Reduced CD38 expression on CD34+ cells as a diagnostic test in myelodysplastic syndromes

Abstract

Diagnosis of myelodysplastic syndrome can be difficult especially in cases with a low blast count and a normal karyotype. Flow cytometry has been used to distinguish myelodysplastic syndrome from non-clonal cytopenias. No one single simple flow cytometric parameter has been proposed to be diagnostic of myelodysplastic syndrome. We have studied samples from 100 myelodysplastic syndrome patients and as control samples; 70 non-clonal cytopenias, 5 subjects with normal hematology, 31 patients with acute myeloid leukemia and 11 with chronic myelomonocytic leukemia or myeloproliferative disorder. We show that reduced relative mean fluorescence of CD38 below a threshold value on CD34(+) cells diagnosed low-grade myelodysplastic syndrome with 95% sensitivity (95% confidence interval, 87-99%) and 92% specificity (95% confidence interval, 82-97%). This simple flow cytometric test may be of value in the routine clinical diagnosis of myelodysplastic syndrome, especially in cases with a low blast count and normal karyotype.

Figure 1.

CD38 Relative Mean Fluorescence Intensity (RMFI) of CD34⁺ cells and percentages of B cell and CD38^low progenitors in MDS patients and control populations. Graphs show: (A) CD38-RMFI values (B) percentage values for CD19⁺CD34⁺ (left) and CD34⁺CD38^low cells (right) of total CD34⁺ population in samples from patients with a range of conditions causing cytopenia including immune causes and/or splenomegaly (pathological controls, triangles) (n=60). Patients with immune thrombocytopenia, hemolytic anemia and liver disease are shown as black bordered red triangles; MDS with a blast count of <5% (n=63) (closed circles) including subgroup of MDS patients without ringed sideroblasts and/or an abnormal karyotype (n=32) (red circles); MDS-RAEB (n=27) (triangles); AML (n=31) (diamonds) and MPD/CMML (n=11) (open circles). The clinical characteristics are set out in the Online Supplementary Table S2. CD34⁺ cells were defined by standard serial gating (CD34⁺SSC^low followed by CD34⁺CD45^low). CD38-RMFI=CD38PE-MFI divided by MFI of isotype control-PE staining. Horizontal bars are means and the SEM for each sample group is shown. The number of samples (n=) in each group are shown in ( A ). Dotted line in (A) shows threshold value of CD38PE-RMFI defined by receiver-operator characteristic curve that in this cohort diagnoses low-grade MDS with 95% sensitivity (95% confidence interval, 87–99%) and 92% specificity (95% confidence interval, 82–97%).

Figure 2.

Examples of typical flow cytometric CD38 expression patterns of CD34⁺ cells from pathological controls compared to MDS patients. CD34⁺ cells were defined by standard serial gating (CD34⁺SSC^lo followed by CD34⁺ CD45^lo). CD38-RMFI (CD38PE-MFI divided by MFI of isotype control PE staining), as well as percentage of B-cell (CD19⁺) and CD38^lo progenitors of total CD34⁺ population, is shown for each example. In the pathological control plots (top), CD34⁺ cells are skewed towards a higher CD38 expression (to right of dotted line), despite no major shifts in frequency of CD19⁺ or CD38^lo progenitors. Plots of the MDS samples show that CD38-RMFI of CD34⁺ cells can be reduced by a relative increase of CD38^moderate cells or CD38lo cells and as well as a depletion of CD38^hi cells. On the left MDS sample plot, the clustering of CD38^moderate cells within CD38^moderate region is shown by the dotted circle indicated by arrow.