A Comprehensive and Quantitative Analysis of the Major Specificities in Rabbit Antithymocyte Globulin Preparations

Abstract

Antithymocyte globulin (ATG) preparations are used for treatment and prevention of graft rejection episodes, graft versus host disease and aplastic anemia. The immunomodulatory and immuosuppressive properties of ATGs are mediated by their interaction with a large variety of antigens expressed on immune and nonimmune cell populations. We have conducted a comprehensive analysis on antibody specificities contained in rabbit ATGs in clinical use, ATG-Fresenius (ATG-F) and Thymoglobulin (THG). We have used retroviral expression cloning to identify novel ATG antigens and demonstrate that together with ATG antigens described earlier, these molecules account for the majority of ATG antibodies directed to human cells. Moreover, we have employed cell lines engineered to express antigens at high levels to quantify the antibodies directed to each ATG antigen. We have used cell lines expressing the T cell receptor complex, CD2 and CD28 to remove antibodies to these antigens from ATG preparations and demonstrate that this treatment abrogated the ability of ATGs to induce activation and forkhead box P3 expression in T cells. Comprehensive information and differences on the antigens targeted by ATG-F and THG as well as novel approaches to assess their functional properties are the basis for a better understanding of their immunomodulatory capacities and might eventually translate into improved ATGbased regimen.

A Comparison of Two Types of Rabbit Antithymocyte Globulin Induction Therapy in Immunological High-Risk Kidney Recipients: A Prospective Randomized Control Study

“…Therefore additional B cell targeting agents have no additional benefit. Popow et al found a clear effect on B-cells despite the lack of significant amount of B-cell-specific antibodies with both compounds [7]. In addition, they observed an immunomodulatory effect of ATGs by upregulation of FOXP3 expression and other regulatory T-cells, which was also observed by others [26;27].…”

“…More than 40 leukocyte surface molecules are known to serve as antithymocyte antigens. There are quantitative differences of antibody concentrations against these different antigens between ATG-F and Thymo as well as small differences in their antigen profile [7]. …”

Short-term kinetics of torque teno virus viraemia after induction immunosuppression confirm T lymphocytes as the main replication-competent cells

“…While the anti-IL-2R/CD25 monoclonal antibody is specific for T lymphocytes, one could argue that ATG (a polyclonal immune serum manufactured by immunizing rabbits with human thymus fragments) contains specificities directed against non-T cells. Nevertheless, it has been shown that the vast amount of antibody specificities in ATG is directed against T lymphocytes (Popow et al, 2013), reducing the probability that the variation in TTV viraemia is due to effects of ATG on other cell populations included in the ALC. Similarly, historical immunophenotyping of kidney±pancreas transplantation recipients has shown that maintenance immunosuppression per se accounts for minimal changes in peripheral blood ALC during the first month in the absence of induction immunosuppression, minimizing the chances that the effects on TTV viraemia are due to drugs other than anti-T antibodies.…”

Differential Rates of Ischemic Cholangiopathy and Graft Survival Associated With Induction Therapy in DCD Liver Transplantation

“…This could be as simple as comparison of the biliary stricture rate after DCD liver transplantation between recipients receiving a longer versus shorter steroid taper postoperatively. Given the polyclonal nature of ATG, one may hypothesize a variety of immunomodulatory properties other than T cell depletion that may be beneficial toward modulation of the warm ischemia/inflammation/biliary fibrosis pathway (28). These immunodulatory properties include interference with leukocyte/endothelium interactions, B cell apoptosis, interference dendritic cells and induction of regulatory T and natural killer T cells (29,30).…”