Abstract 1671: A genome-wide RNA interference screen identifies autophagy mediators with therapeutic implications in chronic myeloid leukemia.

Abstract Autophagy plays a critical role in cancer formation and therapeutic resistance. However, little is known about how autophagy is regulated in cancer and how it mediates therapeutic resistance. Here we elect to use chronic myeloid leukemia (CML) as a cancer model to study autophagy in that it is driven by a single onco-protein BCR-ABL, whose activity can be selectively blocked by imatinib a front-line treatment for CML. Moreover, imatinib resistance frequently occurs in CML patients. Thus, unraveling autophagy regulation in CML and its role in overcoming imatinib resistance has substantial therapeutic benefits not only for CML but also for other cancers that can be treated by imatinib. In this report, we performed a genome-wide RNA interference screen in K562 human CML cells using monodansylcadaverine (MDC) that marks autolysosomes followed by fluorescence-activated cell sorting to label and isolate autophagic cells. We have identified 336 candidate genes, knockdown of which significantly increased MDC fluorescence. Our further validation utilized Cyto-IDTM Green dye that selectively stains autophagy vacuoles and quantitative RT-PCR that measures knockdown efficiency of shRNAs. We have uncovered a set of genes acting as autophagy mediators in K562 cells. To study their role in imatinib resistance, we measured the effect of imatinib in combination with the knocking down of autophagy mediators. Our results showed that the shRNA of VAMP7, a pivotal factor in vesicle transportation, substantially sensitized K562 cells to imatinib. Intriguingly, our further work revealed that depletion of VAMP7 blocked the activity of key autophagy suppressors AKT and mTOR, suggesting that VAMP7 and perhaps other autophagy mediators regulate imatinib sensitivity through signaling pathways that inhibit autophagy. In conclusion, a set of genes revealed by a genome-wide RNA interference screen mediates autophagy in CML cells and, more importantly, some of these genes render CML cells resistant to imatinib thereby becoming appealing drug targets. Citation Format: Zhi Sheng, Sujuan Guo, Susan Murphy, Hanne Varmark, Amy Virbasius, Michael Green. A genome-wide RNA interference screen identifies autophagy mediators with therapeutic implications in chronic myeloid leukemia. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1671. doi:10.1158/1538-7445.AM2013-1671</jats:p

COVID-19 Patients Form Memory CD8+ T Cells that Recognize a Small Set of Shared Immunodominant Epitopes in SARS-CoV-2

AbstractDevelopment of effective strategies to detect, treat, or prevent COVID-19 requires a robust understanding of the natural immune response to SARS-CoV-2, including the cellular response mediated by T cells. We used an unbiased, genome-wide screening technology, termed T-Scan, to identify specific epitopes in SARS-CoV-2 that are recognized by the memory CD8+ T cells of 25 COVID-19 convalescent patients, focusing on epitopes presented by the six most prevalent HLA types: A*02:01, A*01:01, A*03:01, A*11:01, A*24:02, and B*07:02. For each HLA type, the patients’ T cells recognized 3–8 immunodominant epitopes that are broadly shared among patients. Remarkably, 94% of screened patients had T cells that recognized at least one of the three most dominant epitopes for a given HLA, and 53% of patients had T cells that recognized all three. Subsequent validation studies in 18 additional A*02:01 patients confirmed the presence of memory CD8+ T cells specific for the top six A*02:01 epitopes, and single-cell sequencing revealed that patients often have many different T cell clones targeting each epitope, but that the same T cell receptor Vα regions are predominantly used to recognize these epitopes, even across patients. In total, we identified 29 shared epitopes across the six HLA types studied. T cells that target most of these epitopes (27 of 29) do not cross-react with the endemic coronaviruses that cause the common cold, and the epitopes do not occur in regions with high mutational variation. Notably, only 3 of the 29 epitopes reside in the spike protein, highlighting the need to design new classes of vaccines that recapitulate natural CD8+ T cell responses to SARS-CoV-2.</jats:p

Discovery of TSC-101: A First-in-Class Natural HA-2-Specific TCR to Treat Leukemia Following Hematopoietic Stem Cell Transplant Therapy

Abstract Background Approximately 50% of AML patients relapse following allogeneic hematopoietic stem cell transplant therapy, leaving them with very few treatment options (Rautenberg et al. (2019) Int. J. Mol. Sci. 20:228). Rare patients who naturally develop a minor antigen-specific graft-versus-leukemia T cell response show substantially lower relapse rates (Marijt et al. (2003) Proc. Natl. Acad. Sci. U.S.A. 100:2742-2747; Spierings et al. (2013) Biol. Blood Marrow Transplant. 19:1244-1253). HA-2 (YIGEVLVSV, genotype RS_61739531 C/C or T/C) is an HLA-A*02:01- and haematopoietically-restricted minor histocompatibility antigen derived from the class I myosin protein, MYO1G (Pierce et al. (2001) J. Immunol. 167:3223-3230). Patients receiving donor lymphocyte infusion from HA-2-mismatched donors who develop HA-2-specific T cells show a graft vs leukemia response and often experience long-term remission (Marijt et al. (2003) Proc. Natl. Acad. Sci. U.S.A. 100:2742-2747), making HA-2 an ideal candidate for TCR-engineered T cell immunotherapy of liquid tumors. Methods Using TScan's proprietary ReceptorScan platform, we discovered 1,302 HA-2-specific TCRs by screening 237 million naïve CD8 + T cells from 5 healthy HA-2-negative donors. We evaluated these TCRs using our proprietary DexScan platform to select the 15 TCRs with the highest surface expression and greatest affinity for the HA-2 peptide when transferred into primary human T cells. We further tested each TCR individually in our clinical vector backbone for surface expression, selective cytotoxicity, cytokine production, and proliferation using a panel of cell lines that express varying levels of HLA-A*02:01 and MYO1G. Finally, the top 5 TCRs were evaluated for alloreactivity using an array-based screen assessing 108 MHC-I molecules individually, and for off-target cross-reactivity using our proprietary genome-wide TargetScan platform. A lead TCR with limited alloreactivity and a narrow off-target profile was selected as our lead TSC-101 TCR. The avidity of TSC-101 for its putative off-targets was further measured in peptide-pulsed experiments to better appreciate the toxicity risks associated with our lead clinical candidate. Results and Conclusion Of the 1,302 HA-2-specific TCRs identified by our ReceptorScan platform, we identified TSC-101 as the most active TCR. TSC-101 displayed no alloreactivity to 107/108 HLAs tested and limited off-target risks in a genome-wide screens. Potential off-target peptides identified for TSC-101 displayed extremely weak avidities, predicting an absence of toxicity risks for our clinical candidate. Based on these results, TSC-101 has been advanced to IND-enabling activities to prepare for first-in-human testing in 2022. To our knowledge, this is the first clinical grade HA-2-specifc TCR being developed for immunotherapy for liquid tumors. Disclosures Macbeath: TScan Therapeutics: Current Employment, Current equity holder in publicly-traded company. </jats:sec