Suppression of immunological response against a transgene product delivered from microencapsulated cells

A potential obstacle to successful gene therapy for some patients is the in vivo production of neutralizing antibodies against the recombinant therapeutic product delivered. To mimic this clinical situation, we implanted microencapsulated recombinant cells producing human growth hormone into C57B1/6 mice to provoke antihuman growth hormone antibody production. We then investigated the efficacy of different immunosuppressive treatments to inhibit the development of neutralizing antibodies. The experimental mice were treated with either an immunosuppressive drug (FK506 or cyclophosphamide), a cytokine (interferon-gamma [IFN-gamma] or interleukin-12 [IL-12], or a monoclonal antibody (anti-CD4, anti-gp39, or CTLA4-Ig). Serum human growth hormone and mouse anti-human growth hormone antibody levels were measured by enzyme-linked immunosorbent assay (ELISA) for 4 weeks. There were three patterns of response noted among the seven treatment groups. First, the mice receiving IFN-gamma, IL-12, anti-gp39, or CTLA4-Ig were similar to the untreated controls-no suppression of anti-hGH antibodies and no improvement in delivery of hGH. Next, the mice receiving FK506 or cyclosphosphamide showed > or = 90% suppression of antibodies but also no improvement in product delivery. Last, the mice receiving anti-CD4 showed almost complete antibody suppression over 1 month postimplantation. Furthermore, only anti-CD4 permitted a sustained level of human growth hormone delivery to day 28, in contrast to the controls whose human growth hormone delivery was undetectable by day 14 postimplantation. Hence, the use of anti-CD4 inhibited formation of neutralizing antibodies against a recombinant gene product delivered in vivo, and allowed prolonged delivery of a foreign protein. Its role as adjunct treatment for appropriate patients receiving gene therapy should be examined further.