CMRF-44 antibody-mediated depletion of activated human dendridic cells: a potential means for improving allograft survival

BACKGROUND: Activated dendritic cells (DC) initiate immune responses by presenting antigen, including alloantigen from tissue grafts, to T lymphocytes. The potential to deplete or inactivate differentiated-activated DC during allogeneic transplantation represents a new approach to immunosuppression. METHODS: The authors investigated the potential of the monoclonal antibody CMRF-44, which has specificity for a DC-associated differentiation-activation antigen, to induce complement-mediated lysis of activated human DC. Peripheral blood mononuclear cells (PBMC), or purified DC preparations, were cultured overnight to activate endogenous DC, resulting in the expression of CMRF-44 antigen and CD83. These were then treated with CMRF-44 and complement. Depletion of activated DC was monitored by flow cytometry. RESULTS: Eighty-nine percent of activated (CD83+) DC in cultured PBMC were depleted by treatment with CMRF-44 and autologous serum (AS) (complement source; mean percentage of CD83+-CD14--CD19- cells=0.06%; cf 0.50% for heat-inactivated AS controls, P<0.0005, n=7). Ninety-five percent of cultured purified myeloid DC were depleted by this treatment, compared with only 43% of similarly treated lymphoid DC. Overnight culture also increases CMRF-44 antigen on a proportion of B cells and mononuclears, but only 24% of these cells were depleted. This treatment considerably reduced the ability of PBMC to stimulate allogeneic CD4+ CD45RA+ T lymphocytes. Similarly, the T-cell proliferative responses to recall and naive antigens were significantly reduced. CONCLUSIONS: CMRF-44 may be a suitable candidate for a new selective immunosuppressive strategy, targeting differentiated-activated but not resting DC. It may have applications in preventing GVHD in allogeneic bone marrow transplantation and facilitate immunoacceptance of solid organ allografts.