Enhancing T Cell Receptor Stability in Rejuvenated iPSC-Derived T Cells Improves Their Use in Cancer Immunotherapy

3D-organoid culture supports differentiation of human CAR+ iPSCs into highly functional CAR T cells

Unlimited generation of chimeric antigen receptor (CAR) T cells from human-induced pluripotent stem cells (iPSCs) is an attractive approach for "off-the-shelf" CAR T cell immunotherapy. Approaches to efficiently differentiate iPSCs into canonical αβ T cell lineages, while maintaining CAR expression and functionality, however, have been challenging. We report that iPSCs reprogramed from CD62L⁺ naive and memory T cells followed by CD19-CAR engineering and 3D-organoid system differentiation confers products with conventional CD8αβ-positive CAR T cell characteristics. Expanded iPSC CD19-CAR T cells showed comparable antigen-specific activation, degranulation, cytotoxicity, and cytokine secretion compared with conventional CD19-CAR T cells and maintained homogeneous expression of the TCR derived from the initial clone. iPSC CD19-CAR T cells also mediated potent antitumor activity in vivo, prolonging survival of mice with CD19⁺ human tumor xenografts. Our study establishes feasible methodologies to generate highly functional CAR T cells from iPSCs to support the development of "off-the-shelf" manufacturing strategies.

Identification of Neoantigens in Cancer Cells as Targets for Immunotherapy

The clinical benefits of immune checkpoint blockage (ICB) therapy have been widely reported. In patients with cancer, researchers have demonstrated the clinical potential of antitumor cytotoxic T cells that can be reinvigorated or enhanced by ICB. Compared to self-antigens, neoantigens derived from tumor somatic mutations are believed to be ideal immune targets in tumors. Candidate tumor neoantigens can be identified through immunogenomic or immunopeptidomic approaches. Identification of neoantigens has revealed several points of the clinical relevance. For instance, tumor mutation burden (TMB) may be an indicator of immunotherapy. In various cancers, mutation rates accompanying neoantigen loads may be indicative of immunotherapy. Furthermore, mismatch repair-deficient tumors can be eradicated by T cells in ICB treatment. Hence, immunotherapies using vaccines or adoptive T-cell transfer targeting neoantigens are potential innovative strategies. However, significant efforts are required to identify the optimal epitopes. In this review, we summarize the recent progress in the identification of neoantigens and discussed preclinical and clinical studies based on neoantigens. We also discuss the issues remaining to be addressed before clinical applications of these new therapeutic strategies can be materialized.

Sustainable antiviral efficacy of rejuvenated HIV-specific cytotoxic T lymphocytes generated from induced pluripotent stem cells

Persistence of HIV latently infected cells is a barrier to HIV cure. The "kick and kill" strategy for cure includes clearance of the viral reservoir by HIV-specific cytotoxic T lymphocytes (CTLs). However, exhaustion and senescence of T cells accelerates during HIV infection, and does not fully recover, despite complete viral suppression under antiretroviral therapy. We previously established an induced pluripotent stem cell (iPSC) from a parental HIV-specific CTL clone and generated an iPSC-derived rejuvenated HIV-specific CTL clone (iPSC-CTL), which exhibited an early memory phenotype, high proliferation capacity and effector functions in vitro . Here, we assessed the antiviral efficacy of the HIV-specific iPSC-CTL by single- and multiple-round viral suppression assays (VSAs). The HIV-specific iPSC-CTL suppressed viral replication in an HLA-dependent manner with equivalent efficacy to the parental CTL clone in single-round VSA. In multiple-round VSA, however, the ability of the iPSC-CTL to suppress viral replication was longer than that of the parental CTL clone. These results indicate that HIV-specific iPSC-CTL can sustainably exert suppressive pressure on viral replication, suggesting a novel approach to facilitate clearance of the HIV reservoir via adoptive transfer of rejuvenated CTLs.

Importance

Elimination of latently HIV-infected cells is required for HIV cure. In the “kick and kill” strategy proposed for HIV cure, the host immune system, including HIV-specific cytotoxic T lymphocytes (CTLs), play a central role in eliminating HIV antigen-expressing cells following reactivation by latency-reversing agents (LRAs). However, CTL dysfunction due to exhaustion and senescence in chronic HIV infection can be an obstacle to this strategy. Adoptive transfer with effective HIV-specific CTLs may be a solution of this problem. We previously generated an induced pluripotent stem cell (iPSC)-derived rejuvenated HIV-specific CTL clone (iPSC-CTL) with high functional and proliferative capacity. The present study demonstrates that iPSC-CTL can survive and suppress HIV replication in vitro longer than the parental CTL clone, indicating the potential of iPSC-CTL to sustainably exert suppressive pressure on viral replication. Adoptive transfer with rejuvenated HIV-specific CTLs in combination with LRAs may be a new intervention strategy for HIV cure/remission.

TCR-T Immunotherapy: The Challenges and Solutions

T cell receptor-engineered T cell (TCR-T) therapy is free from the limit of surface antigen expression of the target cells, which is a potential cellular immunotherapy for cancer treatment. Significant advances in the treatment of hematologic malignancies with cellular immunotherapy have aroused the interest of researchers in the treatment of solid tumors. Nevertheless, the overall efficacy of TCR-T cell immunotherapy in solid tumors was not significantly high when compared with hematological malignancies. In this article, we pay attention to the barriers of TCR-T cell immunotherapy for solid tumors, as well as the strategies affecting the efficacy of TCR-T cell immunotherapy. To provide some reference for researchers to better overcome the impact of TCR-T cell efficiency in solid tumors.

Prospects for Development of Induced Pluripotent Stem Cell-Derived CAR-Targeted Immunotherapies

Technologies required to generate induced pluripotent stem cells (iPSC) were first described 15 years ago, providing a strong impetus to the field of regenerative medicine. In parallel, immunotherapy has finally emerged as a clinically meaningful modality of cancer therapy. In particular, impressive efficacy has been achieved in patients with selected haematological malignancies using ex vivo expanded autologous T cells engineered to express chimeric antigen receptors (CARs). While solid tumours account for over 90% of human cancer, they currently are largely refractory to this therapeutic approach. Nonetheless, given the considerable innovation taking place worldwide in the CAR field, it is likely that effective solutions for common solid tumours will emerge in the near future. Such a development will create significant new challenges in the scalable delivery of these complex, costly and individualised therapies. CAR-engineered immune cell products that originate from iPSCs offer the potential to generate unlimited numbers of homogeneous, standardised cell products in which multiple defined gene modification events have been introduced to ensure safety, potency and reproducibility. Here, we review some of the emerging strategies in use to engineer CAR-expressing iPSC-derived drug products.

Development of Stem Cell-Derived Immune Cells for Off-the-Shelf Cancer Immunotherapies

Cell-based cancer immunotherapy has revolutionized the treatment of hematological malignancies. Specifically, autologous chimeric antigen receptor-engineered T (CAR-T) cell therapies have received approvals for treating leukemias, lymphomas, and multiple myeloma following unprecedented clinical response rates. A critical barrier to the widespread usage of current CAR-T cell products is their autologous nature, which renders these cellular products patient-selective, costly, and challenging to manufacture. Allogeneic cell products can be scalable and readily administrable but face critical concerns of graft-versus-host disease (GvHD), a life-threatening adverse event in which therapeutic cells attack host tissues, and allorejection, in which host immune cells eliminate therapeutic cells, thereby limiting their antitumor efficacy. In this review, we discuss recent advances in developing stem cell-engineered allogeneic cell therapies that aim to overcome the limitations of current autologous and allogeneic cell therapies, with a special focus on stem cell-engineered conventional αβ T cells, unconventional T (iNKT, MAIT, and γδ T) cells, and natural killer (NK) cells.

Regeneration of antigen-specific T cells by using induced pluripotent stem cell (iPSC) technology

In currently ongoing adoptive T-cell therapies, T cells collected from the patient are given back to the patient after ex vivo cell activation and expansion. In some cases, T cells are transduced with chimeric antigen receptor (CAR) or T-cell receptor (TCR) genes during the ex vivo culture period. Although such strategies have been shown to be effective in some types of cancer, there remain issues to be solved; these methods (i) are time-consuming, (ii) are costly and (iii) it is difficult to guarantee the quality because the products depend on patient-derived T cells. To address these issues, several groups including ours have developed methods in which cytotoxic cells are mass-produced by using induced pluripotent stem cell (iPSC) technology. For the regeneration of T cells, the basic idea is as follows: iPSCs produced from T cells inherit rearranged TCR genes, and thus all regenerated T cells should express the same TCR. Based on this idea, various types of T cells have been regenerated, including conventional cytotoxic T lymphocytes (CTLs), γδT cells, NKT cells and mucosal-associated invariant T (MAIT) cells. On the other hand, any cytotoxic cells can be used as the base cells into which CAR is introduced, and thus iPSC-derived NK cells have been developed. To apply the iPSC-based cell therapy in an allogeneic setting, the authors' group developed a method in which non-T-cell-derived iPSCs are transduced with exogenous TCR genes (TCR-iPSC method). This approach is being prepared for a clinical trial to be realized in Kyoto University Hospital, in which acute myeloid leukemia patients will be treated by the regenerated WT1 antigen-specific CTLs.

Engineered T-cell Receptor T Cells for Cancer Immunotherapy

Engineering immune cells to target cancer is a rapidly advancing technology. The first commercial products, chimeric-antigen receptor (CAR) T cells, are now approved for hematologic malignancies. However, solid tumors pose a greater challenge for cellular therapy, in part because suitable cancer-specific antigens are more difficult to identify and surrounding healthy tissues are harder to avoid. In addition, impaired trafficking of immune cells to solid tumors, the harsh immune-inhibitory microenvironment, and variable antigen density and presentation help tumors evade immune cells targeting cancer-specific antigens. To overcome these obstacles, T cells are being engineered to express defined T-cell receptors (TCR). Given that TCRs target intracellular peptides expressed on tumor MHC molecules, this provides an expanded pool of potential targetable tumor-specific antigens relative to the cell-surface antigens that are targeted by CAR T cells. The affinity of TCR T cells can be tuned to allow for better tumor recognition, even with varying levels of antigen presentation on the tumor and surrounding healthy tissue. Further enhancements to TCR T cells include improved platforms that enable more robust cell expansion and persistence; coadministration of small molecules that enhance tumor recognition and immune activation; and coexpression of cytokine-producing moieties, activating coreceptors, or mediators that relieve checkpoint blockade. Early-phase clinical trials pose logistical challenges involving production, large-scale manufacturing, and more. The challenges and obstacles to successful TCR T-cell therapy, and ways to overcome these and improve anticancer activity and efficacy, are discussed herein.

Enhancing adoptive CD8 T cell therapy by systemic delivery of tumor associated antigens

Adoptive T-cell transfer (ACT) offers a curative therapeutic option for subsets of melanoma and hematological cancer patients. To increase response rates and broaden the applicability of ACT, it is necessary to improve the post-infusion performance of the transferred T cells. The design of improved treatment strategies includes transfer of cells with a less differentiated phenotype. Such T cell subsets have high proliferative potential but require stimulatory signals in vivo to differentiate into tumor-reactive effector T cells. Thus, combination strategies are needed to support the therapeutic implementation of less differentiated T cells. Here we show that systemic delivery of tumor-associated antigens (TAAs) facilitates in vivo priming and expansion of previously non-activated T cells and enhance the cytotoxicity of activated T cells. To achieve this in vivo priming, we use flexible delivery vehicles of TAAs and a TLR7/8 agonist. Contrasting subcutaneous delivery systems, these vehicles accumulate TAAs in the spleen, thereby achieving close proximity to both cross-presenting dendritic cells and transferred T cells, resulting in robust T-cell expansion and anti-tumor reactivity. This TAA delivery platform offers a strategy to safely potentiate the post-infusion performance of T cells using low doses of antigen and TLR7/8 agonist, and thereby enhance the effect of ACT.

Advances in Adoptive Cell Therapy Using Induced Pluripotent Stem Cell-Derived T Cells

Adoptive cell therapy (ACT) using chimeric antigen receptor (CAR) T cells holds impressive clinical outcomes especially in patients who are refractory to other kinds of therapy. However, many challenges hinder its clinical applications. For example, patients who undergo chemotherapy usually have an insufficient number of autologous T cells due to lymphopenia. Long-term ex vivo expansion can result in T cell exhaustion, which reduces the effector function. There is also a batch-to-batch variation during the manufacturing process, making it difficult to standardize and validate the cell products. In addition, the process is labor-intensive and costly. Generation of universal off-the-shelf CAR T cells, which can be broadly given to any patient, prepared in advance and ready to use, would be ideal and more cost-effective. Human induced pluripotent stem cells (iPSCs) provide a renewable source of cells that can be genetically engineered and differentiated into immune cells with enhanced anti-tumor cytotoxicity. This review describes basic knowledge of T cell biology, applications in ACT, the use of iPSCs as a new source of T cells and current differentiation strategies used to generate T cells as well as recent advances in genome engineering to produce next-generation off-the-shelf T cells with improved effector functions. We also discuss challenges in the field and future perspectives toward the final universal off-the-shelf immunotherapeutic products.

Thymus Degeneration and Regeneration

The immune system’s ability to resist the invasion of foreign pathogens and the tolerance to self-antigens are primarily centered on the efficient functions of the various subsets of T lymphocytes. As the primary organ of thymopoiesis, the thymus performs a crucial role in generating a self-tolerant but diverse repertoire of T cell receptors and peripheral T cell pool, with the capacity to recognize a wide variety of antigens and for the surveillance of malignancies. However, cells in the thymus are fragile and sensitive to changes in the external environment and acute insults such as infections, chemo- and radiation-therapy, resulting in thymic injury and degeneration. Though the thymus has the capacity to self-regenerate, it is often insufficient to reconstitute an intact thymic function. Thymic dysfunction leads to an increased risk of opportunistic infections, tumor relapse, autoimmunity, and adverse clinical outcome. Thus, exploiting the mechanism of thymic regeneration would provide new therapeutic options for these settings. This review summarizes the thymus’s development, factors causing thymic injury, and the strategies for improving thymus regeneration.

Single-cell transcriptome of early hematopoiesis guides arterial endothelial-enhanced functional T cell generation from human PSCs

Hematopoietic differentiation of human pluripotent stem cells (hPSCs) requires orchestration of dynamic cell and gene regulatory networks but often generates blood cells that lack natural function. Here, we performed extensive single-cell transcriptomic analyses to map fate choices and gene expression patterns during hematopoietic differentiation of hPSCs and showed that oxidative metabolism was dysregulated during in vitro directed differentiation. Applying hypoxic conditions at the stage of endothelial-to-hematopoietic transition in vitro effectively promoted the development of arterial specification programs that governed the generation of hematopoietic progenitor cells (HPCs) with functional T cell potential. Following engineered expression of the anti-CD19 chimeric antigen receptor, the T cells generated from arterial endothelium-primed HPCs inhibited tumor growth both in vitro and in vivo. Collectively, our study provides benchmark datasets as a resource to further understand the origins of human hematopoiesis and represents an advance in guiding in vitro generation of functional T cells for clinical applications.

Specific Blood Cells Derived from Pluripotent Stem Cells: An Emerging Field with Great Potential in Clinical Cell Therapy

Widely known for self-renewal and multilineage differentiation, stem cells can be differentiated into all specialized tissues and cells in the body. In the past few years, a number of researchers have focused on deriving hematopoietic stem cells (HSCs) from pluripotent stem cells (PSCs) as alternative sources for clinic. Existing findings demonstrated that it is feasible to obtain HSCs and certain mature blood lineages from PSCs, except for several issues to be addressed. This short review outlines the technologies used for hematopoietic differentiation in recent years. In addition, the therapeutic value of PSCs as a potential source of various blood cells is also discussed as well as its challenges and directions in future clinical applications.

The Promise of Personalized TCR-Based Cellular Immunotherapy for Cancer Patients

Mutation-derived neoantigens are now established as attractive targets for cancer immunotherapy. The field of adoptive T cell transfer (ACT) therapy was significantly reshaped by tumor neoantigens and is now moving towards the genetic engineering of T cells with neoantigen-specific T cell receptors (TCRs). Yet, the identification of neoantigen-reactive TCRs remains challenging and the process needs to be adapted to clinical timelines. In addition, the state of recipient T cells for TCR transduction is critical and can affect TCR-ACT efficacy. Here we provide an overview of the main strategies for TCR-engineering, describe the selection and expansion of optimal carrier cells for TCR-ACT and discuss the next-generation methods for rapid identification of relevant TCR candidates for gene transfer therapy.

Cell Fate Reprogramming in the Era of Cancer Immunotherapy

Advances in understanding how cancer cells interact with the immune system allowed the development of immunotherapeutic strategies, harnessing patients' immune system to fight cancer. Dendritic cell-based vaccines are being explored to reactivate anti-tumor adaptive immunity. Immune checkpoint inhibitors and chimeric antigen receptor T-cells (CAR T) were however the main approaches that catapulted the therapeutic success of immunotherapy. Despite their success across a broad range of human cancers, many challenges remain for basic understanding and clinical progress as only a minority of patients benefit from immunotherapy. In addition, cellular immunotherapies face important limitations imposed by the availability and quality of immune cells isolated from donors. Cell fate reprogramming is offering interesting alternatives to meet these challenges. Induced pluripotent stem cell (iPSC) technology not only enables studying immune cell specification but also serves as a platform for the differentiation of a myriad of clinically useful immune cells including T-cells, NK cells, or monocytes at scale. Moreover, the utilization of iPSCs allows introduction of genetic modifications and generation of T/NK cells with enhanced anti-tumor properties. Immune cells, such as macrophages and dendritic cells, can also be generated by direct cellular reprogramming employing lineage-specific master regulators bypassing the pluripotent stage. Thus, the cellular reprogramming toolbox is now providing the means to address the potential of patient-tailored immune cell types for cancer immunotherapy. In parallel, development of viral vectors for gene delivery has opened the door for in vivo reprogramming in regenerative medicine, an elegant strategy circumventing the current limitations of in vitro cell manipulation. An analogous paradigm has been recently developed in cancer immunotherapy by the generation of CAR T-cells in vivo. These new ideas on endogenous reprogramming, cross-fertilized from the fields of regenerative medicine and gene therapy, are opening exciting avenues for direct modulation of immune or tumor cells in situ, widening our strategies to remove cancer immunotherapy roadblocks. Here, we review current strategies for cancer immunotherapy, summarize technologies for generation of immune cells by cell fate reprogramming as well as highlight the future potential of inducing these unique cell identities in vivo, providing new and exciting tools for the fast-paced field of cancer immunotherapy.

ReMeDy: a platform for integrating and sharing published stem cell research data with a focus on iPSC trials

ABSTRACT

Recent regenerative medicine studies have emphasized the need for increased standardization, harmonization and sharing of information related to stem cell product characterization, to help drive these innovative interventions toward public availability and to increase collaboration in the scientific community. Although numerous attempts and numerous databases have been made to manage these data, a platform that incorporates all the heterogeneous data collected from stem cell projects into a harmonized project-based framework is still lacking. The aim of the database, which is described in this study, is to provide an intelligent informatics solution that integrates comprehensive characterization of diverse stem cell product characteristics with research subject and project outcome information. In the resulting platform, heterogeneous data are validated using predefined ontologies and stored in a relational database, to ensure data quality and ease of access. Testing was performed using 51 published, publically available induced pluripotent stem cell projects conducted in clinical, preclinical and in-vitro evaluations. Future aims of this project include further increasing the database size to include all published stem cell trials and develop additional data visualization tools to improve usability. Our testing demonstrated the robustness of the proposed platform, by seamlessly harmonizing diverse common data elements, and the potential of this platform for driving knowledge generation from the aggregation and harmonization of these diverse data.

DATABASE URL

https://remedy.mssm.edu/.

Improved safety of induced pluripotent stem cell-derived antigen-presenting cell-based cancer immunotherapy

The tumorigenicity and toxicity of induced pluripotent stem cells (iPSCs) and their derivatives are major safety concerns in their clinical application. Recently, we developed granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing proliferating myeloid cells (GM-pMCs) from mouse iPSCs as a source of unlimited antigen-presenting cells for use in cancer immunotherapy. As GM-pMCs are generated by introducing c-Myc and Csf2 into iPSC-derived MCs and are dependent on self-produced GM-CSF for proliferation, methods to control their proliferation after administration should be introduced to improve safety. In this study, we compared the efficacy of two promising suicide gene systems, herpes simplex virus-thymidine kinase (HSV-TK)/ganciclovir (GCV) and inducible caspase-9 (iCasp9)/AP1903, for safeguarding GM-pMCs in cancer immunotherapy. The expression of HSV-TK or iCasp9 did not impair the fundamental properties of GM-pMCs. Both of these suicide gene-expressing cells selectively underwent apoptosis after treatment with the corresponding apoptosis-inducing drug, and they were promptly eliminated in vivo. iCasp9/AP1903 induced apoptosis more efficiently than HSV-TK/GCV. Furthermore, high concentrations of GCV were toxic to cells not expressing HSV-TK, whereas AP1903 was bioinert. These results suggest that iCasp9/AP1903 is superior to HSV-TK/GCV in terms of both safety and efficacy when controlling the fate of GM-pMCs after priming antitumor immunity.

Induced Pluripotent Stem Cells (iPSCs) Provide a Potentially Unlimited T Cell Source for CAR-T Cell Development and Off-the-Shelf Products

Chimeric antigen receptor T (CAR-T) cell therapy has been increasingly conducted for cancer patients in clinical settings. Progress in this therapeutic approach is hampered by the lack of a solid manufacturing process, T lymphocytes, and tumor-specific antigens. T cell source used in CAR-T cell therapy is derived predominantly from the patient's own T lymphocytes, which makes this approach impracticable to patients with progressive diseases and T leukemia. The generation of autologous CAR-T cells is time-consuming due to the lack of readily available T lymphocytes and is not applicable for third-party patients. Pluripotent stem cells, such as human induced pluripotent stem cells (hiPSCs), can provide an unlimited T cell source for CAR-T cell development with the potential of generating off-the-shelf T cell products. T-iPSCs (iPSC-derived T cells) are phenotypically defined, expandable, and as functional as physiological T cells. The combination of iPSC and CAR technologies provides an exciting opportunity to oncology and greatly facilitates cell-based therapy for cancer patients. However, T-iPSCs, in combination with CARs, are at the early stage of development and need further pre-clinical and clinical studies. This review will critically discuss the progress made in iPSC-derived T cells and provides a roadmap for the development of CAR iPSC-derived T cells and off-the-shelf T-iPSCs.

The therapeutic potential of multiclonal tumoricidal T cells derived from tumor infiltrating lymphocyte-1derived iPS cells

Tumor-infiltrating lymphocytes (TIL), which include tumor-specific T lymphocytes with frequency, are used for adoptive cell transfer therapy (ACT) in clinical practice. The optimization of TIL preparation has been investigated to reduce the senescence and increase the abundance of TIL, as both the quality and quantity of the transferred cells have great influence on the outcome of TIL-based ACT (TIL-ACT). Considering the effects of cell reprogramming on senescence, we expected that the anti-tumor effect could be enhanced by TIL regeneration. To confirm this hypothesis, we established tumor-specific TIL-derived iPS cells (TIL-iPSC) with human colorectal cancer specimens. T cells differentiated from TIL-iPSC (TIL-iPS-T) retained not only intrinsic T cell functions and tumor specificity, but also exhibited improved proliferation capacity and additional killing activity. Moreover, less differentiated profiles and prolonged persistency were seen in TIL-iPS-T compared with primary cells. Our findings imply that iPSC technology has great potential for TIL-ACT.

Generation of highly proliferative rejuvenated cytotoxic T cell clones through pluripotency reprogramming for adoptive immunotherapy

Adoptive immunotherapy has emerged as a powerful approach to cure cancer and chronic infections. Currently, the generation of a massive number of T cells that provide long-lasting immunity is challenged by exhaustion and differentiation-associated senescence, which inevitably arise during in vitro cloning and expansion. To circumvent these problems, several studies have proposed an induced pluripotent stem cell (iPSC)-mediated rejuvenation strategy to revitalize the exhausted/senescent T-cell clones. Because iPSC-derived cytotoxic T lymphocytes (iPSC-CTLs) generated via commonly used monolayer systems have unfavorable innate-like features such as aberrant natural killer (NK) activity and limited replication potential, we modified the redifferentiation culture to generate CD8αβ⁺CD5⁺CCR7⁺CD45RA⁺CD56^- adaptive iPSC-CTLs. The modified iPSC-CTLs exhibited early memory phenotype, including high replicative capacity and the ability to give rise to potent effector cells. In expansion culture with an optimized cytokine cocktail, iPSC-CTLs proliferated more than 10¹⁵-fold in a feeder-free condition. Our redifferentiation and expansion package of early memory iPSC-CTLs could supply memory and effector T cells for both autologous and allogeneic immunotherapies.

Neoantigen Specific T Cells Derived From T Cell-Derived Induced Pluripotent Stem Cells for the Treatment of Hepatocellular Carcinoma: Potential and Challenges

Immunotherapy has become an indispensable part of the comprehensive treatment of hepatocellular carcinoma (HCC). Immunotherapy has proven effective in patients with early HCC, advanced HCC, or HCC recurrence after liver transplantation. Clinically, the most commonly used immunotherapy is immune checkpoint inhibition using monoclonal antibodies, such as CTLA-4 and PD-1. However, it cannot fundamentally solve the problems of a weakened immune system and inactivation of immune cells involved in killing tumor cells. T cells can express tumor antigen-recognizing T cell receptors (TCRs) or chimeric antigen receptors (CARs) on the cell surface through gene editing to improve the specificity and responsiveness of immune cells. According to previous studies, TCR-T cell therapy is significantly better than CAR-T cell therapy in the treatment of solid tumors and is one of the most promising immune cell therapies for solid tumors so far. However, its application in the treatment of HCC is still being researched. Technological advancements in induction and redifferentiation of induced pluripotent stem cells (iPSCs) allow us to use T cells to induce T cell-derived iPSCs (T-iPSCs) and then differentiate them into TCR-T cells. This has allowed a convenient strategy to study HCC models and explore optimal treatment strategies. This review gives an overview of the major advances in the development of protocols to generate neoantigen-specific TCR-T cells from T-iPSCs. We will also discuss their potential and challenges in the treatment of HCC.

Generation of hypoimmunogenic T cells from genetically engineered allogeneic human induced pluripotent stem cells

Avoiding the immune rejection of transplanted T cells is central to the success of allogeneic cancer immunotherapies. One solution to protecting T-cell grafts from immune rejection involves the deletion of allogeneic factors and of factors that activate cytotoxic immune cells. Here we report the generation of hypoimmunogenic cancer-antigen-specific T cells derived from induced pluripotent stem cells (iPSCs) lacking β₂-microglobulin, the class-II major histocompatibility complex (MHC) transactivator and the natural killer (NK) cell-ligand poliovirus receptor CD155, and expressing single-chain MHC class-I antigen E. In mouse models of CD20-expressing leukaemia or lymphoma, differentiated T cells expressing a CD20 chimeric antigen receptor largely escaped recognition by NKG2A⁺ and DNAM-1⁺ NK cells and by CD8 and CD4 T cells in the allogeneic recipients while maintaining anti-tumour potency. Hypoimmunogenic iPSC-derived T cells may contribute to the creation of off-the-shelf T cell immunotherapies.

Generation of macrophages with altered viral sensitivity from genome-edited rhesus macaque iPSCs to model human disease

Because of their close biological similarity to humans, non-human primate (NHP) models are very useful for the development of induced pluripotent stem cell (iPSC)-based cell and regenerative organ transplantation therapies. However, knowledge on the establishment, differentiation, and genetic modification of NHP-iPSCs, especially rhesus macaque iPSCs, is limited. We succeeded in establishing iPSCs from the peripheral blood of rhesus macaques (Rh-iPSCs) by combining the Yamanaka reprograming factors and two inhibitors (GSK-3 inhibitor [CHIR 99021] and MEK1/2 inhibitor [PD0325901]) and differentiated the cells into functional macrophages through hematopoietic progenitor cells. To confirm feasibility of the Rh-iPSC-derived macrophages as a platform for bioassays to model diseases, we knocked out TRIM5 gene in Rh-iPSCs by CRISPR-Cas9, which is a species-specific HIV resistance factor. TRIM5 knockout (KO) iPSCs had the same differentiation potential to macrophages as did Rh-iPSCs, but the differentiated macrophages showed a gain of sensitivity to HIV infection in vitro. Our reprogramming, gene editing, and differentiation protocols used to obtain Rh-iPSC-derived macrophages can be applied to other gene mutations, expanding the number of NHP gene therapy models.

Extracellular laminin regulates hematopoietic potential of pluripotent stem cells through integrin β1-ILK-β-catenin-JUN axis

Recombinant matrices have enabled feeder cell-free maintenance cultures of human pluripotent stem cells (hPSCs), with laminin 511-E8 fragment (LM511-E8) being widely used. However, we herein report that hPSCs maintained on LM511-E8 resist differentiating to multipotent hematopoietic progenitor cells (HPCs), unlike hPSCs maintained on LM421-E8 or LM121-E8. The latter two LM-E8s bound weakly to hPSCs compared with LM511-E8 and activated the canonical Wnt/β-catenin signaling pathway. Moreover, the extracellular LM-E8-dependent preferential hematopoiesis was associated with a higher expression of integrin β1 (ITGB1) and downstream integrin-linked protein kinase (ILK), β-catenin and phosphorylated JUN. Accordingly, the lower coating concentration of LM511-E8 or addition of a Wnt/β-catenin signaling activator, CHIR99021, facilitated higher HPC yield. In contrast, the inhibition of ILK, Wnt or JNK by inhibitors or mRNA knockdown suppressed the HPC yield. These findings suggest that extracellular laminin scaffolds modulate the hematopoietic differentiation potential of hPSCs by activating the ITGB1-ILK-β-catenin-JUN axis at the undifferentiated stage. Finally, the combination of low-concentrated LM511-E8 and a revised hPSC-sac method, which adds bFGF, SB431542 and heparin to the conventional method, enabled a higher yield of HPCs and higher rate for definitive hematopoiesis, suggesting a useful protocol for obtaining differentiated hematopoietic cells from hPSCs in general.

Engineering of human induced pluripotent stem cells via human artificial chromosome vectors for cell therapy and disease modeling

Genetic engineering of induced pluripotent stem cells (iPSCs) holds great promise for gene and cell therapy as well as drug discovery. However, there are potential concerns regarding the safety and control of gene expression using conventional vectors such as viruses and plasmids. Although human artificial chromosome (HAC) vectors have several advantages as a gene delivery vector, including stable episomal maintenance and the ability to carry large gene inserts, the full potential of HAC transfer into iPSCs still needs to be explored. Here, we provide evidence of a HAC transfer into human iPSCs by microcell-mediated chromosome transfer via measles virus envelope proteins for various applications, including gene and cell therapy, establishment of versatile human iPSCs capable of gene loading and differentiation into T cells, and disease modeling for aneuploidy syndrome. Thus, engineering of human iPSCs via desired HAC vectors is expected to be widely applied in biomedical research.

A clinically applicable and scalable method to regenerate T-cells from iPSCs for off-the-shelf T-cell immunotherapy

Clinical successes demonstrated by chimeric antigen receptor T-cell immunotherapy have facilitated further development of T-cell immunotherapy against wide variety of diseases. One approach is the development of “off-the-shelf” T-cell sources. Technologies to generate T-cells from pluripotent stem cells (PSCs) may offer platforms to produce “off-the-shelf” and synthetic allogeneic T-cells. However, low differentiation efficiency and poor scalability of current methods may compromise their utilities. Here we show improved differentiation efficiency of T-cells from induced PSCs (iPSCs) derived from an antigen-specific cytotoxic T-cell clone, or from T-cell receptor (TCR)-transduced iPSCs, as starting materials. We additionally describe feeder-free differentiation culture systems that span from iPSC maintenance to T-cell proliferation phases, enabling large-scale regenerated T-cell production. Moreover, simultaneous addition of SDF1α and a p38 inhibitor during T-cell differentiation enhances T-cell commitment. The regenerated T-cells show TCR-dependent functions in vitro and are capable of in vivo anti-tumor activity. This system provides a platform to generate a large number of regenerated T-cells for clinical application and investigate human T-cell differentiation and biology.

T-cell immunotherapies, such as CAR-T immunotherapy, are being developed against a wide variety of diseases. Here the authors report the feeder-free, scalable differentiation of human induced pluripotent cells (iPSCs) to T-cells with T-cell receptor dependent anti-tumour function in vitro and in vivo.

Rapid and Reproducible Differentiation of Hematopoietic and T Cell Progenitors From Pluripotent Stem Cells

Cell therapy using T cells has revolutionized medical care in recent years but limitations are associated with the difficulty of genome editing of the cells, the production of a sufficient number of cells and standardization of the product. Human pluripotent stem cells (hPSCs) can self-renew and differentiate into T cells to provide a standardized homogenous product of defined origin in indefinite quantity, therefore they are of great potential to alleviate limitations of therapeutic T cell production. The differentiation of hPSCs takes place in two steps: first the induction of hematopoietic stem/progenitor cells (HSPCs), then the induction of lymphopoiesis by Notch signaling. However, the differentiation of T cells from hPSCs can be difficult and lack reproducibility. One parameter that needs to be better assessed is the potential of DLL1 vs. DLL4 ligands of the Notch pathway to induce T cells. In addition, culture of hPSCs is labor-intensive and not compatible with GMP production, especially when they are cultured on feeder cells. Thus, the definition of a robust GMP-compatible differentiation protocol from hPSCs cultured in feeder-free conditions would increase the accessibility to off-the-shelf hematopoietic and T cell progenitors derived from hPSCs. In this article, we describe an efficient, rapid and reproducible protocol for the generation of hematopoietic and T cell progenitors in two steps: (1) generation of HSPCs from embryoid bodies (EB) in serum free medium and GMP-compatible feeder-free systems, (2) directed differentiation of hPSC-derived HSPCs into T-cell progenitors in the presence of bone marrow stromal cells expressing Notch-ligands OP9-DLL1 vs. OP9-DLL4.

Multilineage differentiation potential of hematoendothelial progenitors derived from human induced pluripotent stem cells

BACKGROUND

Human induced pluripotent stem cells (hiPSCs) offer a renewable source of cells for the generation of hematopoietic cells for cell-based therapy, disease modeling, and drug screening. However, current serum/feeder-free differentiation protocols rely on the use of various cytokines, which makes the process very costly or the generation of embryoid bodies (EBs), which are labor-intensive and can cause heterogeneity during differentiation. Here, we report a simple feeder and serum-free monolayer protocol for efficient generation of iPSC-derived multipotent hematoendothelial progenitors (HEPs), which can further differentiate into endothelial and hematopoietic cells including erythroid and T lineages.

METHODS

Formation of HEPs from iPSCs was initiated by inhibition of GSK3 signaling for 2 days followed by the addition of VEGF and FGF2 for 3 days. The HEPs were further induced toward mature endothelial cells (ECs) in an angiogenic condition and toward T cells by co-culturing with OP9-DL1 feeder cells. Endothelial-to-hematopoietic transition (EHT) of the HEPs was further promoted by supplementation with the TGF-β signaling inhibitor. Erythroid differentiation was performed by culturing the hematopoietic stem/progenitor cells (HSPCs) in a three-stage erythroid liquid culture system.

RESULTS

Our protocol significantly enhanced the number of KDR⁺ CD34⁺ CD31⁺ HEPs on day 5 of differentiation. Further culture of HEPs in angiogenic conditions promoted the formation of mature ECs, which expressed CD34, CD31, CD144, vWF, and ICAM-1, and could exhibit the formation of vascular-like network and acetylated low-density lipoprotein (Ac-LDL) uptake. In addition, the HEPs were differentiated into CD8⁺ T lymphocytes, which could be expanded up to 34-fold upon TCR stimulation. Inhibition of TGF-β signaling at the HEP stage promoted EHT and yielded a large number of HSPCs expressing CD34 and CD43. Upon erythroid differentiation, these HSPCs were expanded up to 40-fold and displayed morphological changes following stages of erythroid development.

CONCLUSION

This protocol offers an efficient and simple approach for the generation of multipotent HEPs and could be adapted to generate desired blood cells in large numbers for applications in basic research including developmental study, disease modeling, and drug screening as well as in regenerative medicine.

Establishment of a heart-on-a-chip microdevice based on human iPS cells for the evaluation of human heart tissue function

Human iPS cell (iPSC)-derived cardiomyocytes (CMs) hold promise for drug discovery for heart diseases and cardiac toxicity tests. To utilize human iPSC-derived CMs, the establishment of three-dimensional (3D) heart tissues from iPSC-derived CMs and other heart cells, and a sensitive bioassay system to depict physiological heart function are anticipated. We have developed a heart-on-a-chip microdevice (HMD) as a novel system consisting of dynamic culture-based 3D cardiac microtissues derived from human iPSCs and microelectromechanical system (MEMS)-based microfluidic chips. The HMDs could visualize the kinetics of cardiac microtissue pulsations by monitoring particle displacement, which enabled us to quantify the physiological parameters, including fluidic output, pressure, and force. The HMDs demonstrated a strong correlation between particle displacement and the frequency of external electrical stimulation. The transition patterns were validated by a previously reported versatile video-based system to evaluate contractile function. The patterns are also consistent with oscillations of intracellular calcium ion concentration of CMs, which is a fundamental biological component of CM contraction. The HMDs showed a pharmacological response to isoproterenol, a β-adrenoceptor agonist, that resulted in a strong correlation between beating rate and particle displacement. Thus, we have validated the basic performance of HMDs as a resource for human iPSC-based pharmacological investigations.

Establishment of a heart-on-a-chip microdevice based on human iPS cells for the evaluation of human heart tissue function

Human iPS cell (iPSC)-derived cardiomyocytes (CMs) hold promise for drug discovery for heart diseases and cardiac toxicity tests. To utilize human iPSC-derived CMs, the establishment of three-dimensional (3D) heart tissues from iPSC-derived CMs and other heart cells, and a sensitive bioassay system to depict physiological heart function are anticipated. We have developed a heart-on-a-chip microdevice (HMD) as a novel system consisting of dynamic culture-based 3D cardiac microtissues derived from human iPSCs and microelectromechanical system (MEMS)-based microfluidic chips. The HMDs could visualize the kinetics of cardiac microtissue pulsations by monitoring particle displacement, which enabled us to quantify the physiological parameters, including fluidic output, pressure, and force. The HMDs demonstrated a strong correlation between particle displacement and the frequency of external electrical stimulation. The transition patterns were validated by a previously reported versatile video-based system to evaluate contractile function. The patterns are also consistent with oscillations of intracellular calcium ion concentration of CMs, which is a fundamental biological component of CM contraction. The HMDs showed a pharmacological response to isoproterenol, a β-adrenoceptor agonist, that resulted in a strong correlation between beating rate and particle displacement. Thus, we have validated the basic performance of HMDs as a resource for human iPSC-based pharmacological investigations.

Leveraging Endogenous Dendritic Cells to Enhance the Therapeutic Efficacy of Adoptive T-Cell Therapy and Checkpoint Blockade

Adoptive cell therapy (ACT), based on treatment with autologous tumor infiltrating lymphocyte (TIL)-derived or genetically modified chimeric antigen receptor (CAR) T cells, has become a potentially curative therapy for subgroups of patients with melanoma and hematological malignancies. To further improve response rates, and to broaden the applicability of ACT to more types of solid malignancies, it is necessary to explore and define strategies that can be used as adjuvant treatments to ACT. Stimulation of endogenous dendritic cells (DCs) alongside ACT can be used to promote epitope spreading and thereby decrease the risk of tumor escape due to target antigen downregulation, which is a common cause of disease relapse in initially responsive ACT treated patients. Addition of checkpoint blockade to ACT and DC stimulation might further enhance response rates by counteracting an eventual inactivation of infused and endogenously primed tumor-reactive T cells. This review will outline and discuss therapeutic strategies that can be utilized to engage endogenous DCs alongside ACT and checkpoint blockade, to strengthen the anti-tumor immune response.

Regeneration of Tumor-Antigen-Specific Cytotoxic T Lymphocytes from iPSCs Transduced with Exogenous TCR Genes

In the current adoptive T cell therapy, T cells from a patient are given back to that patient after ex vivo activation, expansion, or genetic manipulation. However, such strategy depends on the quality of the patient’s T cells, sometimes leading to treatment failure. It would therefore be ideal to use allogeneic T cells as “off-the-shelf” T cells. To this aim, we have been developing a strategy where potent tumor-antigen-specific cytotoxic T lymphocytes (CTLs) are regenerated from T-cell-derived induced pluripotent stem cells (T-iPSCs). However, certain issues still remain that make it difficult to establish highly potent T-iPSCs: poor reprogramming efficiency of T cells into iPSCs and high variability in the differentiation capability of each T-iPSC clone. To expand the versatility of this approach, we thought of a method to produce iPSCs equivalent to T-iPSCs, namely, iPSCs transduced with exogenous T cell receptor (TCR) genes (TCR-iPSCs). To test this idea, we first cloned TCR genes from WT1-specific CTLs regenerated from T-iPSCs and then established WT1-TCR-iPSCs. We show that the regenerated CTLs from TCR-iPSCs exerted cytotoxic activity comparable to those from T-iPSCs against WT1 peptide-loaded cell line in in vitro model. These results collectively demonstrate the feasibility of the TCR-iPSC strategy.

New trends in cellular therapy

Regenerative therapies, including both gene and cellular therapies, aim to induce regeneration of cells, tissues and organs and restore their functions. In this short Spotlight, we summarize the latest advances in cellular therapies using pluripotent stem cells (PSCs), highlighting the current status of clinical trials using induced (i)PSC-derived cells. We also discuss the different cellular products that might be used in clinical studies, and consider safety issues and other challenges in iPSC-based cell therapy.

Breaking Bottlenecks for the TCR Therapy of Cancer

Immune checkpoint inhibitors have redefined the treatment of cancer, but their efficacy depends critically on the presence of sufficient tumor-specific lymphocytes, and cellular immunotherapies develop rapidly to fill this gap. The paucity of suitable extracellular and tumor-associated antigens in solid cancers necessitates the use of neoantigen-directed T-cell-receptor (TCR)-engineered cells, while prevention of tumor evasion requires combined targeting of multiple neoepitopes. These can be currently identified within 2 weeks by combining cutting-edge next-generation sequencing with bioinformatic pipelines and used to select tumor-reactive TCRs in a high-throughput manner for expeditious scalable non-viral gene editing of autologous or allogeneic lymphocytes. "Young" cells with a naive, memory stem or central memory phenotype can be additionally armored with "next-generation" features against exhaustion and the immunosuppressive tumor microenvironment, where they wander after reinfusion to attack heavily pretreated and hitherto hopeless neoplasms. Facilitated by major technological breakthroughs in critical manufacturing steps, based on a solid preclinical rationale, and backed by rapidly accumulating evidence, TCR therapies break one bottleneck after the other and hold the promise to become the next immuno-oncological revolution.

Practical choice for robust and efficient differentiation of human pluripotent stem cells

Human pluripotent stem cells (hPSCs) have the distinct advantage of being able to differentiate into cells of all three germ layers. Target cells or tissues derived from hPSCs have many uses such as drug screening, disease modeling, and transplantation therapy. There are currently a wide variety of differentiation methods available. However, most of the existing differentiation methods are unreliable, with uneven differentiation efficiency and poor reproducibility. At the same time, it is difficult to choose the optimal method when faced with so many differentiation schemes, and it is time-consuming and costly to explore a new differentiation approach. Thus, it is critical to design a robust and efficient method of differentiation. In this review article, we summarize a comprehensive approach in which hPSCs are differentiated into target cells or organoids including brain, liver, blood, melanocytes, and mesenchymal cells. This was accomplished by employing an embryoid body-based three-dimensional (3D) suspension culture system with multiple cells co-cultured. The method has high stable differentiation efficiency compared to the conventional 2D culture and can meet the requirements of clinical application. Additionally, ex vivo co-culture models might be able to constitute organoids that are highly similar or mimic human organs for potential organ transplantation in the future.

Targeted Cellular Micropharmacies: Cells Engineered for Localized Drug Delivery

The recent emergence of engineered cellular therapies, such as Chimeric antigen receptor (CAR) CAR T and T cell receptor (TCR) engineered T cells, has shown great promise in the treatment of various cancers. These agents aggregate and expand exponentially at the tumor site, resulting in potent immune activation and tumor clearance. Moreover, the ability to elaborate these cells with therapeutic agents, such as antibodies, enzymes, and immunostimulatory molecules, presents an unprecedented opportunity to specifically modulate the tumor microenvironment through cell-mediated drug delivery. This unique pharmacology, combined with significant advances in synthetic biology and cell engineering, has established a new paradigm for cells as vectors for drug delivery. Targeted cellular micropharmacies (TCMs) are a revolutionary new class of living drugs, which we envision will play an important role in cancer medicine and beyond. Here, we review important advances and considerations underway in developing this promising advancement in biological therapeutics.

Induced Pluripotent Stem Cell (iPSC)-Derived Lymphocytes for Adoptive Cell Immunotherapy: Recent Advances and Challenges

Purpose of Review

In the rapidly developing field of adoptive cell immunotherapy, there is urgent need for discoveries that would improve outcomes, extend the applicability, and reduce the costs. Induced pluripotent stem cells (iPSC) can be a source of broadly applicable cellular immunotherapeutics, which have been manufactured, validated, and banked in advance, and can be applied across HLA barriers. Here, we discuss the recent advances and challenges in the generation of iPSC-derived cellular products for cancer therapy.

Recent Findings

iPSCs can be differentiated to functional tumor-specific T and NK cells in vitro with demonstrable in vitro and in vivo anti-tumor activity. Genetic modifications employed at the iPSC level can deliver desirable immunotherapeutic attributes to the generated immune effectors. iPSC-NK cells are currently evaluated in a clinical setting and pre-clinical testing of iPSC-T cells shows promising results but their production seems more challenging.

Summary

The use of iPSCs for the generation of tumor-targeting T/NK cells constitutes a feasible strategy to overcome limitations in manufacturing, efficacy, and applicability of cellular therapeutics.

CAR T cell therapy

Chimeric antigen receptor (CAR) is generated by fusing a cancer-specific antibody's antigen recognition site with costimulatory molecules such as CD28 and CD3ζ. T cells transduced with CAR recognizes cancer-specific antigens and kill cancer cells. The effect of CD19-targeted CAR T cells on B-cell hematologic cancer is surprising and has already been approved in many countries including Japan. More targets for several kinds of cancers are being searched now. We have also shown that CAR T cells specific for activated integrin β7 are highly effective for multiple myeloma in pre-clinical tests.

Hematopoietic lineage-converted T cells carrying tumor-associated antigen-recognizing TCRs effectively kill tumor cells

Tumor-associated antigen (TAA) T-cell receptor (TCR) gene-engineered T cells exhibit great potential in antitumor immunotherapy. Considering the high costs and low availability of patient-derived peripheral blood T cells, substantial efforts have been made to explore alternatives to natural T cells. We previously reported that enforced expression of Hoxb5 converted B cells into induced T (iT) cells in vivo Here, we successfully regenerated naive OT1 (major histocompatibility complex I restricted ovalbumin antigen) iT cells (OT1-iT) in vivo by expressing Hoxb5 in pro-pre-B cells in the OT1 transgenic mouse. The OT1-iT cells can be activated and expanded in vitro in the presence of tumor cells. Particularly, these regenerated OT1-iT cells effectively eradicated tumor cells expressing the TAA (ovalbumin) both in vitro and in vivo This study provides insights into the translational applications of blood lineage-transdifferentiated T cells in immunotherapy.

Genome engineering of induced pluripotent stem cells to manufacture natural killer cell therapies

Natural killer (NK) cells play a crucial role in host immunity by detecting cells that downregulate MHC class I presentation and upregulate stress ligands, as commonly seen in cancers. Current NK therapies using primary NK cells are prone to manufacturing issues related to expansion and storage. Alternative cell sources utilizing immortalized NK cell lines require irradiation and are dependent on systemic IL-2 administration, which has been associated with adverse effects. In contrast, NK cells differentiated from induced pluripotent stem cells (iPSC-NK cells) offer an off-the-shelf alternative that may overcome these bottlenecks. The development of a serum-free and feeder-free differentiation protocol allows for the manufacturing of clinically adaptable iPSC-NK cells that are equally as effective as primary NK cells and the NK-92 cell line for many indications. Moreover, genetic modifications targeting NK-mediated antibody-dependent cellular cytotoxicity capabilities, cytotoxicity, and checkpoint inhibitors may increase the therapeutic potential of iPSC-NK products. This review will highlight the current sources for NK therapies and their respective constraints, discuss recent developments in the manufacturing and genetic engineering of iPSC-NK cells, and provide an overview of ongoing clinical trials using NK cells.

SARS-CoV-2 infection and stem cells: Interaction and intervention

The emergence of the novel severe acute respiratory coronavirus 2 (SARS-CoV-2) in China and its rapid national and international spread have created a global health emergency. The resemblance with SARS-CoV in spike protein suggests that SARS-CoV-2 employs spike-driven entry into angiotensin-converting enzyme 2 (ACE2)-expressing cells. From a stem cell perspective, this review focuses on the possible involvement of ACE2⁺ stem/progenitor cells from both the upper and lower respiratory tracts in coronavirus infection. Viral infection-associated acute respiratory distress syndrome and acute lung injury occur because of dysregulation of the immune response. Mesenchymal stem cells appear to be a promising cell therapy given that they favorably modulate the immune response to reduce lung injury. The use of exogenous stem cells may lead to lung repair. Therefore, intervention by transplantation of exogenous stem cells may be required to replace, repair, remodel, and regenerate lung tissue in survivors infected with coronavirus. Ultimately, vaccines, natural killer cells and induced-pluripotent stem cell-derived virus-specific cytotoxic T lymphocytes may offer off-the-shelf therapeutics for preventing coronavirus reemergence.

Induced Pluripotent Stem Cells: Reprogramming Platforms and Applications in Cell Replacement Therapy

The generation of induced pluripotent stem cells (iPSCs) from differentiated mature cells is one of the most promising technologies in the field of regenerative medicine. The ability to generate patient-specific iPSCs offers an invaluable reservoir of pluripotent cells, which could be genetically engineered and differentiated into target cells to treat various genetic and degenerative diseases once transplanted, hence counteracting the risk of graft versus host disease. In this context, we review the scientific research streams that lead to the emergence of iPSCs, the roles of reprogramming factors in reprogramming to pluripotency, and the reprogramming strategies. As iPSCs serve tremendous correction potentials for various diseases, we highlight the successes and challenges of iPSCs in cell replacement therapy and the synergy of iPSCs and clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing tools in therapeutics research.

Cytotoxic T Lymphocytes Regenerated from iPS Cells Have Therapeutic Efficacy in a Patient-Derived Xenograft Solid Tumor Model

Current adoptive T cell therapies conducted in an autologous setting are costly, time consuming, and depend on the quality of the patient's T cells. To address these issues, we developed a strategy in which cytotoxic T lymphocytes (CTLs) are regenerated from iPSCs that were originally derived from T cells and succeeded in regenerating CTLs specific for the WT1 antigen, which exhibited therapeutic efficacy in a xenograft model of leukemia. In this study, we extended our strategy to solid tumors. The regenerated WT1-specific CTLs had a strong therapeutic effect in orthotopic xenograft model using a renal cell carcinoma (RCC) cell line. To make our method more generally applicable, we developed an allogeneic approach by transducing HLA-haplotype homozygous iPSCs with WT1-specific TCR α/β genes that had been tested clinically. The regenerated CTLs antigen-specifically suppressed tumor growth in a patient-derived xenograft model of RCC, demonstrating the feasibility of our strategy against solid tumors.

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Patient-derived xenograft of renal cell carcinoma was used in a cell-therapy model

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Cytotoxic T lymphocytes (CTLs) that target WT1-antigen were used as effector cells

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CTLs produced from iPSCs transduced with WT1-TCR genes showed efficacy in the model

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The present results demonstrate the feasibility of our strategy against solid tumors

Non-clinical efficacy, safety and stable clinical cell processing of induced pluripotent stem cell-derived anti-glypican-3 chimeric antigen receptor-expressing natural killer/innate lymphoid cells

The use of allogeneic, pluripotent stem‐cell‐derived immune cells for cancer immunotherapy has been the subject of recent clinical trials. In Japan, investigator‐initiated clinical trials will soon begin for ovarian cancer treatment using human leukocyte antigen (HLA)‐homozygous‐induced pluripotent stem cell (iPSC)‐derived anti–glypican‐3 (GPC3) chimeric antigen receptor (CAR)‐expressing natural killer/innate lymphoid cells (NK/ILC). Using pluripotent stem cells as the source for allogeneic immune cells facilitates stringent quality control of the final product, in terms of efficacy, safety and producibility. In this paper, we describe our methods for the stable, feeder‐free production of CAR‐expressing NK/ILC cells from CAR‐transduced iPSC with clinically relevant scale and materials. The average number of cells that could be differentiated from 1.8‐3.6 × 10⁶ iPSC within 7 weeks was 1.8‐4.0 × 10⁹. These cells showed stable CD45/CD7/CAR expression, effector functions of cytotoxicity and interferon gamma (IFN‐γ) production against GPC3‐expressing tumor cells. When the CAR‐NK/ILC cells were injected into a GPC3‐positive, ovarian‐tumor‐bearing, immunodeficient mouse model, we observed a significant therapeutic effect that prolonged the survival of the animals. When the cells were injected into immunodeficient mice during non–clinical safety tests, no acute systemic toxicity or tumorigenicity of the final product or residual iPSC was observed. In addition, our test results for the CAR‐NK/ILC cells generated with clinical manufacturing standards are encouraging, and these methods should accelerate the development of allogeneic pluripotent stem cell‐based immune cell cancer therapies.

T-cells with a single tumor antigen-specific T-cell receptor can be generated in vitro from clinically relevant stem cell sources

Chimeric antigen receptor (CAR) T-cells have shown great promise in the treatment of B-cell malignancies. For acute myeloid leukemia (AML), however, the optimal target surface antigen has yet to be discovered. Alternatively, T-cell receptor (TCR)-redirected T-cells target intracellular antigens, marking a broader territory of available target antigens. Currently, adoptive TCR T-cell therapy uses peripheral blood lymphocytes for the introduction of a transgenic TCR. However, this can cause graft-versus-host disease, due to mispairing of introduced and endogenous TCR chains. Therefore, we started from hematopoietic stem and progenitor cells (HSPC), that do not express a TCR yet, isolated from healthy donors, patients in remission after chemotherapy and AML patients at diagnosis. Using the OP9-DL1 in vitro co-culture system and agonist selection, TCR-transduced HSPC develop into mature tumor antigen-specific T-cells with only one TCR. We show here that this approach is feasible with adult HSPC from clinically relevant sources, albeit with slower maturation and lower cell yield compared to cord blood HSPC. Moreover, cryopreservation of HSPC does not have an effect on cell numbers or functionality of the generated T-cells. In conclusion, we show here that it is feasible to generate TA-specific T-cells from HSPC from adult healthy donors and patients and we believe these T-cells could be of use as a very valuable form of patient-tailored T-cell immunotherapy.

Adaptive Immunity and the Tumor Microenvironment

The adaptive immune response is a 500-million-year-old (the "Big Bang" of Immunology) collective set of rearranged and/or selected receptors capable of recognizing soluble and cell surface molecules or shape (B cells, antibody), endogenous and extracellular peptides presented by Major Histocompatibility (MHC) molecules including Class I and Class II (conventional αβ T cells), lipid in the context of MHC-like molecules of the CD1 family (NKT cells), metabolites and B7 family molecules/butyrophilins with stress factors (γδT cells), and stress ligands and absence of MHC molecules (natural killer, NK cells). What makes tumor immunogenic is the recruitment of initially innate immune cells to sites of stress or tissue damage with release of Damage-Associated Molecular Pattern (DAMP) molecules. Subsequent maintenance of a chronic inflammatory state, representing a balance between mature, normalized blood vessels, innate and adaptive immune cells and the tumor provides a complex tumor microenvironment serving as the backdrop for Darwinian selection, tumor elimination, tumor equilibrium, and ultimately tumor escape. Effective immunotherapies are still limited, given the complexities of this highly evolved and selected tumor microenvironment. Cytokine therapies and Immune Checkpoint Blockade (ICB) enable immune effector function and are largely dependent on the shape and size of the B and T cell repertoires (the "adaptome"), now accessible by Next-Generation Sequencing (NGS) and dimer-avoidance multiplexed PCR. How immune effectors access the tumor (infiltrated, immune sequestered, and immune desserts), egress and are organized within the tumor are of contemporary interest and substantial investigation.

T cell regeneration: an update on progress and challenges

T cells play essential roles in antitumor therapy. Via gene engineering technique to enhance tumor-antigen specificity, patient peripheral blood-derived T cells (PBT) show encouraging clinical outcomes in treating certain blood malignancies. However, the high costs, functionality exhaustion, and disease-condition-dependent availability of PBT prompt the attempts of exploring alternative T cell sources. Theoretically, induced T cells from pluripotent stem cells (PSC) are ideal candidates that integrate plenty of advantages that primary T cells lack, including unlimited off-the-shelf cell source and precision gene editing feasibility. However, researchers are still struggling with developing a straightforward protocol to induce functional and immunocompetent human T cells from PSC. Based on stromal cell-expressing or biomaterial-presenting Notch ligands DLL1 or DLL4, natural and induced blood progenitors can differentiate further toward T lineage commitment. However, none of the reported T induction protocols has yet translated into any clinical application, signaling the existence of numerous technical barriers for regenerating T cells functionally matching their natural PBT counterparts. Alternatively, new approaches have been developed to repopulate induced T lymphopoiesis via in vivo reprogramming or transplanting induced T cell precursors. Here, we review the most recent progress in the T cell regeneration field, and the remaining challenges dragging their clinical applications.

High Frequency Production of T Cell-Derived iPSC Clones Capable of Generating Potent Cytotoxic T Cells

Current adoptive T cell therapies conducted in an autologous setting are costly, time-consuming, and depend on the quality of the patient’s T cells, and thus it would be highly beneficial to develop an allogeneic strategy. To this aim, we have developed a method by which cytotoxic T lymphocytes (CTLs) are regenerated from induced pluripotent stem cells that are originally derived from T cells (T-iPSCs). In order to assess the feasibility of this strategy, we investigated the frequency of usable T-iPSC clones in terms of their T cell-generating capability and T cell receptor (TCR) affinity. We first established eight clones of T-iPSCs bearing different MART-1-specific TCRs from a healthy volunteer. Whereas all clones were able to give rise to mature CTLs, cell yield varied greatly, and five clones were considered to be usable. TCR affinity in the regenerated CTLs showed a large variance among the eight clones, but functional avidities measured by cytotoxic activity were almost equivalent among three selected clones representing high, medium, and low TCR affinity. In a total of 50 alloreactivity tests using five CTL clones versus ten target cells, alloreactivity was seen in only three cases. These findings collectively support the feasibility of this T-iPSC strategy.

Chimeric Antigen Receptor T-Cell Therapy for Multiple Myeloma

CD19 Chimeric antigen receptor (CAR) T cell therapy has been shown to be effective for B cell leukemia and lymphoma. Many researchers are now trying to develop CAR T cells for various types of cancer. For multiple myeloma (MM), B-cell maturation antigen (BCMA) has been recently proved to be a promising target. However, cure of MM is still difficult, and several other targets, for example immunoglobulin kappa chain, SLAM Family Member 7 (SLAMF7), or G-protein coupled receptor family C group 5 member D (GPRC5D), are being tested as targets for CAR T cells. We also reported that the activated integrin β7 can serve as a specific target for CAR T cells against MM, and are preparing a clinical trial. In this review, we summarized current status of CAR T cell therapy for MM and discussed about the future perspectives.