Baseline circulating MAIT cell count and colitis in Cohort 3.
We sought to determine if baseline MAIT cell proportion could be used as
a peripheral biomarker to predict IN-COL in a second distinct cohort in
a blinded manner. Our validation of gating analysis using Cohort 3 found
high correlation between the two results (R2=0.989; p
= 1.3x10-72; Supplementary Figure 3a-b). Absence of
non-specific background staining for CD161 and TCR Vα7.2 was
demonstrated in additional experiments using isotype control antibodies
(see Supplementary Figure 2bii). We confirmed in Cohort 3 that melanoma
patients who develop IN-COL (N=14) have a lower proportion of
circulating MAIT cells compared with healthy volunteers (Figure 4c). In
contrast to Cohort 2, where baseline MAIT cells was a useful
discriminator between the IN-COL and IN-NAE groups, in Cohort 3 the
IN-NAE patients also had a lower proportion of circulating MAIT cells at
baseline compared to healthy volunteers and there was no significant
difference between IN-COL and IN-NAE MAIT cell proportions (Figure 4c).