Immature dendritic cells generated with low doses of GM-CSF in the absenceof IL-4 are maturation resistant and prolong allograft survival in vivo

Dendritic cells (DC) were cultured from mouse bone marrow (BM) progenitors in low concentrations of granulocyte-macrophage colony-stimulating factor ( GM-CSF) (GM(lo) DC) by two different protocols. The phenotype and functiona l properties of these GM(lo) DC were compared to those of standard BM-DC cu ltures generated in high concentrations of GM-CSF (GM(hl) DC) or in low GM- CSF plus IL-4 (GM(lo)/IL-4 DC). An effect of IL-4 on maturation was observe d only at low but not high doses of GM-CSF, Compared to mature DC, GM(lo) D C were phenotypically immature, weak stimulators of allogeneic and peptide- specific T cell responses, but substantially more potent in presentation of native protein. Immature GM(lo) DC were resistant to maturation by lipopol ysaccharide, TNF-cr or anti-CD40 monoclonal antibodies, as the expression o f co-stimulatory molecules was not increased, and stimulatory activity in o xidative mitogenesis was not enhanced, These maturation-resistant immature GM(lo) DC induced T cell unresponsiveness in vitro and in vivo. GM(lo) DC a lso prolonged haplotype-specific cardiac allograft survival (from 8 days to >100 days median survival time) when they were administered 7 days (but no t 3, 14 or 28 days) before transplantation. Our findings may have important implications for future studies in T cell tolerance induction in vivo.