Risk of recurrence after primary treatment for advanced breast cancer is high and treatment responses for recurrent disease are limited. There is sufficient evidence to suggest the existence of an immune, mediated antitumour response in breast cancer, which is however impaired by many tumour derived factors. Dendritic cells (DC) are rare leukocytes which function as antigen presenting cells (APC) and direct the immune response. Vaccinations with autologous DC preparations, exogenously loaded with tumour antigen, have demonstrated meaningful immune and modest clinical responses in patients with advanced breast cancer. In this preclinical study we investigate the use of peripheral blood DC, electroporated with tumour total RNA, as adjuvant immunotherapy for advanced breast cancer.
The blood DC were isolated with an immunomagnetic selection procedure which relies upon the CMRF-56 monoclonal antibody and magnetic bead technology. The parameters for efficient electroporation of DC in the CMRF-56 preparation were established with the reporter antigen enhanced green fluorescent protein (EGFP) mRNA. Translation of EGFP mRNA occurred rapidly after electroporation, with near maximal expression within the first four hours. Using an influenza virus matrix protein (FMP) model, antigen presentation in a major histocompatibility complex (MHC) class I restricted fashion was demonstrated. DC activation using the adjuvant polyinosinic polycytidylic acid (poly I:C) was evaluated according to protein translation, costimulatory molecule expression and cytokine production. CMRF-56 preparations transfected with FMP mRNA were able to efficiently expand FMP specific cytotoxic T lymphocyte (CTL) recall responses from autologous responding peripheral blood mononuclear cells (PBMC). In doing so, several protocols for DC activation were investigated. None were clearly superior and doubt was cast over the necessity to activate blood DC in the CMRF-56 preparation. Two attempts were made at generating a primary CTL response to self antigen. CMRF-56 preparations transfected with tumour total RNA derived from the breast cancer cell line MCF-7 were used to expand a CTL response by repeated stimulation of autologous PBMC. No tumour specific responses were generated however insight was gained from a systematic review of potential deficiencies and provided direction for future attempts. This preclinical study provides the basis for the design of a clinical trial of a CMRF-56 blood DC vaccine, loaded with tumour total RNA, as adjuvant therapy for the prevention of disease relapse in patients with advanced breast cancer.