Laboratory tests and reference reagents employed in studies of inactivated hepatitis A vaccine

Immunochemiluminescent focus assays for the quantitation of hepatitis A virus and rotavirus in cell cultures

Two new immunological methods, the luminescent immunofocus assay (LIFA) and the luminescent immunofocus inhibition assay (LIF-IA), are described for the quantitation of cytopathic and non-cytopathic viruses propagated on cell culture monolayers. These methods use enhanced chemiluminescent detection to identify foci (luminescent immunofoci, LIF) of virus-infected cells. Viruses are propagated in susceptible cells under an agarose overlay, inactivated with ultraviolet irradiation, lifted onto nitrocellulose membranes, and probed with virus-specific monoclonal or polyclonal antibody followed by a second antibody conjugated to horseradish peroxidase. Membranes are then treated with a luminol-based detection reagent and exposed to light sensitive film for up to 10 min. The film is developed and foci appear as dark, discrete spots which are proportional to the dose of each virus. The LIFA detected both cytopathic and non-cytopathic hepatitis A viruses (HAV) and simian rotavirus. For the cytopathic HAV, the LIFA and plaque counts were comparable. The LIF-IA was developed for HAV using virus-specific antiserum which effectively attenuated LIF formation. The LIFA and LIF-IA may be completed 5 days faster than conventional radioimmunofocus assays for HAV and rotavirus and do not require the use of radiolabeled antibodies, offering safety advantages and making these techniques more adaptable for general use. Luminescent immunofocus assays should be useful for the detection and quantitation of virtually any cytopathic or non-cytopathic virus that can be propagated in monolayer cultures when virus-specific antiserum is available.

Dose range evaluation of a new inactivated hepatitis A vaccine administered as a single dose followed by a booster

A total of 242 healthy adults were immunised with a first dose of an investigational inactivated hepatitis A vaccine. Three concentrations (3, 6 and 12 EU [ELISA units]) of the experimental vaccine were used and compared to a licensed reference vaccine. The aim was to determine the antigenic concentration of the study vaccine inducing the highest seroconversion rate and anti-Hepatitis A virus (HAV) antibody response at 2 weeks after the primary immunisation. A booster dose was given at month 6. At 15 days after the primary immunisation the seroconversion rates in subjects vaccinated with the 6 and 12 EU vaccines were 78 and 94%, respectively. At 30 and 180 days after the primary immunisation the percentages of seropositivity were 100% for both groups. The antibody response to the 12 EU study vaccine was similar to that to the reference vaccine. The percentages of seropositivity at 15 and 180 days after the primary immunisation were 94 vs 93%, and 100 vs 93% in the experimental and reference vaccine respectively. Thus, because it induces early and lasting seroconversion, the 12 EU study vaccine seems to be the most effective as a high potency HAV vaccine.

Hepatitis A antibodies in liver transplant recipients: evidence for loss of immunity posttransplantation

Liver transplant recipients frequently have chronic liver diseases and should be considered for vaccination against hepatitis A virus (HAV). However, persistence of protective antibodies after orthotopic liver transplantation (OLT) has not been shown in this population, which may have implications for future vaccine recommendations. We evaluated the prevalence and epidemiological significance of immunoglobulin G (IgG) antibody to HAV (anti-HAV) in a nonvaccinated population before OLT (immunity from previous exposure) and determined the persistence of IgG anti-HAV at 1 and 2 years after OLT. One hundred consecutive patients were identified who underwent OLT and had at least 2 years of follow-up post-OLT. They were not vaccinated against HAV infection at any time. Clinical data were summarized from medical records, and stored sera were tested for IgG anti-HAV before OLT and at 1 and 2 years after OLT by a commercially available enzyme immunoassay. Of 100 patients, 24 had IgG anti-HAV before OLT. No epidemiological differences were noted between those with or without detectable IgG anti-HAV before OLT. Among patients with detectable IgG anti-HAV before OLT, 4 of 22 patients (18%) and 7 of 24 patients (29%) became negative for IgG anti-HAV at 1 and 2 years post-OLT, respectively. None of the patients with undetectable IgG anti-HAV before OLT became positive at any time. Most of our patients with end-stage liver disease had no serological evidence for immunity against HAV. A significant proportion of patients with detectable protective antibodies before OLT lost their antibodies at 2 years after OLT.

Hepatitis A virus-specific humoral and cellular immune responses following immunization with a formalin-inactivated hepatitis A vaccine

To evaluate proliferative T cell responses elicited by a formalin-inactivated HAV vaccine, we immunized 10 subjects with an inactivated HAV vaccine, and measured HAV antibody titers and HAV-specific T cell proliferation. gamma-Interferon production by PBMC's was evaluated in selected subjects. By week 30, seroconversion (geometric mean titer=2299 mIU/ml), and HAV-specific proliferation was detected in all subjects. HAV also induced gamma-interferon in the three subjects studied. These data indicate that the inactivated HAV vaccine induces proliferative T cell responses in addition to HAV antibody. This may be important for protection against hepatitis A, and suggests that recall memory for HAV antigen is elicited by the vaccine.

Hepatitis A vaccine in healthy adults: a comparison of immunogenicity and reactogenicity between two- and three-dose regimens

Inactivated hepatitis A virus (HAV) vaccine was administered to 55 healthy seronegative adult volunteers to evaluate the immunogenicity and adverse reactions of two doses of HAV vaccination (25 units) in comparison with a three-dose regimen. The volunteers were randomly assigned to receive one of the two regimens: 26 were vaccinated with two doses at 0 and 24 weeks (Group 1), and 29 were vaccinated with three doses at 0, 2, and 24 weeks (Group 2). The vaccine was well tolerated and there was no serious adverse reaction. In both groups, the seroconversion rate was 100% at week 28. At week 52, all remained positive for anti-HAV regardless of a two- or three-dose regimen. No statistically significant difference in seroconversion rates and geometric mean titers could be demonstrated between the two groups. Thus, the two-dose regimen may be favorable to save cost and time for active immunization against hepatitis A.

Early appearance of neutralizing antibodies after vaccination with an inactivated hepatitis A vaccine

Sera from 30 subjects vaccinated with the Pasteur Merieux Serums & Vaccins (PM) inactivated hepatitis A vaccine, and from 30 subjects vaccinated with the Smithkline Beecham (SB) inactivated hepatitis A vaccine, were tested in two laboratories in order to provide comparative data on neutralizing activities of vaccine-induced antibodies. Sera were also evaluated by a modified radioimmunoassay (mRIA) and results were compared to neutralization assays results. Neutralizing antibody titres provided by the two laboratories correlated well (coefficient or correlation 0.42, P < 0.001). Neutralizing antibodies were detected after vaccination with both vaccines, and the kinetics of neutralizing antibody were the same with both vaccines. The titres gradually increased between the second week after the first dose and the post-booster dose (week 28). A strong booster effect of the booster vaccine dose on neutralizing titres was observed. Significantly higher neutralizing antibody titres with the PM vaccine were observed as early immune response on week 2 titres on both series of results. Vaccine-induced neutralizing antibody titres and vaccine-induced antibody mRIA titres correlated well (coefficient of correlation 0.82 and 0.72, respectively, P < 0.0001 in both cases). These results demonstrate early appearance of neutralizing antibody at high titre with the PM vaccine.

Serologic diagnosis of viral hepatitis

Viral hepatitis has become a difficult field in which clinical and laboratory skills are needed to establish the correct diagnosis and plan for the appropriate therapy. For example, it is no longer enough to diagnose chronic hepatitis B or C. Now, the viral titer or viral genotype must be known. The laboratory test then must be understood in the context of the clinical presentation. This article helps the clinician to acquire such working knowledge. It summarizes available data for hepatitis A, B, C, D, and E. It also includes the recently discovered viral agents, hepatitis G and the hepatitis GB agents.

Safety and Immunogenicity of a High-Potency Inactivated Hepatitis A Vaccine

Background: In recent years, several hepatitis A vaccines have been developed. We wished to evaluate the safety, reactogenicity, and immunogenicity of an inactivated hepatitis A vaccine, containing 1440 EI.U., and to monitor the kinetics of the antibodies monthly for the first year after administration of a single dose of vaccine. Methods: We conducted an open clinical trial, started in March 1992 and completed in July 1993, at two general hospitals and one pediatric hospital in Antwerp, Belgium, with 194 healthy adult healthcare volunteers. Each volunteer received a single dose hepatitis A vaccine, given intramuscularly at month 0 and a booster at month 12. We undertook serologic follow-up of antihepatitis A virus (antiHAV) antibodies and liver enzymes at day 15 and at months 1, 6, 9, 12, and 13. For a random subgroup of participants, blood samples were taken monthly. In addition, all participants noted local and general symptoms following administration of the vaccine. Results: This single dose vaccine was well-tolerated; 2 weeks after the vaccination, 80% of the participants had seroconverted (antiHAV antibodies >=20 mIU/mL); after 1 month, seroconversion reached 99% (geometric mean titer (GMT): 383 mIU/mL). One year after the single dose of vaccine, 94% still had antiHAV antibodies above 20 mIU/mL (GMT: 176 mIU/mL). One month after the booster dose, seroconversion was 100%, and GMT increased from 176 mIU/mL at month 12 to 4775 mIU/mL at month 13. Conclusions: The single dose hepatitis A vaccine is safe and highly immunogenic; it gives a rapid antibody production and a rapid increase of GMT. The persistence of protective antibodies until month 12 allows a booster at month 12. This schedule will easily fit into existing travel or occupational health vaccination schedules and will improve vaccination compliance.

Comparison of modified HAVAB and ELISA for determination of vaccine-induced anti-HAV response

An inhibition ELISA was compared with a modification of the HAVAB assay for measuring antibodies induced by a killed HAV vaccine. GMT's expressed in mIU/ml were higher by ELISA than by modified HAVAB, especially after the first and second doses of vaccine but seroconversion rates were very similar and a good correlation was found between both assays. Because of its higher sensitivity and specificity, the ELISA assay was preferred to modified HAVAB for the evaluation of a Hepatitis A vaccine in human volunteers.