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Transplantation-related lymphoproliferative disorder: a model for human immunodeficiency virus-related lymphomas.

Post-transplant lymphoproliferative disorders (PTLD) share many of the features of human immunodeficiency virus (HIV)-related lymphomas, although important differences exist. PTLD ranges from hyperplastic lesions to aggressive lymphoma or multiple myeloma histology. The coexistence of multiple clones, and the strong association with the Epstein-Barr virus (EBV), represent a uniquely different mechanism for lymphomagenesis when compared with de novo lymphoma. The risk of PTLD increases as the duration of immunodeficiency lengthens, with unusual, newly described entities arising after prolonged immunosuppression. The risk is also strongly influenced by the specific anti-T-cell therapies used to prevent graft rejection, providing insight into the nature of immune surveillance. The presence or absence of bcl-6 mutations may be predictive of the reversibility of the PTLD with reduction in immunosuppressive therapy. The use of cytotoxic agents has been complicated by problems similar to those encountered with HIV-related lymphomas, but can nonetheless be very effective. Long-term remission has been achieved with anti-CD21 and anti-CD24 antibodies, although these have not been equally effective for all categories of PTLD. In vitro-expanded EBV-specific T cells have been effective both as treatment and as prophylaxis in the setting of PTLD occurring after marrow transplantation. EBV viral load measurement correlates with the emergence of PTLD, and may make clinical trials of screening, prophylaxis, or early intervention possible.