Structural and functional characteristics of the B-domain-deleted recombinant factor VIII protein, r-VIII SQ

Recombinant factor VIII SQ (r-VIII SQ), ReFacto, is a recombinant factor VIII product similar to the smallest active factor VIII protein found in plasma-derived factor VIII (p-VIII) concentrates. The protein comprises two polypeptide chains of 80 and 90 kDa and lacks the major part of the heavily glycosylated B-domain i.e. amino acids Gln744 to Ser1637. r-VIII SQ retains six potential glycosylation sites for N-linked oligosaccharides at asparagine residues 41, 239, 582, 1685, 1810 and 2118. We describe a thorough comparison of the characteristics of r-VIII SQ with those of p-VIII. The primary and secondary structures of r-VIII SQ were in good agreement with that of B-domain-deleted p-VIII (p-VIII-LMW) as shown by SDS-PAGE, Western blotting with antifactor VIII antibodies, tryptic mapping, amino acid sequence analysis and circular dichroism spectroscopy. A few divergences also existed. Thus r-VIII SQ was shown to contain a small amount of the single chain primary translation product of 170 kDa and also the product specific sequence of 14 amino acids, the SQ-link, in the C-terminal end of the 90 kDa chain. It was shown that r-VIII SQ had a high specific activity of about 14,000 IU VIII:C/mg as determined by use of a chromogenic substrate assay. The r-VIII SQ protein was comparable to p-VIII forms with a retained B-domain, in terms of potency measured by a chromogenic substrate or a two-stage clotting assay, in interactions with thrombin, and with activated protein C (APC) in combination with Protein S. The ability of r-VIII SQ to participate as a cofactor in factor Xa generation in a mixture of factors IXa and X, phospholipid and calcium was in conformity with that of p-VIII. Furthermore r-VIII SQ had a good binding capacity for phospholipid vesicles and von Willebrand factor (vWF) as shown in gel filtration studies. The same kinetics in binding to von Willebrand factor was found for r-VIII SQ and p-VIII as determined by real-time biospecific interaction analysis (BIA) with use of the BIAcore instrument. The apparent association rate constant was 4 x 10(6) M(-1)s(-1). Two dissociation rate constants were found, 1 X 10(-2)s(-1) and 4 x 10(-4)s(-1). The results extend the present knowledge that the factor VIII B-domain is dispensable for the factor VIII cofactor function in hemostasis.     

NK-cell and T-cell functions in patients with breast cancer: effects of surgery and adjuvant chemo- and radiotherapy

Breast cancer is globally the most common malignancy in women. Her2-targeted monoclonal antibodies are established treatment modalities, and vaccines are in late-stage clinical testing in patients with breast cancer and known to promote tumour-killing through mechanisms like antibody-dependent cellular cytotoxicity. It is therefore increasingly important to study immunological consequences of conventional treatment strategies. In this study, functional tests and four-colour flow cytometry were used to detect natural killer (NK)-cell functions and receptors as well as T-cell signal transduction molecules and intracellular cytokines in preoperative breast cancer patients, and patients who had received adjuvant radiotherapy or adjuvant combined chemo-radiotherapy as well as in age-matched healthy controls. The absolute number of NK cells, the density of NK receptors as well as in vitro quantitation of functional NK cytotoxicity were significantly higher in preoperative patients than the post-treatments group and controls. A similar pattern was seen with regard to T-cell signalling molecules, and preoperative patients produced significantly higher amounts of cytokines in NK and T cells compared to other groups. The results indicate that functions of NK and T cells are well preserved before surgery but decrease following adjuvant therapy, which may speak in favour of early rather than late use of immunotherapeutic agents such as trastuzumab that may depend on intact immune effector functions.     

Preclinical pharmacology of albumin-free B-domain deleted recombinant factor VIII

A second-generation recombinant factor VIII molecule was developed with an albumin-free formulation. In this modified form of factor VIII, the N- and C-terminal sections of the B-domain are retained and fused at serine 743 and glutamine 1638, resulting in a B-domain deleted factor VIII protein known as ReFacto (Genetics Institute, Andover, MA). Preclinical studies of ReFacto have focused on efficacy of the product for the hemophilia A patient population. The efficacy and pharmacokinetic profiles of ReFacto were similar to plasma-derived factor VIII in correcting the hemostatic defect of hemophilia A dogs. Both ReFacto and plasma-derived human factor VIII (Octonativ-M7, Pharmacia, Stockholm, Sweden) were found to associate with von Willebrand factor (vWF) after infusion into hemophilia A dogs as demonstrated by size exclusion chromatography. Infusion of either ReFacto or Octonativ-M7 quickly corrected factor VIII coagulant activity (FVIIIc), whole blood clotting time (WBCT), and activated partial thromboplastin time (aPTT). No obvious differences were seen between ReFacto and Octonativ-M7. Both ReFacto and Octonativ-M7 treatment reduced secondary bleeding time to less than 6 minutes. The clearance was faster and the volume of distribution at steady state was larger for plasma-derived factor VIII compared with ReFacto. The half-life was similar between Octonativ-M7 and ReFacto. These data predict that ReFacto will be effective in correcting human factor VIII deficiency states.     

Factor VIII Concentrate Prepared from DDAVP Stimulated Blood Donor Plasma

Human fraction 1-0 (AHF-Kabi) was prepared from plasma from blood donors who had received an i.v. injection of DDAVP (0.2 μg per kg b.w.) and tranexamic acid (0.01 g per kg b.w.) 15 min before collection of the blood. The factor VIII preparation from such plasma contained twice as much VIII:C, VIIIR:Ag, and VIIIR:RFC as normal fraction 1-0. Normal fraction 1-0 and DDAVP fraction 1-0 were given to 2 patients with severe haemophilia A. The in vivo response of the DDAVP fraction 1-0 corresponded to the in vitro values. No differences in survival time were seen. Hence, it is possible to produce factor VIII concentrates with at least double the yield by increasing the factor VIII level in blood donors by i.v. injection of DDAVP.     

Membranous duodenal stenosis

The experience of our 16 patients treated for membranous duodenal stenosis is reported. Their treatment and course was analysed in a retrospective study. Eight patients were operated on within the first 16 days of life and in the remaining group surgery was performed at 1 month to 4 y of age. The presenting symptom leading to diagnosis was, in all but one case, non-bile-stained vomiting. Associated malformations were found in all but four patients, mostly morbus Down. The operative procedure performed was a partial excision of the duodenal membrane and a duodenoplasty in 10 patients, a duodenojejunostomy in 5 patients, and a duodenoplasty only in 1 patient. The postoperative course was without lethal complications. One late stricture in an anastomosis occurred. We conclude that in its presentation, duodenal stenosis differs from duodenal atresia, and can often be misinterpreted, resulting in a late diagnosis, and should be reported as a separate entity.     

Platelet activation by Shiga toxin and circulatory factors as a pathogenetic mechanism in the hemolytic uremic syndrome

Thrombocytopenia caused by platelet consumption in thrombi is a major manifestation of hemolytic uremic syndrome (HUS) associated with Shiga toxin (Stx) producing Escherichia coli. Platelets have glycosphingolipid receptors capable of binding Stx, but a direct interaction between the toxin and platelets, leading to platelet activation, has not been reported. In this study, it is shown that Stx1 and its B (binding) subunit (Stx1B), at 10 pg/mL to 10 ng/mL, bound to platelets. Toxin was internalized in platelets within 2 hours. This led to increased platelet aggregation, as demonstrated by confocal microscopy. Preincubation of Stx1B with anti-Stx1 antibody inhibited this reaction. Stx1 induced morphologic changes in platelets seen on scanning electron microscopy. In the presence of platelets and tumor necrosis factor-pretreated human umbilical vein endothelial cells (HUVEC), Stx1 and Stx1B induced the binding of platelets to the endothelial cell membrane and were present at this binding site. Incubation of Stx1 and Stx1B with whole blood increased fibrinogen binding to platelets detected by flow cytometry. Fibrinogen binding was partially inhibited by preincubation with anti-Stx1. Stx1 increased platelet retention measured in a glass bead assay. In addition, plasma from 17 patients with HUS, taken during the acute phase of the disease, increased the retention of normal platelets and normalized after recovery. Taken together, the results of this investigation show that Stx1, Stx1B, and a factor or factors in the plasma of patients with HUS activate platelets. The presence of Stx1 at the binding site of platelets to HUVEC suggests that Stx may be directly involved in the prothrombotic state seen in HUS.