While some white blood cells cause inflammation, other types of white blood cells, called T regulatory cells (Tregs), can control inflammation. Tregs may have an important role in controlling or preventing inflammation and rejection. A person's Tregs can be grown in the laboratory to increase their number (polyTreg). These Tregs can be given back through a needle placed in a vein (IV). Researchers can expose a transplant recipient's Tregs to the donor's cells, which results in Tregs that recognize the donor. These are called donor reactive Tregs (darTreg). Both polyTregs and darTreg, when given to the recipient, might reduce inflammation in the transplanted kidney. However, this effect has not yet been shown. The darTregs are thought to be more effective because they might be able to help the body specifically recognize and accept the donated kidney. This is one of the first clinical trials using darTregs.