Katherine Vetter was almost four years old when her brother David was born with an immunodeficiency disorder. The close genetic match between siblings meant that Katherine was David's best hope for a cure at the beginning and at the end of his life.

Not a Match
The doctors at Texas Children's Hospital hoped that Katherine's bone marrow, the production center of white blood cells in the human body, could be transplanted into David's system and create a working immune system. Unfortunately, the siblings' marrow was not a perfect match and the transplant could not be performed. David spent the rest of his twelve years of life in plastic isolator bubbles at the hospital and at home.

Balancing Act
When David was at home, he naturally required more attention than his sister. Their mother, Carol Ann, recalled that when Katherine was outside while David required attending, "I would volley back and forth to watch them both, and it got pretty frustrating. I'd say a little prayer every time Katherine was playing outside: 'God, I'll take care of David if you'll watch over Katherine.'" At least one doctor worried about the "emotional deprivation" of Katherine "if the parents choose to invest all of their emotional capital in their packaged child."

Protective Sister
Despite the physical barrier, the siblings were close. Katherine slept in the living room next to the bubble every night David was at home, until she became an adolescent. When strangers gawked at David in his transport bubble, Katherine would shield her brother from the unwanted attention.

Sibling Fights
Of course, as siblings, they also fought. Katherine called David a "brat" and he called her a "dummy." They even had physical fights, although they didn't last long. Their mother remembers an instance when David, using the rubber gloves that communicated through the bubble, punched Katherine. Before she could retaliate, he had scooted to the far corner of the bubble where she couldn't reach him. Other times, the rubber gloves that allowed access into the bubble were used for shoving matches.

Ultimate Control
Katherine always had the upper hand, though. If they argued -- over what television program to watch, say -- she would threaten and then actually unplug David's bubble (if his play area deflated, he still had other rooms that he could seal himself into). David would plead, "plug me back in," and she always did, having won the argument.

Reminder of Limits
Their physical interactions were unique, but they had an emotional bond similar to any other brother and sister. Still, Katherine's outside life must have been a constant reminder to David of his own limited world. After his sister announced that she was going out to have hamburgers with a friend's family, one academic paper reported, "D[avid] jumped up shouting, 'I want to go too.' Within seconds, however, he stopped very abruptly, stepped back, and said softly, 'No I don't.'"

A Gift of Hope
By 1983 research in bone marrow transplants had advanced to the point where donors did not have to be exact matches to recipients. There was new hope that David might be able to receive his sister's bone marrow, generate an immune system, and leave his protective environment. After the entire family discussed the procedure, the teenaged Katherine had her marrow extracted in Boston. Doctors treated it and then flew it down to be donated to David. That Christmas, as a thank you gift, David gave Katherine a sapphire and diamond ring that their mother had helped pick out.

Out of the Bubble
Sadly, Katherine's gift of bone marrow -- her brother's only hope for a cure -- would bring about his end. David unexpectedly got violently ill for the first time, and had to be removed from the bubble. Katherine and her parents were there when he came out. He died two weeks later. An autopsy revealed that David had died of cancer, a complication of the Epstein Barr virus which must have been inadvertently transmitted through Katherine's bone marrow.

Today
Katherine is now married with two young sons of her own. She expressed the hope that they may one day attend The David Elementary School, named after her brother. "Little David, even though he's gone, still lives on," she said.