On the crossroad between tolerance and posttransplant lymphoma.

The role of the Epstein-Barr virus in the development of post-transplant lymphomas is well established. However, not all lymphomas that arise in these patients contain Epstein-Barr virus, suggesting that other cofactors are involved in tumor pathogenesis. We propose that immunologic interactions that result from the introduction of immunocompetent donor cells during transplantation contribute to a lymphomagenic environment in the host. Murine models of lymphoma that arises following transfer of allogeneic hematopoietic cells are discussed and are related to the transplant setting. One contemporary viewpoint of transplantation immunology holds that interactions between the host and donor components of the immune system determine the ultimate degree of tolerance or reciprocal immunoreactivity (eg, rejection, graft-versus-host disease) within the transplant patient. We conclude that host-donor immunologic microchimerism may also be an over-looked factor in the development of posttransplant lymphomas.