Posttransplant lymphoproliferative disorders, or PTLDs, are uncontrolled growths of cells called lymphocytes that may occur in transplant recipients after receiving a solid organ, such as a kidney or a lung, or stem cells.
Transplant recipients require medications to suppress their immune systems which may contribute to the development of a PTLD.
Normally, immune cells can differentiate between healthy “self” and “other” cells by inspecting for the presence or absence of the normal “self” major histocompatibility complexes, also called human leukocyte antigens, present on the surface of every cell that contains a nucleus.
Healthy “self” cells are left alone.
“Others” include cells from other people or donors and “self” cells that are infected, damaged, or stressed.
Lymphocytes, are a class of rapidly dividing cells and, therefore, tends to develop mutations more often.
Cytotoxic T-cells can directly destroy “other” cells and helper T-cells assist other immune cells.
Normally, if B-cells start to replicate out of control, it's the T-cells that keep them in check, and keep the immune response organized.
When people receive a transplanted organ or stem cells, they also must take immunosuppressive medications to prevent the immune system from rejecting, or attacking, the transplant.
In PTLDs, immunosuppression also prevents the destruction of abnormal lymphocytes that exhibit uncontrolled replication.
Resulting uncontrolled growth of lymphocytes can either be a benign hyperplasia, meaning there’s a large collection of noncancerous cells, or the cells can become malignant, resulting in a cancer called lymphoma.
While PTLD may result from the overproduction of T-cells, it is more typically associated with the overproduction of B-cells.