Age-Specific Induction of Mutant p53 Drives Clonal Hematopoiesis in Adult Mice Leading to Acute Myeloid Leukemia

Background: Acute Myeloid Leukemia (AML) is a devastating hematological malignancy commonly observed in the elderly population. Mutations in TP53 can give rise to clonal hematopoiesis (CH), a condition preceding leukemia, where mutated hematopoietic stem cells (HSCs) proliferate without developing overt malignancy. The mechanisms underlying progression of TP53 mutant CH to AML and lymphoma remain incompletely understood. Through the creation of a traceable conditional Trp53-mutant CH model and complementary genetic models, we demonstrate that the age of HSCs is critical in determining whether the transformation leads to myeloid or lymphoid malignancy. Methods: To induce p53 mutation in early hematopoietic stem cells, we generated two cohorts of mice, one with Vav-Cre-mediated recombination of a conditional Trp53 allele ( Vav-Cre; Trp53 fl/wmR172H) and another with recombination of homozygous conditional floxed alleles ( Vav-Cre; Trp53 fl/fl), allowing us to compare the effects of p53 mutation versus complete loss of p53 in hematopoietic stem cells. To investigate the impact of Trp53 mutation on adult HSCs and their clonal evolution into myeloid malignancies, we developed an inducible mouse model driven by Mx1-cre. The inducible conditional mouse model allowed us to induce a somatic Trp53 mutation in HSCs of mice at 4 months of age, which is equivalent to young adult humans, and track the recombined cells using the mTmG allele ( Fig. 1A). Results: Mice with Trp53 mutations and Trp53 deletion introduced early in life developed lymphoma with complete penetrance, indicating that early-age mutation or deletion of Trp53 is more likely to lead to lymphoma development. However, when a somatic Trp53 mutation was induced in adult HSCs ( Mx1-Cre;Trp53 wmR172H/fl;mTmG mice), it resulted in myeloid-biased hematopoiesis leading to AML. Fluorescence microscopy analysis of the bone marrow (BM) clearly showed the presence of clonal clusters of GFP+ cells ( Fig. 1B). These GFP+ cells formed distinct colonies ( Fig. 1C) and were detectable in the peripheral blood ( Fig. 1D). The population of Trp53 mutant (GFP+) cells increased over time ( Fig. 1E). Flow cytometry analysis of peripheral blood after three months revealed an increased myeloid population defined as CD11b+ ( Fig. 1F). While the p53 wild-type group showed relatively stable population levels over time, the p53 mutant population displayed a significant expansion with increasing duration following pIpC injection. Cy