Jennifer Mathews: Eight-year-old Ryan Patrick knows a lot about trains.

Ryan Patrick: These are both diesel. These three are all steam.

Jennifer Mathews: But he doesn't talk much about his health.

Ryan Patrick: This is, I think, a European caboose.

Jennifer Mathews: He has a rare immune disease that's left him with diabetes and life-threatening allergies.

Amy Ryan: Allergies to wheat, rye, barley, soy, eggs, legumes, apples, fish.

Jennifer Mathews: Kids in Ryan's condition are lucky to live past five, so his parents took a gamble on a treatment that could save his life.

Amy Ryan: This was going to be a very high-risk transplant.

Jennifer Mathews: Dr. Shalini Shenoy and her colleagues at Washington University are studying a new kind of transplant. Patients typically get radiation and chemo so they won't reject the transplant. But toxic doses can cause brain damage and infertility.

Dr. Shalini Shenoy: There are numerous organs that can be affected.

Jennifer Mathews: The drug Campath helps prevent rejection and is usually given at the time of transplant. Now, Dr. Shenoy gives it three weeks before. That eliminates radiation and lowers the dose of chemo.

Dr. Shalini Shenoy: If you told me 10 years or 15 years ago that a transplant could be done without a lot of chemotherapy or radiation, I would have said, "Oh, you've got to be kidding me."

Jennifer Mathews: Most patients recover immune function about one year later with no major infections. Ryan had the transplant and now eats food that could have killed him before.

Amy Ryan: It's like we woke up and we found out the last eight-and-a-half years were a horrible, horrible nightmare. And now, it's morning.

Jennifer Mathews: This is Jennifer Mathews reporting.