EFFICIENT GENE-TRANSFER WITH ADENOASSOCIATED VIRUS-BASED PLASMIDS COMPLEXED TO CATIONIC LIPOSOMES FOR GENE-THERAPY OF HUMAN PROSTATE-CANCER

We have shown previously that treatment of rats bearing the Dunning R3 327 MatLyLu prostatic tumor with human interleukin 2 (IL-2) gene-modif ied tumor cell preparations induces potent antitumor immunity in the a nimal. To test the clinical feasibility of using genetically modified tumor vaccines for the treatment of prostate cancer, we have explored the use of a simplified gene delivery system based on liposomes to int roduce and express the IL-2 gene in the Dunning rat R3327 MatLyLu pros tatic tumor cell line (MatLyLu) and in short-term cultures of primary human prostatic tumor cells, Liposome-DNA complexes containing the ade noassociated virus inverted terminal repeats exhibited 3-10-fold highe r levels of gene transfer and IL-2 expression than did liposome comple xes with non-adeno-associated virus containing plasmids. Single transf ections resulted in IL-2 expression for an extended period of time tha t exceeded severalfold the amount of IL-2 secreted from retrovirally t ransduced MatLyLu cells, X-irradiation of cells (4000 rads) prior to t ransfection did not affect cytokine secretion, indicating that liposom e-mediated gene transfer does not depend on cell proliferation, High l evels of gene transfer and IL-2 expression were also achieved in short -term cultures of primary human prostatic tumor cells established from tumor specimens obtained following radical prostatectomy of cancer pa tients, Depending on the type of liposome used, IL-2 levels secreted f rom the human prostatic tumor cells were comparable to or exceeded the levels of IL-2 secreted from retrovirally transduced MatLyLu cells, w hich induced antitumor immunity in the rat model, The ability to cultu re and expand ex vivo human prostatic tumor cells, and the use of a si mple and highly efficient gene transfer method to generate genetically modified tumor vaccines, set the stage for clinical exploration of ge ne-based immunotherapy of prostate cancer.