The generation of tumour-specific cytotoxic T-lymphocyte (CTL) responses is the primary focus in the design of immunotherapeutic cancer vaccines. We have recently demonstrated generation of ovalbumin (OVA)-specific CTLs and tumour-protection in a murine tumour model using vaccination with dendritic cells (DCs) pulsed with E. coli expressing listeriolysin O (LLO) and OVA as a model antigen. In this system paraformaldehyde fixation of E. coli/LLO provided an additional safety feature without compromising vaccine efficacy. We therefore reasoned that paraformaldehyde-fixed recombinant E. coli expressing LLO would be an efficient vehicle for the delivery of human tumour antigens to human DCs. In the present study, we demonstrate that fixed E. coli expressing LLO are taken up efficiently by human monocytederived DCs (MoDCs) with minimal toxicity. As a consequence of the interaction with bacteria, human DCs undergo marked phenotypic and functional maturation. Furthermore, we show that fixed E. coli/LLO expressing the well-characterised human melanoma antigen, MART1, efficiently deliver the HLA-A2-restricted MART1 27-35 epitope for processing and presentation on human MoDCs, suggesting the potential of this system as a novel strategy for human tumour immunotherapy. © 2003 Wiley-Liss, Inc.
Key words: dendritic cell; E. coli; tumour immunotherapyThe generation of tumour-specific cytotoxic T-lymphocyte (CTL) responses is the primary focus in the design of immunotherapeutic cancer vaccines. It is generally accepted that the initiation of effective antitumour immune responses relies upon antigen-presenting cells (APCs), most notably dendritic cells (DCs), priming CTLs and T helper cells, by processing antigen and presenting it on major histocompatibility (MHC) class I and class II molecules, respectively. DCs are unique in their potent ability to prime naïve T-cell responses, 1,2 and DCs loaded with tumour antigens show increasing potential as vaccine candidates in animal models 3,4 and early-phase clinical trials. [5][6][7][8][9] The generation of appropriate immune responses, and therefore successful vaccination, is highly dependent on the development of effective methods of antigen delivery to DCs. The ideal antigen delivery system should combine efficient processing and presentation of tumour antigens to CD8 ϩ T cells, along with potent DC activation in order to deliver the costimulatory signals necessary for T-cell priming. Preparations of tumour-specific antigens are desirable as less well defined whole tumour cell preparations or lysates contain selfantigens and may result in the induction autoimmunity. In addition, it is desirable to deliver the whole antigen to enable presentation of multiple epitopes without prior knowledge of the patient's HLA haplotype or the nature of the peptide epitopes.A number of vaccine strategies have already been shown to induce potent CTL responses, including infection with recombinant viruses, and DNA or RNA transfection. However, there are safety concerns with the expression of whole a...