An improved Francisella tularensis live vaccine strain (LVS) is well tolerated and highly immunogenic when administered to rabbits in escalating doses using various immunization routes.
Tularemia is a severe disease for which there is no licensed vaccine. An attenuated F. tularensis live vaccine strain (LVS) was protective when administered to humans but safety concerns precluded its licensure and use in large-scale immunization. An improved F. tularensis LVS preparation was produced under current good manufacturing practice (cGMP) guidelines for evaluation in clinical trials. Preclinical safety, tolerability and immunogenicity were investigated in rabbits that received LVS in escalating doses (1 x 10(5)-1 x 10(9)CFU) by the intradermal, subcutaneous or percutaneous (scarification) route. This improved LVS formulation was well tolerated at all doses; no death or adverse clinical signs were observed and necropsies showed no signs of pathology. No live organisms were detected in liver or spleen. Transient local reactogenicity was observed after scarification injection. Erythema and edema developed after intradermal injection in the highest dose cohorts. High levels of F. tularensis-specific IgM, IgG and IgA developed early after immunization, in a dose-dependent fashion. Scarification elicited higher levels of IgA. Antibodies elicited by LVS also recognized F. tularensis Schu-S4 antigens and there was a significant correlation between antibody titers measured against both LVS and Schu-S4. The ELISA titers also correlated closely with those measured by microagglutination. This is the first report describing comprehensive toxicological and immunological studies of F. tularensis LVS in rabbits. This animal model, which closely resembles human disease, proved adequate to assess safety and immunogenicity of F. tularensis vaccine candidates. This new LVS vaccine preparation is being evaluated in human clinical studies.
Pasetti
Marcela F
MF
Center for Vaccine Development, Department of Pediatrics, University of Maryland School of Medicine, 685 West Baltimore St., Room 480, Baltimore, MD 21201, United States. mpasetti@medicine.umaryland.edu
Cuberos
Lilian
L
Horn
Thomas L
TL
Shearer
Jeffry D
JD
Matthews
Stephen J
SJ
House
Robert V
RV
Sztein
Marcelo B
MB
D000372:Agglutination Tests; D000818:Animals; D000917:Antibody Formation / Q000276:immunology; D000942:Antigens, Bacterial / Q000737:chemistry / Q000276:immunology / Q000302:isolation & purification; D001428:Bacterial Vaccines / Q000008:administration & dosage / Q000009:adverse effects / Q000276:immunology*; D002626:Chemistry, Pharmaceutical; D004306:Dose-Response Relationship, Immunologic; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005604:Francisella tularensis / Q000276:immunology*; D007070:Immunoglobulin A / Q000096:biosynthesis; D007074:Immunoglobulin G / Q000096:biosynthesis; D007075:Immunoglobulin M / Q000096:biosynthesis; D007271:Injections, Intradermal; D007279:Injections, Subcutaneous; D007700:Kinetics; D008297:Male; D011817:Rabbits; D014481:United States; D014486:United States Food and Drug Administration; D014613:Vaccines, Attenuated / Q000276:immunology
D000942:Antigens, Bacterial; D001428:Bacterial Vaccines; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D014613:Vaccines, Attenuated