Lymphoma is the third most diagnosed malignancy in canine cancer patients and mostly presents as a multicentric lymph node cancer. Most cases are diagnosed as B-cell lymphomas (BCL), the majority of which manifests as aggressive large BCL that cannot be cured with chemotherapy. With over 90 million pet dogs in the EU and the annual incidence of cancer increasing, it is time for an update of the state of the art on both diagnostics and (immunotherapeutic) treatment of canine BCL. First, I will investigate which immune cells and putative biomarkers are present within the lymph nodes and in blood of dogs suffering from BCL via flow cytometry (immunophenotyping) and mass spectrometry (proteomics). Secondly, I will validate my immunophenotyping panel and biomarkers for diagnosis, prognosis and follow-up of dogs treated with standard BCL chemotherapy. Thirdly, I will evaluate whether (these) markers can be used as a basis for neoantigen immune therapy to subsequently synthesize novel nanobodies against the two most promising identified targets. As a proof of concept, I will investigate the ex vivo efficacy of these nanobodies on canine BCL-derived neoplastic B-cells in a 3D canine lymphoma model . This proposal will lead to better diagnostics and therapy options for dogs suffering from BCL. Apart from benefits to canine patients, a better understanding of this disease could further confirm the potential of dogs as a model for immunotherapy research in human patients.