IMMUNOTYPING OF BLASTS IN REFRACTORY-ANEMIA WITH EXCESS OF BLASTS

A study of immunological markers was performed in 16 patients with new ly diagnosed refractory anaemia with excess of blasts (RAEB) and RAEB in transformation (RAEB-T) and in 12 other patients with acute myeloid leukaemia evolving from RAEB or RAEB-T. Immunocytochemical investigat ion of bone marrow blasts was done using a modified indirect immunoper oxidase technique. This method permitted accurate morphological identi fication of blasts and other cells in bone marrow. The monoclonal anti bodies used in RAEB and RAEB-T samples were anti-CD34, -c-kit, -HLA-DR and -CD13. The range of CD34 expression of blasts in RAEB samples was 1-14% (mean 6.2%) and in RAEB-T samples 29-48% (mean 35.5%). CD34 pos itivity was detected in 3-94% (mean 47.4%) of the bone marrow blasts i n acute myeloid leukaemia evolving from RAEB and RAEB-T. Expression of c-kit was demonstrated only in a low percentage of blast cells in RAF B, RAEB-T and acute myeloid leukaemia following myelodysplasia. A high percentage (> 30%) of blasts in most patients with RAEB, RAEB-T and a cute myeloid leukaemia was HLA-DR and CD13 positive. We observed the t ransformation from RAEB to acute myeloid leukaemia in three patients. The proportion of CD34 positive blasts increased to 25% and 32% in two patients. The third patient showed an unchanged percentage of CD34 po sitivity of blasts. These findings indicate that the CD34 positivity o f blasts increases with the progression of myelodysplasia to RAEB-T an d acute myeloid leukaemia demonstrating the instability of the clonal defect in myelodysplasia.