Khloe Land, of Coos Bay, Oregon, has been nicknamed "the superhero" by her family -- and for good reason.
The 4-year-old is scheduled to donate bone marrow today to her younger brother, Colton, who was born without an immune system.
Khloe's bone marrow was a "perfect match" for her brother, according to Dr. Evan Shereck, who is leading the transplant Monday at OHSU Doernbecher Children's Hospital in Portland, Oregon.
The likelihood of a sibling being a perfect match for a bone marrow donation is only about 25%, according to Shereck.
"He's incredibly lucky to have had a matched sibling," she said of Colton. "We prefer matched sibling donors because we know the outcomes of transplant are really good."
Colton was a healthy baby when born July 24, according to his mom, Kayla Land.
About a week after his birth, when doctors got back the results of the standard newborn screen, they realized he'd been born with a genetic form of severe combined immunodeficiency, or SCID.
The condition is known more broadly as "the bubble boy disease" because people who have it often must be largely isolated to protect themselves from infection.
(MORE: 7-year-old boy chooses to meet his bone marrow donor from Germany over going to Disney World)"Nobody would ever know that he has SCID," Land said. "He's just a healthy, normal sweet baby. He's been poked and prodded a lot, but he's a little fighter."
In Colton's case, doctors said a bone marrow transplant would be the only way to save his life. Without it, even the smallest germs could put him at risk for an infection that his body could not handle, according to Shereck.
The family quickly tested his two siblings, Khloe and 8-year-old Krissy, through the Be the Match registry, a process that involves just a simple swab of a cheek to collect DNA.
Just two weeks ago, the Lands found out that Khloe had the right immune system genes to save her brother.
"My husband and I were hoping it was our older daughter because she understood and she wanted to be the one to help her little brother," said Land. "When we found it was Khloe, she was really excited at first and then fear kicked in within about 30 seconds and she broke down and told us how scared she was."
Land bought a special superhero dress for Khloe to wear on transplant day and to help make her feel special in the days ahead.
"Khloe tells Colton all the time that she's going to save his life, so she knows that he wouldn't have a good chance of living if it wasn't for her," Land said. "But we've tried to make things as minimal as possible."
Khloe is expected to leave the hospital on the same day as the procedure, which requires removing marrow from her back. Her cells will then be transplanted into Colton through a PICC line. The infant will stay in the hospital for at least one month as his body adapts to his sister's cells.
(MORE: This woman donated her kidney to a co-worker and now they hope to send a message)The Lands, who live about four hours from the hospital, will have to live nearby for another three months as doctors continue to monitor Colton's progress.
Land quit her job to be able to stay with Colton in Portland while her husband and daughters commute back and forth for visits.
The family is also home-schooling Khloe and Krissy this year as they also need to be careful about catching an infection that could be passed on to their brother.
Once Colton recovers from the transplant, he's expected to lead a healthy life, according to Shereck, who advocates for everyone, especially people in minority groups, to register with Be the Match to see if they, like, Khloe, can help save a life.
Land is looking forward to the day she can watch Colton and his sisters go outside and play together.
"Doctors have told us that around one year after transplant he can live a normal life as a kid and be out playing in the dirt and being with other kids," she said.
