For vaccines to teach the body to recognize a pathogen, they must insert a diagnostic fragment in macrophages and other cells of the immune system. Viruses can do the job, but they can be dangerous - especially in patients whose immune system is already weakened by a viral infection. Now researchers report that a single bacterial protein may act as carrier, priming the immune system to respond to specific foreign proteins. The new technology, reported in the current issue of Proceedings of the National Academy of Sciences could be adaptable in a delivery system for vaccines against AIDS.
The key to the new technology is a protein called hsp70, which belongs to a group of proteins called "heat shock proteins" or "stress proteins" have been found in bacteria and higher organisms. These protein strongly stimulate the immune system of mammals. in recent years, several research groups have created vaccines that protect mice against cancer by injecting them isolated stress proteins from own tumor cells of the mouse. Now, Rick Young immunologist and his colleagues at the Whitehead Institute and Massachusetts Institute of Technology have coaxed a mouse immune system to recognize other proteins by attaching them to a heat shock isolated tuberculosis bacilli proteins and injecting the combination into the animal.
the group has created a prototype vaccine to mice by binding a protein to chicken ovalbumin called hsp70 tuberculosis proteins. They then implanted in mice genetically a cancer cell line festooned with the ovalbumin protein. Generally, these cancer cells overwhelm the immune system of the host. But because hsp70 somehow made known target the immune systems of host mice, ovalbumin on cancer cell surfaces was like a bull's eye in the sights of a sniper. The mouse immune system responded enthusiastically, killing invasive cancer cells. After 40 days, 80% protected mice were still alive, whereas all the control mice died of tumors.
Heat shock proteins are "much safer" than viral vaccines, said Michael Starnbach, immunologist at Harvard Medical School in Boston. And although researchers do not know how the heat shock proteins to sneak into killer T cells, they might be able to deliver almost any antigen. "It's exciting," says Starnbach.
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