Phase I Trial of TGF-β2 Antisense GM-CSF Gene-Modified Autologous Tumor Cell (TAG) Vaccine

Abstract

On the basis of the hypothesis that the combined expression of immunostimulatory granulocyte macrophage colony stimulating factor (GM-CSF) and antitumor suppressor TGF-β2 antisense (AS) transgenes can break tolerance and stimulate immune responses to cancer-associated antigens, we constructed an expression plasmid [the tumor-associated glycoprotein (TAG) plasmid] that coexpresses GM-CSF and TGF-β2 AS nucleotide sequences and which was incorporated into an autologous whole-cell vaccine. Patients undergoing resection were enrolled. Freshly harvested autologous tumor cells were mechanically and enzymatically disaggregated, then electroporated with the TAG vector. The resulting vaccine was irradiated, then aliquoted and cryopreserved until the time of injection. Patients received a minimum of 5 to a maximum of 12 monthly intradermal injections. Immune function was monitored at baseline and at months 3 and 6. Vaccine manufacturing efficiency was 84% (32/38). Twenty-three patients received at least 1 vaccination. There were no grade 3 or 4 toxicities, and grade 1 and 2 events were local in nature. Seventeen of 21 patients had stable disease (SD) at month 2 or later as their best response, and 1 patient with stage IVa malignant melanoma achieved a complete response (CR) following 11 vaccinations and remains without evidence of disease 2 years following initiation of therapy. Six of 13 patients displayed a positive enzyme-linked immunospot (ELISPOT) response to autologous TAG vaccine at week 12 including 3 patients with prolonged SD or CR. The 3 other patients survived through week 24, as compared with none of the 7 ELISPOT-negative patients. On the basis of safety and clinical and immunologic results, further evaluation of bifunctional vaccines is warranted.