Philip Bedford

Chimeric Live, Attenuated Vaccine against Japanese Encephalitis (ChimeriVax-JE): Phase 2 Clinical Trials for Safety and Immunogenicity, Effect of Vaccine Dose and Schedule, and Memory Response to Challenge with Inactivated Japanese Encephalitis Antigen

ChimeriVax-JE is a live, attenuated vaccine against Japanese encephalitis, using yellow fever (YF) 17D vaccine as a vector. In a double-blind phase 2 trial, 99 adults received vaccine, placebo, or YF 17D vaccine (YF-VAX). ChimeriVax-JE was well tolerated, with no differences in adverse events between treatment groups. Viremias resulting from administration of ChimeriVax-JE and YF-VAX were of short duration and low titer; 82 (94%) of 87 subjects administered graded doses (1.8-5.8 log(10)) of ChimeriVax-JE developed neutralizing antibodies. A second dose, administered 30 days later, had no booster effect. Previous inoculation with YF did not interfere with ChimeriVax-JE, but there was a suggestion (not statistically significant) that ChimeriVax-JE interfered with YF-VAX administered 30 days later. A separate study explored immunological memory both in subjects who had received ChimeriVax-JE 9 months before and in ChimeriVax-JE-naive subjects challenged with inactivated mouse-brain vaccine (JE-VAX). Anamnestic responses were observed in preimmune individuals. ChimeriVax-JE appears to be a safe vaccine that provides protective levels of neutralizing antibody after a single dose.

Clinical proof of principle for ChimeriVax™: recombinant live, attenuated vaccines against flavivirus infections

ChimeriVax is a live, attenuated recombinant virus constructed from yellow fever (YF) 17D in which the envelope protein genes of YF 17D are replaced with the corresponding genes of another flavivirus. A ChimeriVax vaccine was developed against Japanese encephalitis (JE). A randomized, double-blind, outpatient study was conducted to compare the safety and immunogenicity of ChimeriVax-JE and YF 17D. Six YF immune and six non-immune adults were randomized to receive a single SC inoculation of ChimeriVax-JE (5log(10)PFU), ChimeriVax-JE (4log(10)PFU) or YF-VAX((R)) (5log(10)PFU). Mild, transient injection site reactions and flu-like symptoms were noted in all treatment groups, with no significant difference between the groups. Nearly all subjects inoculated with ChimeriVax-JE at both dose levels developed a transient, low-level viremia which was similar in magnitude and duration to that following YF-VAX). Neutralizing antibody seroconversion rates to ChimeriVax-JE was 100% in the high and low dose groups in both naïve and YF immune subjects; seroconversion to wild-type JE strains was similar or lower than to the homologous (vaccine) virus. Mean neutralizing antibody responses were higher in the ChimeriVax-JE high dose groups (naïve subjects LNI 1.55, PRNT(50) 254; YF immune subjects LNI 2.23, PRNT(50) 327) than in the low dose groups (naïve subjects 1.38, PRNT(50) 128; YF immune subjects LNI 1.62, PRNT(50) 270). JE antibody levels were higher in YF immune than in naïve subjects, dispelling concerns about anti-vector immunity. The safety and immunogenicity profile of ChimeriVax-JE vaccine appears to be similar to that of YF 17D. The new vaccine holds promise for prevention of JE in travelers and residents of endemic countries. The ChimeriVax technology platform is being exploited for development of new vaccines against dengue and West Nile.

Live Attenuated Chimeric Yellow Fever Dengue Type 2 (ChimeriVax™-DEN2) Vaccine: Phase I Clinical Trial for Safety and Immunogenicity: Effect of Yellow Fever Pre-immunity in Induction of Cross Neutralizing Antibody Responses to All

A randomized double-blind Phase I Trial was conducted to evaluate safety, tolerability, and immunogenicity of a yellow fever (YF)-dengue 2 (DEN2) chimera (ChimeriVax™-DEN2) in comparison to that of YF vaccine (YF-VAX®). Forty-two healthy YF naïve adults randomly received a single dose of either ChimeriVax™-DEN2 (high dose, 5 log plaque forming units [PFU] or low dose, 3 log PFU) or YF-VAXâ by the subcutaneous route (SC). To determine the effect of YF pre-immunity on the ChimeriVaxTM-DEN2 vaccine, 14 subjects previously vaccinated against YF received a high dose of ChimeriVax™-DEN2 as an open-label vaccine. Most adverse events were similar to YF-VAX® and of mild to moderate intensity, with no serious side-effects. One hundred percent and 92.3% of YF naïve subjects inoculated with 5.0 and 3.0 log10 PFU of ChimeriVaxTM-DEN2, respectively, seroconverted to wt DEN2 (strain 16681); 92% of subjects inoculated with YF-VAX® seroconverted to YF 17D virus but none of YF naïve subjects inoculated with ChimeriVax-DEN2 seroconverted to YF 17D virus. Low seroconversion rates to heterologous DEN serotypes 1, 3, and 4 were observed in YF naïve subjects inoculated with either ChimeriVax™-DEN2 or YF-VAX®. In contrast, 100% of YF immune subjects inoculated with ChimeriVax™-DEN2 seroconverted to all 4 DEN serotypes. Surprisingly, levels of neutralizing antibodies to DEN 1, 2, and 3 viruses in YF immune subjects persisted after 1 year. These data demonstrated that 1) the safety and immunogenicity profile of the ChimeriVax™-DEN2 vaccine is consistent with that of YF-VAX®, and 2) pre-immunity to YF virus does not interfere with ChimeriVaxTM-DEN2 immunization, but induces a long lasting and cross neutralizing antibody response to all 4 DEN serotypes. The latter observation can have practical implications toward development of a dengue vaccine.

Yellow Fever 17D Vaccine Safety and Immunogenicity in the Elderly

The incidence of serious and severe multisystem adverse events (AEs) following yellow fever (YF) 17D vaccine is higher in persons of advanced age. One hypothesis for the occurrence of these AEs in the elderly is immunological senescence and a reduced ability to clear the vaccine virus infection. We determined age-specific rates of serious and nonserious AEs in two large clinical trials of two YF 17D vaccines from different manufacturers. In addition, we analyzed AEs reported in a large general practice data base in the United Kingdom. Neutralizing antibody responses were compared in young and elderly subjects. In the clinical trials, involving a total of 4,532 subjects, there were no neurological and viscerotropic AEs; interestingly, the incidence of common injection site and systemic AEs was significantly lower in elderly than in younger subjects. The neutralizing antibody categorical and quantitative responses were equivalent across younger and elderly subjects. In contrast, the larger retrospective analysis of 43,555 persons receiving YF 17D in the UK general practice database revealed a higher incidence of significant neurologic and multisystem AEs with advancing age. The age-specific reporting rate ratio (RRR) was approximately twice that in the 25-44 year-old reference group for subjects in the 45-64 year age group (RRR 1.82; 95% CI 0.88,3.77) and 3-fold higher for the 65-74 year-old age group (RRR 2.82; 95% CI 0.81, 9.81). These results are consistent with previous reports on YF vaccine safety in the US (Martin M, et al. Emerg Infect Dis 2001;6:945-951; Khromova et al., Vaccine 2005;23:3256-3263). In elderly persons, YF 17D vaccine is associated with a higher frequency of significant AEs in the elderly but a lower incidence of common non-serious side-effects. The neutralizing antibody response, which is the mediator of protective immunity to YF, is not diminished in healthy, elderly persons.

Safety and efficacy of E coli enterotoxin adjuvant for urease-based rectal immunization against Helicobacter pylori.

Low dose E. coli heat-labile enterotoxin (LT), delivered orally or enterically, has been used as an adjuvant for Helicobacter pylori (H. pylori) urease in healthy adults. In this study we aim to test the safety and adjuvant efficacy of LT delivered rectally together with recombinant H. pylori urease. Eighteen healthy adults without present or past H. pylori infection were enrolled in a double blind, randomized, ascending dose study to receive either urease (60 mg), or urease (60 mg) + LT (5 or 25 microg). The immunization preparation was administered per rectum on days 0, 14 and 28. Serum, stool and saliva anti-urease and anti-LT IgG and IgA antibodies (Abs) were measured and urease-specific and LT-specific antigen secreting cells (ASCs) were counted in peripheral blood at baseline and 7 (ASC counts) or 14 days (antibody levels) after each dosing. Peripheral blood lymphoproliferation assays were also performed at baseline and at the end of the study. Rectally delivered urease and LT were well tolerated. Among the 12 subjects assigned to urease+LT, 2 (16.7%) developed anti-urease IgG Abs, 1 (8.3%) developed anti-urease IgA Abs, and 3 (25%) showed urease-specific IgA(+) ASCs. Immune responses to LT were more vigorous, especially in subjects exposed to 5 microg LT. In the urease+ 5 microg LT group, anti-LT IgG and IgA Abs developed in 60 and 80% of the subjects, respectively, while LT-specific IgG(+) and IgA(+) ASCs were detected in all subjects. The magnitude of the anti-LT response was much higher than the response to urease. No IgA anti-urease or anti-LT Abs were detected in stool or saliva and lymphocyte proliferative responses to urease were unsatisfactory. In conclusion, rectal delivery of 5 microg LT is safe and induces vigorous systemic anti-LT immune responses. Further studies are needed to determine if LT can be an effective adjuvant for rectally delivered antigens.

Comparative safety and immunogenicity of two attenuated enterotoxigenic Escherichia coli vaccine strains in healthy adults

ABSTRACT A vaccine against enterotoxigenic Escherichia coli (ETEC) is needed to prevent diarrheal illness among children in developing countries and at-risk travelers. Two live attenuated ETEC strains, PTL002 and PTL003, which express the ETEC colonization factor CFA/II, were evaluated for safety and immunogenicity. In a randomized, double-blind, placebo-controlled trial, 19 subjects ingested one dose, and 21 subjects ingested two doses (days 0 and 10) of PTL-002 or PTL-003 at 2 × 109 CFU/dose. Anti-CFA/II mucosal immune responses were determined from the number of antibody-secreting cells (ASC) in blood measured by enzyme-linked immunospot assay, the antibody in lymphocyte supernatants (ALS) measured by enzyme-linked immunosorbent assay (ELISA), and fecal immunoglobulin A (IgA) levels determined by ELISA. Time-resolved fluorescence (TRF) ELISA was more sensitive than standard colorimetric ELISA for measuring serum antibody responses to CFA/II and its components, CS1 and CS3. Both constructs were well tolerated. Mild diarrhea occurred after 2 of 31 doses (6%) of PTL-003. PTL-003 produced more sustained intestinal colonization than PTL-002 and better IgA response rates: 90% versus 55% (P = 0.01) for anti-CFA/II IgA-ASCs, 55% versus 30% (P = 0.11) for serum anti-CS1 IgA by TRF, and 65% versus 25% (P = 0.03) for serum anti-CS3 IgA by TRF. Serum IgG response rates to CS1 or CS3 were 55% in PTL-003 recipients and 15% in PTL-002 recipients (P = 0.02). Two doses of either strain were not significantly more immunogenic than one. Based on its superior immunogenicity, which was comparable to that of a virulent ETEC strain and other ETEC vaccine candidates, PTL-003 will be developed further as a component of a live, oral attenuated ETEC vaccine.

Exercise-Induced Serum Enzyme Elevations Confounding the Evaluation of Investigational Drug Toxicity: Report of Two Cases in a Vaccine Trial

Two subjects developed marked elevations in creatine kinase and other serum enzymesassociated with mild myalgia during a randomized, double-blind, controlled Phase 1 clinical trial ofan investigational live, attenuated vaccine against West Nile virus (ChimeriVax™-WN02). Onesubject had received ChimeriVax™-WN02 while the other subject was enrolled in an activecontrol group and received licensed yellow fever 17D vaccine (YF-VAX®). Subsequently, theclinical trial was interrupted, and an investigation was begun to evaluate the enzymeabnormalities. As daily serum samples were collected for determination of quantitative viremia, itwas possible to define the enzyme elevations with precision, and to relate these elevations tophysical activity of the subjects, symptoms, and virological and serological measurements.Evaluation of both subjects clearly showed that skeletal muscle injury, and not cardiac or hepaticdysfunction, was responsible for the biochemical abnormalities. This investigation also implicatedstrenuous exercise as the cause of the apparent muscle injury rather than the study vaccines. Asa result of this experience, subjects engaged in future early-stage trials of these live, attenuatedviral vaccines will be advised not to engage in contact sports or new or enhanced exerciseregimens for which they are not trained or conditioned. The inclusion of placebo control arm (inlieu of or addition to an active vaccine control) will also be useful in differentiating causally relatedserum enzyme elevations.