Identification of Chondroitin Sulfate Proteoglycan-4 In Acute Myeloid Leukemia Using Monoclonal Antibody 225.28

Abstract 4885

Chondroitin sulfate proteoglycan-4 (CSPG4) is a membrane-bound proteoglycan that is expressed on the surface of differentiated malignant cells, progenitor cells, and cancer initiating cells in various types of solid tumors. CSPG4 is highly conserved through evolution; its structure, amino acid sequence and functional properties show a high degree of homology with its rat counterpart, named neuron-glial antigen 2 (NG2). CSPG4 has been shown to be involved in the activation of several signaling pathways that play an important role in tumor progression. Because of its high levels of expression on malignant cells and its restricted distribution in normal tissues, CSPG4 is potential candidate tumor marker and target for immune- and targeted therapy. CSPG4 has been shown previously to be expressed on AML cells using an antibody raised against the rat counterpart and levels of expression were correlated with the clinical course of the disease. In this report we extend these findings by identifying a monoclonal antibody (mAb) directed at a human CSPG4 epitope and then used this antibody to examine co-expression with other common markers in AML as well as important molecular/cytogenetic abnormalities. Initially we screened a panel of 15 CSPG4-specific mAb which recognize 7 distinct epitopes for reactivity with leukemic blasts. mAb 225.28 was shown to have the highest reactivity and was selected for further studies. CSPG4 expression using mb225.28 was detected in 18/18 peripheral blood samples containing AML blasts at levels ranging from 0.2% to 98%. 7 samples showed less than 10% CSPG4 positive cells, 2 showed 10 – 20% positivity, 4 showed 20 – 30% positivity, and 5 showed greater than 30% positivity. CSPG-4 expression was not confined to any single blast sub-population defined by co-staining with CD34, CD117 and CD33. The expression of CSPG4 was shown on leukemic cells with mixed lineage leukemia (MLL) gene rearrangements, FTL3 mutation, NPM1 mutation, and complex cytogenetic abnormalities. These results indicate that the expression of CSPG4 is not restricted to any sub-type of AML or confined to one developmental compartment and using the mAb 225.28 CSPG4 may constitute a potential marker for AML.