- The National Institutes of Health (NIH) performs up to 100 allogenic stem cell transplants (allo-HSCT) each year. Many studies already look at different problems that can follow a transplant. But there are many types of transplants, diseases, responses, and treatments. An organized study of this information could help researchers learn more about how often transplant complications occur and what problems they cause. It could also lead to ideas for future research. This study will focus on complications thought to be the most significant.