The discovery that the Lag-3 gene acts as a brake to prevent immune system responses from running out of control solves a mystery that has puzzled researchers since the gene was discovered 14 years ago. A report on this discovery, from investigators at St. Jude Children's Research Hospital and The Johns Hopkins Kimmel Cancer Center, is published in the October issue of the journal Immunity.
The researchers solved the mystery of what Lag-3 does by showing that the gene permits so-called regulatory T cells to act as brakes on the immune system.
Regulatory T cells, which carry the Lag-3 protein on their surfaces, interfere with the action of effector T cells--the "warrior" cells that orchestrate attacks on specific targets in the body, such as cancer cells and microorganisms.
The finding could form the basis for new strategies for improving the efficacy of anti-cancer vaccines or preventing autoimmune diseases. Autoimmune diseases are those in which the immune system attacks specific tissues of a person's own body as if they were foreign matter. The researchers showed that the ability of regulatory T cells to control an attack by effector T cells is substantially prevented or eliminated in the absence of Lag-3.
Both the effector and regulatory cells arise from the same populations of cells, called CD4+ T lymphocytes, according to Dario A. A. Vignali, PhD, associate member of St. Jude Immunology. Vignali is senior author of the immunity report.
The Lag-3 gene is activated in some of the CD4+ cells during an immune system response, turning them into regulatory cells that put the brakes on the activity of their fellow CD4+ T cells that are launching the attack.
"The braking action of regulatory T cells prevents the destructive effects of autoimmune diseases, such as diabetes type 1, which occurs when effector T cells mount an attack on the cells of the pancreas that produce insulin," Vignali said.
However, regulatory T cells can also block the beneficial activity of anti-tumor effector cells. This braking action could inhibit an immune system attack on cancer cells.
"This study adds to the mounting evidence that regulatory T cells play a major role in dampening the immune system's anti-tumor activity," said Charles Drake, MD, PhD, assistant professor of oncology at the Johns Hopkins Kimmel Cancer Center. "The identification of a specific molecule on the surface of these cells that we can block represents an exciting new opportunity to amplify the potency of immune-system-based cancer therapies. We're actively pursuing the best strategy to test these findings in patients."
Drake is co-author of the paper.
In mouse studies, the researchers first showed that regulatory T cells can protect against a potentially lethal, large-scale immune system attack by effector T cells that ordinarily would have caused a fatal lung disease.
Next, the team used a technique called DNA array analysis to identify which genes in the CD4+ T cells are activated in cells that develop into regulatory T cells. The investigators found that the Lag-3 gene was "expressed" (being used by the cell to make protein) to a much greater extent in regulatory T cells than in effector T cells. The team then showed that inserting the Lag-3 gene into CD4+ T cells turned them into regulatory T cells. These newly minted regulatory T cells suppressed effector T cell activity.
In addition, the researchers showed that antibodies against the Lag-3 protein block this moderating effect of regulatory T cells on the effector T cells, allowing the effector cells to continue an aggressive attack. This finding provided further evidence that Lag-3 is a key protein on regulatory T cells that controls effector T cell function.
"The tumor-specific T cells generated by some anti-cancer vaccines are not very effective because regulatory T cells block their therapeutic activity," said Creg J. Workman, PhD, a postdoctoral researcher in Vignali's lab and co-author of the paper. "But if researchers could block Lag-3 on regulatory T cells it might possible to free such vaccines to generate an especially aggressive attack on cancer cells." "We'd like to put that kind of control over immune function into the hands of physicians," Vignali said.
The work at St Jude was supported by the National Institutes of Health (NIH) and ALSAC, while the work at The Johns Hopkins Kimmel Cancer Center was supported by the NIH, and gifts from Mrs. Dorothy Needle, William and Betty Topercer, Jack Goldsmith, and the Janey Fund and Seraph Foundation.
Other authors are Creg J. Workman (St. Jude) and Ching-Tai Huang (co-first author), Dallas Flies, Xiaoyu Pan, Aimee L. Marson, Gang Zhou, Edward L. Hipkiss, Sowmya Ravi, Jeanne Kowalski, Hyam I. Levistsky and Jonathan D. Powell (Johns Hopkins Kimmel Cancer Center). Ching-Tai Huang is also affiliated with the Chang Gung University School of Medicine and Hospital, Taiwan.
Source: St. Jude Children's Research Hospital