What is Viral Vector Vaccines?

Viral vector vaccines use live viruses to carry DNA into human cells. The DNA contained in the virus encodes antigens that, once expressed in the infected human cells, elicit an immune response.

Overview

Viral vector vaccines combine many of the positive qualities of DNA vaccines with those of live attenuated vaccines.1 Like DNA vaccines, viral vector vaccines carry DNA into a host cell for production of antigenic proteins that can be tailored to stimulate a range of immune responses, including antibody, T helper cell (CD4+ T cell), and cytotoxic T lymphocyte (CTL, CD8+ T cell) mediated immunity. Viral vector vaccines, unlike DNA vaccines, also have the potential to actively invade host cells and replicate, much like a live attenuated vaccine, further activating the immune system like an adjuvant. The viral vector vaccine therefore generally consists of a live attenuated virus that is genetically engineered to carry DNA encoding protein antigens from an unrelated organism.

Although viral vector vaccines are generally able to produce stronger immune responses than DNA vaccines, for some diseases viral vectors are being used in combination with other vaccine technologies in a strategy called heterologous prime-boost. In this system, one vaccine is given as a priming step, followed by vaccination using an alternative vaccine as a booster. The heterologous prime-boost strategy aims to provide a stronger overall immune response. Viral vector vaccines are being pursued as both prime and boost vaccines as part of this strategy.

Existing Products

There are no viral vector vaccines currently on market for use in humans. There are twelve viral vector vaccines currently in use for veterinary diseases. The approved vaccines include adenovirus, fowlpox virus, attenuated yellow fever (YFV-17D), and vaccinia virus vectors, all of which are relevant as potential human viral vectored vaccines.1

References

  1. Draper SJ and Heeney JL (2010) “Viruses as vaccine vectors for infectious diseases and cancer.” Nature Reviews Microbiology 8: 62-73.

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Pipline

Analysis

Although there are no viral vector vaccines currently in use in humans, viral vector vaccines are in development for a variety of neglected tropical diseases. The relative strengths, weaknesses, opportunities, and risks for different viral vectors currently being developed for neglected tropical diseases are profiled here. The most advanced products in development are for the viral diseases dengue fever and HIV. Antigens from other viruses may be easier to engineer into viral-based vaccines, but there is potential to translate these technologies to a variety of other neglected tropical disease organisms.

Strengths Weaknesses
Potential to elicit a wide range of immune responses (both humoral and cellular) Regulatory pathway uncertain as no viral vectored vaccines are approved for humans
Potential for combination with other vaccination technologies, especially as part of prime-boost regimens Humans previously exposed to human vector may have a blunted immune response to related virus vectored vaccines; immune response to the vector, either from natural exposure or prior vaccination, may inactivate the vaccine before it can replicate and induce the desired immune response
Antigens are manufactured using the host cellular machinery there may be an advantage in achieving native conformation/structure Most ongoing vaccine trials are prime-boost combinations with other vaccines making it difficult to determine how much each individual vaccine contributed to immunity
Replicating viral vector, as compared to DNA vectors, may provide advantage of stronger immune response Somewhat limited capacity for carrying multiple antigens
  Viral vector must be sufficiently attenuated as to not cause disease

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To learn how you can get involved in neglected disease drug, vaccine or diagnostic research and development, or to provide updates, changes, or corrections to the Global Health Primer website, please view our FAQs.

Viral vector vaccines benefit from improved understanding of viral biology. Several online resources for information on viral biology are available online, including:

For more detailed information on the current state of viral vector vaccine design see the recent review by Draper and Heeney, available here.

Get Involved

To learn how you can get involved in neglected disease drug, vaccine or diagnostic research and development, or to provide updates, changes, or corrections to the Global Health Primer website, please view our FAQs.