Molecular characterization of JAK-STAT driven aggressive B-cell lymphomas

• Applicant: Dr. Fabian Frontzek
• Subject Area: Hematology, Oncology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 508468226

Diffuse large B-cell lymphoma (DLBCL) represents the most common aggressive B-cell lymphoma. In the current WHO classification, a variety of partially overlapping but distinct aggressive lymphoma entities are considered. The plasmablastic lymphoma (PBL) represents a rare entity that is associated with very adverse prognosis. Despite a large molecular diversity, DLBCL and related B-cell lymphomas are still uniformly treated with a R-CHOP based therapy. However, roughly one third of patients are primarily refractory or suffer from relapse. Thus, a profound molecular understanding is pivotal to develop novel targeted therapeutic approaches and to improve outcome for these patients. For PBL patients no substantial insights into the molecular pathogenesis had been available due to the rareness of this disease. Recently, we revealed novel foundational mechanisms characterizing the worldwide largest collection of 96 primary PBL samples. Applying whole exome sequencing, we detected recurrent mutations affecting JAK-STAT signaling in 35% of all cases. In 29% we discovered a specific focal amplification of the oncogene IRF4. Using FISH we found recurrent MYC translocation in 47% of all cases. Finally, we validated the essential role of JAK-STAT, IRF4, and MYC signaling by functional experiments in an in vitro model of PBL. We hypothesize a direct molecular interconnection of JAK-STAT, IRF4 and MYC signaling, not only in PBL but also in other aggressive JAK-STAT driven B-cell lymphomas (JAK-STAT BCL). Although the JAK-STAT pathway creates a direct link between tumor cells and the surrounding tumor microenvironment (TME), the role of the TME has not specifically addressed in JAK-STAT BCL so far. Therefore, we will characterize the interaction of lymphoma cells and the TME with a special focus on the potential interaction of JAK-STAT, IRF4, and MYC signaling. First, we will visualize the spatial TME composition at single-cell resolution applying imaging mass cytometry (IMC) in vast cohorts of primary DLBCL, PMBCL, and PBL samples. Identified TME phenotypes will be independently validated by applying single-cell RNA-sequencing. Second, we will investigate a direct molecular interplay of JAK-STAT, IRF4, and MYC in in vitro models of PBL and ABC DLBCL. Novel protein interactions will be directly validated in primary lymphoma samples using in situ primary ligation assays and will be associated with specific TME phenotypes. Finally, we will uncover the efficacy of JAK-STAT targeting drugs in created xenograft-mouse models. Overall, this project aims to discover novel molecular mechanisms in JAK-STAT driven aggressive B-cell lymphomas to develop novel therapeutic approaches for our patients.

• DFG Programme: WBP Fellowship
• International Connection: Canada
• Host: Professor Dr. Christian Steidl