Immunology

H. Groux, A. O'Garra, M. Bigler, M. Rouleau, S. Antoneko, J.E. de Vries, M.G. Roncarolo, "A CD4+ T-cell subset inhibits antigen-specific T-cell responses and prevents colitis," Nature, 389:737-42, Oct. 16, 1997. (Cited in more than 210 papers since publication) Comments by Maria Grazia Roncarolo, codirector of the Telethon Institute of Gene Therapy, Milano, Italy Maria Grazia Roncarolo has searched for more than 10 years for a way to overcome a major complication in bone marrow transplants: graft-vs.-host disease (GVHD), a rejection of the recipient by the donor marrow. Even with immunosuppressive drugs, doctors often cannot control the reaction, which can be lethal. She took her clinical observations and developed some basic research tenets with the goal of helping patients. Pictured from left: Mike Bigler, Matthieu Rouleau, Reiko Namikawa, Maria Grazia Roncarolo, Herve Groux, Meri Firpo, Nicole Carballido As a pediatrician, Roncarolo noticed some patients did not develop GVHD when mismatched bone marrow was used for transplant therapy. These patients had a genetic disease called severe combined immune deficiency (SCID), which somehow seemed to provide a favorable environment for tolerance. At the time in 1986, Roncarolo and her colleagues showed that SCID patients still had GVHD-mediating T cells in their blood, but the cells were not causing disease. "So we speculated that other cells in the blood were keeping the GVHD-mediating cells under control," recalls Roncarolo. The clue to finding the cells responsible for GVHD tolerance came a few years later when murine interleukin-10 (IL-10) was cloned. Interleukins are regulatory proteins secreted by cells involved in immune defense mechanisms. Then a T- cell clone isolated by Roncarolo from a SCID patient, who had transplanted bone marrow, led to the cloning of human IL-10. "I realized that T cells isolated from SCID patients produce a lot of IL-10. I knew I was on the right track to finding T-regulatory cells," says Roncarolo. This paper describes a procedure to generate T-regulatory cells (Tr1) in vitro starting from human and mouse T cells in the presence of IL-10. Roncarolo and colleagues then used a mouse model to successfully test Tr1 cells in vivo for their ability to suppress colitis, inflammation of the colon. The Nature paper is significant because it is the first time that T-regulatory cells were cloned. "[Immunologists had been discussing] suppressor/regulatory cells for over 20 years, but it was a vague concept," explains Roncarolo. Finally, researchers could characterize these cells at the single-cell level. Cloning Tr1 cells may have taken a long time because scientists were using the wrong screening criteria. Roncarolo initially tried to isolate the T-regulatory cells by screening for proliferation. However, after IL-10 was cloned, researchers focused on the secretion of suppressor proteins, IL-10 and TGF-beta, and this led to the isolation of the T-regulatory cells. Follow-up research with Bruce Blazar, professor of pediatrics at University of Minnesota Medical School, showed that IL-10-transformed T cells induced tolerance in the murine model of GVHD.1 Roncarolo is now improving the method of generating Tr1 cells in vitro from human peripheral blood. Roncarolo explains, "For clinical application we need to not only be efficient, but also be quick." She would like to shorten the process of generating cells from six weeks to a couple of weeks. "If these T cells really mediate tolerance as we saw in the SCID patients, we should be able to give the cells generated in vitro to patients at the time of the transplant and [prevent GVHD]," comments Roncarolo. Though cellular therapies like this are usually expensive, she feels the expense will be worthwhile if the result is patients with fewer complications and a higher survival rate. One advantage of this procedure is that it appears to be selective. "With T-regulatory cells we induce tolerance to the graft, but we still preserve immunity toward other pathogens," says Roncarolo. She hopes this will also be true in patients, but the final proof will come from clinical trials, which may start as early as next year. 1. J.C. Zeller et al., "Induction of CD4+ T cell alloantigen-specific hyporesponsiveness by IL-10 and TGF-beta," Journal of Immunology, 163[7]:3684-91, Oct. 1, 1999.

Immunology

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