Regulatory T cells are rare, difficult to grow in the laboratory and prone to sudden identity shifts. Furthermore, they churn out a surprising variety of molecules, the roles of which are not fully understood.
But this class of immune cell also forms the main line of defence against autoimmune disease and many inflammatory conditions in which the immune system, led by effector T (Teff) cells, mistakenly turns on the body.
Clinical trials of therapies using regulatory T (Treg) cells, in which a person’s own Treg cells are removed, expanded and re-administered, began in 2004. But the results have been less than dazzling. Dozens of small trials, to facilitate organ transplants as well to treat as autoimmune conditions, have demonstrated that although the procedure is safe, it is, in general, not that effective. Proponents, however, expect that a new class of genetically engineered Treg cell transplant, which a number of companies hope to test soon in clinical trials, will prove much more effective.