Assessment of Batch to Batch Variation in Polyclonal Antithymocyte Globulin Preparations

Background. Antithymocyte globulins (ATGs) are used to prevent and treat allograft rejection and graft versus host disease. They are purified IgG fractions derived from rabbits immunized with the Jurkat T-cell line (ATG-Fresenius) or thymus cells (Thymoglobulin). Differences not only in the amounts of leukocyte reactive antibodies but also in the antigens targeted by ATGs could potentially affect the clinical efficacy of different batches of these polyclonal antibody preparations. Methods. Four batches of ATG-Fresenius and Thymoglobulin were compared regarding their capacity to interact with human leukocytes from healthy donors and kidney transplant recipients. Using flow cytometric assays, we analyzed the reactivity of these ATG preparations with Jurkat cells and with primary leukocytes. In addition, ATGs derived from different batches were probed with a panel of cell lines expressing high levels of ATG antigens. Their ability to mediate complement-mediated lysis of human monocytes and lymphocytes was also compared. Results. Binding studies to leukocyte antigens and functional analysis pointed to a high conformity among different batches in both ATG preparations. Conclusions. From our in vitro data, it can be expected that ATGs derived from different batches will not differ in their clinical efficacy. Furthermore, the methods described in this study allow for a reliable analysis of ATG batches.