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DNA vaccines represent a relatively new and promising approach to vaccination. A DNA vaccine is produced by incorporating genes for antigens into a recombinant plasmid vaccine. Introduction of the DNA vaccine into a patient leads to uptake of the recombinant plasmid by some of the patient’s cells, followed by transcription and translation of antigens and presentation of these antigens with MHC I to activate adaptive immunity. This results in the stimulation of both humoral and cellular immunity without the risk of active disease associated with live attenuated vaccines.
Although most DNA vaccines for humans are still in development, it is likely that they will become more prevalent in the near future as researchers are working on engineering DNA vaccines that will activate adaptive immunity against several different pathogens at once. First-generation DNA vaccines tested in the 1990s looked promising in animal models but were disappointing when tested in human subjects. Poor cellular uptake of the DNA plasmids was one of the major problems impacting their efficacy. Trials of second-generation DNA vaccines have been more promising thanks to new techniques for enhancing cellular uptake and optimizing antigens. DNA vaccines for various cancers and viral pathogens such as HIV, HPV, and hepatitis B and C are currently in development.
Some DNA vaccines are already in use. In 2005, a DNA vaccine against West Nile virus was approved for use in horses in the United States. Canada has also approved a DNA vaccine to protect fish from infectious hematopoietic necrosis virus. M. Alonso and J. C. Leong. “Licensed DNA Vaccines Against Infectious Hematopoietic Necrosis Virus (IHNV).” Recent Patents on DNA&Gene Sequences (Discontinued) 7 no. 1 (2013): 62–65, issn 1872-2156/2212-3431. doi 10.2174/1872215611307010009. A DNA vaccine against Japanese encephalitis virus was approved for use in humans in 2010 in Australia. S.B. Halstead and S. J. Thomas. “New Japanese Encephalitis Vaccines: Alternatives to Production in Mouse Brain.” Expert Review of Vaccines 10 no. 3 (2011): 355–64.
Based on Olivia’s symptoms, her physician made a preliminary diagnosis of bacterial meningitis without waiting for positive identification from the blood and CSF samples sent to the lab. Olivia was admitted to the hospital and treated with intravenous broad-spectrum antibiotics and rehydration therapy. Over the next several days, her condition began to improve, and new blood samples and lumbar puncture samples showed an absence of microbes in the blood and CSF with levels of white blood cells returning to normal. During this time, the lab produced a positive identification of Neisseria meningitidis , the causative agent of meningococcal meningitis , in her original CSF sample.
N. meningitidis produces a polysaccharide capsule that serves as a virulence factor. N. meningitidis tends to affect infants after they begin to lose the natural passive immunity provided by maternal antibodies. At one year of age, Olivia’s maternal IgG antibodies would have disappeared, and she would not have developed memory cells capable of recognizing antigens associated with the polysaccharide capsule of the N. meningitidis. As a result, her adaptive immune system was unable to produce protective antibodies to combat the infection, and without antibiotics she may not have survived. Olivia’s infection likely would have been avoided altogether had she been vaccinated. A conjugate vaccine to prevent meningococcal meningitis is available and approved for infants as young as two months of age. However, current vaccination schedules in the United States recommend that the vaccine be administered at age 11–12 with a booster at age 16.
Go back to the previous Clinical Focus box.
In countries with developed public health systems, many vaccines are routinely administered to children and adults. Vaccine schedules are changed periodically, based on new information and research results gathered by public health agencies. In the United States, the CDC publishes schedules and other updated information about vaccines.
Match each type of vaccine with the corresponding example.
| ___inactivated vaccine | A. Weakened influenza virions that can only replicate in the slightly lower temperatures of the nasal passages are sprayed into the nose. They do not cause serious flu symptoms, but still produce an active infection that induces a protective adaptive immune response. |
| ___live attenuated vaccine | B. Tetanus toxin molecules are harvested and chemically treated to render them harmless. They are then injected into a patient’s arm. |
| ___toxoid vaccine | C. Influenza virus particles grown in chicken eggs are harvested and chemically treated to render them noninfectious. These immunogenic particles are then purified and packaged and administered as an injection. |
| ___subunit vaccine | D. The gene for hepatitis B virus surface antigen is inserted into a yeast genome. The modified yeast is grown and the virus protein is produced, harvested, purified, and used in a vaccine. |
C, A, B, D
A(n) ________ pathogen is in a weakened state; it is still capable of stimulating an immune response but does not cause a disease.
attenuated
________ immunity occurs when antibodies from one individual are harvested and given to another to protect against disease or treat active disease.
Artificial passive
In the practice of ________, scabs from smallpox victims were used to immunize susceptible individuals against smallpox.
variolation
Briefly compare the pros and cons of inactivated versus live attenuated vaccines.
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