SHORT REPORT The human CD40 gene lies within chromosome 20q deletions associated with myeloid malignancies F OTIOS A. ASIMAKOPOULOS,NICHOLAS J. WHITE ,E LISABETH P. NACHEVA AND ANTHONY R. G REEN University of Cambridge Department of Haematology, MRC Centre, Cambridge Received 23 June 1995; accepted for publication 22 August 1995 Summary. Deletions of chromosome 20q are associated with myeloid malignancies and have been previously shown to arise in a multipotent progenitor of both myeloid and B cells. However, B-cell differentiation from the abnormal progenitor was impaired. The CD40 antigen is a surface glycoprotein which is expressed in B cells and haemopoietic stem cells and is important for B-cell growth and development. Following the recent mapping of CD40 to chromosome 20q we sought to determine its position relative to 20q deletions. Analysis of lymphoblastoid cell lines carrying 20q deletions placed CD40 within a 19–21 cM interval which is almost coincidental with the common deleted region defined by previous analysis of patient samples. Our results raise the possibility that genetic alteration of this locus may contribute to the pathogenesis of myeloid disorders associated with 20q deletions. Keywords: deletions, chromosome 20, CD40, B cells. The CD40 antigen is a 45–50kD integral membrane glycoprotein, a member of the tumour necrosis factor receptor superfamily (reviewed by Banchereau et al, 1994). CD40 is expressed in a variety of cell types, including normal and malignant B cells, dendritic cells, follicular dendritic cells, thymic epithelium and early haemopoieticprogenitors. Signal transduction through CD40 appears to be of particular importance for the growth and differentiation of B cells. Cross linking of CD40 in vitro stimulates sustained proliferation of resting B lymphocytes. Furthermore, stimulation of CD40 in the presence of appropriate cytokines results in B-cell maturation and isotype switching. An interstitial deletion of chromosome 20q is a recurring abnormalityin myeloid malignancies,but only rarely found in association with lymphoid tumours (Nacheva et al, 1995). The spectrum of disorders associated with 20q deletions suggests that they may mark the site of a tumour suppressor gene involved in the regulation of normal haemopoietic progenitors. Cytogenetic analyses have suggested that most 20q deletions involve band 20q12 (Nacheva et al, 1995; Roulston et al, 1993). More recently we have carried out a detailed molecular analysis of 20q deletions associated with myeloid disorders (Asimakopoulos et al, 1994). Microsatellite PCR and Southern blot analysis were used to demonstrate molecular heterogeneity of both centromeric and telomeric breakpoints, thus supporting the existence of a tumour suppressor gene on 20q. Furthermore, our results defined a common deleted region of 16–21 cM which is flanked by anonymous markers D20S174 and D20S75 and which contains ADA, PLC1, TOP1, SEMG1 and PPGB. The human CD40 gene has been assigned to chromosome 20 by somatic cell hybrid mapping (Ramesh et al, 1993) and more recently to 20q by isotopic in situ hybridization (Lafage- Pochitaloff et al, 1994). However, the positionof CD40 relative to 20q deletions associated with myeloid malignancies has not been investigated directly. We report here that CD40 lies within chromosome 20q deletions associated with malignant myeloid disorders. Furthermore, we demonstrate that the residual allele directs the production of detectable levels of CD40 protein in cell lines carrying 20q deletions. RESULTS AND DISCUSSION Quantitative Southern blot analysis was used to study the location of CD40 relative to 20q deletions present in two cell lines. KS7 is a lymphoblastoid cell line carrying an acquired 20q deletion (46XY, del (20)(q11.2–q13.1)) and KS10 is a cytogenetically normal lymphoblastoidcell line derived from the same patient (Morris et al, 1989). We have previously shown that KS7 carries a 26–29 cM deletion flanked by markers D20S191 and D20S109 (Asimakopoulos et al, 1994). MH1B14 is a lymphoblastoid cell line carrying an acquired 20q deletion (46XX, del (20)(q11.2–q13.1)) and MH1A1 is a cytogenetically normal lymphoblastoid cell line derived from the same patient (White et al, 1994). MH1B14 British Journal of Haematology, 1996, 92, 127–130 127 1996 Blackwell Science Ltd Correspondence: Dr A. R. Green, Universityof Cambridge Department of Haematology, MRC Centre, HillsRoad,Cambridge CB2 2QH.