J M Ketley

SAFETY, IMMUNOGENICITY, AND EFFICACY OF RECOMBINANT LIVE ORAL CHOLERA VACCINES, CVD 103 AND CVD 103-HgR

The genes encoding the A (toxic) subunit of cholera toxin were deleted from pathogenic Vibrio cholerae O1 strain 569B by recombinant techniques, leaving intact production of immunogenic, non-toxic B subunit. The resultant strain, CVD 103, evaluated for safety, immunogenicity, and efficacy as a live oral vaccine, was highly attenuated and elicited strong antibacterial and antitoxic immune responses; a single dose significantly protected volunteers against challenge with pathogenic V cholerae O1 of either serotype or biotype. A further derivative, CVD 103-HgR, which has an Hg++-resistance gene to differentiate it from wild-type vibrios, was also well-tolerated, immunogenic, and protective; moreover, faecal excretion of this derivative was significantly lower than that of CVD 103, which should minimise environmental spread of the vaccine. CVD 103-HgR is a candidate for expanded clinical trials in endemic areas.

PRODUCTION OF A SECOND DIARRHEAGENIC FACTOR

In the last decade a great effort has been made to produce an efficient vaccine against cholera. When fed to volunteers, some genetically engineered mutants lacking the cholera toxin(CT)genes(CVD 101) induced mild diarrhea(1), while others(395N1)did not(2). Aim of the present study was to evaluate whether toxic factors other than CT are involved in the pathogenesis of cholera.Methods: crude culture supernatants from V. cholerae 395 and from two similarly constructed CT- mutunts(CVD101 and 395N1) were added to rabbit intestine stripped of serosal and muscular layers and mounted in Ussing chambers. At the end of the experiments, tissues were processed for electron microscopy.Results: a)395 and CVD101 supernatants added to the mucosa of small intestine gave a significant increase in tissue conductance(Gt) peaking after 2hrs. This increase caused an early increase in short circuit current(Isc)that was not related to CT activity. No change in Gt was observed when 395 supernatant was added to the caecal tissue; b)395N1 did not increase Gt for 100 min. when added to the small intestine; c)preliminary freeze-fracture data showed that tight-junctions (tj) became less complex, having fewer intersections, in tissues exposed to 395 or CVD101 supernatants, compared to those exposed to medium alone.Conclusions: 1) 395 and CVD101 supernatants induced a significant increase in Gt in rabbit small intestine, while 395N1(non diarrheagenic CT- mutant) did not. Exposing caecum to 395 did not alter Gt; 2)the Gt increase was associated with morphological changes of tj; 3)this factor may be responsible for the residual diarrhea observed in some CT-mutants.1. Infect.Immun.56, 161-168 (1988); 2.J.Exp.Med.168, 1487-1492(1988).