RNA-loading of CMRF-56 positive blood dendritic cells is a promising strategy for multiple myeloma immunotherapy

Abstract

Immunologic responses to the malignant plasma cells of multiple myeloma (MM) patients are beinginvestigated for their ability to prevent disease relapse after autologous and allogeneic haematopoietic stem cell transplantation. Dendritic cells (DC) are specialized leukocytes that have the capacity to prime and direct an immune response against tumour-associated antigens (TAA). We have used new Trucount® technology to evaluate the whole blood DC subset composition of healthy donors and MM patients. MM donors have similar numbers of CD11c+ CD16+ and CD11c+CD16-blood DC subsets but about half the number of CD11c-CD123+ blood DC compared to normal donors. A CMRF-56 monoclonal antibody-based immunomagnetic selection procedure was used to enrich blood DC for functional studies from the peripheral blood mononuclear cells of healthy donors and MM patients. CMRF-56+ blood DC from MM patients are efficiently activated ex vivo and induce autologous and allogeneic mixed lymphocyte responses. The CMRF-56+ blood DC preparation is able to present MHC class I -restricted peptide antigens and has been used to generate cytotoxic T lymphocytes (CTL) against MM -related TAA, hTERT and MUC1. We have optimised the loading of CMRF -56+ blood DC preparations with antigen-encoding mRNA and have shown that enhanced green fluorescent protein mRNA is rapidly transl ated after electroporation into blood DC. In addition, influenza matrix protein (FMP) mRNA -loaded blood DC can process and present antigen to FMP-specific CTL clones and prime FMP-specific CTL responses in whole PBMC populations. We are currently in the process of generating responses against total RNA extracted from MM cell lines prior to initiating a clinical trial of RNA-loaded CMRF-56+ blood DC in patients.