Nonmyeloablative Stem Cell Transplant in Children With Sickle Cell Disease and a Major ABO-Incompatible Matched Sibling Donor

This study tests a non-myeloablative (reduced-intensity) stem cell transplant approach for children and teenagers with sickle cell disease (SCD) who need a transplant but whose sibling donor has an incompatible blood type (ABO mismatch). Sickle cell disease causes red blood cells to become misshapen and block blood flow, leading to pain crises, strokes, and organ damage. This protocol aims to achieve a successful transplant with fewer side effects than full-intensity conditioning. You may be eligible if: - You are between 12 months and 19 years old - You have sickle cell disease (HbSS, HbSC, HbS/β+, or HbS/β0) - You meet standard criteria for stem cell transplantation, including a history of strokes, repeated pain crises, acute chest syndrome, priapism, pulmonary hypertension, or other serious complications - You have a matched sibling donor available You may NOT be eligible if: - You are unable to comply with the study protocol - You have a known allergy or sensitivity to sirolimus (the anti-rejection medication used) Talk to your doctor to see if this trial is right for you.