Abstract LT003: Fetal differentiation programs afford a protective barrier to NUP98 fusion-driven AML initiation

Abstract Mutations that drive pediatric acute myeloid leukemia (AML) are often age-restricted. NUP98 rearrangements (NUP98r) cause high-risk AML primarily in early-to-mid childhood but are rare in adults. Moreover, NUP98r AML almost never occurs before birth. This pattern suggests that there are developmental windows and associated molecular programs that modulate the transforming effects of mutations like NUP98r, raising the questions of why NUP98r-driven AML predominates in early-to-mid childhood. To address these questions, we developed a novel strategy to model NUP98r AML initiation during different stages of life. We generated mouse induced pluripotent stem cells (iPSCs) that give rise to chimeric mice that express NUP98::HOXA9 (NHA9) specifically in the blood and at specific stages of ontogeny and aging. A similar approach was used to express NHA9 mutants (e.g., intrinsically disordered region or homeodomain mutants) and NUP98::KDM5A (NK). This strategy allows us to efficiently model effects of diverse NUP98 fusions in situ without complex mouse breeding strategies. To test whether NHA9 initiates AML more efficiently in fetal, neonatal, juvenile, or adult mice, we induced NHA9 at embryonic day (E)10.5, postnatal day (P)0, P21, 8 weeks, or 8 months old. We introduced a cooperating Flt3-internal tandem duplication through genome editing. NHA9-expressing juvenile and adult progenitors gave rise to AML with high penetrance whereas fetal and neonatal progenitors did not. This raised the question of why fetal/neonatal progenitors resist transformation and how resistance is overcome in contexts of infant NUP98r AML. To understand why fetal/neonatal progenitors resist transformation, we performed single-cell RNA sequencing on NHA9-expressing progenitor cells after fetal, juvenile, or adult induction. NHA9 drove precocious erythroid differentiation at the expense of self-renewing progenitors in fetal but not juvenile or adult mice. The erythroid bias required a functional homeodomain. Interestingly, mutating the intrinsically disordered region (IDR) proved highly toxic to hematopoietic progenitors in vivo but not in vitro, again reflecting the importance of context in fusion protein function. Fetal NK expression also elicited precocious erythroid differentiation, though the effects were less severe than NHA9. Thus, NK mutations may overcome engrained fetal barriers to transformation more efficiently than NHA9. These results show that age greatly influences the capacity of oncoproteins to drive leukemic transformation and that when infant NUP98r AML does arise, it must overcome barriers to transformation that reflect fetal/neonatal ontogeny. Citation Format: Jihye Yoon, Elisabeth Denby, Wei Yang, Run Zhang, Emily B. Casey, Riddhi M. Patel, Yanan Li, J. Michael White, Luis Batista, Jeffrey Magee. Fetal differentiation programs afford a protective barrier to NUP98 fusion-driven AML initiation [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Fusion-Positive Cancer: From Discovery to Therapy; 2026 Jan 13-15; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(1_Suppl):Abstract nr LT003.