Immunogenicity and tolerance of ascending doses of a recombinant protective antigen (rPA102) anthrax vaccine: a randomized, double-blinded, controlled, multicenter trial.
BACKGROUND
We report the results of a phase I dose escalation, safety and immunogenicity trial of a new recombinant protective antigen (rPA102) anthrax vaccine.


METHODS
Hundred healthy volunteers were randomized in a 4:1 ratio to receive intramuscular doses of rPA102 in the following formulations: 5, 25, 50, or 75 microg of rPA102 in 82.5 microg aluminum hydroxide adjuvant at 0, 4, and 8 weeks; or the US licensed Anthrax Vaccine Adsorbed (AVA) at weeks 0 and 4.


RESULTS
Local reactogenicity (mostly pain) was more common with AVA than with rPA102 following the first (94.7% versus 44.4%; p < 0.001) and the second (84.2% versus 35.4%; p < 0.001) vaccinations. Systemic reactogenicity (mostly headache) was more common among rPA102 vaccinees, but only following the first vaccination (49.4% versus 15.8%; p = 0.025). A dose-response relationship for anti-PA antibodies was present after the 2nd and 3rd vaccinations. Two weeks following the 2nd vaccination, the geometric mean titers (GMT) for lethal toxin neutralization activity (TNA), for the 5, 25, 50 and 75 microg rPA102 and AVA groups were 38.6, 75.4, 373.9, 515.3, and 855.2, respectively. The geometric mean concentrations (GMC) measured by anti-PA IgG ELISA were 3.7, 11.5, 25.9, 44.1, and 171.6, respectively. Two weeks following the 3rd vaccination, TNA GMTs for the four rPA102 groups, were: 134.7, 719.7, 2116.6, 2422.4; and ELISA GMCs were: 22.9, 104.7, 196.4, and 262.6, respectively.


CONCLUSIONS
No clinically serious or dose-related toxicity or reactogenicity was observed. The TNA response after two injections of the 75 microg dose of rPA102 was similar to the response after two injections of AVA. The third rPA102 vaccination substantially increased the antibody response.
Gorse
Geoffrey J
GJ
Saint Louis Veterans Affairs Medical Center and St. Louis University School of Medicine, St. Louis, MO, USA.
Keitel
Wendy
W
Keyserling
Harry
H
Taylor
David N
DN
Lock
Michael
M
Alves
Katia
K
Kenner
Julie
J
Deans
Lynne
L
Gurwith
Marc
M
D000276:Adjuvants, Immunologic / Q000008:administration & dosage; D000293:Adolescent; D000328:Adult; D000536:Aluminum Hydroxide / Q000008:administration & dosage / Q000276:immunology; D022122:Anthrax Vaccines / Q000008:administration & dosage / Q000009:adverse effects* / Q000235:genetics / Q000276:immunology*; D000907:Antibodies, Bacterial / Q000097:blood; D000942:Antigens, Bacterial / Q000008:administration & dosage / Q000009:adverse effects* / Q000235:genetics / Q000276:immunology*; D001427:Bacterial Toxins / Q000008:administration & dosage / Q000009:adverse effects* / Q000235:genetics / Q000276:immunology*; D004306:Dose-Response Relationship, Immunologic; D004311:Double-Blind Method; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007115:Immunization Schedule; D007273:Injections, Intramuscular; D008297:Male; D009500:Neutralization Tests; D014614:Vaccines, Synthetic / Q000008:administration & dosage / Q000009:adverse effects / Q000235:genetics / Q000276:immunology
D000276:Adjuvants, Immunologic; D022122:Anthrax Vaccines; D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D014614:Vaccines, Synthetic; C030325:anthrax toxin; D000536:Aluminum Hydroxide