The effect on skin allograft survival of a monoclonal antibody specific for a polymorphic CD3-like cell surface molecule in rhesus monkeys

FN18, a monoclonal antibody specific for the polymorphic rhesus monkey CD3 antigen on peripheral T cells, has been tested for its immunosuppressive effect in a rhesus monkey skin graft model. Animals were injected i.v. daily with antibody and they received an allogeneic skin graft two or three days after the initial antibody treatment. All animals were carefully monitored regarding levels of the major lymphocyte subsets. In animals in which RhT3 (a CD3-like antigen) is demonstrable (i.e. FN18⁺ phenotype), all T cells initially disappeared from the circulation. However, T cells without RhT3 on their surface reappeared after several days, indicating that these cells must have been modulated. The survival times of the skin grafts were significantly prolonged in these animals. In monkeys in which RhT3 is not demonstrable (i.e. FN18⁻ phenotype), mainly part of the CD4⁺ lymphocyte subset was depleted. Although less explicit, skin graft survival was significantly prolonged in these animals as well. In both the FN18⁺ and FN18⁻ groups a difference in sensitivity between the CD4⁺ and CD8⁺ cells for the FN18 antibody could be noticed. From the data it appears that FN18 is immunosuppressive and does not have serious side effects. The data are in agreement with information available for the use of OKT3 in clinical immunosuppression. Thus, extrapolation of data from the rhesus monkey model to the clinical situation seems feasible.