This is a study of children with a condition referred to as post-transplant lymphoproliferative disorder (PTLD). This a major concern for heart and other transplant patients in North America. This condition usually arises as a result of primary (new-onset) infection caused by the EpsteinBarr virus (EBV). EBV can cause a wide range of problems in people who get infected. However, the virus often infects white blood cells, causing the cells to multiply out of control in some individuals with weakened immune systems. This change in the white blood cells often leads to PTLD. Transplant patients have weakened immune systems and as such may develop PTLD. Doctors need more information to help them better understand the reasons why some individuals do well with PTLD, while others have extremely severe disease. Some experts refer to the latter as “extreme phenotypes”. This information will help us to design the best tailormade treatments for those at high risk of having the severe forms of PTLD. We will study organ transplant recipients, with healthy individuals as a comparison group. We will use a procedure called exome sequencing. This procedure will allow us to determine the sequence patterns of special regions of certain immune-related genes that influence how well a person’s immune system is able to fight off the bad consequences of PTLD. The sequencing will be done on DNA samples obtained from the study participants. The study will be done over 12 months. It will yield exciting new information that will improve the care of individuals with PTLD of different severity.

To define the relationship between cytokines mediating the immune responses associated with T helper cells and extreme PTLD phenotypes (mild vs severe).