Macrophage migration inhibitory factor (MIF) is a pro-inflammatory and tumor-promoting cytokine that occurs in two redox-dependent immunologically distinct conformational isoforms. The disease-related structural isoform of MIF (oxMIF) can be specifically and predominantly detected in the circulation of patients with inflammatory diseases and in tumor tissue, whereas the ubiquitously expressed isoform of MIF (redMIF) is abundantly expressed in healthy and diseased subjects. In this article, we report that cysteine 81 within MIF serves as a "switch cysteine" for the conversion of redMIF to oxMIF. Modulating cysteine 81 by thiol reactive agents leads to significant structural rearrangements of the protein, resulting in a decreased β-sheet content and an increased random coil content, but maintaining the trimeric quaternary structure. This conformational change in the MIF molecule enables binding of oxMIF-specific antibodies BaxB01 and BaxM159, which showed beneficial activity in animal models of inflammation and cancer. Crystal structure analysis of the MIF-derived EPCALCS peptide, bound in its oxMIF-like conformation by the Fab fragment of BaxB01, revealed that this peptide adopts a curved conformation, making the central thiol protein oxidoreductase motif competent to undergo disulfide shuffling. We conclude that redMIF might reflect a latent zymogenic form of MIF, and formation of oxMIF leads to a physiologically relevant, i.e., enzymatically active, state.

Sickle cell disease (SCD) is an inherited red blood cell disorder with a worldwide prevalence. Acute vaso-occlusive crisis (VOC) is the main cause of hospitalization in patients with SCD. Growing evidence highlights the key role of inflammatory vasculopathy in both acute and chronic SCD related clinical manifestations. In a humanized mouse model for SCD, we found an increase of vWF activity and a reduction in ADAMTS13/vWF activity ratio similar to that observed in the human counterpart. rADAMTS13 was administered to humanized SCD mice before exposure to hypoxia/reoxygenation (H/R) stress as model of VOC. In SCD mice, rADAMTS13 reduced H/R induced hemolysis and systemic and local inflammation in lungs and kidneys. rADAMTS13 also diminished H/R induced worsening of inflammatory vasculopathy, reducing local nitric oxidase synthase expression. Collectively, our data provide for the first-time evidence that pharmacologic treatment with rADAMTS13 (TAK-755) diminished H/R induced sickle cell related organ damage. Thus, rADAMTS13 might be considered as a potential effective disease-modifying treatment option for sickle cell related acute events.

The description of hyper-functional factor IX (FIX) Padua triggered the development of BAX 335, an AAV8-based hemophilia B gene therapy vector designed to compensate for low FIX protein expression levels by expressing the FIX Padua variant, thereby reducing the exposure to viral vector. The presence of inactive FIX protein at baseline hindered conventional FIX:Ag ELISA from contributing to a more profound understanding of clinical data from the BAX 335 Phase 1/2 study (ClinicalTrials.gov: NCT01687608). By applying phage display technology, a Fab2 mini-antibody selectively binding to FIX Padua was developed and used to establish a FIX Padua-specific ELISA. The assay adequately performed, utilizing human and monkey plasma samples, and enabled the selective quantification of FIX Padua protein in human plasma samples from the BAX 335 trial. The mini-antibody also allowed the development of a chromogenic FIX Padua-specific activity assay, which adequately performed in human and mouse plasma. Collectively, the isolated FIX Padua-specific mini-antibody enabled the development of transgene-product-specific assays, which should improve the monitoring of hemophilia B gene therapies. The approach applied here for FIX Padua could be leveraged to develop variant-specific activity assays for other therapies where highly active enzymes are instrumental in achieving therapeutic levels of the transgene product.