FAILURE TO OBTAIN HYBRIDOMAS BETWEEN HUMAN MACROPHAGES AND HUMAN TUMORAL U-937 CELLS IS PROBABLY DUE TO PARENTAL MACROPHAGES

Despite more than 50 attempts and the use of various methods, it has b een impossible to establish homologous hybridomas between human mature macrophages and 8-azaguanine-resistant U-937 clones prepared in the l aboratory. To rule out the possibility that these clones were unsuitab le for the selection of hybrids, a study of their properties was done. It was shown that U-937 wild type cells were able to produce HPRT, wh ereas 8-azaguanine (8-aza)-resistant clones did not. Curiously, exonic and intronic HPRT sequences were undetectable both in wild type and i n 8-aza-resistant cell genomes, under conditions where they were detec ted in control cells. Chromosome analysis of the clone UM9, one of the most frequently used in fusion experiments, revealed many qualitative and quantitative differences with the U-937 wild type cells. 8-aza-re sistant U-937 cells were capable of fusion with human macrophages and gave rise to heterokaryons and probably to synkaryons, which survived for weeks without dividing in hypoxanthine-aminopterin-thymidine mediu m. The results could be interpreted in terms of the existence of a tra nsacting negative regulatory mechanism of the macrophage genome on the proliferative capacity of homospecific hybridomas.