JDRF-funded researchers have discovered further evidence that regulatory T cells are a promising cell-based therapy for type 1 diabetes. Jeffrey Bluestone, Ph.D., and colleagues from the Diabetes Center at the University of California, San Francisco have shown that regulatory T cells can be isolated from people with type 1 diabetes, and then expanded in the laboratory to levels that could be therapeutically useful without a loss of function or stability.

A type of immune cell, regulatory T cells serve the important role of putting the brakes on immune responses. When other immune T cells begin to attack the insulin-producing beta cells in the pancreas, regulatory T cells orchestrate their removal and slow their destructive actions. Previous research shows that regulatory T cells can prevent and even reverse type 1 diabetes in mice when administered in large quantities. The current study, published in the journal Diabetes, confirms the feasibility of that approach-isolating, expanding, and ultimately reintroducing the regulatory T cells-as a potential treatment for people.

The work was supported by a JDRF Collaborative Center for Cell Therapy Grant to Dr. Bluestone, and a postdoctoral fellowship award to researcher Todd Brusko.

Barry Jones, Ph.D., director of JDRF's autoimmunity program, said the study's solid pre-clinical results provide "clear mechanistic rationale" for a human clinical trial using regulatory T cells. A small phase I study, representing an initial assessment of the therapeutic benefits of such a therapy in people, is being planned. 

The goal of the proposed therapy is to restore balance within the immune system by shifting immune system activity toward greater regulation and tolerance. Although the mechanism underlying this shift is not fully understood, there is strong and compelling evidence of the success of the approach in mice with diabetes. The transfer of regulatory T cells expanded in the laboratory somehow "can overcome intrinsic defects and restore tolerance in type 1 diabetes," the scientists said, emphasizing that early treatment would likely provide the best outcomes.

"The therapeutic benefits of restoring tolerance early in type 1 diabetes would likely result in the preservation of endogenous beta-cell mass and subsequent reduction in complications resulting from hyperglycemia."

Method of Regulatory T cell Expansion
The researchers isolated regulatory T cells from the blood of nine adults who were recently diagnosed with type 1 diabetes, and from three healthy control subjects. The cells were then grown in the laboratory. The researchers evaluated the capacity of the cells to expand as well the behavior of the expanded cells.

Large Numbers of Cells Are Grown
The researchers identified two separate populations of functional regulatory T cells that expanded to large numbers and could potentially be used for treatment. However, one group was deemed better for clinical use based on several findings:

• After two weeks in culture, these regulatory T cells increased by about 1,500-fold while still maintaining their ability to suppress other types of T cells;
• These cells were attained without using immunosuppressive drugs that help maintain the function of the cells, but inhibit proliferation and growth;
• The enriched T cells continued to express the proteins needed for proper development and function; and
• The expanded cells tended to produce more of a cytokine known to have regulatory properties and less of one known to activate pathogenic T cells.

Next Steps and Considerations
Regulatory T cells are present in the blood in very low numbers, and so to use them in any type of treatment requires their isolation and expansion. But a major concern with expanding these cells from people with an autoimmune disease like diabetes is that the very cells that initiate the autoimmune attack could also be expanded-an unwanted consequence called "outgrowth." In the current study, the researchers minimized this risk by sorting the cells for markers found only on regulatory T cells.

One of the strengths of the study is that the isolated and expanded cells represent a multitude of distinct regulatory T cell lines-each with a specific regulatory task. This aspect of the therapy, the researchers said, is a "necessary advancement" in the treatment of type 1 diabetes because it provides a broader, more encompassing assault against the T cells that are mediating the disease.

However, before regulatory T cells can be used as a cell therapy for type 1 diabetes, several questions must be addressed. These include how long the expanded cells will survive after they are transferred, where in the body they will reside, and whether they will retain their desired suppressive nature once transferred.

"This study outlines important tools and principles for translating [regulatory T cell] therapies into clinical treatments for patients with type 1 diabetes and other autoimmune disorders," the researchers concluded.

 

JDRF research frontline, june 2009