Vaccines made with bacteria killed by gamma irradiation, rather than by standard methods of heat or chemical inactivation, may be more effective, say researchers supported by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH). Vaccines made from gamma-irradiated bacteria also may not need to be kept cold; an advantage in settings where refrigerating vaccines is impractical or impossible. A report on the research appears in the current issue of the journal Immunity.

In experiments with mice, scientists including Eyal Raz, M.D., Sandip Datta, M.D., and Joshua Fierer, M.D., of the University of California, San Diego, School of Medicine demonstrated that a vaccine made from irradiated Listeria monocytogenes bacteria, unlike a vaccine made from heat-killed bacteria, provides protection against challenge with live Listeria. The irradiated bacteria also stimulated a protective response from immune system cells called T cells. Previously, only vaccines made from live, weakened Listeria bacteria were believed capable of eliciting a T-cell response