The molecular genetics of post-transplantation lymphoproliferative disorders

The Role of Gammaherpesviruses in Cancer Pathogenesis

Worldwide, one fifth of cancers in the population are associated with viral infections. Among them, gammaherpesvirus, specifically HHV4 (EBV) and HHV8 (KSHV), are two oncogenic viral agents associated with a large number of human malignancies. In this review, we summarize the current understanding of the molecular mechanisms related to EBV and KSHV infection and their ability to induce cellular transformation. We describe their strategies for manipulating major cellular systems through the utilization of cell cycle, apoptosis, immune modulation, epigenetic modification, and altered signal transduction pathways, including NF-kB, Notch, Wnt, MAPK, TLR, etc. We also discuss the important EBV latent antigens, namely EBNA1, EBNA2, EBNA3’s and LMP’s, which are important for targeting these major cellular pathways. KSHV infection progresses through the engagement of the activities of the major latent proteins LANA, v-FLIP and v-Cyclin, and the lytic replication and transcription activator (RTA). This review is a current, comprehensive approach that describes an in-depth understanding of gammaherpes viral encoded gene manipulation of the host system through targeting important biological processes in viral-associated cancers.

Burkitt's Lymphoma Presenting as Late-Onset Posttransplant Lymphoproliferative Disorder following Kidney and Pancreas Transplantation: Case Report and Review of the Literature

Posttransplant lymphoproliferative disorders (PTLD) are a rare, but serious complication following transplantation. Late-onset PTLD are often associated with more monoclonal lesions and consequently have a worse prognosis. There are only isolated case reports of Burkitt's lymphoma presenting as PTLD. We present an extremely rare, aggressive Burkitt's lymphoma years after kidney and pancreas transplantation which was successfully treated with combination chemotherapy along with withdrawal of immunosuppression. The patient remains in complete remission more than 2 years after his diagnosis. We also provide a succinct review of treatment of various PTLD and discuss the role of Epstein-Barr virus infection in the pathogenesis of PTLD.

Post-transplant lymphoproliferative disorders: role of viral infection, genetic lesions and antigen stimulation in the pathogenesis of the disease

Post-transplant lymphoproliferative disorders (PTLD) are a life-threatening complication of solid organ transplantation or, more rarely, hematopoietic stem cell transplantation. The majority of PTLD is of B-cell origin and associated with Epstein–Barr virus (EBV) infection. PTLD generally display involvement of extranodal sites, aggressive histology and aggressive clinical behavior. The molecular pathogenesis of PTLD involves infection by oncogenic viruses, namely EBV, as well as genetic or epigenetic alterations of several cellular genes. At variance with lymphoma arising in immunocompetent hosts, whose genome is relatively stable, a fraction of PTLD are characterized by microsatellite instability as a consequence of defects in the DNA mismatch repair mechanism. Apart from microsatellite instability, molecular alterations of cellular genes recognized in PTLD include alterations of cMYC, BCL6, TP53, DNA hypermethylation, and aberrant somatic hypermutation of protooncogenes. The occurrence of IGV mutations in the overwhelming majority of PTLD documents that malignant transformation targets germinal centre (GC) B-cells and their descendants both in EBV–positive and EBV–negative cases. Analysis of phenotypic markers of B-cell histogenesis, namely BCL6, MUM1 and CD138, allows further distinction of PTLD histogenetic categories. PTLD expressing the BCL6+/MUM1+/-/CD138− profile reflect B-cells actively experiencing the GC reaction, and comprise diffuse large B-cell lymphoma (DLBCL) centroblastic and Burkitt lymphoma. PTLD expressing the BCL6−/MUM1+/CD138− phenotype putatively derive from B-cells that have concluded the GC reaction, and comprise the majority of polymorphic PTLD and a fraction of DLBCL immunoblastic. A third group of PTLD is reminiscent of post-GC and preterminally differentiated B-cells that show the BCL6−/MUM1+/CD138+ phenotype, and are morphologically represented by either polymorphic PTLD or DLBCL immunoblastic.

The impact of the World Health Organization classification and clonality assessment of posttransplant lymphoproliferative disorders on disease management

CONTEXT

The World Health Organization classification of posttransplant lymphoproliferative disorders divides them into 4 main categories.

OBJECTIVE

To classify cases of posttransplant lymphoproliferative disorders diagnosed in our institution according to the World Health Organization scheme and correlate the classification and clonality with clinical data.

DESIGN

Cases of posttransplant lymphoproliferative disorders were reviewed. They were classified according to the World Health Organization scheme. Clonality was determined by flow cytometry and/or polymerase chain reaction. Patients' charts were reviewed.

RESULTS

Thirty-one cases were identified. Median age was 33 years. There were 19 cases of kidney, 8 cases of liver, and 4 cases of bone marrow transplant. Immunosuppression consisted of cyclosporin A and prednisone (N = 24) or FK506 and prednisone (N = 7). Twenty cases (63%) were World Health Organization type 3, 7 cases (23%) type 2, 3 cases (6.4%) type 1, and 1 case type 4 posttransplant lymphoproliferative disorder. Ten patients received chemotherapy, 20 patients had reduction of immunosuppression, and 1 had no treatment. Follow-up was available on 25 patients. Seven (43.75%) of 16 with type 3 lesions with available follow-up died of their disease. Five of these patients received reduction of immunosuppression alone. Only 2 of 9 patients with type 3 disease who received chemotherapy died of disease. Two patients with type 2 disease died of unrelated causes. One patient is alive with disease; the remaining patients with types 1 and 2 disease are alive with no disease.

CONCLUSIONS

The World Health Organization classification of posttransplant lymphoproliferative disorders is valuable in the identification of subtypes. It helps identify early lesions (1 and 2) requiring reduction of immunosuppression and type 3 disease, which requires chemotherapy from the outset.

Epstein-Barr virus and cancer

EBV was the first human virus to be directly implicated in carcinogenesis. It infects >90% of the world's population. Although most humans coexist with the virus without serious sequelae, a small proportion will develop tumors. Normal host populations can have vastly different susceptibility to EBV-related tumors as demonstrated by geographical and immunological variations in the prevalence of these cancers. EBV has been implicated in the pathogenesis of Burkitt's lymphoma, Hodgkin's disease, non-Hodgkin's lymphoma, nasopharyngeal carcinoma, and lymphomas, as well as leiomyosarcomas arising in immunocompromised individuals. The presence of this virus has also been associated with epithelial malignancies arising in the gastric region and the breast, although some of this work remains in dispute. EBV uses its viral proteins, the actions of which mimic several growth factors, transcription factors, and antiapoptotic factors, to usurp control of the cellular pathways that regulate diverse homeostatic cellular functions. Recent advances in antiviral therapeutics, application of monoclonal antibodies, and generation of EBV-specific CTLs are beginning to show promise in the treatment of EBV-related disorders.

Incidence of novel N-glycosylation sites in the B-cell receptor of lymphomas associated with immunodeficiency

Novel N-glycosylation sites are introduced by somatic mutation into the V genes of the majority of follicular lymphomas. Sites are positively selected and rare in normal memory B cells, indicating a potential role in tumour survival in the germinal centre (GC). The incidence of c. 40% in diffuse large B-cell lymphomas (DLBCL) parallels the known heterogeneity of the disease. Immunodeficiency-related non-Hodgkin's lymphomas (NHL) include post-transplant lymphoproliferative disorders (PTLD) and acquired immunodeficiency syndrome-related NHL (AIDS-NHL). Most PTLD derive from B cells that carry mutated VH genes and that have completed the GC reaction. All AIDS-NHL carry mutated VH genes and variable features of GC or post-GC cells. To determine if N-glycosylation is a feature of immunodeficiency-related lymphomas, we analysed the VH genes of 19 PTLD and 36 AIDS-NHL. Novel sites were rare in PTLD (4/19), similar to memory B cells (P = 0.15). AIDS-NHL, including DLBCL and Burkitt's lymphomas (BL), showed heterogeneity with 16 of 36 (44%) having novel sites. The findings indicate no selection of N-glycosylation sites in PTLD, consistent with post-GC features. The variable incidence of N-glycosylation sites in AIDS-NHL mirrors that in DLBCL and sporadic BL of immunocompetent hosts, supporting the known heterogeneity of these disorders, and possibly pointing to distinct routes of tumour development.

B cells under influence: transformation of B cells by Epstein-Barr virus

Epstein-Barr virus (EBV) is an extremely successful virus, infecting more than 90% of the human population worldwide. After primary infection, the virus persists for the life of the host, usually as a harmless passenger residing in B cells. However, EBV can transform B cells, which can result in the development of malignant lymphomas. Intriguingly, the three main types of EBV-associated B-cell lymphoma - that is, Burkitt lymphoma, Hodgkin lymphoma and post-transplant lymphomas - seem to derive from germinal-centre B cells or atypical survivors of the germinal-centre reaction in most, if not all, cases, indicating that EBV-infected germinal-centre B cells are at particular risk for malignant transformation.