Bone-marrow transplants typically involve destroying all the body's bone marrow and replacing it with donor marrow. This is still one of the mainstays for treating leukemia.
There are often complications with this kind of procedure, because the risk of infection is high and there can be powerful side effects of the chemotherapy or radiation used to destroy the bone marrow.
But about four or five years ago, new protocols were developed that don't require the eradication of all a patient's bone marrow.
"The new protocols tried to take advantage of the fact that for sickle cell disease, you don't have to replace all the cells with donor cells," said Dr. Martin Andreansky, director, pediatric blood and marrow transplant program at the University of Miami Sylvester Cancer Center.
As a result, there is less chemotherapy and fewer toxic side effects.
"Most patients end up being a mixture of their own cells and donor cells," Andreansky added. Those cells are the ones that give rise to red blood cells, white blood cells and platelets.
Trials with this modified procedure have yet to be evaluated, but so far, they seem to work.
But so far, Alejandra is doing well.
"I think the amount of her own cells in the blood will increase, but she will still be OK from the clinical perspective," Andreansky said. "But it's too early to say if the transplant has worked in the long run. We will have to wait a couple of years."
With luck, Alejandra will no longer have sickle cell disease. She will still carry the trait for it, but these people, said Andreansky, can lead normal lives.
Melgar also has another tough battle to fight. While Alejandro hasn't suffered a stroke, he is starting to have complications related to his sickle cell disease and also needs a transplant.
The Melgars, who are Latino, are having trouble finding a matched donor because there are so few donors of color.
"The problem with minorities is they are severely underrepresented in bone-marrow registries," Andreansky said.
Melgar said she's grateful her daughter found a donor, and she desperately hopes she can find one for her son.
"I want to let people know about this. People, especially kids, need bone marrow," she said. "They can save a lot of lives."