Although CSF3R/RUNX1/CXXC4 mutant cells could repopulate and form AML in multiple secondary (n = 6) and tertiary (n = 8) recipients, the CXXC4-ITD mutation originally arose in a single primary recipient (1/9), who acted as a donor for subsequent retransplantation studies. Here, CXXC4 is linked to acute myeloid leukemia.