RADIATION STUDIES ON B-CELL DIFFERENTIATION MARKER CD24/SCLC CLUSTER-4 ANTIGEN EXPRESSING AND NON-EXPRESSING LUNG-CANCER CELL-LINES AND MOUSE FIBROBLASTS

A correlation between CD24 expression and higher intrinsic radiation sensitivity has been described in B-lineage acute lymphoblastic leukaemia (B-ALL). We recently identified the SCLC surface antigen Cluster-4 (CL-4) to be identical to the B cell differentiation marker CD24, except for one amino acid residue. The CD24/CL-4 antigen is highly expressed on SCLC, but rarely on NSCLC cells. In order to investigate the influence of the expression of CD24/CL-4 on the radiation sensitivity in a non-leukaemic cell system, sublines of the human SCLC H249 cell line transfected with mutated ras oncogene, and differing in their CD24/CL-4 expression, were studied. In addition, we stably transfected the NSCLC A125 cell line and the mouse fibroblast NIH3T3 cell line with the CL-4 cDNA. The differential expression of CD24/CL-4 on the cells had no influence on morphology, proliferation and cloning efficiency. Radiation studies were done with cells in exponential growth phase. In the highly resistant NSCLC A125 cells no difference in radioresponsiveness was observed between CD24/CL-4 expressing and non-expressing cells. In the rather radiosensitive cells, similar responses to radiation were observed between CD24/CL-4 expressing and non-expressing SCLC H249-ras cells, whereas the CL-4 transfected NIH3T3 mouse fibroblasts showed a substantially higher radioresistance than the CD24/CL-4 non-expressing control cells. In conclusion, the correlation between CD24/CL-4 expression and radiation sensitivity is controversial and depends on the cell type.