1. ¹ML Research, Keele University Science Park, Keele, Staffordshire, UK
2. ²Immune Regulation Research Group, Department of Biochemistry, Trinity College Dublin, Dublin 2, Ireland
3. ³Kinexus Bioinformatics Corporation, Vancouver, British Columbia, Canada

Correspondence: Dr KS Lipinski, Viral Vector Group, ML Laboratories, Stephenson Building, Keele University Science Park, Newcastle under Lyme, Staffordshire ST5 5SP, UK. E-mail: kai.lipinski@mlresearch.co.uk

^aThese authors contributed equally to this work.

^bCurrent address: Institute for Pathology, Karl-Franzens-University, Auenbrugger- platz 25, A-8036, Graz, Austria.

Received 14 July 2004; Published online 21 January 2005.

Abstract

Gene-directed enzyme prodrug therapy (GDEPT) is a promising approach to local management of cancer through targeted chemotherapy. Killing localized tumors by GDEPT in a manner that induces strong antitumor cellular immune responses might improve local management and allow benefit in disseminated cancer. Here we evaluated the combination of nitroreductase (NTR)/CB1954 GDEPT with high-level expression of heat shock protein 70 (HSP70, a stress protein that can shuttle cytosolic peptides into antigen-presenting cells) for induction of antitumor immunity using adenovirus gene delivery in an aggressive and nonimmunogenic BALB/c syngeneic 4T1 breast cancer model. The mechanism of cell death and spectrum of stress proteins induced are likely to be important determinants of the resulting immune responses. We showed that NTR/CB1954 treatment of 4T1 cells gave both apoptotic and nonapoptotic killing. In vivo killing of 4T1 cells expressing NTR gave weak antitumor immunity and very limited induction of stress proteins including HSP70. High-level coexpression of HSP70 during NTR/CB1954-mediated killing of 4T1 cells in vivo gave much greater protection from tumor challenge (67% long-term survivors compared to 17%) and induced 4T1-specific cytotoxic T-cell responses. The enhancement of antitumor responses resulting from HSP70 coexpression was similar to that conferred by coexpression of GM-CSF.