Trouble Ahead for Peptide Vaccines?

By Meagan White
ScienceNOW Daily News
19 January 2006

Protein-based vaccines--commonly called peptide vaccines--are still in their infancy; so far, they have only been tested in lab animals. The vaccines teach the body how to recognize invaders by exposing the immune system to harmless snippets of viral proteins. Upon vaccination, the body cranks out a supply of T cells that remember these proteins in case they are encountered again. A common concern with any type of vaccine, however, is whether it can cause adverse affects if the person has already been exposed to the virus in question.

To see if this poses a problem for peptide vaccines, researchers led by J. Lindsay Whitton of the Scripps Research Institute in San Diego, California, infected 4 mice with lymphocytic choriomeningitis virus (LCMV). Eight days later, the team vaccinated these mice either with a peptide representing the LCMV epitope or with saline. The saline-injected mice mounted a normal T-cell response and displayed no harmful side effects; the peptide-injected mice, on the other hand, had a much larger pool of active T cells. One would think that extra T cells would be a good thing, says Whitton, but these mice developed hunched backs, reduced mobility, and other symptoms. All died within 24 hours of injection.

The reason, the team explains online 19 January in the Journal of Clinical Investigation, is that T cells secrete toxic compounds, so too many can harm the host. "This study is a cautionary flag for peptide vaccines," Whitton says. Still, he believes that with the proper dosage, the vaccines can be made safe. "[This is] not an indication to abandon ship," he says.

Immunologist Mark Larché of the Imperial College London, United Kingdom, agrees. "The message of this study is that yes, you will have problems with the wrong dose of peptides," he says, "but that does not mean peptides will not be good vaccine components."

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