In Vivo Studies Using Bispecific Antibodies (Anti-CD3 X Anti-Idiotype) and CD28-Induced Costimulation in the BCL 1 Lymphoma

Abstract

We previously reported the successful treatment of the BCL₁ lymphoma in Balb/c mice using bispecific (anti-CD3 X anti-idiotype) antibodies (BsAb). The in vivo effect was dependent on the bridging of tumor cells and CD3-positive cells. This direct CD3/TCR cross-linking induced targeted cytolytic and cytotoxic activity toward the tumor cells. Definitive proof of an underlying T cell-mediated mechanism was obtained, as the therapeutic effect was completely lost when animals were T cell depleted before treatment. In all these experiments, animals were injected intraperitoneally (i.p.) with 5000 tumor cells (day 0) and treated with one single intravenous (i.v.) injection of 5 μg BsAb (day 9). At a higher tumor load, the therapy lost its effectiveness. We evaluated repeated injections of bispecific antibodies (BsAb) to treat mice with a higher tumor burden (10⁵ tumor cells). However, a dose-related immunosuppression (even with 5 μg BsAb) was induced. Therefore, this approach was only beneficial if the immune system could recover from the previous injection of BsAb. To prevent this induction of anergy, costimulation with bivalent anti-CD28 has been proposed, but despite the high in vitro T cell proliferation using BsAb + anti-CD28 versus BsAb alone, we were repeatedly unsuccessful in improving our in vivo results using immunologically naive animals. Only when T cell preactivation was induced was a significantly better outcome observed when the animals were treated with a mixture of BsAb + anti-CD28 compared with BsAb or anti-CD28 alone. The potency of the BsAb + anti-CD28 combination was demonstrated by the fact that 10 times less BsAb was necessary to cure animals with a 20 times higher tumor burden.