Patch vaccines may increase autoimmune disease risk

Australian researchers have shown in a mouse model that a bacterial toxin used as an immune-stimulating agent in some vaccines may increase the risk of developing autoimmune disease, where the immune system reacts against the body's own proteins.

The study, by Alan Baxter at James Cook University and Prof Anthony Basten at Sydney's Centenary Institute of Cancer Research and Cell Biology, examined the effects of cholera toxin when applied together with specific auto- or self-antigens to the skin of a mouse, to see whether the adjuvant effects of the toxin would increase the severity of autoimmune disease.

The results were published in the January 1 issue of the Journal of Immunology.

Unexpectedly, the researchers found that the toxin did increase the severity of disease in two different autoimmune disease models for multiple sclerosis and type 1 diabetes when applied to the skin together with the appropriate auto-antigen.

What's more, in both models the toxin also increased the severity of disease in the absence of the auto-antigen, suggesting that the inflammatory effects of the adjuvant were somehow exacerbating the early development of autoimmune disease.

The results are surprising, according to the published discussion, as cholera toxin and other strong bacterial toxin-derived adjuvants tend to induce tolerance, or suppression of autoimmune responses when administered by intravenous, subcutaneous or mucosal routes.

Significantly, these adjuvants are being tested by companies for use in patch vaccines, which promise needle-free transdermal delivery of the vaccine antigens. The concept is attractive -- the skin contains a rich supply of immune cells, and the technology promises to be inexpensive, simple and pain-free.

Neither Baxter nor Basten would comment on their results, citing commercial concerns. But their conclusions suggest that patch vaccines containing cholera toxin and other similar bacterial adjuvants may pose risks to individuals with a genetic susceptibility to autoimmune diseases, which should be considered when conducting clinical trials.