Intratumoral heterogeneity can affect the competitive fitness and chemoresistance of individual cancer cells. In acute myeloid leukemia (AML), both genetic and functional heterogeneity contribute to chemoresistance, resulting in relapse. Whereas the role of cell-extrinsic factors has been described for AML relapse, whether interactions between cancer cells affect chemoresistance is not fully known. In this study, we demonstrated that a dominant leukemic fraction can suppress the proliferation and expansion of other leukemic cells and that this suppression is reversible. This suppression is mediated in part by both type I and type II intra-leukemic interferon signaling and dependent on BST2. Importantly, blocking antibodies to type II interferon receptor activated the cycling of this suppressed cell fraction and sensitized the cells to subsequent chemotherapy treatment. Our findings suggest that interactions between functionally heterogeneous leukemic fractions can affect competitive fitness and treatment response, highlighting interferon signaling as a potential therapeutic target to counter chemoresistance. SIGNIFICANCE:AML presents a significant challenge in clinical management due to its poor prognosis and high rates of relapse following chemotherapy. Using multiple models of primary human AML, we demonstrate that competitive interactions between leukemia cells affect clonal dynamics and therapy resistance, thereby identifying a potential strategy to improve patient outcomes. See related commentary by Papaioannou and Aifantis, p. 18.

Supplementary Table 1 shows List of genes for gene set enrichment analysis Supplementary Table 2 shows Sequences of gRNA Supplementary Table 3 shows List of antibody Supplementary Table 4 shows Sequences of primers and probes

Supplementary Figure 1 shows Suppressed leukemia cells maintain disease-initiating capacity. Supplementary Figure 2 shows iAML isogenic competition model with fluorescent G0 reporter. Supplementary Figure 3 shows Oxidative phosphorylation does not account for suppression Supplementary Figure 4 shows IFN signaling inhibits suppressed samples Supplementary Figure 5 shows BST2 contributes to IFN-mediated AML suppression. Supplementary Figure 6 shows IFN signaling is associated with chemoresistance in experimental models. Supplementary Figure 7 shows IFN signaling is associated with chemoresistance in primary AML patient samples. Supplementary Figure 8 shows Blocking IFN signaling affects cycling and chimerism of patient samples.

A long-sought goal of cancer immunotherapy is to mass-produce T cells that specifically target tumor neoantigens. One decisive challenge is the identification of neoantigens derived from cancer driver genes. Here, we identify T cells that recognize the NSCLC-associated EGFR C797S mutation, which confers resistance to current inhibitors and is linked to poor prognosis. To overcome limitations in T cell availability, we reprogrammed EGFR C797S-specific T cells into induced pluripotent stem cells (iPSCs) and re-differentiated them into CD8+ T cells. These iPSC-derived T cells specifically recognized the EGFR C797S mutation and effectively killed cancer cells expressing this mutation. Our findings underscore the potential of targeting driver mutation-derived neoantigens for immunotherapy and demonstrate that iPSC-derived T cells can mediate antitumor effects. Collectively, this approach combining neoantigen identification with T cell reprogramming may offer a promising strategy for targeting drug-resistant tumors.

Abstract Engineered Induced Pluripotent Stem Cells (iPSCs) are the core foundational technology for Century Therapeutics. In our constant effort to identify iPSC lines with diverse functional activity, we have derived a large panel of clinical-grade peripheral blood mononuclear cell (PBMC)-derived and gamma-delta T cell-derived IPSC lines (PiPSCs and TiPSCs, respectively) from multiple donors. These lines have been screened by multiple criteria to select the top lines for clinical development in our iPSC-derived NK (iNK) and T cell (iT) programs. Initial screening included in-depth genomic and transcriptomic analysis of PiPSC and TiPSC lines to eliminate those with any unwanted genetic abnormalities, as well as to build multi-omics datasets for correlating gene polymorphisms and transcript variation to function. Next, all lines were differentiated to iNK or iT effector cells, and phenotypically characterized throughout the differentiation process. In those studies, 86.5% of PiPSCs and 69.2% of TiPSCs lines were compatible with our protocols and able to be successfully differentiated and acquire NK cell and gamma delta T cell phenotypes respectively. Yield and lineage commitment (%CD56+ for NK cells and %CD3+ for T cells) variability was found to be higher across clones than donors in this initial analysis. Finally, we evaluated in vitro cytotoxicity, cytokine secretion, and persistence for all clones that met differentiation thresholds (>90% lineage commitment). As part of that evaluation, 39 PiPSCs lines were differentiated to iNK cells. Cytotoxicity against tumor lines was observed to be consistently between 85-100% at an effector to target ratio of 1:1. Although no trends in functionality were found to be associated with the PBMC donor, iPSC lines derived from CD34+ enriched PBMCs exhibited higher levels of innate killing as compared to those derived from bulk PBMCs. For this presentation, we will present genetic, transcriptomic, and phenotypic correlations with favorable differentiation and functional efficacy and illustrate how our screening process enables efficient selection of founder lines with the highest therapeutic potential for allogeneic cell therapies. Citation Format: Barry A. Morse, Amarin Cogburn, Alex Chialastri, Matthew S. Hall, Ohad Manor, Andriana Lebid, Dae Hwan Kim, Luis Cocka, Daniel J. Perry, Ciara Budd, Aarti Kolluri, Liam Campion, Toshinobu Nishimura, Michael Naso, Hyam Levitsky. Screening iPSC lines for optimal characteristics of differentiation into immune effector cells for clinical programs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3613.

The developmental origin of blood -forming hematopoietic stem cells (HSCs) is a longstanding question. Here, our non-invasive genetic lineage tracing in mouse embryos pinpoints that artery endothelial generate HSCs. Arteries are transiently competent to generate HSCs for 2.5 days (similar to E8.5-E11) but subsequently cease, delimiting a narrow time frame for HSC formation in vivo . Guided by the arterial origins blood, we efficiently and rapidly differentiate human pluripotent stem cells (hPSCs) into posterior primitive streak, lateral mesoderm, artery endothelium, hemogenic endothelium, and >90% pure hematopoietic genitors within 10 days. hPSC-derived hematopoietic progenitors generate T, B, NK, erythroid, and myeloid cells in vitro and, critically, express hallmark HSC transcription factors HLF and HOXA5-HOXA10 , which previously challenging to upregulate. We differentiated hPSCs into highly enriched HLF + HOXA + hematopoietic progenitors with near-stoichiometric efficiency by blocking formation of unwanted lineages at each ferentiation step. hPSC-derived HLF + HOXA + hematopoietic progenitors could avail both basic research cellular therapies.

CRISPR-Cas9 paired with adeno-associated virus serotype 6 (AAV6) is among the most efficient tools for producing targeted gene knockins. Here, we report that this system can lead to frequent concatemeric insertions of the viral vector genome at the target site that are difficult to detect. Such errors can cause adverse and unreliable phenotypes that are antithetical to the goal of precision genome engineering. The concatemeric knockins occurred regardless of locus, vector concentration, cell line or cell type, including human pluripotent and hematopoietic stem cells. Although these highly abundant errors were found in more than half of the edited cells, they could not be readily detected by common analytical methods. We describe strategies to detect and thoroughly characterize the concatemeric viral vector insertions, and we highlight analytical pitfalls that mask their prevalence. We then describe strategies to prevent the concatemeric inserts by cutting the vector genome after transduction. This approach is compatible with established gene editing pipelines, enabling robust genetic knockins that are safer, more reliable and more reproducible. AAV vectors form difficult-to-detect concatemers at Cas9 target sites.

The discovery and development of induced pluripotent stem cells (iPSCs) opened a novel venue for disease modeling, drug discovery, and personalized medicine. Additionally, iPSCs have been utilized for a wide variety of research and clinical applications without immunological and ethical concerns that arise from using embryonic stem cells. Understanding the in vivo behavior of iPSCs, as well as their derivatives, requires the monitoring of their localization, proliferation, and viability after transplantation. Bioluminescence imaging (BLI) gives investigators a non-invasive and sensitive means for spatio-temporal tracking in vivo. For scientists working within the field of iPSCs, this protocol provides a walk-through on how to conduct in vitro and in vivo experiments with an iPSCs constitutively expressing luciferase.

Background CAR-T cell therapies have proven safe and efficacious for hematologic malignancies, but there remains a significant unmet need for effective cell therapy options for solid tumors. CAR-engineered induced pluripotent stem cell (iPSC)-derived effector cells allow for the treatment of cancer as an off-the-shelf allogeneic cell therapy. Gamma delta (γδ) T cells exhibit the cytolytic features of conventional alpha beta (αβ) CD8+ T cells with additional capabilities for innate recognition of tumors. For example, expression of CD16 on γδ T cells can mediate antibody-dependent cellular cytotoxicity (ADCC) against tumors. Here we describe development of an iPSC-derived CAR γδ T cell platform which can target solid tumors through both CAR-mediated recognition and ADCC when combined with a therapeutic antibody. Methods Primary γδ T cells were enriched and expanded in culture to enable reprogramming to iPSCs by delivery of pluripotency genes. These T cell derived iPSCs (TiPSCs) were used to produce γδ T cells using a proprietary differentiation process. The TiPSC line was engineered with a CAR targeting EGFR and a membrane bound form of IL-15 to enhance T cell persistence. Tumor spheroids were generated from EGFR+Her-2+ SKOV-3 ovarian tumor cells. Cytolysis of spheroids was evaluated using CAR-T cells alone or in combination with anti-HER2 antibody (trastuzumab). Results Batches of CAR-T cells were generated using a proprietary differentiation process yielding >90% pure CAR+ γδ T cells. The TiPSCs contained the rearranged γδ TCR gene and upon differentiation to T cells, uniformly expressed a Vγ9Vδ2 TCR and expressed high levels of CD16. CAR γδ T cells were effective in killing SKOV-3 spheroids. When cultured with SKOV-3 spheroids in an ADCC assay, CAR γδ T cells exhibited enhanced cytotoxicity in the presence of trastuzumab but not isotype control antibody. Activity of the γδ T cells was not reliant on additional exogenous cytokine due to the engineered form of membrane-associated IL-15. Conclusions We have demonstrated that iPSC-derived γδ T cells mediate anti-tumor activity in human solid tumor models through multiple pathways. The combination of two modes of tumor recognition (CAR and CD16/antibody) enabled more potent killing of solid tumor spheroids. The ability to manufacture large batches of iPSC derived CAR γδ T cells will enable a true off-the-shelf allogenic cell therapy for solid tumors.

Abstract Introduction Allogenic CAR-T cell therapies for cancer provide a new option to reduce barriers faced by autologous cell therapies, but several challenges remain. One challenge is the risk of graft versus host disease (GvHD) caused by the infused T cells. A potential solution is the use of a subset of gamma delta (γδ) CAR-T cells whose T cell receptors (TCRs) recognize invariant antigens rather than hypervariable MHC molecules. Here we describe an off-the-shelf, induced pluripotent stem cell (iPSC)-derived γδ CAR-T (γδ CAR-iT) for treatment of cancer and a process for deriving such cells. Methods T cell-derived iPSCs (TiPSC) are generated by reprogramming γδ T cells to yield pluripotent stem cells. For proof-of-concept studies, TiPSC were engineered using CRISPR gene editing to deliver a CD19 CAR transgene. TiPSC are then subjected to a two-stage differentiation process. First, TiPSC are differentiated into CD34-expressing hematopoietic progenitor cells (HPCs). HPCs are then exposed to a feeder-free differentiation process that results in uniform γδ CAR-iT cells. The purity and identity of γδ CAR-iT cells were assessed by flow cytometry and the ability of γδ CAR-iT cells to respond to homeostatic growth factors was determined by intracellular staining of phosphorylated signaling proteins and mRNA transcriptome analysis. Cytokine production by CAR-iT cells was measured by immunoassays following stimulation of the CAR. Tumor cell killing by γδ CAR-iT cells was performed using IncuCyte cytotoxicity assays. In vivo control of tumors by γδ CAR-iT in immunodeficient mice was determined using a NALM-6 B cell lymphoblastic xenograft model. Results A research-grade γδ TiPSC line was used to develop an iT differentiation process. This γδ TiPSC line was engineered to express a CD19 CAR molecule and then subjected to the differentiation process after which >95% of cells were CD3 + γδ TCR + CAR + iT cells. These γδ CAR-iT cells responded to IL-2 and IL-15. STAT5 phosphorylation levels were similar but STAT3 phosphorylation levels were greater in response to IL-15 compared to IL-2 at equimolar concentrations of cytokine. IL-2 and IL-15 elicited qualitatively similar transcriptional responses, but the magnitude of cytokine-induced gene expression was generally greater in IL-15-treated cells. Upon activation, γδ CAR-iT cells released markedly less IFN-γ and other inflammatory cytokines than conventional blood-derived ab CAR-T cells. In an IncuCyte serial killing assay, γδ CAR-iT cells exhibited sustained killing of NALM-6 tumor cells for at least one week in the presence of IL-15. In vivo, γδ CAR-iT cells caused a significant reduction in NALM-6 tumor burden with a single dose of γδ CAR-iT resulting in >95% tumor growth inhibition. To establish an efficient method for derivation of clinical grade γδ TiPSC lines, we investigated methods to isolate, expand, and reprogram human γδ T cells. When γδ T cells were expanded by exposure to the chemical zoledronic acid (zoledronate) and IL-2, we found a large disparity between donors; some donors exhibit robust expansion while others are seemingly resistant to zoledronate. In order to enhance γδ T cell expansion we screened dozens of activation conditions and eventually established a universal activation protocol that can elicit robust expansion of γδ T cells from all donors tested. When expanded γδ T cells were subjected to reprogramming conditions, dozens to hundreds of individual TiPSC colonies were obtained from each donor. The identity of the rearranged γδ TCR locus was confirmed using molecular assays. New γδ TiPSC lines were engineered with a CD19 CAR molecule and killing activity was confirmed in an in vitro serial killing assay. Conclusions γδ CAR-iT cells provide a new opportunity to treat cancers with an off-the-shelf universal T cell platform without the risk for GvHD. γδ CAR-iT cells are readily manufacturable, and we have derived an end-to-end process that enables new TiPSC line reprogramming, genetic modification of TiPSC lines, and feeder-free differentiation. γδ CAR-iT cells exhibit potent antigen-specific tumor killing and they release less inflammatory cytokine than conventional CAR-T cells, potentially reducing the risk for cytokine-mediated toxicities. We believe that this off-the-shelf platform will enable safer and more accessible allogenic cell therapies for hematologic and solid cancers. Disclosures Wallet: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Nishimura: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Del Casale: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Lebid: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Salantes: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Santostefano: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Bucher: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Mendonca: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Beqiri: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Thompson: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Morse: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Millar Quinn: Century Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Borges: Century Therapeutics: Current Employment, Current equity holder in publicly-traded company.

Diamond Blackfan Anemia (DBA) is a congenital bone marrow failure syndrome associated with ribosomal gene mutations that lead to ribosomal insufficiency. DBA is characterized by anemia, congenital anomalies, and cancer predisposition. Treatment for DBA is associated with significant morbidity. Here, we report the identification of Nemo-like kinase (NLK) as a potential target for DBA therapy. To identify new DBA targets, we screen for small molecules that increase erythroid expansion in mouse models of DBA. This screen identified a compound that inhibits NLK. Chemical and genetic inhibition of NLK increases erythroid expansion in mouse and human progenitors, including bone marrow cells from DBA patients. In DBA models and patient samples, aberrant NLK activation is initiated at the Megakaryocyte/Erythroid Progenitor (MEP) stage of differentiation and is not observed in non-erythroid hematopoietic lineages or healthy erythroblasts. We propose that NLK mediates aberrant erythropoiesis in DBA and is a potential target for therapy.

Despite their rapidly-expanding therapeutic potential, human pluripotent stem cell (hPSC)-derived cell therapies continue to have serious safety risks. Transplantation of hPSC-derived cell populations into preclinical models has generated teratomas (tumors arising from undifferentiated hPSCs), unwanted tissues, and other types of adverse events. Mitigating these risks is important to increase the safety of such therapies. Here we use genome editing to engineer a general platform to improve the safety of future hPSC-derived cell transplantation therapies. Specifically, we develop hPSC lines bearing two drug-inducible safeguards, which have distinct functionalities and address separate safety concerns. In vitro administration of one small molecule depletes undifferentiated hPSCs >106-fold, thus preventing teratoma formation in vivo. Administration of a second small molecule kills all hPSC-derived cell-types, thus providing an option to eliminate the entire hPSC-derived cell product in vivo if adverse events arise. These orthogonal safety switches address major safety concerns with pluripotent cell-derived therapies.

The induction of the master erythroid transcription factor, GATA1 during early erythropoiesis is critical for efficient red blood cell production. However, GATA1 is expressed at low levels in hematopoietic stem cells (HSCs) and is moderately induced at both the common myeloid progenitor (CMP) and megakaryocyte/erythroid progenitor (MEP) stages prior to lineage commitment. Diamond Blackfan Anemia is a rare disease, usually associated with ribosomal gene mutations, leading to significant decrease in GATA1 expression and block in early committed erythroid differentiation. Mild defects in other myeloid lineages are also observed, with limited clinical relevance. The importance of GATA1 downregulation in disease pathogenesis is manifested by rare patients with DBA carrying GATA1 mutations. To understand signaling pathways that contribute to the pathogenesis DBA, we perform RNA-seq with mRNA from human CD34+ fetal liver cells and found that the chromatin organizer, Special AT-rich sequence binding protein 1 (SATB1) was prematurely downregulated. Our results further demonstrated that sustained SATB1 expression is critical to maintain required levels of GATA1 protein at both the CMP and MEP stages of differentiation, but not in committed erythroid progenitors. In mice, SATB1 is modestly expressed in HSCs and upregulated during lymphopoiesis. SATB1 is downregulated during myeloid and erythroid differentiation and antagonizes myeloid and erythroid expansion. However, in human hematopoietic stem and progenitor cells (HSPCs), SATB1 is required for efficient expansion of these lineages. SATB1 maintains 78% expression in human MEPs, but is undetectable in early committed erythroid progenitors. In RPS19-insufficient human HSPCs, SATB1 was downregulated to 22% in MEPs (p=0.02). Re-expression of SATB1 corrected a significant subset of deregulated mRNAs, including GATA1 regulators. In the absence of SATB1, one such GATA1 regulator, heat shock protein 70 (HSP70), failed to be induced in ribosome-competent human MEPs, reducing GATA1 protein expression by 35.7% (p= 0.026). Concurrently, MEP expansion was inhibited by 64.5% (p=0.023), reducing erythroid and megakaryocyte expansion by 18.2% (p=0.024) and 20.4% (p=0.183) respectively. SATB1 facilitated the formation of chromatin loops linking together an enhancer element with HSP70 promoters required for HSP70 induction in early differentiation. Although GATA1 is significantly upregulated in committed erythroid progenitors, RPS19-insufficient human CD235+ erythrocytes express GATA1 28.4% of controls (p= 0.011). SATB1 re-expression increased GATA1 expression to 31.4% (p=0.089). Similarly, SATB1 re-expression increased CD235+ expansion from 13.9% to 39.5% (p=0.02) compared to controls. Our data indicate that premature SATB1 downregulation contributes to erythroid failure in DBA by reducing MEP expansion, but aberrant GATA1 expression observed in more mature erythrocytes is predominantly SATB1-independent. However, SATB1-re-expression improved CD11b+ myeloid expansion from 81.2% to 90.4% (p=0.045) and CD41a+ megakaryocyte expansion from 76.7% to 214.7% (p=0.038) respectively. Our results demonstrate that SATB1 plays an important role in human hematopoiesis and is an important regulator of GATA1. Disclosures Glader: Agios Pharmaceuticals, Inc.: Consultancy.

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have promising potential for opening new avenues in regenerative medicine. However, since the tumorigenic potential of undifferentiated pluripotent stem cells (PSCs) is a major safety concern for clinical transplantation, inducible Caspase-9 (iC9) is under consideration for use as a fail-safe system. Here, we used targeted gene editing to introduce the iC9 system into human iPSCs, and then interrogated the efficiency of inducible apoptosis with normal iPSCs as well as diseased iPSCs derived from patients with acute myeloid leukemia (AML-iPSCs). The iC9 system induced quick and efficient apoptosis to iPSCs in vitro. More importantly, complete eradication of malignant cells without AML recurrence was shown in disease mouse models by using AML-iPSCs. In parallel, it shed light on several limitations of the iC9 system usage. Our results suggest that careful use of the iC9 system will serve as an important countermeasure against posttransplantation adverse events in stem cell transplantation therapies.

Serum albumin has long been an essential supplement for ex vivo hematopoietic and immune cell cultures. However, serum albumin medium supplements represent a major source of biological contamination in cell cultures and often cause loss of cellular function. As serum albumin exhibits significant batch-to-batch variability, it has also been blamed for causing major issues in experimental reproducibility. We recently discovered the synthetic polymer polyvinyl alcohol (PVA) as an inexpensive, Good Manufacturing Practice-compatible, and biologically inert serum albumin replacement for ex vivo hematopoietic stem cell cultures. Importantly, PVA is free of the biological contaminants that have plagued serum albumin-based media. Here, we describe that PVA can replace serum albumin in a range of blood and immune cell cultures including cell lines, primary leukemia samples, and human T lymphocytes. PVA can even replace human serum in the generation and expansion of functional chimeric antigen receptor (CAR) T cells, offering a potentially safer and more cost-efficient approach for this clinical cell therapy. In summary, PVA represents a chemically defined, biologically inert, and inexpensive alternative to serum albumin for a range of cell cultures in hematology and immunology.

For scientists working within the field of induced pluripotent stem cells (iPSCs), this protocol will provide a thorough walk-through on how to conduct in vitro and in vivo experiments that validate the function of a particular safeguard system technology. In short, we provide instructions on how to generate inducible Caspase-9 (iC9) safeguard system with human iPSCs that act as normal or abnormal models of the cells for therapeutics to be tried after differentiation. These iC9-iPSCs should be modified prior to beginning this protocol by constitutively expressing luciferase, an enzyme capable of generating bioluminescent signals through the oxidation of the substrate luciferin. Monitoring the bioluminescent signal over time provides the information on whether a safeguard system is working or not.

Genome editing of human pluripotent stem cells (hPSCs) provides powerful opportunities for in vitro disease modeling, drug discovery, and personalized stem cell-based therapeutics. Currently, only small edits can be engineered with high frequency, while larger modifications suffer from low efficiency and a resultant need for selection markers. Here, we describemarker-free genome editing in hPSCs using Cas9 ribonucleoproteins (RNPs) in combination with AAV6-mediated DNA repair template delivery. We report highly efficient and bi-allelic integration frequencies across multiple loci and hPSC lines, achieving mono-allelic editing frequencies of up to 94% at the HBB locus. Using this method, we show robust bi-allelic correction of homozygous sickle cell mutations in a patient-derived induced PSC (iPSC) line. Thus, this strategy shows significant utility for generating hPSCs with large gene integrations and/or single-nucleotide changes at high frequency and without the need for introducing selection genes, enhancing the applicability of hPSC editing for research and translational uses.

Human induced pluripotent stem cells (iPSCs) are a potential source of blood cells for transfusion therapies and a promising tool for studying the ontogeny of hematopoiesis. The development of widely varying reprogramming methods has enabled us nowadays to obtain iPSCs even from a small number of antigen-specific T cells from patients. As these T-cell-derived iPSCs (T-iPSCs) carry TCR gene rearrangements in their genomic DNA, they are likely useful for producing antigen-specific T cells and for studying T-cell development. T-cell immunotherapy is potentially an effective therapeutic strategy against many types of cancers and viral infections. If antigen-specific T cells tailored against diseases and for patients can be easily obtained, T-cell immunotherapy should become a popular choice of therapy. Here, we show the in vitro way to guide T-iPSCs sequentially to yield hematopoietic stem/progenitor cells (HSPCs), T-lineage cells, and mature CD8 single-positive T cells. These in vitro-generated CD8(+) T cells display antigen-specific cytotoxity and perform general T-cell functions. This novel protocol thus provides means to generate antigenspecific T cells as well as chances to study normal human lymphopoiesis. It may help identify, and then clear away, barriers to T-cell immunotherapy such as immunological tolerance and cell exhaustion. T-iPSCs can confer their juvenile status upon their descendant T cells during pluripotency reprogramming and redifferentiation. This phenomenon should help to eliminate T-cell exhaustion.

Scarless genome editing in human pluripotent stem cells (hPSCs) represents a goal for both precise research applications and clinical translation of hPSC-derived therapies. Here we established a versatile and efficient method that combines CRISPR-Cas9-mediated homologous recombination with positive-negative selection of edited clones to generate scarless genetic changes in hPSCs.