Safety and efficacy of low dose Escherichia coli enterotoxin adjuvant for urease based oral immunisation against Helicobacter pylori in healthy volunteers

Background and aims: Escherichia coli heat labile enterotoxin (LT) at doses of 5 mug or 10 mug has adjuvant activity for oral immunisation in humans infected with Helicobacter pylori, but causes severe diarrhoea. This study was undertaken to establish a safe and effective dose of LT, to confirm the safety of recombinant urease, and to compare the immunogenicity of orally compared with enterically delivered urease. Methods: 42 healthy adults without present or past H pylori infection were randomised to receive 60 mg recombinant H pylori urease in soluble or in encapsulated form given with doses of LT ranging from 0 mug to 2.5 mug. Four oral doses were administered at day 1, 8, 29, and 57 Specific IgA IgA, and g 9 g antibody secreting cells were measured as well as total alpha4beta7 integrin positive lymphocyte responses. Results: Enterically delivered urease was well tolerated and no serious adverse events occurred. Mild diarrhoea (one to four loose stools) occurred after the first immunisation in 50% (6 of 12) of the volunteers exposed to 2.5 mug LT (p=0.06; paired t test, compared with baseline) but not in volunteers exposed to lower LT doses. Immune responses occurred in five (p=0.048; Fisher's exact test), one, two, and one of six subjects exposed to 2.5 mug, 0.5 mug, 0.1 mug, and no LT, respectively. Significant CD4(+), CD69(+), and CD45RO(hi) responses occurred over time among alpha4beta7(hi) lymphocytes in volunteers receiving 2.5 mug LT. Enterically delivered urease induced higher lymphocyte responses than soluble urease. Conclusions: The safety of H pylori urease is confirmed. Oral LT may conserve its adjuvant activity at low doses with minimal side effects.