Enhancing Mucosal-Associated Invariant T (MAIT) cell function and expansion with human selective serum

Mucosal-associated invariant T (MAIT) cells are promising innate-like lymphocytes with potential for use in anti-tumor immunotherapy. Existing MAIT cell expansion protocols are associated with potentially decremental phenotypic changes, including increased frequency of CD4+ MAIT cells and higher inhibitory receptor expression. In this study, we compared the effect on expansion of human MAIT cells of a serum replacement, Physiologix XF SR (Phx), with traditional serum fetal bovine serum (FBS) for supplementing RPMI-1640 media. Using flow cytometry, we found that Phx supported a significantly higher proliferative capacity for MAIT cells and resulted in a lower frequency of CD4+ MAIT cells, which have been associated with reduced Th1 effector and cytolytic functions. We saw that culturing MAIT cells in Phx led to better survival of MAIT cells and lower frequency of PD-1+ MAIT cells compared to FBS-supplemented media. Functionally, we saw that Phx supplementation was associated with a higher frequency of IFN-γ+ MAIT cells after stimulation with E. coli compared to FBS-supplemented RPMI. In conclusion, we show that MAIT cells cultured in Phx have higher proliferative capacity, lower expression of inhibitory receptors, and have higher capacity to produce IFN-γ after E. coli stimulation, compared to FBS-supplemented RPMI. This work shows that expanding MAIT cells with Phx compared to FBS-supplemented RPMI result in a more functionally desirable MAIT cell for future anti-tumor immunotherapy. ### Competing Interest Statement The authors have declared no competing interest.