Tumor specific cerebrospinal fluid (CSF) B cell response in cancer patients with CNS manifestation -Tumor antigen identification by CSF plasmablast derived recombinant antibodies-

• Applicant: Privatdozent Dr. Markus Kowarik
• Subject Area: Molecular and Cellular Neurology and Neuropathology ; Hematology, Oncology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 517964704

The concept of immuno-surveillance in humans has first been described in the late 1950s suggesting that lymphocytes act as sentinels that continuously eliminate neo-transformed cells thus preventing the manifestation of cancer. Decades later, this theory has been widely accepted and the use of checkpoint inhibitors has revolutionized treatment strategies in cancer. Regarding the role of lymphocytes during carcinogenesis, T cells have been in the focus of research whereas systemic studies on B cells are scarce. Although several studies found correlations between tumor B cell infiltrates and favorable clinical outcomes, other results suggested tumor promoting roles of B cells. Besides the occurrence of B cell infiltrates, tumor specific antibodies could be identified in the peripheral blood / tumor tissues of cancer patients. However, a major drawback has been that the analysis of blood derived B cells is very prone to “background noise” from latent infections and everyday pathogens. Concerning tumors with CNS manifestations including brain or meningeal metastasis, hardly any information is available on the role of B cells yet.In previous work we could show, that increased cerebrospinal fluid (CSF) B cell counts are detectable in a subset of patients with CNS neoplasia including brain metastasis and meningeal carcinomatosis. Preliminary experiments on CSF immunoglobulin (Ig) repertoires in 5 patients with meningeal carcinomatosis showed clonal expansion of CSF B cells using a single cell approach. In one patient with malignant melanoma, we were able to produce 7 recombinant antibodies out of recovered CSF Ig repertoires and antibodies indeed showed tumor specificity. These antigens may be extremely useful since they seem to be sufficiently immunogenic to trigger an immune response and may target specific epitopes reducing off-target effects by B cell receptor selection.Taking advantage of the CNS being a separated compartment, we propose a systematic analysis of the CSF B cell response in 20 cancer patients with CNS or meningeal metastasis concentrating on immunogenic tumors. We will apply single cell analysis of CSF plasmablasts in order to assess Ig repertoires and corresponding antibodies. Additionally, we will assess peripheral blood Ig repertoires and Ig proteomics to provide an in-depth analysis of the intrathecal B cell response. Recovered antibodies will be analyzed by using microarrays, immunoprecipitation, phage libraries, immunofluorescence and ELISA test in order to identify specific antigen targets. We thereby aim to identify antigens that might be applied for future treatments including e.g. vaccinations, antibody or CAR T cell therapies or combined treatment strategies. We believe that by exploiting the intrinsic immune response of cancer patients within the CSF, we can open new avenues to advanced treatment options for tumor patients.

• DFG Programme: Research Grants