MR1 and acquired polycythemia vera: In our PV dataset, the total size of the atypical CD3+MR1-restricted, TCRVα7.2- compartment was inversely related to serum IL-18 levels (Figure 5A), whereby peripheral DP (Figure 5B) and CD4+ (Figure 5C) MR1-tet+TCRVα7.2- T cell subsets were largely responsible for the observed effect.