Around 5000 people in the Netherlands are diagnosed with lymphoma each year. This thesis focused on two types of B-cell-derived lymphomas: marginal zone lymphoma and diffuse large B-cell lymphoma. We explored the clinical and biological factors underlying the development and transformation of lymphoma, as well as ways to improve its treatment.

We found that marginal zone lymphomas occurring in the salivary glands of patients with Sjögren’s syndrome are characterized by a small number of mutations. In addition, several factors associated with the development of transformed marginal zone lymphoma were identified: age above 60 years, prior systemic therapy before transformation, and the acquisition of germinal center B-cell features. These findings contribute to a better understanding of lymphoma transformation and may help to detect it earlier and treat it more effectively.

We also investigated the value of circulating tumor DNA (ctDNA) as a biomarker to evaluate treatment response in patients with diffuse large B-cell lymphoma. ctDNA showed to be a promising tool. However, further research is needed to improve its sensitivity, and its use should be standardized before it can be implemented in clinical practice.

Finally, we observed that adding the PD-L1 inhibitor atezolizumab to R-CHOP treatment improved survival outcomes in patients with diffuse large B-cell lymphoma.

Around 5000 people in the Netherlands are diagnosed with lymphoma each year. This thesis focused on two types of B-cell-derived lymphomas: marginal zone lymphoma and diffuse large B-cell lymphoma. We explored the clinical and biological factors underlying the development and transformation of lymphoma, as well as ways to improve its treatment.

We found that marginal zone lymphomas occurring in the salivary glands of patients with Sjögren’s syndrome are characterized by a small number of mutations. In addition, several factors associated with the development of transformed marginal zone lymphoma were identified: age above 60 years, prior systemic therapy before transformation, and the acquisition of germinal center B-cell features. These findings contribute to a better understanding of lymphoma transformation and may help to detect it earlier and treat it more effectively.

We also investigated the value of circulating tumor DNA (ctDNA) as a biomarker to evaluate treatment response in patients with diffuse large B-cell lymphoma. ctDNA showed to be a promising tool. However, further research is needed to improve its sensitivity, and its use should be standardized before it can be implemented in clinical practice.

Finally, we observed that adding the PD-L1 inhibitor atezolizumab to R-CHOP treatment improved survival outcomes in patients with diffuse large B-cell lymphoma.

Breast cancer is a significant global health issue, impacting millions of women worldwide. ER-positive breast cancer, the most common subtype, accounts for over 70% of cases. While hormone-based therapies like tamoxifen are effective, resistance develops in many patients, posing clinical challenges. Recent research has focused on the molecular mechanisms behind this resistance, aiming to identify new therapeutic targets.
This thesis investigates the regulatory role of microRNAs (miRNAs) in ER-positive breast cancer, particularly their impact on ER expression, cell proliferation, and tamoxifen sensitivity. Through a genome-wide miRNA high-throughput screen, we analysed regulatory networks involving miRNAs to understand their mechanisms better.
Two miRNAs affected ER expression in MCF7 cells, including miR-130a and miR-18b/miR-106a. MiR-18b was highlighted as a key regulator, influencing ER expression and cell proliferation. Analysis of potential targets of miR-18b identified amongst others target genes like ESR1, HMGCS1, and SON, supporting a role of miR-18b in these processes.
Additionally, we identified five miRNAs associated with tamoxifen resistance and validated their role in response to tamoxifen for miR-130a, let-7g, and miR-15b/miR-16-2. For miR-130a, 20 genes, including ESR1 and AIB1, were identified as predicted targets influencing tamoxifen sensitivity. Downregulation of ESR1 and AIB1 by miR-130a was confirmed via Western blotting.
These findings underscore the importance of miRNA regulation in ER-positive breast cancer and pave the way for potential miRNA-based therapeutic strategies to improve treatment outcomes. The research also highlights the complexity of miRNA-mediated regulation and the need for further studies to validate these findings across different breast cancer models.

Classic Hodgkin lymphoma (cHL) is a B-cell malignancy marked by Hodgkin and Reed/Sternberg (HRS) cells that highly express CD30. We explored the roles of microRNAs (miRNAs) in cHL pathogenesis and CD30-targeting therapy using Brentuximab Vedotin (BV) through high-throughput screening techniques. Review of miRNA-related studies on known and potential miRNA-target gene interactions identified multiple miRNA-gene pairs with potential relevance for cHL pathogenesis. This highlighted the relevance of miRNAs in cHL, warranting further studies to deepen our understanding.
A microRNA overexpression library screen revealed 11 miRNA-target gene pairs implicated in cHL pathogenesis and 66 miRNA constructs that regulate BV treatment response. Among these, miR-590 was found to inhibit CD30 expression and induce BV resistance. Additionally, miR-191-5p not only conferred BV resistance but also promoted cell growth. By using AGO2-immunoprecipitation, we identified a network of involved target genes, including PTEN.
To investigate endogenous miRNAs involved in BV resistance mechanisms, we established two BV-resistant cHL cell lines and observed dynamic changes in CD30 expression. Moreover, we utilized a miRNA-focused CRISPR-Cas9 screen to identify endogenous miRNAs that regulate CD30 expression and/or BV sensitivity. To this end, we generated two inducible Cas9 monoclonal cell lines and optimized the entire screening process. These screens await further data analysis.
In summary, this thesis highlights the functional importance of specific miRNAs in cHL and provides detailed procedures of the miRNA-focused screening approaches, from initial setup to optimization and validation of results.

Parasporal proteins from Bacillus thuringiensis (Bt) are well studied in various fields of environmental biotechnology and recently in medical biology. Correspondingly, this dissertation presents the use of site-directed mutagenesis technologies to obtain mutant cry and parasporin proteins with different effects against vector-borne diseases and human cancer cell lines. The use of in silico modeling offers a possible explanation of how the altered residues are involved in changing their structure and interacting with cell membrane receptors. The proteins from this work can be used as targets for new studies that will provide more information about the mechanism of action of Bt proteins, and open the door to the employment of these biomolecules in combating diseases.