Michael J. Branks, Todd H. Davis, Eric M. Smith, David S. Ramirez, Mary-Ann Campbell, Keith A. Cockerill.

La Jolla Pharmaceutical Company, 6455 Nancy Ridge Drive, San Diego, CA 92121, USA

Anti-b2glycoprotein1 (b2GP1) autoantibodies have been implicated as a potential causative agent of the thrombotic events in Anti-Phospholipid Syndrome. We have shown that the majority of APS patients have antibodies specific for domain 1 of b2GP1 (D1). Induction of tolerance to b2GP1 presents a novel approach to therapy in this syndrome. This study was performed to determine the relationship between the structure, plasma clearance rate and efficacy of b2GP1 Tolerogens in an immunized rat model.

Human D1 was expressed in Pichia pastoris. Multiple copies of the purified D1 were conjugated to synthetic platforms in different formats to produce Tolerogens of different size and configuration.

The Tolerogens were radiolabeled and injected into naïve catheterized rats to determine their clearance rate from plasma. Modifications to the size and configuration of the D1 conjugate had an effect on the clearance rate of the Tolerogen from rat plasma.

To investigate the efficacy of the conjugates as Tolerogens, rats were immunized with D1 coupled to KLH and treated with D1 Tolerogens or placebo prior to boosting with D1-KLH. Tolerance was defined as a significant reduction in anti-D1 antibody titers and a reduction in D1-specific antibody forming cells. Our results show in an immunized rat model that multivalent D1 conjugates clear at different rates from plasma and are effective Tolerogens.

Presented at the 9th International Symposium on Antiphospholipid Antibodies, September 12-16, 2000, Tours, France.