Such changes wouldn't increase available kidneys. Hence the need for the new kidney match-making called desensitization aimed at patients like Preloh who otherwise might not get a chance at a new organ.

A transplant starts by matching patient and donor kidney according to blood and tissue type. Today's anti-rejection drugs are so good that tissue-typing can be far from perfect.

A different threat is what's called antibody-mediated rejection, where patients increasingly are "sensitized" — their bodies produce antibodies that are super-vigilant at attacking most available kidneys. What causes that? Pregnancy, blood transfusions, a previous transplant, increased time on dialysis. So longer transplant wait times are fueling sensitization, a vicious cycle.

The more antibodies, the harder it is to find a compatible kidney. So the quest is to rid patients of antibodies targeted to a specific donated kidney, and keep them from making more.

One method: Filtering a patient's blood, called plasma pheresis, before transplant. Another is intravenous immune globulin, or IVIG, a mix of infection-fighting antibodies that basically crowd out the bad kidney kind with run-of-the-mill types. They're treatments pioneered at a few hospitals — including Los Angeles' Cedars-Sinai Medical Center and Baltimore's Johns Hopkins University — and now slowly spreading.

But that's not strong enough for many super-sensitized patients, so a new experiment is testing the lymphoma drug Rituxan, which fights the immune-system cancer by killing certain antibody-producing cells. Cedars-Sinai researchers reported the first preliminary but promising evidence in the New England Journal of Medicine this summer: Rituxan helped slash antibody levels enough that 16 of 20 patients could be transplanted, and all but one of the new kidneys was working a year later. Back at Georgetown, Cynthia Preloh, 50, had been told to expect a seven-year wait for a donated kidney when diabetes destroyed her own. Diabetics have particularly poor survival on dialysis and her son offered a faster living donation, but Preloh had too many antibodies that would attack his tissue.

Melancon — who moved from Hopkins to Georgetown in the nation's capital to spread this work — hoped Rituxan would give Preloh enough extra desensitization to try the transplant. Her new kidney started working on the operating table, "which was the best thing you could hope to hear," she said last week as she recovered.