Utility of Chimerism Analysis to Determine Tissue of Origin in Post Transplant Lymphoproliferative Disorder (PTLD).

Abstract 4305

Post-transplant lymphoproliferative disorder (PTLD) is one of the major complications of organ transplantation. Most PTLDs are associated with Epstein-Barr virus (EBV) infection of B-lineage lymphocytes. Central nervous system (CNS) involvement is rare. Although most PTLDs following solid organ transplants is of recipient origin, PTLDs following bone marrow or stem cell transplant are mostly of donor cell origin. Origin of the tumor cells are of crucial importance in deciding treatment and predicting prognosis. Here we report a case of PTLD of diffuse large B cell Lymphoma of donor tissue origin determined by chimerism analysis. The patient was a 52-year-old woman with myelofibrosis (Myeloproliferative disorder) who received unrelated donor peripheral blood stem cell transplantation. The donor was an ABO compatible, HLA matched unrelated donor. Post transplant immunosuppression therapy was administered. The post transplant history was complicated by multiple viral infections, including BK, CMV and EB virus. Four months after transplantation, the patient developed fever and mental status changes, MRI of brain showed multiple enhancing lesions. Brain biopsy revealed brain tissue with dense infiltration of large atypical lymphoid cells predominantly perivascular in location. Immunohistochemical stains reveal that the large atypical lymphoid cells are of B-cell origin and these cells are 100% positive for Ebstein Barr virus by EBV encoded RNA by in-situ hybridization. The flowcytometry study revealed a monoclonal population of B cells with Kappa light chain restriction. These findings support the diagnosis of post transplant lymphoproliferative disorder (PTLD) of diffuse large B-cell lymphoma type. To determine the origin of tumor cells, chimerism analysis of the host DNA (buccal) and tumor DNA were performed. Short tandem repeat (STR) multiplex PCR assay were performed using the AmpFlSTR Identifiler PCR amplification kit (Applied Biosystems, Foster City, CA). After amplification, samples were analyzed on an ABI 310 DNA Sequencer (Applied Biosystems). The allele distribution was significantly different between the recipient DNA (from buccal swab) compared to tumor DNA indicating donor origin of the tumor (PTLD). The patient was then placed on high dose methotrexate and dexamethasome, however her condition deteriorated dramatically and the patient expired shortly following the diagnosis. It is known that the major pathogenetic defect of PTLD is the insufficient EBV-specific cytotoxic T-cell control of EBV-driven B-cell proliferations. Despite this understanding, determining the right therapy for any given patient with PTLD remains a major clinical issue. It is important to identify patients who will benefit from reduction of immunosuppression, who will benefit from Rituximab. It is also important to develop more effective, less toxic chemotherapies for resistant or aggressive disease. The chimerism analysis performed on our patient to identify tumor cell origin is an unique and reliable method to help directing clinical management of PTLD.