TP53 and leukemia: Although the CCF of JAKV617F+ leukemia cells was increased in P0/P1 xenografts derived from the other 2 patients (Pts 1 and 4) (Table 3), JAKV617F alone did not confer a proliferative advantage to MPN-BP ICs, but rather other coexisting mutations such as TP53 (Pt 1, Supplemental Figure 6A; Pt 4, Figure 4C) were responsible for the expansion of JAKV617F+ MPN-BP IC.