Molecular Understanding of Pathogenesis and Immune Responses in Endemic Burkitt Lymphoma

Abstract

Endemic Burkitt lymphoma (eBL) is a malignant B-cell lymphoma in children living in Sub-Saharan Africa, including Ghana. Where it occurs, eBL is often the most common cause of cancer death in children under 15 years, although it is potentially curable if diagnosed early and treated appropriately. The disease is associated with exposure to Epstein-Barr virus (EBV) and Plasmodium falciparum malaria parasites, but the molecular details of how the combination of these infections can precipitate eBL are not well understood. The mechanisms of the host immune response in the pathogenesis and control of eBL are similarly unclear. It has been suggested that P. falciparum-specific B cells are particularly prone to malignant transformation by activated-induced cysteine deaminase-dependent c-myc translocation in EBV-infected B cells, and that many eBL cells therefore encode a P. falciparum-specific antibody. It has furthermore been proposed that auto-regulatory V1+ T cells play an important role in the normal control of activated B cells, including malignant eBL cells. The physiologic role of this rather enigmatic cell subset is currently essentially unknown. This PhD research project was undertaken to investigate the above hypotheses. It has resulted in the production of antibodies from the BCR of the tumour cells that is an important new knowledge regarding the antigen specificity of eBL tumour cells that support the hypothesis that particular antigens (likely P. falciparum-derived) are important drivers of eBL pathogenesis. There was a highly biased V(D)J rearrangements observed, as most tumour-derived B cells expressed sequences homologous to VH3 (3-7*01, 3-9*03, 3-23*04, and especially 3-30*04) and VL2 (2-14*01), when compared to peripheral B cells from the same patients. It has also provided empirical support for the hypothesis that Vδ1+ T cells are critically involved in the immune response to this devastating tumour. Interestingly, high frequency of Vδ1+ T cells were found in the cancer patients (both eBL and non-eBL). However, there was marked differentiation and maturation of Vδ1+ T cells in the eBL patients compared to the other study groups (non-eBL, malaria and healthy). Most cells (80%) from the tumour were B- cell confirming previous studies that eBL is a B cell lymphoma. Nonetheless, atypical memory B cells were of higher frequency in eBL as compared to malaria and health controls. In comparing the Giemsa stained FNA (fine needle aspiration) and haematoxylin and eosin stained FFPE (formalin fixed Paraffin embedded) samples, there was a good agreement with the original diagnoses of eBL made in Ghana compared to that in Denmark for the FNA samples (Accuracy, Sensitivity and Specificity were all 100%) . However, there were some disparities with the diagnosis with the FFPE tissues due to poor tissue preservation (Accuracy- 84%, Sensitivity - 83% and Specificity- 84%). The research undertaken has so far resulted in one manuscript (Reliable Cell and Tissue morphology based diagnosis of endermic Burkitts lymphoma in a resource constrained setting in Ghana) submitted for publication. Another manuscript is currently being prepared for submission with at least one additional original research paper and one additional review paper expected as a result of this work. In conclusion the data supports that V1+ T cells are important modulators of the B-cell proliferation in eBL, there is a state of chronic B-cell activation, and that eBL tumour cells are have been activated by an antigen that caused them to be differentiated in germinal centres. It is also concluded that the original diagnoses, which involved laboratory assessment of tumour cell morphology, were reliable, when evaluated by independent retrospective analysis of specimens similar to those available at time of the original diagnosis.