Gene Therapy for Genetic Disease and Cancer

Abstract

Numerous strategies have been developed for the application of gene transfer techniques to the treatment of human genetic and neoplastic diseases. Strategies for genetic therapy of cancer have included those which aim to provide improved antitumor immunity, provide improved chemotherapy (either by prodrug activation or by protection of drug-sensitive normal tissues to the toxic side effects of cancer chemotherapy), inhibit angiogenesis, and/or restore disrupted growth regulatory function. As a chemoprotective approach, we have been using a transgenic mouse model system to study the expression of drug-resistant forms of dihydrofolate reductase (DHFR) as a means of protecting against the toxic side-effects of antifolate chemotherapy. Antifolate administration may also be applied for the purpose of selectively expanding cells which express drug-resistant DHFR, thus increasing the representation of cells expressing any therapeutic gene co-introduced along with the selectable DHFR gene.

One of the challenges to be faced in the treatment of genetic diseases is in the access of more occluded tissues for introduction of new, potentially therapeutic sequences. We have found that adeno-associated virus vectors are particularly effective in mediating gene transfer and expression in cerebellar Purkinje cells after stereotactic injection either into the cerebellar cortex or into the deep cerebellar nuclei. Current research is focused on the use of antisense and ribozyme approaches for down-regulation of ataxin expression, first in cultured cells and then in a transgenic mouse model of spinocerebellar ataxia type 1.

For many therapeutic applications of gene transfer, an effective outcome will require sustained expression of newly introduced sequences. Stable integration into the host cell genome, for example by using retroviral vectors, ensures the maintenance of newly-introduced sequences in the target cell population. In order to provide integrating function, we are testing the use of a vertebrate transposon, Sleeping Beauty (SB), reconstructed from isolated fish sequences. Current research is focused on utilizing the SB transposase for in vivo integration of engineered transposons introduced into animal tissues using non-viral and viral methods.