Treatment with tumor-reactive Fab-IL-2 and Fab-Staphylococcal enterotoxin A fusion proteins leads to sustained T cell activation, and long-term survival of mice with established tumors

C215Fab-IL-2 fusion protein, with full IL-2 and antigen binding activity, w as produced in E. coli at high level (>50 mg/l). When co-administered with Fab-superantigen fusion protein (C215Fab-SEA) in mice strong and sustained T cell activation was observed. Combination treatment of mice carrying B16 melanoma transfected with C215 antigen was also more efficient than using C 215Fab-SEA (p<0.01) or C215Fab-IL-2 alone (p<0.001). In a long-term surviva l experiment 5/12 mice having received combination treatment 5 days after i .v. inoculation of B16 cells survived >85 days. Improved therapeutic effica cy correlated with increased tumor infiltration by activated CD25(+) T cell s, indicating a T cell mediated mechanism.