INTERFERENCE OF ANTI-LYMPHOCYTE THERAPY WHEN MONITORING DONOR SPECIFIC ANTIBODIES AFTER ALLOTRANSPLANTATION
DM Fitzpatrick, TC Girouard, R Pei, and SL Saidman Histocompatibility Lab, Massachusetts General Hospital, Boston, MA, and One Lambda, Inc., Canoga Park, CA
Monitoring patients post-transplant for de novo donor specific antibodies can be a challenge, especially when patients are given immunosuppressive agents that may interfere with standard antibody (Ab) detection methods. A number of different anti-lymphocyte (AL) agents can be used for induction therapy or to treat acute rejection. Sources include horse or rabbit serum, as well as murine or humanized monoclonal antibodies (mab). These agents have variable reactivity patterns when tested with lymphocytotoxic, ELISA or flow cytometric techniques. When using a binding assay such as ELISA or flow, the secondary Ab may or may not be absorbed to prevent cross-reactivity with these AL agents. We have tested the effects of Zenopax (Roche, humanized anti-IL2 receptor mab), OKT3 (Ortho, mouse anti-CD3 mab), MEDI 507 (BioTransplant, humanized anti-CD2 mab), ATGam (Pharmacia-Upjohn, horse anti-human thymocytes) and Thymoglobulin (Sangstat, rabbit anti-human thymocytes) in CDC assays with T or B lymphocytes, and ELISA (One Lambda LATM) with purified class I or II antigens. Zenopax has no effect in any assay. OKT3 and MEDI 507 both react with T cells in CDC, but not with B cells. Neither react in ELISA. OKT3 can easily be removed from sera using beads coated with sheep anti-mouse Ig, but removal of MEDI 507 without removing patient Ig would require beads with bound anti-idiotype. ATGam and Thymoglobulin react with both T and B cells in CDC. Thymoglobulin can be absorbed with sheep anti-rabbit Ig coated beads, but large numbers of beads are needed so the cost is prohibitive. ATGam does not cross-react in the ELISA assay, but Thymoglobulin reacts with both class I and II in ELISA. However, this reactivity of the secondary Ab to rabbit Ig can be blocked with 10% rabbit serum, without inhibiting human anti-class I or class II Ab. Knowing how these agents react can simplify post-transplant monitoring and allow modification of standard techniques when necessary to prevent non-specific reactivity.