Flow cytometric analysis of CD34⁺ CD38^- cells; cell frequency and immunophenotype based on CD45RA expression pattern

The CD34⁺ CD38^- population in bone marrow includes hematopoietic stem/progenitor cells. Recently, in acute myeloid leukemia, the focus has shifted to flow cytometry analysis targeting CD34⁺ CD38^- leukemic cells due to their effectiveness in minimal/measurable residual disease detection and prognosis prediction. Nevertheless, the immunophenotype and cell frequency of these cells in the bone marrow, in the absence of leukemic cells, remains unknown. We aimed to evaluate detailed characteristics of CD34⁺ CD38^- cells in both normal and leukemic cells by flow cytometry.

We compared the cell frequency and immunophenotype of the CD34⁺ CD38^- fraction in the following groups: patients with idiopathic thrombocytopenic purpura and malignant lymphoma as controls (n = 17), post-treatment patients without abnormal blasts (n = 35), and patients with myeloid malignancies (n = 86). The comparison was based on the presence or absence of CD45RA expression, a marker commonly used to prospectively isolate lymphoid-primed cell populations within the CD34⁺ CD38^- fraction.

The CD34⁺ CD38^- CD45RA⁺ cell population exhibited a significant expansion in bone marrow without leukemic cells 1 month after cord blood transplantation and in various type of myeloid malignancies, compared to the control group (p < 0.01). Continuous CD45RA expression and notable expansion of the CD34⁺ CD38^- CD45RA^- population were exclusively observed in myelodysplastic syndrome-related diseases. The CD34⁺ CD38^- CD45RA⁺ population displayed frequent expression of various markers in both leukemic and non-leukemic cells, in contrast to the CD34⁺ CD38^- CD45RA^- population.

The CD34⁺ CD38^- fraction should be carefully evaluated considering the nature of normal hematopoietic precursor cells, their cell frequency and immunophenotype, including CD45RA expression pattern, for improving the accuracy of myeloid malignancy diagnosis.