Epitope Engineered Human Haematopoietic Stem Cells are Shielded from CD123-targeted Immunotherapy

Targeted eradication of transformed or otherwise dysregulated cells using monoclonal antibodies (mAb), antibody-drug conjugates (ADC), T cell engagers (TCE) or chimeric antigen receptor (CAR) cells is very effective for haematologic diseases. Unlike the breakthrough progress achieved for B cell malignancies, there is a pressing need to find suitable antigens for immunotherapy of myeloid malignancies. CD123, the interleukin-3 (IL-3) receptor alpha-chain, is highly expressed in various haematological malignancies, including acute myeloid leukaemia (AML) and blastic plasmacytoid dendritic cell neoplasm (BPDCN). However, shared expression of CD123 on healthy haematopoietic stem and progenitor cells (HSPCs) bears the risk for extensive myelotoxicity upon targeted depletion. Here, we demonstrate that rationally designed, epitope-engineered HSPCs were completely shielded from CD123-targeted immunotherapy but remained fully functional while CD123-deficient HSPCs displayed a competitive disadvantage. Thus, molecularly shielded HSPCs could allow tumor-selective targeted immunotherapy and in parallel enable rebuilding a fully functional haematopoietic system. We envision that this approach is broadly applicable to many targets and cells, could render hitherto undruggable targets accessible to immunotherapy and will allow continued posttransplant immunotherapy, for instance to treat minimal residual disease (MRD) or be used as a salvage therapy. Since the function of the engineered targets is preserved, multiplexed molecular shielding could also enable targeted combination immunotherapies to address tumor heterogeneity. More generally, epitope shielding will be applicable for replacement of other cell types including the many immune cells which are currently being considered for engineered cellular therapies. ### Competing Interest Statement Funding: Research was supported by the European Research Council (L.T.J.). Sponsored research agreement with Cimeio Therapeutics AG (Cimeio) (L.T.J., M.P., T.I.C.). Cimeio scientists actively contributed to the research and are therefore listed as co-authors. Decision to publish was the sole responsibility of L.T.J. L.T.J.s employer, the Basel University Hospital, receives financial compensation for L.T.J.s consulting. Employment: Ridgeline Discovery GmbH: R.L., A.W., A.S., A.H., C.D., S.U.; Cimeio Therapeutics AG: R.L., V.DS., L.G.P., A.C., S.U.; Personal financial interests: L.T.J.: co-founder, board member of Cimeio; Holding Cimeio equity: University of Basel, R.L., A.W., A.S., V.DS., A.H., L.G.P., C.D., A.C., S.U., L.T.J.; inventors on a patent application related to the findings reported here: E.L., A.D., R.L., R.M., A.W., A.S., A.H., A.C., S.U., L.T.J.; JEC is a cofounder and SAB member of Spotlight Therapeutics, an SAB member of Hornet Bio, and has consulted for Cimeio Therapeutics. The lab of JEC has funded collaborations with Allogene and Cimeio; T.Ca. is an advisor to Cimeio Therapeutics, Excision BioTherapeutics, GenCC, and Novo Nordisk. T.Ca. and T.I.C. have a sponsored research collaboration with Cellectis. T.Ca. and G.A. hold a patent on CAST-Seq (US11319580B2); F.S. consulting fees from BMS/Celgene, Incyte, Kite/Gilead; speaker fees from Kite/Gilead, Incyte; travel support from Kite/Gilead, Novartis, AstraZeneca, Neovii, Janssen; research funding from Kite/Gilead, Novartis, BMS/Celgene. All other authors do not declare any conflict of interest.