Juvenile myelomonocytic leukemia (JMML) is a rare myeloproliferative disorder of early childhood characterized by expansion of clonal myelomonocytic cells and hyperactive Ras/MAPK signaling. The disorder is caused by somatic and/or germline mutations in genes involved in the Ras/MAPK and JAK/STAT signaling pathways, including CBL. Here we describe the generation of an iPSC line with a homozygous CBL c.1111T->C (Y371H) mutation, designated CHOPJMML1854.

Juvenile myelomonocytic leukemia (JMML) is an uncommon myeloproliferative neoplasm driven by Ras pathway mutations and hyperactive Ras/MAPK signaling. Outcomes for many children with JMML remain dismal with current standard-of-care cytoreductive chemotherapy and hematopoietic stem cell transplantation. We used patient-derived induced pluripotent stem cells (iPSCs) to characterize the signaling profiles and potential therapeutic vulnerabilities of PTPN11-mutant and CBL-mutant JMML. We assessed whether MEK, JAK, and PI3K/mTOR kinase inhibitors (i) could inhibit myeloproliferation and aberrant signaling in iPSC-derived hematopoietic progenitors with PTPN11 E76K or CBL Y371H mutations. We detected constitutive Ras/MAPK and PI3K/mTOR signaling in PTPN11 and CBL iPSC-derived myeloid cells. Activated signaling and growth of PTPN11 iPSCs were preferentially inhibited in vitro by the MEKi PD0325901 and trametinib. Conversely, JAK/STAT signaling was selectively activated in CBL iPSCs and abrogated by the JAKi momelotinib and ruxolitinib. The PI3Kδi idelalisib and mTORi rapamycin inhibited signaling and myeloproliferation in both PTPN11 and CBL iPSCs. These findings demonstrate differential sensitivity of PTPN11 iPSCs to MEKi and of CBL iPSCs to JAKi, but similar sensitivity to PI3Ki and mTORi. Clinical investigation of mutation-specific kinase inhibitor therapies in children with JMML may be warranted.

Multipotent and pluripotent stem cells are potential sources for cell and tissue replacement therapies. For example, stem cell-derived red blood cells (RBCs) are a potential alternative to donated blood, but yield and quality remain a challenge. Here, we show that application of insight from human population genetic studies can enhance RBC production from stem cells. The SH2B3 gene encodes a negative regulator of cytokine signaling and naturally occurring loss-of-function variants in this gene increase RBC counts in vivo. Targeted suppression of SH2B3 in primary human hematopoietic stem and progenitor cells enhanced the maturation and overall yield of in-vitro-derived RBCs. Moreover, inactivation of SH2B3 by CRISPR/Cas9 genome editing in human pluripotent stem cells allowed enhanced erythroid cell expansion with preserved differentiation. Our findings therefore highlight the potential for combining human genome variation studies with genome editing approaches to improve cell and tissue production for regenerative medicine.