February 15, 2018 (Vol. 38, No. 4)

Well-Designed Assays Conserve Samples and Discern Immune Subtleties

Developing new vaccines has never been simple, but the growing need to create combination and polyvalent vaccines has put increasing pressure on the development process. Compared to single-component vaccines, combination vaccines are complex, but they do enable consolidated dosing strategies.

The best-known combination vaccine is the common vaccine against measles, mumps, and rubella. Such vaccines, which incorporate protection against several different pathogens in a single vaccine dose, can reduce the number of individual vaccinations or visits to the pediatrician. In remote regions or in the developing world, where repeat access to each person may not be feasible, combination vaccines make the most of each vaccination opportunity.

Consolidated dosing can also enhance vaccine protection against pathogens for which there are many closely related disease-causing strains or serotypes. Consider the advantages of providing coverage against as many pathogen strains as possible in a single polyvalent vaccine. By including antigens for different strains of the same pathogen, combination vaccines may deliver broader protection for patients. Pneumococcal vaccines are good examples of this approach.

There is tremendous public health value in creating combination and polyvalent vaccines, but scientists must consider potential challenges in assay development. Confirming immune responses to vaccines is far more complex when the vaccines incorporate multiple closely related antigens and when there is the potential for cross-reactivity among them. For this kind of vaccine development, multiplexing assay technology can be very helpful. Compared to running a multitude of individual ELISA tests, multiplex assays are faster, more reliable, and more cost-effective. This approach can streamline development of complex vaccines and bring products to market more quickly.

Assay Development

There are several elements of the development process that are made more complex by combination and polyvalent vaccines. After acquiring a bacteria, virus isolate, or a synthetic virus-like particle and carefully studying the structure and sequence of the pathogen, there are certain key factors to address before an assay can be considered ready for clinical trial use.

Sample volume. Confirmation of vaccine protection during clinical trials is an essential part of development. However, study sample volumes collected during these trials can be limited—especially when it comes to vaccines designed for a pediatric population. For vaccines that include multiple components to protect against several pathogens or strains of a pathogen, sufficient testing must be performed for each component to guarantee effectiveness. Run individually, all of those tests likely require far more sample than it is possible to obtain from each trial participant.

Multiplexing technology affords the ability to test for multiple analytes simultaneously, greatly reducing the amount of sample needed, and therefore generates far more information. Without multiplexing assays, scientists often must prioritize their testing schemes, eliminating certain useful biomarkers or analyses because there is not enough sample. Multiplexing allows development teams to test more of the parameters they believe are relevant to vaccine evaluation, leading to the development of higher-quality vaccines with a more thorough understanding of their biological effects.

Adding new antigens. For optimal results in developing a combination or polyvalent vaccine, designing the assay to measure results should be done in a stepwise fashion. In other words, each time a new antigen is added, it is important to look at the specific individual assay reactions to ensure that the new component has not had an unexpected impact on the previous ones and vice versa.

Measuring immune response. Understanding immunogenicity is a critical step in vaccine development. Scientists perform this kind of testing before and during clinical trials. With combination and polyvalent vaccines, however, the very presence of multiple antigens becomes a confounding factor. Antigens may be cross-reactive, or viral strains so closely related, that it is very difficult to tease out the immune response to each component of a vaccine.

Discriminating the immunogenicity of each element in the vaccine must be done throughout the clinical trial. In some cases, it may also be important to determine whether a specific immune response was induced by the vaccine or by a naturally occurring infection during the study.

Confirming that the vaccine is spurring the desired response can also be improved with multiplexing technology, which enables multiple analytes to be tested simultaneously. If the sensitivity of these assays is high, it is possible in many cases to discriminate the response against multiple antigens. This type of technology generates a significant amount of data about the immune response to the pathogen of interest, as well as to closely related viruses and epitopes because these can all be included in a single reaction tube.

Multiplexing Discussion

If a single measurement is all that is required—for example, if just one element of the immune response against a single component is to be assessed—assay multiplexing may not be advantageous. Assay multiplexing may be desirable, however, if multiple measurements are needed. A vaccine may incorporate multiple elements, each of which may influence a different element of the immune response, or a single-component vaccine may affect multiple elements of the immune response. A miniaturized reaction medium may make it possible to generate hundreds of data points for each element being measured, magnifying the amount of information that can be mined for a thorough profile of sensitivity, specificity, and repeatability of reactions.

Multiplexing provides more information and streamlines what would otherwise be an incredibly laborious and expensive process into a faster, more cost-effective workflow. The efficiencies gained from multiplexing during both analytical and clinical trial phases of vaccine development can conserve resources and save time at multiple steps in development, reducing overall development times. The implementation of multiplex technology allows for significant progress in the development of complex vaccines.

Eric Shaw ([email protected]) is head of clinical assay development at Takeda Vaccines

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