1. ¹The Swim Across America Laboratory, Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York, USA
2. ²Section of Surgery and Committee on Immunology, University of Chicago, Chicago, Illinois, USA
3. ³Division of General Surgery, Massachusetts General Hospital, Boston, Massachusetts, USA

Correspondence: Jedd D Wolchok, Melanoma-Sarcoma Service, Ludwig Center for Cancer Immunotherapy, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, Room Z-1462, New York, New York 10021, USA. E-mail: wolchokj@mskcc.org

Received 29 October 2007; Accepted 28 December 2007; Published online 26 February 2008.

Abstract

Successful approaches to tumor immunotherapy must overcome the physiological state of tolerance of the immune system to self-tumor antigens. Immunization with appropriate variants of syngeneic antigens can achieve this. However, improvements in vaccine design are needed for efficient cancer immunotherapy. Here we explore nine different chimeric vaccine designs, in which the antigen of interest is expressed as an in-frame fusion with polypeptides that impact antigen processing or presentation. In DNA immunization experiments in mice, three of nine fusions elevated relevant CD8⁺ T-cell responses and tumor protection relative to an unfused melanoma antigen. These fusions were: Escherichia coli outer membrane protein A (OmpA), Pseudomonas aeruginosa exotoxin A, and VP22 protein of herpes simplex virus-1. The gains of immunogenicity conferred by the latter two are independent of epitope presentation by major histocompatibility complex class II (MHC II). This finding has positive implications for immunotherapy in individuals with CD4⁺ T-cell deficiencies. We present evidence that antigen instability is not a sine qua non condition for immunogenicity. Experiments using two additional melanoma antigens identified different optimal fusion partners, thereby indicating that the benefits of fusion vectors remain antigen specific. Therefore large fusion vector panels such as those presented here can provide information to promote the successful advancement of gene-based vaccines.