VARIABLE DETECTION OF MYELOID ANTIGENS IN CHILDHOOD ACUTE LYMPHOBLASTIC-LEUKEMIA

Aims-To determine whether the use of different sources of anti-CD13 an d anti-CD33 monoclonal antibodies leads to discrepant results in child hood acute lymphoblastic leukaemia (ALL), which might contribute to th e wide variation in the reported incidence of myeloid antigen expressi ng ALL in childhood. Methods-Stored leukaemic cells from 10 children w ith previously defined myeloid positive ALL were examined. A range of commercially available anti-CD13 and anti-CD33 monoclonal antibodies, directly conjugated with phycoerythrin or fluorescein isothyocyanate, or both, was used. Positively reacting cells were detected by how cyto metry. Results-There was a noticeable discordance between the differen t commercial sources of antibody and between the two fluorochromes in their ability to detect myeloid antigens, as well as variation in the intensity of staining. For CD13, one antibody reacted with eight cases and another with only four. Similarly, CD33 was detected in all 10 ca ses by one antibody and in only three by another. Conclusions-The lack of any consistent pattern of results suggests that various commercial antibodies against the same CD antigen might recognise different epit opes and that the number of molecules per cell might vary from case to case. These observations partly explain the variation in reported inc idence and the failure to establish the clinical importance of myeloid positivity, and they highlight the importance of standardisation in m ulticentre studies in which immunophenotypic data are collected.