Each year, Children's Hospital saves the lives of critically ill patients who would have died from the same ailment just a few years earlier. One of the hospital's latest success stories is a 2-year-old whose twin brother became a transplant donor -- and saved his brother's life. My associate, Alexandra B. Stoddard, filed this report:

Michele Foster-El first noticed in April that her 18-month-old son, Kevin, was having trouble walking. Some mornings he could not get out of bed. He often seemed tired and uninterested in playing with his twin brother, Calvin. Michele had no idea that her son was seriously ill with a rare disease -- or that Calvin would soon help save Kevin's life.

Michele, who is 17, had been living in a homeless shelter for seven months with her sons and other members of her family when Kevin was diagnosed as having neuroblastoma, a type of cancer that originates in the adrenal gland.

Approximately 500 children contract neuroblastoma each year. Physician Nita Seibel diagnosed Kevin when Michele brought him to Children's Hospital, complaining of severe leg and abdominal pain. His cancer was in "stage four," which gave Kevin less than a 1-in-10 chance of surviving the next two years, according to his doctors.

In May, Kevin began the first of four cycles of chemotherapy. His mother, who is a single parent, withdrew from high school soon after Kevin was diagnosed. While her parents took care of Calvin, Michele spent most of her time at Children's with Kevin.

By the end of the summer, Seibel and Ralph Quinones, director of bone marrow transplants at Children's, found that Kevin's tumor had been reduced by the chemotherapy. So on Sept. 11, they removed the growth that remained.

Following surgery, Kevin was given radiation treatment, then more chemotherapy, this time an intense dose of a single strong drug not normally used in children. However, the combination of the two powerful therapies destroyed Kevin's bone marrow. So the doctors at Children's determined that his best chance of long-term survival was a bone marrow transplant.

Fortunately for Kevin, Calvin is an identical twin, and therefore a near-perfect match. According to Quinones, there is a much smaller risk of rejection or side effects when a twin is a transplant donor. A non-twin sibling would have a 1-in-4 chance of being a perfect match.

The transplant was performed at Children's on Oct. 13. Calvin's healthy bone marrow was administered to Kevin through a catheter placed under the skin in his chest and inserted into one of the large veins in his neck.

Calvin was out of bed that evening, but Kevin remained in strict isolation. He breathed nothing but filtered air and drank nothing but sterile water for several days. Visitors were sharply limited, and he had a special diet for the next five weeks.

During his many stays at the hospital this year, Kevin has grown more comfortable as the staff at Children's has become more familiar.

"When he first came, he was scared to death. He only wanted to see his mother. Then he became used to us and was only unhappy when there was no one to play with," said Sarah Houts, one of Kevin's nurses. "We were just so happy when he started laughing instead of crying."

Kevin was released on Nov. 13. He has been re-admitted twice because of fevers, but he spends most of his time recovering at the family's home in Capitol Heights, which the homeless shelter helped them find in May. He and Calvin celebrated their second birthday on Nov. 26.

Kevin must make weekly visits to Children's for physical examinations and blood sampling, and while he is at home, he isn't allowed to play outside or venture into crowds because of the risk of infection. It will take approximately three months for his bone marrow to regenerate, and it will be from six to 12 months before he will develop normal immunity again.

Kevin will have to receive immunity shots like those he received when he was an infant as his immune system rebuilds itself. He will be tested at Children's every three months to ensure that his bone marrow is reproducing and that the cancer does not return.

Michele says her son is very lucky to have been treated by the team of experts at Children's Hospital. When Michele meets other parents whose children are sick and are being treated at Children's, she tells them they are at the right place.

"I tell them that they {Children's} do good work. They do successful work," she said. "I know that they pray for me every day, and they pray for Kevin every day."

TO CONTRIBUTE TO THE CAMPAIGN:

Make a check or money order payable to Children's Hospital and mail it to Bob Levey, The Washington Post, Washington, D.C., 20071.