A 4-year-old girl in Oregon already filled the role of hero for her infant brother after she provided lifesaving bone marrow for him earlier this week. In an emotional update posted on Monday, Kayla Land said that her daughter Khloe and infant son Colton are doing “great.”

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Khloe was found to be a donor match for her 7-week-old brother Colton, who was diagnosed with severe combined immunodeficiency (SCID) when he was about a week old. The disorder is also referred to as “bubble boy” disease. Infants with SCID appear healthy at birth but are highly susceptible to severe infections, as the disorder is caused by mutations in different genes involved in the development and function of immune cells.

Symptoms occur in infancy and can include serious or life-threatening infections, particularly viral infections, according to the National Institute of Allergy and Infectious Disease. Standard treatment involves stem cell transplantation, with the ideal donor being a sibling who is a close tissue match.

The transplants are considered life-saving, but often only partially restore immunity, according to NIAID.

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Both Khloe and Colton’s other big sister, Krissy, were tested as potential donors.

“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,” Kayla Land told Good Morning America. “When we found it was Khloe, she was really excited at first and then fear kicked in within about 30 seconds she broke down and told us how scared she was.”

In Monday’s Facebook post, Kayla Land said it took some convincing to calm Khloe down as they began pre-op procedures at OHSU Doernbecher Children’s Hospital in Portland.

“After Daniel and I both begged and pleaded and bribed with everything we could think of, I finally just felt very desperate because I had one child that was sitting here scared to death and another that needed this more than anything,” Kayla Land said. “So I just had to tell her your brother is not going to survive if you don’t do this I have to have you do this Khloe. We finally got there – it took some time.”

Land said after surgery the doctor said they were able to get enough marrow from Khloe for two additional transplants, which they will freeze in case Colton needs more in the future. She said in a month he will be evaluated to see how many of his cells are Khloe’s.

His doctor told Good Morning America that Colton was "incredibly lucky" to have a sibling donor.

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On Tuesday, Land shared photos of her husband Daniel and their daughters with Colton, as well as a visit to the “Make A Wish Tree,” where the girls had written messages for their brother’s health.