5-azacitidine has been considered to be safe and efficient medication for use as a bridge to hemotopoietic stem cell transplantation in JMML patients. Patients under clinical treatment can be stratified as complete or partial response, stable disease or disease progression. Recently, the features found in JMML immunophenotyping (FCI) at diagnosis have been described and so, they could be useful for examining these characteristics for determining response of the patients to treatment.

to follow the immunophenotypic pattern of JMML patients during treatment with 5-azacitidine, with an already validated IFC protocol and also look for cytometric features that correlate with the type of clinical response.

An 8-color antibody panel described for pediatric population with JMML at diagnosis was used. Patients treated with cycles of 5-azacitidine 75 mg/m2 subcutaneous for consecutive 7 days, each 28 days were evaluated at diagnosis and after 3 and 6 cycles of medication. The findings were compared with the type of clinical response.

32 patients entered the study. Among them, only 28 patients could be analyzed by FCI after 3 cycles and 25 patients after 6 cycles. After treatment with 5-azacitidine, patients showed a reduction in CD34+ cells, with median CD34/CD117+ cells going from 3.35% to 2.8% after 3 cycles of medication. Values dropped to <2% in 12 and 22 patients after 3 and 6 cycles respectively, and this was observed only in patients responding to treatment. B cell progenitors (H1), that were decreased at diagnosis, had a further reduction after treatment. The monocytic population also decreased, from 11.91% to 7.5% and 6.4% after 3 and 6 cycles, respectively. Those presenting with complete response had an apparent increase in classical monocytes and a decrease in intermediate monocytes. Finally, the population of T lymphocytes, that were reduced at diagnosis, showed an important increase, especially in patients with a clinical response (p <0.001); an increase of NK lymphocytes was also observed mainly after 3 cycles from 1.01% to 1.85%. Immunophenotypic changes including aberrant expression of CD7 in myeloid progenitors remained after 3 and 6 cycles of 5-aza. Aberrant CD7 expression in myeloid progenitors was associated with a worse response to treatment, as well as NF1.

FCI was a feasible tool in JMML patients after treatment with 5-azacitidine. Clinical response was associated with decrease of CD34+ myeloid progenitor and total monocytes and a rise in T and NK lymphocytes. But abnormal co-expressions remained, even in patients with complete clinical response and this speaks in favor of the persistence of the leukemic clone during the whole clinical treatment. The largest effect was seen after 3 cycles. CD34/117+ cell and T lymphocytes are variables that could be incorporated into the assessment of response to clinical treatment of JMML patients. A more detailed study of the several subsets of T cells should be included. The same MFC protocol could be used pre and post transplantation identifying patients with beneficial use of 5-aza after transplant, as it has recently been shown according to methylation status. Prospective studies are necessary to confirm the data with a larger number of patients, and including assessment of the pre and post transplantation status.