Contribution to hepatitis B prevention.

Hepatitis B is widely recognized as an important public health problem. The only effective way to control hepatitis B is by vaccination. First generation plasma-derived hepatitis B vaccines have limitations. Advances in recombinant DNA technology have led to the development of yeast-derived recombinant hepatitis B vaccine which is now used extensively in the developed world. This article reviews the development of this new generation vaccine and the efforts to facilitate universal vaccination programmes particularly in the developing world. The issue of the cost of new generation vaccines, in relation to the major investment required for research and development and also the quality of the final product, is discussed.

Safety and immunogenicity of an inactivated hepatitis A candidate vaccine in healthy adult volunteers.

The reactogenicity and immunogenicity of a formaldehyde-inactivated hepatitis A vaccine have been investigated. Three different dose levels of vaccine (180, 360 and 720 ELISA units) were administered to healthy volunteers according to a 0, 1, 2 and 12 month schedule. The vaccine was safe and well tolerated. Reactions observed following vaccination were essentially mild and were not dependent upon the quantity of antigen administered. All subjects had measurable titres of anti-HAV antibodies after the full vaccination course; the immune response to the vaccine was dose-related. Antibody titres in vaccinees at month 13 were between 60- and 190-fold higher than those observed in a group of subjects given anti-HAV immunoglobulin.

Development and production aspects of a recombinant yeast-derived hepatitis B vaccine.

Any attempt to control or eradicate hepatitis B on a global scale requires the availability of large quantities of effective, safe and affordable hepatitis B vaccine. The drawbacks of the first generation of plasma-derived vaccines--poor acceptance, relatively high cost, limited availability--have led to the search for alternative means of producing hepatitis B vaccines. This article reviews the development and production of a yeast-derived vaccine based on recombinant DNA technology and discusses potency, stability and potential availability for use in the implementation of vaccination programmes.

Recombinant versus plasma-derived hepatitis B vaccines: issues of safety, immunogenicity and cost-effectiveness.

Any attempt to reduce the incidence of hepatitis B on a worldwide scale requires the availability of large quantities of potent, safe and affordable hepatitis B vaccine. However, ongoing doubts or concerns--justified or not--persist about the comparative safety, immunogenicity and cost-effectiveness of commercially available hepatitis B vaccines, whether derived from plasma or produced via recombinant expression systems. This review compares plasma versus recombinant hepatitis B vaccines in terms of these alleged differences and in the light of increasing clinical data acquired following administration of recombinant yeast-derived hepatitis B vaccines.

Immunological properties of recombinant HBsAg produced in yeast.

Although currently available plasma-derived vaccines (PDV) against hepatitis B based on the surface antigen of the virus (HBsAg) are well-tolerated and effective, their supply is limited and time-consuming controls are necessary to assess their safety. It is therefore desirable that an alternative source of HBsAg be found. Recombinant DNA technology has provided the possibility of obtaining HBsAg in large quantities. However, it is important that a recombinant DNA hepatitis B vaccine be not only antigenically similar but also elicits a similar immune response in humans. Using the Ausria kit, the recombinant DNA vaccine of SmithKline Biologicals produced in yeast appears to have a higher antigenic content than a reference plasma-derived HBsAg preparation of similar purity when compared at equivalent protein concentrations. In competition experiments, however, antibodies obtained by immunization with PDV similarly recognized yeast-derived and plasma-derived antigens. Monoclonal antibodies directed to the common a determinant of the whole virus were also used to identify distinct epitopes on the recombinant DNA vaccine. The yeast-derived HBsAg is therefore antigenically similar to plasma-derived HBsAg. The yeast-derived vaccine (YDV) was highly immunogenic in mice, rabbits, goats, monkeys, chimpanzees, and humans. High titres of anti-HBs were reached in humans after three doses administered at 0, 1, and 6 months. The antibodies raised in humans after three doses of YDV were predominantly directed to the common a determinant. Competition studies using monoclonal antibodies raised against the whole virus showed that the antibodies had the same specificity as the antibodies induced by PDV. The affinity for the plasma-derived antigen of antibodies stimulated by YDV and PDV and antibodies present in the sera of convalescent subjects were also similar. Finally, competition experiments showed that the antibodies induced in humans by YDV and antibodies from convalescent subjects were directed to the same binding sites of the plasma-derived antigen. These studies indicate that the yeast-derived vaccine is immunologically similar to the plasma-derived vaccines both in vitro and in vivo and can therefore be expected to have similar protective efficacy.

Production of Aujeszky vaccine by the microcarrier technology "from the ampoule to the 500 litre fermentor".

A process for the production of Aujeszky vaccine on microcarrier cultures in large fermentors is described. The NLST cells are routinely produced in fermentors of 150 litres; cell density reaches 0.7-0.8 10(6)/ml. The authors describe the method used to obtain those results. The different parameters used in fermentors are discussed and especially pO2 regulation. A study of subculturing method is being carried out to reach a volume of 500 litres. The comparison between stationary culture and microcarrier cultures shows the advantages of such a technique for the viral antigen produced versus infective and the increase of the bulk capacity. This experience also shows that specific development is required for each cell line.

Stability of freeze-dried and reconstituted measles vaccines.

The stability of the titer of live vaccines is a very important factor for successful immunization, especially in countries with a hot climate. For the freeze-dried vaccine, the results of stability tests show that the second generation Rimevax possesses the desired resistance to thermodegradation. In the refrigerator, the shelf life is at least 2 years. Exposure at 20--25 degress C for 1 month, at 37 degrees C for 7 to 14 days or at 41 degrees C for 3 to 7 days results in a vaccine retaining its full immunogenic activity. The value of an accelerated stability test at 37 degrees C for 7 days for the prediction of the potency of each lot is proven. This test should be part of the minimum requirements for live vaccines. The potency of reconstituted measles vaccines is evaluated. Rimevax shows a remarkable stability at higher temperatures. At 37 degrees C, the immunogenic activity is retained for 2 to 3 hours. Reconstitution with diluent at 41 degrees C and subsequent exposure to this temperature does not affect the titer significantly during the first half hour. The comparison of published stability data of measles vaccines shows that Rimevax is one of the most thermoresistant preparations.

Stability of live, freeze-dried virus vaccines.

Stability of live, freeze-dried vaccines is a major factor for successful vaccinations. Vaccines may be stored at -20 degrees C or less for long periods without loss of activity and this storage does not affect stability during subsequent storage. Storage in the refrigerator for long periods is harmless for certain very stable vaccines such as influenza, rubella, NDV, Marek's. Other vaccines, such as IBV, show a significant loss in titer after 2 years. The routine use of an accelerated stability test, e.g. exposure of each lot manufactured to 37 degrees C during 7 days, provides useful information regarding the stability of the vaccine at +4 degrees C. In general the loss during the accelerated stability test is higher than the loss after 24 months storage in the refrigerator. Specifications requiring that each vaccine lot must possess, after the accelerated test, a titer equal to or higher than the minimum titer needed for immunization, are a guarantee of sufficient potency at the time of administration. To solve the problems in tropical countries stable vaccines are essential. Cendevax and Rimevax exposed to tropical temperatures still possess the minimum required titer after several days.