Profiling the myeloma cell surface proteome reveals CCR10 as a potential immunotherapeutic target

Background Targeting surface antigens upregulated on malignant plasma cells is one of the most promising approaches to improve outcomes for multiple myeloma (MM) patients. Surface markers with approved therapeutics include CD38, BCMA, and SLAMF7, with many more under development. However, none of these therapies are known to be curative. Furthermore, the “surfaceome” of cancer cells regulates tumor proliferation, migration, and endogenous immune cell interactions. There remains a need to identify new surface antigens that can serve as new immunotherapeutic targets and/or reveal surface protein biology in MM. Methods We used glycoprotein “Cell Surface Capture” proteomics to define the MM “surfaceome”. Across four cell line models, we quantified 1245 proteins annotated as membrane-spanning in Uniprot; 530 are high-confidence plasma membrane proteins. We integrated our proteomic data with publicly-available mRNA datasets and bioinformatic prediction algorithms to create a ranking system for possible single-antigen immunotherapy targets. Primary patient samples were obtained under an IRB-approved tissue banking protocol. Results Four of the top six targets by our ranking are already being clinically investigated in MM: BCMA, TACI, ITGB7, and SLAMF7. We thus probed other high-scoring proteins found in our proteomic data that, to our knowledge, have not yet been explored as therapeutic targets. To this end, we found the chemokine receptor CCR10 to be robustly expressed on MM cells per the CCLE but with minimal expression on other tumor cell lines. Data from GTEx and the Human Blood Atlas also suggest low mRNA expression on non-hematopoietic tissues and markedly higher mRNA expression on plasmablasts than other hematopoietic cells. By flow cytometry we verified markedly increased CCR10 expression on MM models compared to B-cell cancers. In patient bone marrow aspirates we also confirmed CCR10 expression on patient tumor cells as well as T-regulatory cells. We developed proof-of-concept Chimeric Antigen Receptor (CAR) constructs using CCL27, the native chemokine ligand of CCR10. We found these CAR’s could robustly activate Jurkat T-cells when co-cultured with CCR10+ MM cell lines, suggesting CAR functionality. However, we found that while peripheral blood CD8+ T-cells do not express detectable CCR10 at baseline, T-cell activation during CAR-T production leads to CCR10 upregulation and thus fratricide with functional cyotoxic CAR-T’s. Current efforts involve T-cell engineering to avoid this fratricide and thus develop preclinical therapeutic candidates targeting CCR10. Conclusion Our surface proteomic profiling provides a powerful resource to discover new biology and immunotherapeutic strategies in MM. CCR10 serves as potential immunotherapeutic target in this disease. CCR10 upregulation on plasma cells warrants further investigation into the role of the CCL27-CCR10 axis in MM pathology.