Multiple hypersensitivity to mutagens in a cell strain (46BR) derived from a patient with immuno-deficiencies

46BR is a fibroblast cell strain established from an individual with hypogammaglobulinaemia. The cells are unique in showing hypersensitivity to the lethal effects of a wide range of DNA-damaging agents. Thus they are hypersensitive to gamma- and 254-nm UV-irradiation and show a limited capacity to repair potentially lethal gamma-irradiation damage when compared with fibroblasts from normal individuals. A slight hypersensitivity to mitomycin C was also revealed but we were not able to discriminate 46BR from normals with 4-nitroquinoline oxide. The cells were hypersensitive to the alkylating agents, dimethyl sulphate, methyl methanesulphonate, ethyl methanesulphonate, N-methyl-N'-nitro-N-nitrosoguanidine and N-methyl-N-nitrosourea but not N-ethyl-N-nitrosourea. A consideration of the spectra of DNA lesions produced by these alkylating agents together with the sensitivity to ionising radiation and mitomycin C suggests that 46BR cells are defective in a repair step that is common to all agents. We suggest that the cells are defective in DNA polymerisation or ligation. Support for this suggestion comes from the absence of any hypersensitivity to N-ethyl-N-nitrosourea since its major reaction products are not removed by excision pathways that require polymerisation and ligation.