Universität zu Köln

Reemann, Lea (2024). Investigation of the potential regulation of the PD-1-PD-1 ligand immune checkpoint axis by inhibition of the B cell receptor signaling pathway. PhD thesis, Universität zu Köln.

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Abstract

Chronic lymphocytic leukemia (CLL) is characterized by abnormal proliferation of monoclonal B lymphocytes. A hallmark of CLL is the strong dependency of the malignant B cells on the interactions with the tumor microenvironment. CLL cells have established various strategies to escape the endogenous anti-tumor immune response. One key mechanism that is known to regulate T cell-mediated immune responses is the PD-1-PD-L1/2 immune checkpoint axis. The PD-1 receptor is located on the surface of effector T cells, and upon binding to its cognate ligands PD-L1 or PD-L2, activation of the T cell is suppressed. It has been shown that PD-1 and PD-L1 might be upregulated on T cells and CLL cells, respectively, in this malignancy as a way of escaping the immune system. The B cell receptor (BCR) signaling pathway is crucial for B cell survival and function. In aberrant cells such as CLL, it contributes importantly to anti-apoptotic, pro-survival signaling. Some recent evidence could show that the BCR signaling pathway might regulate PD-L1 expression, for example, in diffuse large B cell lymphoma. Preliminary data from our group suggested that BCR-inhibition could lead to a decrease in PD-L1 surface levels. Based on these findings, this study aims to investigate the potential regulation of the PD- 1-PD-L1/2 immune checkpoint axis by the BCR signaling pathway, focusing on CLL cells. The central element of this work is to analyze the effects of various BCR kinase inhibitors on a wide range of B cell lines as well as primary CLL cells. Flow cytometry was used as the main readout assay for PD-L1 expression. In those experiments, a reduction of PD-L1 surface levels could often be observed, but with considerable variation depending on the cell line, inhibitor, and treatment timepoint. Effects of BCR inhibition on PD-L1 varied even in the different biological replicates, suggesting very dynamic regulation of PD-L1 expression and instead seems to contradict a clear, one-dimensional way of regulation by the BCR pathway. However, we found that the SRC-kinase inhibitor dasatinib exerted a consistent and significant downregulation of PD-L1 expression. Furthermore, it was examined whether a stimulation of the BCR-pathway with Immunoglobulin M (IgM) could increase PD-L1 surface levels. Also in this experimental set-up, targeting the BCR-pathway had no clear impact on PD-L1. Taken together, a clear mechanism that links BCR inhibition to a reduction of PD-L1 surface levels could not be found, but we identified dasatinib as a substance which could possibly have synergistic effects with PD-1 inhibitors. This effect is probably independent from the BCR-pathway and related to other targets of this kinase inhibitor. The results of this work thus led to a research project further investigating the influence of dasatinib on PD-L1 expression. Furthermore, additional data using patient-derived primary CLL cells suggest that PD-L1 surface levels, in contrast to previous publications, might not be significantly higher than on healthy B cells.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Reemann, Lea Lea.Reemann@gmx.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-733008
Date:	2024
Language:	English
Faculty:	Faculty of Medicine
Divisions:	Faculty of Medicine > Innere Medizin > Klinik I für Innere Medizin - Hämatologie und Onkologie
Subjects:	Medical sciences Medicine
Uncontrolled Keywords:	Keywords Language Chronic lymphocytic leukemia English B cell receptor signaling pathway English PD-1/PD-1 ligand immune checkpoint axis English
Date of oral exam:	4 June 2024
Referee:	Name Academic Title Hallek, Michael Universitätsprofessor Dr. med. Kashkar, Hamid Universitätsprofessor Dr. rer. nat.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/73300