In recent years, PEGylated factor VIII (FVIII) has become one of the mainstay therapeutic agents for hemophilia A. In the present study, the frequency and characteristics of anti-PEG IgG antibodies were investigated in 177 hemophilia A patients in Japan. Twenty-five patients (14.1%) were determined to be anti-PEG IgG antibody-positive by ELISA using three PEGylated proteins (Rurioctocog alfa pegol, Damoctocog alfa pegol, and PEGylated BSA) as antigens. The anti-PEG IgG antibody-positive rates in the groups with and without administration of PEGylated therapeutic drugs for hepatitis were 8.2% and 16.4%, respectively. Similarly, the antibody-positive rates in the groups with and without administration of Rurioctocog alpha pegol were 8.7% and 14.9%, respectively, and a causal relationship with history of PEGylated agent use could not be confirmed. The results suggested that anti-PEG IgG antibodies were more commonly observed in younger patients than in older patients, and may be continuously retained. Anti-PEG IgG antibodies did not inhibit the activity of FVIII. In one patient with anti-PEG IgG antibody positivity, the expected recovery rate and half-life-prolonging effect of Rurioctocog alfa pegol were not obtained.

We described the history of an international conference in the field of thrombosis, hemostasis and vascular biology. Well known investigators were invited from abroad, and heated discussion were experienced. It was hoped that this meeting may be useful to promote progress in Japan.