Bacterial Capsule Conjugate Vaccines

Dear Colleagues,

Emerging infectious diseases, particularly COVID-19, have invigorated the field of vaccinology. The dramatic success in terms of the speed of development and the efficacy of the new class of mRNA vaccines have raised expectations for vaccines to control future outbreaks. mRNA is just one of many platforms that will be used for vaccine development. DNA vaccines made from eukaryotic expression plasmids have shown great promise for decades. Viral vectors including those made from adenoviruses, VSV, and Vaccinia viruses have developed into mature vaccine platforms. Even bacteriophages and bacteria spores have been used to express foreign antigens to the immune system. Nanoparticle vaccines made from self-assembling proteins such as the HBV capsid protein and ferritin have made their way into clinical trials. More conventional protein subunit vaccines are also becoming easier to design and produce, taking advantage of sequencing data, recombinant DNA technologies, and synthetic methods.

Those strategies are especially useful when a protein immunogen has been identified as a viable vaccine target. With viruses, that is often an envelope or spike protein. With bacterial pathogens, the immunogens may be secreted protein toxins. For example, there are efficacious toxoid vaccines against B. anthracis, C. diphtheria, B. pertussis, and multiple Clostridium species. However, some of the most important vaccines target non-protein antigens. Among those are the capsule-based vaccines against S. pneumoniae, N. meningitidis, and H. influenza. Capsules tend to be negatively charged polymers composed of carbohydrates and occasionally amino acids. These polymers tend to be poor immunogens unless conjugated to carrier proteins. The development of new capsule conjugate vaccines offers unique challenges that are being met in new ways. These involve the use of technologies to produce capsule polymers, either synthetically or with surrogate bacteria that can overexpress the polymer. They can involve new chemical conjugation methods, including some methods that use bacteria to do the conjugation. The use of adjuvants can also be critical to the success of conjugate vaccines.

This Special Issue is intended to highlight some new studies advancing the field of conjugate vaccinology. We invite you to contribute original research or review articles dealing with conjugate vaccines, focusing on conjugation strategies, adjuvants, vaccine stability, protection studies, or commentaries that may help us to understand the challenges we have faced and new ones that may await us.

Dr. Donald Chabot
Guest Editor

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• capsule vaccine
• conjugate vaccine
• capsule polymer
• adjuvant
• LPS vaccine