Juvenile myelomonocytic leukemia (JMML) is a myelodysplastic/myeloproliferative neoplasm of early childhood driven by RAS pathway mutations. Allogeneic hematopoietic stem cell transplantation (HSCT) is the therapy of choice for most patients. However, relapse rate is high, in patients with adverse features, frequently noted in PTPN11-mutated JMML, or in patients without evidence of graft-versus-host disease (GvHD). Here we set out to understand the mechanisms associated with oncogenic PTPN11 immune escape. Analyzing primary PTPN11-mutated JMML samples and MxCre;Ptpn11D61Y/+ mice, we observed elevated expression of immune checkpoint molecules, including ectonucleotidases CD39 and CD73 - key mediators of the adenosine pathway - on monocytic and granulocytic leukemic cells. Stimulation with GM-CSF, a central mediator of JMML pathogenesis, induced ectonucleotidases expression on granulocytes and monocytes. In contrast, MEK inhibition downstream of Ptpn11D61Y/+ reduced ectonucleotidases expression. Functionally, Ptpn11D61Y/+-mutated myeloid cells suppressed activation and proliferation of wild-type (WT) T lymphocytes, an effect recapitulated by adenosine and reversed by pharmacological CD39 inhibition with POM-1. In vivo, POM-1 treatment of MxCre;Ptpn11D61Y/+ mice presenting with myeloproliferation reduced spleen size and partially restored immune responsiveness. Moreover, POM-1 induced apoptosis in murine Ptpn11D61Y/+ myeloid cells, highlighting a dual therapeutic benefit of CD39 inhibition in JMML. Together, these findings suggest that targeting the adenosine pathway may represent an immunomodulatory approach to enhance T cell-mediated control of JMML, particularly in the context of HSCT and relapse prevention.
Rajak et al. (Thu,) studied this question.