CD34+ Leukemic Cells Assessed by Different CD:34 Monoclonal Antibodies

Abstract

CD34 monoclonal antibodies (McAbs) are widely used to identify and isolate hemopoietic progenitors and to classify acute and chronic leukemias. We assessed the reactivity of 17 CD34 McAbs from the 5th International Workshop on Leukocyte Differentiation Antigens with a variety of cells types: normal bone marrow hemopoietic progenitors, 10 AML, 6 ALL, 11 CML. The reactivity for these McAbs was compared with that of reference CD34 McAbs (Q-Bend 10 and 13G12). For each cell population the % of McAb binding cells, the peak channel and the mean fluorescence intensity (MFI) of the positive cells was evaluated. The peak channel, the MFI and the number of positive cells varied significantly from case to case, depending on the McAb and the type of leukemia. According to the spectrum of reactivity three groups of McAbs were defined; however, 7 McAbs do not belong to any of these subgroups. These groups here not entirely in accordance with McAb classification based on enzyme cleavage that identified three epitopes of the CD34 molecule. Some reagents were found to be more specific for AML, other for ALL, CML or normal CD34+ cells. Normal bone marrow light density cells showed a significantly higher percentage of positive cells for 43A1 and MD34.2 McAbs compared to that documented for the remaining McAbs. AML cells showed the most variable pattern of expression for the CD34 McAbs. In leukemic samples, MESF (molecular equivalents of soluble fluorochrome) values ranged from 18,200 to 322,000 and the number of binding sites per cells was 5,000–81,000. The capacity of forming CFU-CEMM and CFU-GM colonies was evaluated in both normal and leukemic samples allowing us to speculate that some of the McAbs which do not belong to the three classes recognise mainly Lin-/CD34+ progenitors that were capable of forming CFU-GEMM colonies. These discrepancies could be related to different biologic characteristics of normal and leukemic progenitors and the presence of at least three epitopes of this molecule.

Key Words:

• CD34 molecule
• CD34 antibodies
• acute and chronic
• leukemias
• clonogenic capacity
• expression of lineage markers
• progenitor subsets