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AM Hudson, V Makrynikola, A Kabral and KF Bradstock
Haematology Department, Westmead Hospital, Australia.
A culture system was used to analyze the expression of membrane
differentiation antigens on the proliferative or clonogenic fraction of
cells from cases of common (precursor B) acute lymphoblastic leukemia
(c-ALL). Colonies of leukemic cells were obtained in 18 of 20 cases after 1
week in culture in a liquid layer containing recombinant interleukin-2
(IL-2), phytohemagglutinin (PHA), and B-cell growth factor over an agar
feeder layer containing irradiated peripheral blood mononuclear cells plus
fetal calf serum (FCS) and horse serum. Cultured cells expressed HLA-DR,
CD-9, CD-10, CD-20, and CD-34 antigens, indicating conservation of
precursor B phenotype. Differentiation antigen expression on the clonogenic
subpopulation giving rise to leukemic colonies was assessed by treating
cells prior to culture with selected cytotoxic monoclonal antibodies
(MoAbs) and complement or by fluorescence-activated cell sorting. Lytic
treatment with HLA-DR, CD- 10, CD-9, and CD-20 antibodies produced median
reductions in colony formation of 93%, 81%, 73%, and 58% respectively.
Combined treatment with CD-9 and CD-10 antibodies produced complete
inhibition in 11 of 13 cases. Cell-sorting experiments after CD-10 staining
indicated a good correlation with complement lysis studies and also
demonstrated that the CD-19 antigen is expressed on a high proportion of
clonogenic cells. Colony formation was also significantly reduced in 13 of
17 cases by lytic treatment of cells with the CD-33 antibody MY-9,
suggesting expression of this "myeloid" lineage antigen on ALL clonogenic
cells. The substantial case-to-case variation in expression of individual
differentiation antigens indicates that leukemic cellular heterogeneity is
a major consideration in ex vivo bone marrow purging using MoAbs and
emphasizes the need for more critical evaluation of purging techniques.
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