Analytical Aspects of the Implementation of Biomarkers in Clinical Transplantation

Improving Therapeutic Decisions: Pharmacodynamic Monitoring as an Integral Part of Therapeutic Drug Monitoring

Although the monitoring of drug therapies based on the determination of drug concentrations in biological materials is certainly an important instrument for individualized dosing and dose adjustment with a broad variety of pharmaceuticals, its role is limited by the fact that it does not reflect pharmacodynamic (PD) and toxicodynamic interactions such as those caused by individual and environment-related factors. However, these interactions are important for both the efficacy and the safety of the drug therapy. Therefore, during recent years, there is an increased interest in personalized drug therapy as reflected by the development and clinical implementation of molecular "biomarkers" that are direct or surrogate markers of pharmacological effects [PD therapeutic drug monitoring (TDM)]. Moreover, this process is driven by new developments in instrumentation, such as mass spectrometry and array technologies, and in computational biology/pharmacology, databases, and bioinformatics. This Focus Issue of the journal focuses on current achievements in and status of PD TDM with different classes of drugs. The contributions to the present issue of Therapeutic Drug Monitoring provide a critical analysis of current practices of TDM with their limitations, introduce newer promising biomarkers in the field of PD TDM, discuss the challenges faced to date in translating preclinical tools into clinical settings, and point out recent advances in the establishment of modeling approaches that apply to pharmacokinetics (PK)/PD as well as pharmacogenetic information.

T-Cell Surface Antigens and sCD30 as Biomarkers of the Risk of Rejection in Solid Organ Transplantation

T-cell activation is a characteristic of organ rejection. T cells, located in the draining lymph nodes of the transplant recipient, are faced with non-self-molecules presented by antigen presenting cells and become activated. Activated T cells are characterized by up-regulated surface antigens, such as costimulatory molecules, adhesion molecules, chemokine receptors, and major histocompatibility complex class II molecules. Surface antigen expression can be followed by flow cytometry using monoclonal antibodies in either cell function assays using donor-specific or nonspecific stimulation of isolated cells or whole blood and without stimulation on circulating lymphocytes. Molecules such as CD30 can be proteolytically cleaved off the surface of activated cells in vivo, and the determination of the soluble protein (sCD30) in serum or plasma is performed by immunoassays. As promising biomarkers for rejection and long-term transplant outcome, CD28 (costimulatory receptor for CD80 and CD86), CD154 (CD40 ligand), and sCD30 (tumor necrosis factor receptor superfamily, member 8) have been identified. Whereas cell function assays are time-consuming laboratory-developed tests which are difficult to standardize, commercial assays are frequently available for soluble proteins. Therefore, more data from clinical trials have been published for sCD30 compared with the surface antigens on activated T cells. This short review summarizes the association between selected surface antigens and immunosuppression, and rejection in solid organ transplantation.