Expression of chimeric antigen receptor therapy targets detected by single-cell sequencing of normal cells may contribute to off-tumor toxicity

Chimeric antigen receptor (CAR)-engineered cell therapy, which leverages genetically modified immune cells to generate a tailored immune response, has revolutionized cancer treatment ( Dougan et al., 2021 Dougan M. Luoma A.M. Dougan S.K. Wucherpfennig K.W. Understanding and treating the inflammatory adverse events of cancer immunotherapy. Cell. 2021; 184: 1575-1588 Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar ; Hong et al., 2020 Hong M. Clubb J.D. Chen Y.Y. Engineering CAR-T Cells for Next-Generation Cancer Therapy. Cancer Cell. 2020; 38: 473-488 Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar ). The number, type, and indications of clinical trials for CAR-engineered cell therapies have increased rapidly in recent years ( MacKay et al., 2020 MacKay M. Afshinnekoo E. Rub J. Hassan C. Khunte M. Baskaran N. Owens B. Liu L. Roboz G.J. Guzman M.L. et al. The therapeutic landscape for cells engineered with chimeric antigen receptors. Nat. Biotechnol. 2020; 38: 233-244 Crossref PubMed Scopus (81) Google Scholar ). However, serious and potentially life-threatening toxicities, such as on-target, off-tumor effects, remain a major limitation of CAR-engineered cell therapies ( Dougan et al., 2021 Dougan M. Luoma A.M. Dougan S.K. Wucherpfennig K.W. Understanding and treating the inflammatory adverse events of cancer immunotherapy. Cell. 2021; 184: 1575-1588 Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar ; MacKay et al., 2020 MacKay M. Afshinnekoo E. Rub J. Hassan C. Khunte M. Baskaran N. Owens B. Liu L. Roboz G.J. Guzman M.L. et al. The therapeutic landscape for cells engineered with chimeric antigen receptors. Nat. Biotechnol. 2020; 38: 233-244 Crossref PubMed Scopus (81) Google Scholar ). By interrogating bulk expression data from multiple tissues from the Human Protein Atlas and Genotype-Tissue Expression project, a therapeutic landscape for CAR targets has been created ( MacKay et al., 2020 MacKay M. Afshinnekoo E. Rub J. Hassan C. Khunte M. Baskaran N. Owens B. Liu L. Roboz G.J. Guzman M.L. et al. The therapeutic landscape for cells engineered with chimeric antigen receptors. Nat. Biotechnol. 2020; 38: 233-244 Crossref PubMed Scopus (81) Google Scholar ). Recent studies have demonstrated that single-cell RNA sequencing (scRNA-seq) may provide unprecedented high-resolution expression profiling to enable us to understand the efficacy ( Chen et al., 2021 Chen G.M. Chen C. Das R.K. Gao P. Chen C.-H. Bandyopadhyay S. Ding Y.-Y. Uzun Y. Yu W. Zhu Q. et al. Integrative Bulk and Single-Cell Profiling of Premanufacture T-cell Populations Reveals Factors Mediating Long-Term Persistence of CAR T-cell Therapy. Cancer Discov. 2021; 11: 2186-2199 Crossref PubMed Scopus (29) Google Scholar ; Deng et al., 2020 Deng Q. Han G. Puebla-Osorio N. Ma M.C.J. Strati P. Chasen B. Dai E. Dang M. Jain N. Yang H. et al. Characteristics of anti-CD19 CAR T cell infusion products associated with efficacy and toxicity in patients with large B cell lymphomas. Nat. Med. 2020; 26: 1878-1887 Crossref PubMed Scopus (124) Google Scholar ) and safety ( Parker et al., 2020 Parker K.R. Migliorini D. Perkey E. Yost K.E. Bhaduri A. Bagga P. Haris M. Wilson N.E. Liu F. Gabunia K. et al. Single-Cell Analyses Identify Brain Mural Cells Expressing CD19 as Potential Off-Tumor Targets for CAR-T Immunotherapies. Cell. 2020; 183: 126-142.e17 Abstract Full Text Full Text PDF PubMed Scopus (138) Google Scholar ) of CAR therapy based on the expression of the target in rare cell subpopulations. For example, a small population of mural cells in normal brain tissue express CD19 and are targeted by CD19 CAR T cells, and this may result in neurotoxicity through increased vascular permeability in the brain ( Parker et al., 2020 Parker K.R. Migliorini D. Perkey E. Yost K.E. Bhaduri A. Bagga P. Haris M. Wilson N.E. Liu F. Gabunia K. et al. Single-Cell Analyses Identify Brain Mural Cells Expressing CD19 as Potential Off-Tumor Targets for CAR-T Immunotherapies. Cell. 2020; 183: 126-142.e17 Abstract Full Text Full Text PDF PubMed Scopus (138) Google Scholar ). To better understand the effects of CAR-directed immunotherapy, a systematic single-cell-level dissection of the expression of divergent CAR targets in various cell types across different normal tissues is urgently required.