Chemical conjugation of a novel antibody-interleukin 2 immunoconjugate against c-erbB-2 product

To develop a new chemical method to produce a monoclonal antibody (MoAb) 520C9/recombinant human interleukin 2 (rhIL-2) conjugate. MoAb 520C9 reactive with the protooncogene c-erbB-2 product P185 was chemically conjugated with rhIL-2 by using a simple two-step method. First, the rhIL-2 was activated by Sulfosuccinimidyl 4-[N-maleimidomethyl] cyclohexane-1-carboxylate, a heterobifunctional linker, and N-succinimidyl s-acetylthioacetate was introduced onto 520C9. Then SATA on the 520C9 was reacted with the maleimide group on the activated rhIL-2 to generate 520C9-rhIL-2 immunoconjugate. The immunoconjugate retained the antigen binding activity compared to the respective native antibody as determined by an indirect live cell binding assay. The immunoconjugate also possessed IL-2 activity as measured by the standard CTLL-2 cells proliferation assay and the stimulation of human peripheral blood mononuclear cells (PBMCs) into lymphokine-activated killer cells. Our method of conjugation of rhIL-2 to 520C9 preserves the binding activity of the antibody and the cytokine function of IL-2. This simple and efficient method of conjugation should be applicable to other types of MoAbs and recombinant cytokines.