Cryopreservation of human monocytes for pharmacopeial monocyte activation test.

EU Directive 2010/63/EU regarding the protection of experimental animals came into force in November 2010 with an obligation for EU member states to incorporate its requirements into their respective national legislations by 1st of January 2013. The directive stipulates the application of in vitro methods to replace animal experiments whenever such an in vitro method exits and is recognized by EU legislation. The monocyte activation test (MAT) for the detection and quantification of pyrogenic contamination in medicines is recognized by the European Directorate for the Quality of Medicines & Health Care (EDQM) and was published in the European Pharmacopeia (Pharm. Eur.) in April 2010. The methodology described here facilitates the use of the MAT by making monocytes available, in the form of cryopreserved human peripheral blood mononuclear cells (PBMCs). We have developed and qualified a procedure to prepare functional monocytes in the form of PBMCs from the leukocyte filters that are used for the separation of blood in blood donation centers. Once used, these filters are normally treated as biological waste. Here we describe the procedures that are critical for the successful cryopreservation of PBMCs, demonstrate protection of PBMC functionality using various ligands for the toll-like receptors (TLRs) that mediate pyrogenic responses, report validation of the methodology for linearity, precision and robustness and show examples of the practical application of cryopreserved in MATs with samples of drugs and vaccines. Another application of cryopreserved PBMCs, only mentioned here, is to serve as an alternative to freshly isolated PBMCs in tests for unwanted intrinsic pro-inflammatory activities of new biological therapeutics. Such tests use PBMCs or PBMCs over a layer of endothelial cells to detect (unwanted) cytokine release, PBMCs being more suited to this purpose than tests using whole blood.

Evidence for the detection of non-endotoxin pyrogens by the whole blood monocyte activation test.

Threats of pyrogenicity were discovered more than a century ago. Measures to determine the safety of parenterals and, more recently, medical devices and cell therapies for human use have been in place for 70 years. Currently, there are three testing possibilities available: the Rabbit Pyrogen Test, the Limulus Amebocyte Lysate test (Bacterial Endotoxin Test), and test systems using human whole blood or human monocytes, called Monocyte Activation Test (MAT). The MAT is based on the human fever reaction and thus most closely reflects the human situation. Unfortunately, regulations and testing guidelines are not fully harmonized, despite formal international validation. Furthermore, data showing that the MAT is capable of covering the totality of possible pyrogens relevant to humans were not included in the MAT validations of the last decade. For this review we collate evidence from published literature, unpublished data of our own, and results from the international validation study to show that there is overwhelming scientific evidence to conclude that the whole blood MAT reliably detects non-endotoxin pyrogens. Therefore, further validation exercises do not seem warranted.

Contact allergens and irritants show discrete differences in the activation of human monocyte-derived dendritic cells: consequences for in vitro detection of contact allergens.

In recent years test systems have been described that may be applied routinely to discriminate between contact allergens and irritants in vitro. Using human monocyte-derived dendritic cells (MoDC), this study was designed to refine the settings of a potential routine screening protocol for contact allergens and to investigate the so far poorly defined concentration dependency of contact allergen-specific effects. MoDC were generated by 6 days of culture in the presence of IL-4 and GM-CSF and were then cultured for 24 or 48 h in medium with lipopolysaccharide (LPS), contact allergens [picrylsulphonic acid (TNBS), 1-chloro-2,4-dinitrobenzene (DNCB)] or irritants [sodium dodecyl sulphate (SDS), benzalkonium chloride (BAC)] that were free of detectable endotoxin contamination. The induction of CD86 and HLA-DR expression was quantified by flow cytometry as markers for MoDC activation. LPS activation upregulated CD86 about 20-fold and HLA-DR expression about 4-fold. Compared to LPS, contact allergens had weaker effects. TNBS and DNCB induced activation marker upregulation starting slightly below the cytotoxic concentration and increasing in a dose-dependent manner. However, at partially cytotoxic concentrations, irritants also induced CD86 and HLA-DR expression, as confirmed by flow cytometry and quantitative RT-PCR. Both SDS and BAC induced activation marker expression on surviving MoDC, when more than 50% of the MoDC population had been killed by the treatment. Consequently, routine testing of unknown substances would need to quantify activation marker expression as well as cytotoxicity in parallel. In the concentration range around the lowest cytotoxic concentration, the assay may be able to discriminate between contact allergens and irritants.