Gene transplantation: combined antisense inhibition and gene replacement strategies.

Optimal gene replacement protocols would include both inhibition of the endogenous gene and overexpression of the preferred (or mutant) gene. We have developed a novel gene transfer method to test whether antisense-resistant genes (designed by deletion of antisense RNA target sequences) can replace the function of endogenous genes. Immunoprecipitation studies demonstrated that inducible anti-fos RNA (antisense directed against the c-fos gene) reduces endogenous c-fos expression by 90%, but did not affect the transfected antisense-resistant mutant c-fos genes. Cell growth studies demonstrated that full-length and minimally truncated c-fos expression vectors could restore serum-induced DNA synthesis but that C-terminally truncated Fos mutants including FBR v-fos could not. Transcriptional studies demonstrate that the endogenous c-fos protein contributes to AP-1 activity and normally suppresses regulated SRE (serum response element) activity. This "gene transplant" method for inhibition of endogenous genes and replacement with preferred genes has implications for gene therapy of hereditary hematologic disorders and for the correction or "repair" of oncogenes or tumor suppressor genes in leukemias and lymphomas.