RETROVIRAL INTERLEUKIN-7 GENE-TRANSFER INTO HUMAN DENDRITIC CELLS ENHANCES T-CELL ACTIVATION

Tumor vaccination with dendritic cells (DC) presenting tumor antigens to T cells is a promising approach in immunotherapy. the aim of this s tudy was to enhance T cell stimulatory ability of human DC by retrovir al expression of the interleukin-7 (IL-7) gene. IL-7 has been shown to provide a potent costimulatory signal for the proliferation of T cell s and the generation of cytotoxic T cells (CTL). DC were generated fro m human peripheral blood mononuclear cells (PBMC). DC were analyzed by light- and electron-microscopy, immunophenotype (CD1a(+), CD14(-), CD 80(+), CD86, HLA-DR+) and functional assays. According to these criter ia, 75-85% of the cells were DC. The cells did not produce measurable amounts of IL-7 spontaneously nor did they express the IL-7 receptor. A retroviral IL-7 expression vector was constructed. Retroviral infect ion was performed with either the LXSN-hIL-7 vector or its variant LXS N. Using the LXSN-hIL-7 vector, IL-7 production of 2296 pg/10(6) cells /24 h could be achieved on average. Transduction of DC was confirmed b y RT-PCR in a CD1a-enriched cell fraction. Transduction efficiency by a control virus coding for beta-galactosidase was about 30%. In autolo gous mixed lymphocyte reaction (MLR), IL-7 transduced DC augmented T c ell proliferation by a factor of two compared with unmodified or mock- transfected DC, and in allogeneic MLR there was a 2.7-fold increase in T cell proliferation. The increase in T cell proliferation could be c orrelated to IL-7 secretion by DC. Dendritic cells that have been simu ltaneously peptide-loaded and gene-modified to secrete IL-7 are a pote ntial tool to amplify activation of tumor-specific T cells.