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Engineered Bcor mutations lead to acute leukemia of progenitor B-1 lymphocyte origin in a sensitized background

Mianmian Yin, Yang Jo Chung, R. Coleman Lindsley, Robert L. Walker, Yuelin J. Zhu, Benjamin L. Ebert, Paul S. Meltzer and Peter D. Aplan

Key Points

  • Engineered Bcor truncation mutations collaborate with NUP98-PHF23 (NP23) fusion to generate progenitor B-1 acute lymphoblastic leukemia.

  • NP23/Bcor pro-B-1 ALL acquire somatic Jak mutations and are sensitive to therapy with Jak inhibitors in vitro and in vivo.

Abstract

Approximately 10% of NUP98-PHF23 (NP23) mice develop an aggressive acute lymphoblastic leukemia of B1-lymphocyte progenitor origin (pro B-1 ALL), accompanied by somatic frameshift mutations of the BCL6 interacting corepressor (Bcor) gene, most commonly within a 9 bp "hot spot" in Bcor exon 8. To determine whether experimentally engineered Bcor mutations would lead to pro B-1 ALL, we used CRISPR-Cas9 to introduce a Bcor frameshift mutation into NP23 hematopoietic stem and progenitor cells through the use of Bcor small guide RNAs (Bcor sgRNA). Recipient mice transplanted with NP23 bone marrow (BM) or fetal liver (FL) cells that had been transduced with a Bcor sgRNA developed pro B-1 ALL, characterized by a B-1 progenitor immunophenotype, clonal Igh gene rearrangement, and Bcor indel mutation, whereas control recipients did not. Similar to a subset of human B cell precursor ALL, the murine pro B-1 ALL had acquired somatic mutations in Jak kinase genes. JAK inhibitors (ruxolitinib and tofacitinib) inhibited the growth of pro B-1 ALL cell lines established from Bcor sgRNA/NP23 recipients at clinically achievable concentrations (100 nM). Our results demonstrate that Bcor mutations collaborate with NP23 to induce pro B-1 ALL, and that JAK inhibitors are potential therapies for pro-B1 ALL.

  • Submitted July 17, 2018.
  • Revision received April 11, 2019.
  • Accepted April 11, 2019.