COMPLEMENTATION OF THE RADIOSENSITIVE PHENOTYPE IN SEVERE COMBINED IMMUNODEFICIENT MICE BY HUMAN CHROMOSOME-8

Severe combined immunodeficient (scid) C.B-17 mice are deficient in va riable (diversity) joining region recombination, the process of assemb ling the immunoglobulin and T-cell receptor genes from gene segments, thereby creating much of the enormous diversity of antigen-binding cap acity. scid mice are also sensitive to ionizing radiation, as a result of their deficiency in double-strand break repair. Here we report the complementation of the radiation-sensitive scid phenotype by transfer ring human chromosome 8 into scid cells. Somatic cell hybrids were gen erated by fusing scid cells with human HT-1080 cells, resulting in rad ioresistant hybrids with several human chromosomes. One of the identif ied human chromosomes in the radioresistant scid cell line 4.61, which retains only two human chromosomes, is a rearranged 8/21 translocatio n. Proof that chromosome 8 confers the complementation was achieved by transferring only human chromosome 8 into scid cells by microcell-med iated chromosome transfer (scid/hu8 cell line). The presence of chromo some 8 in our scid/hu8 cell line was monitored by fluorescence in situ hybridization and polymerase chain reaction. We demonstrated the radi oresistance of this hybrid not only to high dose rate but also to low dose rate radiation. We also showed that transference of human chromos ome 8 to scid cells fully complements the DNA double-strand break repa ir deficiency and the high sensitivity of scid cells to radiation-indu ced chromosome aberrations. Mapping the scid gene to human chromosome 8 is an important first step in cloning the scid gene, which will enha nce our understanding of double-strand break repair pathways in humans .