Molecular pathological analysis of follicular T-helper cells and their neoplasias
Final Report Abstract
Angioimmunoblastic T-cell lymphoma (AITL) is one of the most frequent mature T-cell lymphomas. In recent years much effort has been made to elucidate the molecular mechanisms that drive the pathogenesis of AITL. Most likely, neoplastic cells in AITL are derived from follicular T helper cells (TFH). These cells are characterized by the expression of CD4, ICOS, CXCR5 and Bcl6. Expression of ICOS is pivotal for the formation of TFH. Currently, there is no ICOS overexpressing mouse model available. Therefore, the aims of the presented study were to assess a potential oncogenic role of ICOS in the transformation of mature T cells and to characterize the microenvironment of AITL. During our studies, we were able to identify ICOS as a potential factor contributing to lymphoma formation by acting as a co-oncogene, as ICOS+ T cells appeared to be more susceptible to transformation than ICOS- T cells. Moreover, the number of germinal center B cells was strongly enlarged in stem cell transplanted animals overexpressing ICOS. Unfortunately, AITL represents a very rare lymphoma entity and we did not have the opportunity to analyze many fresh primary AITL single cell suspensions during the first funding period. Therefore, we established a new protocol to process frozen-thawed single cell suspensions, to be able to expand the number of analyzed cases, by receiving additional patient material from other institutions. Thus, we were able to analyze ICOS+ and ICOS- populations in AITL. Interestingly, ICOS+ and ICOS- CD4 T cells from the AITLs clustered in the analysis, as well as the bulk AITL suspension with the CD4-population. Further analysis has to be performed in order to verify the expression of several overexpressed genes in ICOS+ cells of AITL. In a second part of the project we aimed to characterize the microenvironment of AITL, which is mainly composed of follicular dendritic cells (FDCs) and which is very prominent for this lymphoma. As there is currently no exclusive FDC-marker available, the FDC-specific transcriptome was determined by in silico subtraction, excluding all differentially expressed genes from the T- and B- cell population. Thereby, we were able to illuminate the whole microenvironment of AITL and identified a list of differentially expressed genes specific for the FDC-dominated microenvironment. Finally, we were able to validate some of these genes by immunohistological staining and qPCR.
