The 'in vivo' survival characteristics of factor VIII procoagulant antigen (VIII:C Ag) in haemophilia A subjects

Severely heated therapeutic factor VIII concentrate of high specific activity

A new method for the manufacture of a heated factor VIII concentrate of high specific activity (2-6 IU factor VIII:C/mg protein) has been developed. Addition of heparin to cryoprecipitate extract at acid pH precipitated fibrinogen and fibronectin. Factor VIII was then recovered from the supernatant by precipitation with glycine and sodium chloride. After re-solution and desalting on Sephadex G-25, the concentrate was sterile-filtered and lyophilised. The dried product was stable to heating in the final container at 80 degrees C for 72 h. Data from 25 consecutive batches of concentrate prepared from 1,200-1,500 kg plasma pools are presented. The mean final yield of heated product was 190 IU factor VIII:C/kg plasma. The concentrate has been found to be safe and effective in clinical use.

The influence of D.D.A.V.P. on the survival of factor VIII in severe haemophiliacs

The effect of D.D.A.V.P. (desamino-cys'-D-arg8-Vaso-pressin) on the survival characteristics of transfused VIII concentrate was studied in six severe, adolescent, haemophiliacs (VIII:C 1 iu/dl). D.D.A.V.P. was administered at a concentration of 0.3 ug/kg immediately following or 24 hours post infusion. No significant alteration in the half disappearance (1/2 d) or biological half-life (t 1/2) was detected for either VIII procoagulant (VIII:C) or its antigenic counterpart VIII:C Ag. As anticipated there was a significant (if sub-optimal) increase in VIII:R Ag within 2-4 hours of D.D.A.V.P. administration.

The relationship of biological and immunological activities of factor VIII

Factor VIII is an essential blood clotting factor which consists of two protein moieties, each with distinct biological functions and antigenic determinants. The immunological markers were originally seen as indicators of the biological activities; however this view has been increasingly challenged. We have investigated the biological and immunological properties of Factor VIII to clarify these relationships. Plasma stored at room temperature for 21 days lost biological activity, but retained immunological activity: The procoagulant activity was reduced to 35% and the ristocetin cofactor activity to 75.4% of their original levels; but the reactivities of both procoagulant antigen and Factor VIII related antigen were maintained. A dissociation of activities was also demonstrated in serum, in which the procoagulant activity was 10% and the procoagulant antigen 72% of corresponding plasma values. These results indicate that the antigenic reactivities are not appropriate markers for Factor VIII biological activity.

The stability of VIII:C in frozen stored plasma samples--re-examined

VIII procoagulant activity (VIII:C) was estimated by a two-stage assay method, on 100 pre- and post-transfusion samples obtained from severe haemophiliacs receiving regular treatment with a variety of VIII concentrate preparations. Close and significant correlation (r = 0.97 P less than 0.01) was obtained between freshly tested samples and samples stored for one month at -35 degrees C. No significant difference between the two samples was demonstrated by Student's paired-t-test. Forty-nine of the stored samples were also measured for VIII procoagulant antigen (VIII:C Ag) level. A similar close and significant correlation was found for this parameter (r = 0.9 P less than 0.01), when compared with the VIII:C of the freshly tested samples. On average the VIII:C Ag value was 10% lower than the corresponding VIII:C value, although the difference was not statistically significant.