Context: Group A streptococcal infections and their sequelae represent a global health problem. Recent advances have allowed previous obstacles associated with group A streptococcal vaccine development to be overcome.
Objective: To preliminarily evaluate the safety and immunogenicity of ascending doses of a recombinant fusion peptide group A streptococcal vaccine containing N-terminal M protein fragments from serotypes 1, 3, 5, 6, 19, and 24 in healthy volunteers.
Design, setting, and participants: An open-label, uncontrolled, dose-ascending phase 1 vaccine trial of 28 healthy adult volunteers aged 18 to 50 years recruited from the metropolitan area of Baltimore, Md, between October 5, 1999, and February 26, 2003, using newspaper advertisements and posted fliers, and evaluated in the outpatient facility of the Center for Vaccine Development.
Interventions: Each volunteer received 3 spaced intramuscular injections of 50 microg (n = 8), 100 micro g (n = 10), or 200 microg (n = 10) of hexavalent group A streptococcal vaccine formulated with aluminum hydroxide into the deltoid muscle of alternating arms.
Main outcome measures: Assessments of clinical safety, including elicitation of antibodies that cross-react with host tissues, and immunogenicity as measured by enzyme-linked immunosorbent assay (ELISA) and assays of opsonophagocytic- and bactericidal-antibody responses.
Results: One year of intensive follow-up revealed the vaccine to be well tolerated. There was no evidence of tissue cross-reactive antibodies or immunological complications. At the highest (200 microg) dose, vaccination elicited significant increases in geometric mean antibody levels to all 6 component M antigens by ELISA (all P<.01) and to 5 of 6 M types in the opsonophagocytosis assay (all P<.05). In addition, postvaccination increases in serum bactericidal activity of at least 30% were observed in 31 (55%) of 56 assays.
Conclusion: These results provide the first evidence in humans that a hybrid fusion protein is a feasible strategy for evoking type-specific opsonic antibodies against multiple serotypes of group A streptococcus without eliciting antibodies that cross-react with host tissues, which represents a critical step in the development of a vaccine.