People who have certain immune system diseases often need a procedure called allo HSCT. This is short for allogeneic hematopoietic stem cell transplant. This might cure people with these diseases. Many people who need allo HSCT need donors who are relatives with similar genes. But the disease may also affect those in the donor pool. This may mean there are fewer options for people with inherited diseases. Researchers want to collect data on how transplant candidates and their donors are found.