Vaccine Overview: Summary by Vaccine Types, continued

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The page below is a sample from the LabCE course Cancer Vaccines: Milestones, Promises, Opportunities, and Challenges. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Vaccine Overview: Summary by Vaccine Types, continued

    • Toxoid vaccines
      • The term “toxoid” comes from the word “toxin.” By definition, this type of vaccine relies on toxic materials or products produced by disease-causing germs to trigger an immune reaction and to establish immunity against the germ of interest. Unlike live attenuated or inactivated types of vaccines, toxoid vaccines do not target the whole germ but preferentially focus on the toxin associated with the germ.
      • Examples of toxoid vaccines include diphtheria and tetanus.

    • Vaccines based on viral vectors
      • Viruses survive by introducing their genetic materials to the host nucleus followed by hijacking the host replication apparatus for replication to produce progenies to extend the infectious processes. Going to school on this, scientists have developed viral vectors to introduce materials of interest into cells. One such application is the use of viral vectors to design snippets from disease-causing germs as a type of vaccine to stimulate an immune response and subsequent immunity. Of utmost importance is that the pathogen engineered into the viral vector does not harbor viral replication genes, in other words, the pathogens are replication incompetent to avoid infecting individuals who receive the viral vector-based vaccines.
      • A commonly used viral vector for vaccine design is adenovirus. Examples of adenovirus-based vaccines include vaccines against SARS-CoV-2 viral infection, such as: ChAdOx1 nCoV-19, VAXZEVRIA AZD1222, Ad26.COV2.S (Johnson & Johnson), Sputnik V, and Ad5-nCOV. Other adenovirus-based vaccines in use or development target Ebolavirus, HIV, Zika virus, and influenza virus.

    • mRNA vaccines
      • The idea of using messenger RNA (mRNA) as a tool to deliver molecular materials for medicinal purposes was first proposed several decades ago. The idea stagnated as a result of a rate-limiting step—native mRNA molecules are very unstable with a limited shelf life. Moreover, native mRNA also stimulated the host immune system which led to immune overreaction and cytokine storms that could be life-threatening.
      • Two molecular geneticists persisted in their pursuit of a working mRNA. They are Dr. Caitilin Kariko and Dr. Drew Weissman at the University of Pennsylvania School of Medicine.1 They eventually identified uracil, one of the four nitrogenous bases of RNA, as the culprit for the two shortcomings. Through trial and error, Dr. Kariko and Weissman replaced native uracil with a modified version termed “pseudo-uracil.” This revolutionary step solved all problems and paved the way for modified mRNA as a ready tool for clinical applications.
      • Early January 2020 at the beginning of the COVID-19 pandemic that hit much of the globe, two laboratories, Pfizer/BioNTech based in Meinze, Germany, and Moderna based in Boston, MA, U.S.A. acquired the license for the modified mRNA.2 Losing no time, both laboratories achieved huge success in the development of an mRNA vaccine that targets the spike protein of SARS-CoV-2. Both Dr. Kariko and Dr. Weissman received the 2023 Nobel Prize in Physiology or Medicine for their contribution of mRNA research work that has helped save the world from the pandemic.
      • The mRNA-based vaccines are suitable for both infectious diseases and cancer (with both preventive and therapeutic purposes). It is wrong to assume the mRNA platform is for designing vaccines against infectious diseases only, as in the development of the mRNA vaccine targeting the spike protein of SARS-CoV-2. More will be discussed about the mechanism of action of mRNA-based vaccines in subsequent topics on mRNA-based cancer vaccines later in this course.
    1. The Nobel Assembly at Karolinska Institutet. "Scientific background 2023: Discoveries concerning nucleoside base modifications that enabled the development of effective mRNA vaccines against COVID-19." Nobelprize.org. 2023. https://www.nobelprize.org/uploads/2023/10/advanced-medicinprize2023-3.pdf
    2. Saleh A, Qamar S, Tekin A, Singh R, Kashyap R. Vaccine development throughout history. Cureus. 2021;13(7):e16635. Published 2021 Jul 26. doi:10.7759/cureus.16635