A phase II, randomised clinical trial to demonstrate the non-inferiority of low-dose MF59-adjuvanted pre-pandemic A/H5N1 influenza vaccine in adult and elderly subjects.

BACKGROUND: Effective planning and preparedness against a possible future A/H5N1 influenza pandemic is a major global challenge. Because dose sparing strategies are required to meet the global demand for vaccine, efforts have focused on the development of adjuvanted vaccine formulations of relatively lower antigen content. AIM: This study aimed to demonstrate the non-inferiority of a low-antigen-dose (3.75 µ) [DOSAGE ERROR CORRECTED] A/H5N1 pre-pandemic vaccine compared with a licensed, higher-dose (7.5 mg) formulation in adult and elderly subjects. Immunogenicity was assessed according to European and U.S. licensure criteria. METHODS: A total of 722 subjects were randomized in equal numbers to receive either the licensed or low-dose formulation. All subjects received two vaccine doses administered three weeks apart. Immunogenicity was assessed three weeks after the administration of each vaccine dose by hemagglutination inhibition (HI), single radial haemolysis (SRH) and microneutralization assays (MN). Local and systemic reactions were assessed over a seven day period post-vaccination. Adverse events were recorded throughout. RESULTS: The low-dose vaccine was demonstrated to be non-inferior to the licensed formulation in terms of antibody titres against the vaccine strain. All three European licensure criteria were met by adult subjects in response to the low-dose vaccine; two criteria were met by the elderly age group. Cross-reactive antibodies were detected against the heterologous A/H5N1 antigen strains A/Indonesia/05/05 and A/turkeyTurkey/01/05. Both vaccines were generally well tolerated by both age groups. CONCLUSION: These data demonstrate that a low antigen dose in combination with MF59 adjuvant is adequate for the routine pre-pandemic immunization of adult and elderly subjects.

The co-crystal structure of unliganded bovine alpha-thrombin and prethrombin-2: movement of the Tyr-Pro-Pro-Trp segment and active site residues upon ligand binding.

Unliganded bovine alpha-thrombin and prethrombin-2 have been co-crystallized, in space group P21212, using either ammonium sulfate or polyethylene glycol 2000 (PEG2K), and their structures determined at 2.2 A and 2.3 A, respectively. Initial phases were determined by molecular replacement and refined using XPLOR to final R factors of 0.187 (Rfree = 0.255) and 0.190 (Rfree = 0.282) for the salt and PEG2K models, respectively. The apo-enzyme form of bovine alpha-thrombin shows dramatic shifts in placement for the Tyr-Pro-Pro-Trp segment, for Glu-192, and for the catalytic residues His-57 and Ser-195, when compared to 4 thrombin complexes representing different states of catalysis, namely (1) the Michaelis complex (residues 7-19 of fibrinogen A alpha with a non-cleavable scissile bond), (2) enzyme-inhibitor complex (D-Phe-Pro-Arg chloromethylketone), (3) enzyme product complex (residues 7-16 of fibrinopeptide A), and (4) the exosite complex (residues 53-64 of hirudin). The structures of bovine and human prethrombin-2 are generally similar to one another (RMS deviation of 0.68 A) but differ significantly in the Arg-15/Ile-16 cleavage region and in the three activation domains, which are disordered in bovine prethrombin-2, analogous to that seen for trypsinogen.