MODIFICATION OF FACTOR-VIII IN THERAPEUTIC CONCENTRATES AFTER VIRUS INACTIVATION BY SOLVENT-DETERGENT AND PASTEURIZATION

3The addition of a pasteurisation step to a solvent/detergent (SD) tre ated FVIII concentrate has recently resulted in enhanced inhibitor inc idence in patients in Germany and Belgium. We have investigated the ef fect of virus inactivation procedures on FVIII function by preparing e xperimental concentrates from the same starting cryoprecipitate with t he following procedures: none (N); dry heat (DH); pasteurisation (P); solvent/detergent (SD); solvent detergent + dry heat (SDDH); solvent d etergent + pasteurisation (SDP). In addition, several clinical SD conc entrates with and without pasteurisation were studied. There were no s ignificant differences in fibrinogen and vWF content and in the ratio of one-stage/chromogenic FVIII activity among any of the samples studi ed. In thrombin proteolysis and FXa generation experiments, there were no differences in results on samples N, DH, P, and SDDH from those on sample SD. However sample SDP gave markedly different results from sa mple SD in the following respects: slower thrombin proteolysis (t1/2 = 12.0 min vs 1.9 min); more rapid FXa generation (rate 2.5 times that of SD); enhanced phospholipid binding (K-D = 3.89 x 10(-11)M vs 5.53 X 10(-10)M). Similar differences between SDP and SD were seen in the cl inical samples. The observed changes in the FVIII activity occurred in combination with SD and pasteurisation, but not with either treatment alone. These results suggest that SDP treatment may enhance exposure of the phospholipid binding site in the C2 domain of FVIII, and since inhibitors to the SDP product are predominantly against C2, these find ings could be relevant to the enhanced immunogenicity of the SDP produ ct.