Patent Evaluation: Bifunctional Selectable Fusion Genes

Summary

Novelty: A bifunctional fusion protein and the sequence encoding it are disclosed. The protein is said to provide both a positive selectable marker from one of the components and a dominant negative selectable marker from the other part. This enables cells carrying the gene to be selected for in the first stages of gene therapy and then allows those cells to be selectively killed when the gene therapy is over.

Biology: The bifunctional protein was formed by the fusion of the gene for hygromycin B resistance (positive selectable phenotype) and the HSV-TK gene for ganciclovir sensitivity (negative selectable phenotype). Having both activities expressed as a fusion protein appears to avoid problems of differential expression or loss of one of the genes. The 76 kD fusion protein was expressed in rat-2 cells using a retroviral vector. This allowed both cell selection and then complete cell killing.