Elsevier Vaccine, Vol. 14, No. 8, pp. zyxwvutsrqponmlkjih 780-784, 1996 Copyright 0 1996 Elsevier Science Ltd. All rights reserved Printed in Great Britain zyxwvut ELSEVIER 0264-410X(95)00246-4 0264-41OW96 $15+0.00 zyxwvutsr Protective immunization against Helicobacter stimulates long-term immunity Fiona J. RadclifP, Minhu Chenl_ and Adrian Lee*8 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB Immunization with an oral vaccine composed of whole cell sonicates of Helicobacter felis zyxwvutsrqponmlkjihgfedc plus cholera toxin (CT) can protect mice from H. felis challenge. The aim of this study was to determine whether this protective immunity was long-lived. Mice were given the vaccine then left for up to 15 months before challenge. After 15 months, all mice were still protected from H. felis infection, indicating that oral immunization using bacterial antigens plus CT can stimulate long-term local immunological memory. Copyright 0 1996 Elsevier Science Ltd. Keywords: H. felis rn~u~e model; H. pylori; immunization; cholera toxin Helicobacter pylori is now firmly established as a major gastroduodenal pathogen1-7. Acquiring H. py lori early in life has been linked with gastric cancer when other predisposing factors such as poor diet are present, hence the organism is particularly prevalent in developing nations where crowded living conditions and lower hygiene standards increase the risk of infection*-12. The diseases associated with this bacterium, namely peptic ulcer disease and gastric cancer, remain major causes of death in the world. Therefore eradication of H. py lori in both developed and developing countries is now a priority. Antibiotic regimens such as “triple therapy” using a combination of bismuth, tetracycline and metroni- dazole have been successful in clearing infections of ‘13-15. H. pylorr however, the regimen required is com- plex, has side-effects, and metronidazole resistance is becoming increasingly common16-18. While other treat- ment regimens are becoming available, vaccination either prophylactically or therapeutically is the only viable option for large-scale prevention of H. py lori infection. There was doubt as to whether effective immunization could be achieved against H. py lori because the organ- ism can remain in the stomach despite a significant host immune response being directed against it. However, oral immunization using whole cell sonicates of H. felis plus cholera toxin (CT) has been used with great success in a mouse model, resulting in 77-96% protection against H. felis challenge19-21. *School of Microbiology and Immunology, University of New South W ales, Sydney 2052, Australia. TAffiliated First Hospital, Sun Yat-sen University of Medical Science, Guangzhou, P.R. China. $To whom correspondence should be addressed. (Received 1 May 1995; revised 26 October 1995; accepted 26 October 1995) To date none of the prophylactic immunization studies published have examined whether the protec- tion conferred by immunization with H. fehs plus CT lasts longer than 1 month. Earlier studies using other antigens have indicated that local mucosal memory lasted for only a few weeks or months22; however, such conclusions were drawn after exposing animals to anti- gens which were not highly immunogenic or caused tolerance in the mucosal system. Since then CT has been identified as an extremely powerful mucosal immunogen, and there is a substantial body of data indicating that long-standing mucosal memory can be evoked in both humans and rodents when CT is presented orally, either as an adjuvant for an unrelated antigen or as a component of a cholera vaccine23-27. The effectiveness of CT as a mucosal adjuvant is emphasized by the demonstration that 2 years after oral immunization with keyhole limpet haemocyanin (KLH) plus CT, exposure to KLH alone induced a good memory response in mice25. As H. py lori has a restricted host range, with only humans, other higher primates and pigs being easily infected, alternative animal models of Heh’cobacter in- fection, particularly the H. felis mouse mode128, have been used extensively in the oral vaccine studies. This model’s relevance to the human situation has been well verified: H. fehs causes chronic active gastritis in some strains of mice29, antibiotic therapies trialed using this model are effective in humans3’, and immunization of mice with H. py lori antigens confers protection against H. felis challenge. For a vaccine to be considered useful for prophylaxis of H. py lori infection, particularly in societies where there is a high prevalence of infection, it is essential that immunity be iong-lasting. Therefore the aim study was to determine whether immunity H. feZis challenge still existed more than post-immunization. of this against a year 780 Vaccine 1996 Volume 14 Number 8