Abstract A112: Mapping the impact of proteasome inhibitor therapy on the antigenic landscape of multiple myeloma: Identifying robust targets for T cell immunotherapy
Authors: Kowalewski Daniel J. , Walz Simon , Backert Linus , Schuster Heiko , Kohlbacher Oliver , Kanz Lothar , Salih Helmut R. , Rammensee Hans-Georg , Stevanovic Stefan , Stickel Juliane S. 
Published: May 2016

Abstract
Recent studies underscore that multiple myeloma is an immunogenic disease and suggest that it can be effectively treated by T cell based immunotherapy via immunomodulation. Unspecific immune checkpoint inhibition might be synergistically complemented by therapeutic vaccination, which may help induce and guide specific anti-cancer T cell responses. We have recently conducted a study which directly characterized the antigenic landscape of myeloma by mass spectrometric analysis of naturally presented HLA ligands and identified a panel of T cell epitopes characterized by exquisite myeloma-specificity. As novel immunotherapeutic interventions will have to be implemented as 2nd line treatments, it is of great importance to thoroughly characterize and take into account the effects of previous therapies on the antigenic landscape of target cells.
Here we present a longitudinal study of the HLA-presented immunopeptidome of myeloma cells under treatment with the 2nd generation proteasome inhibitor carfilzomib. We characterize and quantify the plasticity of the antigenic landscape and identify targets characterized by robust presentation.
We quantified HLA surface expression on 4 human myeloma cell lines (MM.1s, U266, RPMI8226 & JJN3) at t0, t24h and t48h after incubation with carfilzomib. Strikingly, we detected elevated levels of HLA class I post treatment for 3/4 cell lines, with absolute molecule counts ranging from 50,000-400,000 molecules/cell. Out of the &gt;5,000 different HLA ligands we could identify on MM.1s and U266 by mass spectrometry, we were able to detect and longitudinally quantify 38 and 54 myeloma-associated epitopes described in previous studies, respectively. Importantly, the vast majority of these antigens (88.2%) showed robust presentation on myeloma cells under therapy. Around 12% of HLA ligands showed significant changes in abundance after carfilzomib treatment. Strikingly, we observed a significant reduction in aromatic residues at the C-terminal anchor position, which directly reflects the mechanism of action of carfilzomib on the HLA ligand level.
Our study provides direct insights into the plasticity of T cell antigen presentation on myeloma cells in a model of proteasome inhibitor therapy. We were able to characterize general changes in the immunopeptidome composition and identify robustly presented myeloma-associated epitopes. Our findings may help guide future clinical trials for 2nd line T cell immunotherapy of multiple myeloma.
Citation Format: Daniel J. Kowalewski, Simon Walz, Linus Backert, Heiko Schuster, Oliver Kohlbacher, Lothar Kanz, Helmut R. Salih, Hans-Georg Rammensee, Stefan Stevanovic, Juliane S. Stickel. Mapping the impact of proteasome inhibitor therapy on the antigenic landscape of multiple myeloma: Identifying robust targets for T cell immunotherapy. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A112.