MR1 and acquired polycythemia vera: We complement and expand these findings by reporting an inverse association of canonical (TCRVα7.2+) circulating MR1-tet+ CD4+CD8- and CD4+CD8+, but not CD4-CD8+ and CD4-CD8-, or MR1-restricted TCRVα7.2- T cells with PV, adding to a growing body of literature on immune cell aberrations in PV.