Jürgen Siekmann

Recombinant factor VIII and factor VIII-von Willebrand factor complex do not present danger signals for human dendritic cells

Several lines of evidence have shown that antibody responses to coagulation factor VIII (FVIII) in patients with hemophilia A depend on the help of activated CD4(+) T cells. The primary activation of CD4(+) T cells requires interaction with mature dendritic cells (DCs) that present antigenic peptides in the context of MHC class II and express costimulatory molecules. Maturation of DCs requires danger signals provided by exogenous or endogenous stimuli such as pathogen-derived products or inflammatory cytokines. We asked the question whether FVIII itself, FVIII complexed with von Willebrand factor (VWF) or thrombin-activated FVIII contain danger signals for human DCs that induce the upregulation of costimulatory molecules or the expression of proinflammatory cytokines necessary for effective activation of CD4(+) T cells. Human peripheral monocytes were differentiated into DCs. FVIII, thrombin-activated FVIII, VWF, VWF-FVIII, lipopolysaccharide (LPS), LPS + FVIII, LPS + VWF or LPS + FVIII-VWF were added either on day 0 or on day 5 of differentiation cultures. Differentiation markers, cytokines in cell culture supernatants and the capacity of DCs to stimulate autologous and allogeneic T cells were analysed after seven days of differentiation cultures. Our results indicate that neither FVIII, thrombin-activated FVIII, VWF nor a complex of FVIII and VWF modulate the maturation of human DCs or their capacity to stimulate autologous or allogeneic T cells. We conclude that neither of these proteins present danger signals to human DCs.

MALDI linear TOF mass spectrometry of PEGylated (glyco)proteins.

PEGylation of proteins is a fast growing field in biotechnology and pharmaceutical sciences owing to its ability to prolong the serum half-life time of recombinant proteins. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) has been shown to be a powerful tool in the analysis of several PEGylated small proteins. Here we present data obtained with a standard secondary electron multiplier (SEM) and a high mass (HM) detector combined with a MALDI linear TOF MS system for the detection of PEGylated (glyco)proteins in the range of 60-600 kDa. Examples of MALDI TOF MS of small (interferon alpha2a), middle (human serum albumin (HSA)) and high molecular mass proteins (coagulation factor VIII and von Willebrand factor (vWF), both heavily glycosylated proteins) are presented. The particular challenge for the analysis was the heterogeneity of the (glyco)proteins in the high molecular weight range in combination with additional PEGylation, which even introduced more heterogeneity and was more challenging for interpretation. Nevertheless, the performance of MALDI linear TOF MS with both detector systems in terms molecular weight and heterogeneity determination depending on the m/z range was superior to the other methods. Although the SEM was able to obtain information about protein PEGylation in the mass range up to 100 kDa (e.g. PEGylated HSA), the HM system was crucial for detection of HM ions (e.g. PEGylated recombinant vWF), which was impossible with the standard SEM.

The Mystery of Antibodies Against Polyethylene Glycol (PEG) - What do we Know?

PurposeRecent findings demonstrated anti-PEG antibody formation in some healthy individuals and patients who have not received PEGylated biotherapeutics. Some of these findings evoked criticism because of shortcomings in the antibody assays used. To better understand this topic, we established robust antibody analytics and screened two cohorts of healthy individuals and one cohort of hemophilia patients for the expression of anti-PEG antibodies.MethodsA flow cytometry approach and a fully validated ELISA platform were established to detect specific anti-PEG antibodies. Immunohistochemistry was used to test for potential binding of anti-PEG antibodies to human tissues.ResultsIgM and/or IgG anti-PEG antibodies are expressed by some healthy individuals and by some patients with hemophilia who have not received PEGylated biotherapeutics. These antibodies can be either transient or persistent and recognize PEGs of different sizes with or without terminal methoxy groups. Age and location of healthy individuals influence the prevalence of IgG but not of IgM antibodies. Anti-PEG antibodies do not cross-react with human tissues supporting the safety of the antibodies.ConclusionWe confirm that some healthy individuals and some patients with hemophilia express specific antibodies against PEG which are not associated with any pathology and do not bind to human tissues.

Microchip capillary gel electrophoresis of multiply PEGylated high-molecular-mass glycoproteins

PEGylation is the most successful approach, to date, to prolong the in vivo survival of recombinant proteins. The conjugation of the polymer to glycoproteins results in challenging analysis, and furthermore, requires a wide variety of analytical tools for the determination of the extent of PEGylation. Herein, we present microchip capillary gel electrophoresis (MCGE) with a non‐commercial high‐molecular‐weight protein assay for the analysis of the PEGylation degree with a focus on multiple PEGylation. To show the potential of the modified MCGE system, high‐mass PEGylated glycoproteins (e.g. coagulation factor VIII) were analyzed. For the von Willebrand factor, the influence of glycans and the hydrodynamic radius on migration time and molecular weight determination is shown. The modified MCGE assay system is a powerful tool for the rapid assessment of the degree of PEGylation, demonstrating conjugate quality or reaction control of PEGylated proteins. This is the main advantage over time‐consuming conventional SDS‐PAGE. Furthermore, electrophoretic separation, staining, destaining, and fluorescence detection in one step combined with automated data analysis show that the MCGE system is a promising technique for high‐throughput monitoring. The MCGE system can be used for rapid structure confirmation (“MCGE fingerprinting”) of multiply PEGylated glycoproteins beyond the 230 kDa molecular mass range.