abstract

Mucosal-associated invariant T (MAIT) cells constitute one of the most numerous unconventional T cell subsets, and are characterized by rapid release of Th1- and Th17-associated cytokines and increased cytotoxic functions following activation. MAIT cells accumulate in tumor tissue but show an exhausted phenotype. Here, we investigated if immune checkpoint blockade (ICB) with antibodies to PD-1 or PD-L1 affects the function of circulating MAIT cells from non-small cell lung cancer patients. ICB increased the proliferation and co-expression of the activation markers HLA-DR and CD38 on MAIT cells in most patients after the first treatment cycle, irrespective of treatment outcome. Furthermore, production of cytokines, especially TNF and IL-2, also increased after treatment, as did MAIT cell polyfunctionality. These results indicate that MAIT cells respond to ICB, and that MAIT cell reinvigoration may contribute to tumor regression in patients undergoing immune checkpoint therapy.

Keywords: Immune checkpoint blockade; MAIT cell; PD-1; immunotherapy; non-small cell lung cancer.

Figure 1.

Activation markers in MAIT cells. Circulating MAIT cells were collected before and after the first treatment cycle with ICB and analyzed by flow cytometry for their expression of Ki67 (a), HLA-DR (b), CD38 (c), and co-expression of HLA-DR and CD38 (d). Left-hand graphs show all patients, and the right-hand graphs show patients grouped by treatment outcome. Symbols represent individual values. Bright green circles represent patients receiving ICB as their only treatment and dark green circles patients receiving ICB together with or after chemotherapy. Dot-plots show the expression of Ki67 and HLA-DR vs CD38 in MAIT cells gated as in Supplementary Figure S1 before and after the first treatment cycle. *p< .05, n=10–14.

Figure 2.

Cytokine production by MAIT cells. Circulating MAIT cells were collected before and after the first treatment cycle with ICB, activated by treatment with PMA and Ionomycin and analyzed by flow cytometry for their production of TNF (a), IL-2 (b), IFN-γ (c), and GrB (d). Left-hand graphs show all patients, and the right-hand graphs show patients grouped by treatment outcome. Symbols represent individual values. Bright green circles represent patients receiving ICB as their only treatment and dark green circles patients receiving ICB together with chemotherapy. Dot-plots show the expression of IL-2 vs TNF (e) and GrB vs IFN-γ (f) in MAIT cells gated as in Supplementary Figure S1 before and after the first treatment cycle. *p < .05, n=9.

Figure 3.

Polyfunctionality in MAIT cells. Circulating MAIT cells were collected before and after the first treatment cycle with ICB and analyzed by flow cytometry for their production of TNF, IL-2, IFN-γ, and GrB. (a) Polyfunctionality index before and after the first treatment cycle. (b) Percentage of cells with 4, 3, 2, 1, or 0 functions before (pink and light grey circles) and after (red and dark grey circles) the first treatment cycle. Symbols represent individual values and the lines the median. Pink and red circles represent patients receiving ICB as their only treatment and light and dark grey circles patients receiving ICB together with chemotherapy. *p < .05, n=9.