D661Y STAT3 mutation in a hypocellular MDS case. (A-B) Immunodominant Vβ1 fraction before sorting; among the CD8 Vβ repertoire; and blood mononuclear cells. (C-D) Vβ1-positive and -negative fraction after blood mononuclear cell sorting. (E) Presence of the ARMS-PCR D661Y allele only in the Vβ1⁺ population.