Humanization of Immunodeficient Animals for the Modeling of Transplantation, Graft Versus Host Disease, and Regenerative Medicine

Advancing Parkinson's disease treatment: cell replacement therapy with neurons derived from pluripotent stem cells

The motor symptoms of Parkinson's disease (PD) are caused by the progressive loss of dopamine neurons from the substantia nigra. There are currently no treatments that can slow or reverse the neurodegeneration. To restore the lost neurons, international groups have initiated clinical trials using human embryonic or induced pluripotent stem cells (PSCs) to derive dopamine neuron precursors that are used as transplants to replace the lost neurons. Proof-of-principle experiments in the 1980s and 1990s showed that grafts of fetal ventral mesencephalon, which contains the precursors of the substantial nigra, could, under rare circumstances, reverse symptoms of the disease. Improvements in PSC technology and genomics have inspired researchers to design clinical trials using PSC-derived dopamine neuron precursors as cell replacement therapy for PD. We focus here on 4 such first-in-human clinical trials that have begun in the US, Europe, and Japan. We provide an overview of the sources of PSCs and the methods used to generate cells for transplantation. We discuss pros and cons of strategies for allogeneic, immune-matched, and autologous approaches and novel methods for overcoming rejection by the immune system. We consider challenges for safety and efficacy of the cells for durable engraftment, focusing on the genomics-based quality control methods to assure that the cells will not become cancerous. Finally, since clinical trials like these have never been undertaken before, we comment on the value of cooperation among rivals to contribute to advancements that will finally provide relief for the millions suffering from the symptoms of PD.

Efficient generation of human immune system rats using human CD34+ cells

Human immune system (HIS) mice generated using human CD34+ hematopoietic stem cells serve as a pivotal model for the in vivo evaluation of immunotherapies for humans. Yet, HIS mice possess certain limitations. Rats, due to their size and comprehensive immune system, hold promise for translational experiments. Here, we describe an efficacious method for long-term immune humanization, through intrahepatic injection of hCD34+ cells in newborn immunodeficient rats expressing human SIRPα. In contrast to HIS mice and similar to humans, HIS rats showed in blood a predominance of T cells, followed by B cells. Immune humanization was also high in central and secondary lymphoid organs. HIS rats treated with the anti-human CD3 antibody were depleted of human T cells, and human cytokines were detected in sera. We describe for the first time a method to efficiently generate HIS rats. HIS rats have the potential to be a useful model for translational immunology.

A Novel Immunodeficient Hyperglycemic Mouse Carrying the Ins1 Akita Mutation for Xenogeneic Islet Cell Transplantation

BACKGROUND

For patients who have difficulty controlling blood glucose even with insulin administration, xenogeneic islet cells, including human stem cell-derived pancreatic islets (hSC-islet) and porcine islets, have garnered attention as potential solutions to challenges associated with donor shortages. For the development of diabetes treatment modalities that use cell transplantation therapy, it is essential to evaluate the efficacy and safety of transplanted cells using experimental animals over the long term.

METHODS

We developed permanent diabetic immune-deficient mice by introducing the Akita (C96Y) mutation into the rodent-specific Insulin1 gene of NOD/Shi-scid IL2rγcnull (NOG) mice (Ins1C96Y/C96Y NOG). Their body weight, nonfasting blood glucose, and survival were measured from 4 wk of age. Insulin sensitivity was assessed via tolerance tests. To elucidate the utility of these mice in xenotransplantation experiments, we transplanted hSC-islet cells or porcine islets under the kidney capsules of these mice.

RESULTS

All male and female homozygous mice exhibited persistent severe hyperglycemia associated with β-cell depletion as early as 4 wk of age and exhibited normal insulin sensitivity. These mice could be stably engrafted with hSC-islets, and the mice that received porcine islet grafts promptly exhibited lowered blood glucose levels, maintaining blood glucose levels below the normal glucose range for at least 52 wk posttransplantation.

CONCLUSIONS

The Ins1C96Y/C96Y NOG mouse model provides an effective platform to assess both the efficacy and safety of long-term xenograft engraftment without the interference of their immune responses. This study is expected to contribute essential basic information for the clinical application of islet cell transplantation.

Humanized Mouse Models of Bacterial Infections

Bacterial infections continue to represent a significant healthcare burden worldwide, causing considerable mortality and morbidity every year. The emergence of multidrug-resistant bacterial strains continues to rise, posing serious risks to controlling global disease outbreaks. To develop novel and more effective treatment and vaccination programs, there is a need for clinically relevant small animal models. Since multiple bacterial species have human-specific tropism for numerous virulence factors and toxins, conventional mouse models do not fully represent human disease. Several human disease characteristic phenotypes, such as lung granulomas in the case of Mycobacterium tuberculosis infections, are absent in standard mouse models. Alternatively, certain pathogens, such as Salmonella enterica serovar typhi and Staphylococcus aureus, can be well tolerated in mice and cleared quickly. To address this, multiple groups have developed humanized mouse models and observed enhanced susceptibility to infection and a more faithful recapitulation of human disease. In the last two decades, multiple humanized mouse models have been developed to attempt to recapitulate the human immune system in a small animal model. In this review, we first discuss the history of immunodeficient mice that has enabled the engraftment of human tissue and the engraftment methods currently used in the field. We then highlight how humanized mouse models successfully uncovered critical human immune responses to various bacterial infections, including Salmonella enterica serovar Typhi, Mycobacterium tuberculosis, and Staphylococcus aureus.

An Infection Model for SARS-CoV-2 Using Rat Transplanted with hiPSC-Airway Epithelial Cells

Investigating the infection mechanism of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the airway epithelium and developing effective defense strategies against infection are important. To achieve this, establishing appropriate infection models is crucial. Therefore, various in vitro models, such as cell lines and primary cultures, and in vivo models involving animals that exhibit SARS-CoV-2 infection and genetically humanized animals have been used as animal models. However, no animal model has been established that allows infection experiments with human cells under the physiological environment of airway epithelia. Therefore, we aimed to establish a novel animal model that enables infection experiments using human cells. Human induced pluripotent stem cell-derived airway epithelial cell-transplanted nude rats (hiPSC-AEC rats) were used, and infection studies were performed by spraying lentiviral pseudoviruses containing SARS-CoV-2 spike protein and the GFP gene on the tracheae. After infection, immunohistochemical analyses revealed the existence of GFP-positive-infected transplanted cells in the epithelial and submucosal layers. In this study, a SARS-CoV-2 infection animal model including human cells was established mimicking infection through respiration, and we demonstrated that the hiPSC-AEC rat could be used as an animal model for basic research and the development of therapeutic methods for human-specific respiratory infectious diseases.

Alpha-Synuclein Gene Alterations Modulate Tyrosine Hydroxylase in Human iPSC-Derived Neurons in a Parkinson's Disease Animal Model

Parkinson's disease (PD) caused by SNCA gene triplication (3XSNCA) leads to early onset, rapid progression, and often dementia. Understanding the impact of 3XSNCA and its absence is crucial. This study investigates the differentiation of human induced pluripotent stem cell (hiPSC)-derived floor-plate progenitors into dopaminergic neurons. Three different genotypes were evaluated in this study: patient-derived hiPSCs with 3XSNCA, a gene-edited isogenic line with a frame-shift mutation on all SNCA alleles (SNCA 4KO), and a normal wild-type control. Our aim was to assess how the substantia nigra pars compacta (SNpc) microenvironment, damaged by 6-hydroxydopamine (6-OHDA), influences tyrosine hydroxylase-positive (Th+) neuron differentiation in these genetic variations. This study confirms successful in vitro differentiation into neuronal lineage in all cell lines. However, the SNCA 4KO line showed unusual LIM homeobox transcription factor 1 alpha (Lmx1a) extranuclear distribution. Crucially, both 3XSNCA and SNCA 4KO lines had reduced Th+ neuron expression, despite initial successful neuronal differentiation after two months post-transplantation. This indicates that while the SNpc environment supports early neuronal survival, SNCA gene alterations-either amplification or knock-out-negatively impact Th+ dopaminergic neuron maturation. These findings highlight SNCA's critical role in PD and underscore the value of hiPSC models in studying neurodegenerative diseases.

Orthotopic and metastatic tumour models in preclinical cancer research

Mouse models of disease play a pivotal role at all stages of cancer drug development. Cell-line derived subcutaneous tumour models are predominant in early drug discovery, but there is growing recognition of the importance of the more complex orthotopic and metastatic tumour models for understanding both target biology in the correct tissue context, and the impact of the tumour microenvironment and the immune system in responses to treatment. The aim of this review is to highlight the value that orthotopic and metastatic models bring to the study of tumour biology and drug development while pointing out those models that are most likely to be encountered in the literature. Important developments in orthotopic models, such as the increasing use of early passage patient material (PDXs, organoids) and humanised mouse models are discussed, as these approaches have the potential to increase the predictive value of preclinical studies, and ultimately improve the success rate of anticancer drugs in clinical trials.

Nuclear Matrix-associated Protein SMAR1 Attenuated Acute Graft-versus-host Disease by Targeting JAK-STAT Signaling in CD4 + T Cells

BACKGROUND

Acute graft-versus-host disease (aGVHD) mediated by alloreactive T cells remains a serious and life-threatening complication of allogeneic hematopoietic cell transplantation (allo-HCT). The contribution of the different CD4 + T helper cell subtypes to the pathogenesis and regulation of aGVHD is a central point in current research. The specialized effector subsets of T cells that differentiate from naive T cells into mature cells are closely related to scaffold/matrix-associated region-1-binding protein (SMAR1). However, the role of SMAR1 in aGVHD is unclear.

METHODS

Peripheral blood was collected from the patients with or without aGVHD after allo-HCT. The differences in CD4 + T cells transduced with the SMAR1 lentivirus vector and empty vector were analyzed. A humanized aGVHD mouse model was constructed to evaluate the function of SMAR1 in aGVHD.

RESULTS

The expression of SMAR1 was significantly reduced in the CD4 + T cells from aGVHD patients and related to the occurrence of aGVHD. SMAR1 overexpression in human CD4 + T cells regulated CD4 + T-cell subsets differentiation and inflammatory cytokines secretion and inhibited the Janus kinase/signal transducer and activator of transcription pathway. Moreover, SMAR1 changed chromatin accessibility landscapes and affected the binding motifs of key transcription factors regulating T cells. Additionally, upregulation of SMAR1 expression in CD4 + T cells improved the survival and pathology in a humanized aGVHD mouse model.

CONCLUSIONS

Our results showed that upregulation of SMAR1 regulated the CD4 + T-cell subpopulation and cytokines secretion and improved survival in a humanized aGVHD mouse model by alleviating inflammation. This study provides a promising therapeutic target for aGVHD.

Comprehensive review of CRISPR-based gene editing: mechanisms, challenges, and applications in cancer therapy

The CRISPR system is a revolutionary genome editing tool that has the potential to revolutionize the field of cancer research and therapy. The ability to precisely target and edit specific genetic mutations that drive the growth and spread of tumors has opened up new possibilities for the development of more effective and personalized cancer treatments. In this review, we will discuss the different CRISPR-based strategies that have been proposed for cancer therapy, including inactivating genes that drive tumor growth, enhancing the immune response to cancer cells, repairing genetic mutations that cause cancer, and delivering cancer-killing molecules directly to tumor cells. We will also summarize the current state of preclinical studies and clinical trials of CRISPR-based cancer therapy, highlighting the most promising results and the challenges that still need to be overcome. Safety and delivery are also important challenges for CRISPR-based cancer therapy to become a viable clinical option. We will discuss the challenges and limitations that need to be overcome, such as off-target effects, safety, and delivery to the tumor site. Finally, we will provide an overview of the current challenges and opportunities in the field of CRISPR-based cancer therapy and discuss future directions for research and development. The CRISPR system has the potential to change the landscape of cancer research, and this review aims to provide an overview of the current state of the field and the challenges that need to be overcome to realize this potential.

The role of GATA2 in adult hematopoiesis and cell fate determination

The correct maintenance and differentiation of hematopoietic stem cells (HSC) in bone marrow is vital for the maintenance and operation of the human blood system. GATA2 plays a critical role in the maintenance of HSCs and the specification of HSCs into the different hematopoietic lineages, highlighted by the various defects observed in patients with heterozygous mutations in GATA2, resulting in cytopenias, bone marrow failure and increased chance of myeloid malignancy, termed GATA2 deficiency syndrome. Despite this, the mechanisms underlying GATA2 deficiency syndrome remain to be elucidated. The detailed description of how GATA2 regulates HSC maintenance and blood lineage determination is crucial to unravel the pathogenesis of GATA2 deficiency syndrome. In this review, we summarize current advances in elucidating the role of GATA2 in hematopoietic cell fate determination and discuss the challenges of modeling GATA2 deficiency syndrome.

Functional neurological restoration of amputated peripheral nerve using biohybrid regenerative bioelectronics

The development of neural interfaces with superior biocompatibility and improved tissue integration is vital for treating and restoring neurological functions in the nervous system. A critical factor is to increase the resolution for mapping neuronal inputs onto implants. For this purpose, we have developed a new category of neural interface comprising induced pluripotent stem cell (iPSC)-derived myocytes as biological targets for peripheral nerve inputs that are grafted onto a flexible electrode arrays. We show long-term survival and functional integration of a biohybrid device carrying human iPSC-derived cells with the forearm nerve bundle of freely moving rats, following 4 weeks of implantation. By improving the tissue-electronics interface with an intermediate cell layer, we have demonstrated enhanced resolution and electrical recording in vivo as a first step toward restorative therapies using regenerative bioelectronics.

Modelling Graft-Versus-Host Disease in Mice Using Human Peripheral Blood Mononuclear Cells

Graft-versus-host disease (GvHD) is a significant complication of allogeneic hematopoietic stem cell transplantation. In order to develop new therapeutic approaches, there is a need to recapitulate GvHD effects in pre-clinical, in vivo systems, such as mouse and humanized mouse models. In humanized mouse models of GvHD, mice are reconstituted with human immune cells, which become activated by xenogeneic (xeno) stimuli, causing a multi-system disorder known as xenoGvHD. Testing the ability of new therapies to prevent or delay the development of xenoGvHD is often used as pre-clinical, proof-of-concept data, creating the need for standardized methodology to induce, monitor, and report xenoGvHD. Here, we describe detailed methods for how to induce xenoGvHD by injecting human peripheral blood mononuclear cells into immunodeficient NOD SCID gamma mice. We provide comprehensive details on methods for human T cell preparation and injection, mouse monitoring, data collection, interpretation, and reporting. Additionally, we provide an example of the potential utility of the xenoGvHD model to assess the biological activity of a regulatory T-cell therapy. Use of this protocol will allow better standardization of this model and comparison of datasets across different studies. Graft-versus-host disease (GvHD) is a significant complication of allogeneic hematopoietic stem cell transplantation. In order to develop new therapeutic approaches, there is a need to recapitulate GvHD effects in pre-clinical, in vivo systems, such as mouse and humanized mouse models. In humanized mouse models of GvHD, mice are reconstituted with human immune cells, which become activated by xenogeneic (xeno) stimuli, causing a multi-system disorder known as xenoGvHD. Testing the ability of new therapies to prevent or delay the development of xenoGvHD is often used as pre-clinical, proof-of-concept data, creating the need for standardized methodology to induce, monitor, and report xenoGvHD. Here, we describe detailed methods for how to induce xenoGvHD by injecting human peripheral blood mononuclear cells into immunodeficient NOD SCID gamma mice. We provide comprehensive details on methods for human T cell preparation and injection, mouse monitoring, data collection, interpretation, and reporting. Additionally, we provide an example of the potential utility of the xenoGvHD model to assess the biological activity of a regulatory T-cell therapy. Use of this protocol will allow better standardization of this model and comparison of datasets across different studies. This protocol was validated in: Sci Transl Med (2020), DOI: 10.1126/scitranslmed.aaz3866 Graphical abstract.

Virus-Based Immuno-Oncology Models

Immunotherapy has been extensively explored in recent years with encouraging results in selected types of cancer. Such success aroused interest in the expansion of such indications, requiring a deep understanding of the complex role of the immune system in carcinogenesis. The definition of hot vs. cold tumors and the role of the tumor microenvironment enlightened the once obscure understanding of low response rates of solid tumors to immune check point inhibitors. Although the major scope found in the literature focuses on the T cell modulation, the innate immune system is also a promising oncolytic tool. The unveiling of the tumor immunosuppressive pathways, lead to the development of combined targeted therapies in an attempt to increase immune infiltration capability. Oncolytic viruses have been explored in different scenarios, in combination with various chemotherapeutic drugs and, more recently, with immune check point inhibitors. Moreover, oncolytic viruses may be engineered to express tumor specific pro-inflammatory cytokines, antibodies, and antigens to enhance immunologic response or block immunosuppressive mechanisms. Development of preclinical models capable to replicate the human immunologic response is one of the major challenges faced by these studies. A thorough understanding of immunotherapy and oncolytic viruses’ mechanics is paramount to develop reliable preclinical models with higher chances of successful clinical therapy application. Thus, in this article, we review current concepts in cancer immunotherapy including the inherent and synthetic mechanisms of immunologic enhancement utilizing oncolytic viruses, immune targeting, and available preclinical animal models, their advantages, and limitations.

Direct Impact of Human Platelets on the Development of Transplant Arteriosclerosis

BACKGROUND

Platelets play an important role in the pathogenesis of inflammatory and proliferative vascular changes. The aim of this study was to investigate whether human platelets are able to induce transplant arteriosclerosis in a humanized C57/Bl6-Rag2-/-γc-/- mouse xenograft model.

METHODS

Nonactivated and in vitro-activated human platelets were analyzed and phenotyped for surface markers by flow cytometry. Side branches of human mammary arteries were implanted into the infrarenal aorta of recipients, followed by daily application of human platelets and histological analyzed on day 30 after transplantation.

RESULTS

Human platelets collected by apheresis had low levels of platelet activation markers. However, after in vitro activation, expression was markedly increased. Sixty minutes after injection in recipient mice, nonactivated human platelets become significantly activated. Increased adhesion of platelets to the vascular endothelium was detected by in vivo fluorescence microscopy. After intravenous injection of nonactivated or activated platelets, human xenografts showed pronounced intimal proliferation. Immunohistological analysis showed that the group treated with activated human platelets exhibited significantly increased intragraft protein expression of intracellular adhesion molecule-1 and platelet-derived growth factor receptor beta and smooth muscle cell migration into the neointima.

CONCLUSIONS

These data demonstrate that an isolated daily application of both in vivo- and in vitro-activated human platelets results in the development of transplant arteriosclerosis in a humanized mouse transplantation model.

Human Hepatocyte Transduction with Adeno-Associated Virus Vector

As the adeno-associated virus (AAV) vectors hold unique advantages over other viral vectors, AAV gene therapy has accumulated rapid progress and development. Liver-targeted gene therapy by AAV vectors has been successfully applied in clinical trials for many diseases. Low transduction efficiency and high prevalence of neutralizing antibodies (Nabs), however, are the major obstacles to further translate this therapeutic strategy into clinical trials. Pre-clinical evaluation on hepatocytes could help to elucidate the tropism of AAV serotypes for liver-targeted gene therapy, and could also provide a test model to develop novel AAV mutants with Nabs evasion and high liver tropism. Here, we described the basic laboratory procedure to apply the AAV vector to transduce human hepatocytes in vitro and in vivo with some tips gained from our own experience.

Stem Cell-Based Disease Models for Inborn Errors of Immunity

The intrinsic capacity of human hematopoietic stem cells (hHSCs) to reconstitute myeloid and lymphoid lineages combined with their self-renewal capacity hold enormous promises for gene therapy as a viable treatment option for a number of immune-mediated diseases, most prominently for inborn errors of immunity (IEI). The current development of such therapies relies on disease models, both in vitro and in vivo, which allow the study of human pathophysiology in great detail. Here, we discuss the current challenges with regards to developmental origin, heterogeneity and the subsequent implications for disease modeling. We review models based on induced pluripotent stem cell technology and those relaying on use of adult hHSCs. We critically review the advantages and limitations of current models for IEI both in vitro and in vivo. We conclude that existing and future stem cell-based models are necessary tools for developing next generation therapies for IEI.

Therapeutically expanded human regulatory T-cells are super-suppressive due to HIF1A induced expression of CD73

The adoptive transfer of regulatory T-cells (Tregs) is a promising therapeutic approach in transplantation and autoimmunity. However, because large cell numbers are needed to achieve a therapeutic effect, in vitro expansion is required. By comparing their function, phenotype and transcriptomic profile against ex vivo Tregs, we demonstrate that expanded human Tregs switch their metabolism to aerobic glycolysis and show enhanced suppressive function through hypoxia-inducible factor 1-alpha (HIF1A) driven acquisition of CD73 expression. In conjunction with CD39, CD73 expression enables expanded Tregs to convert ATP to immunosuppressive adenosine. We conclude that for maximum therapeutic benefit, Treg expansion protocols should be optimised for CD39/CD73 co-expression.

Immunological considerations and challenges for regenerative cellular therapies

The central goal of regenerative medicine is to replace damaged or diseased tissue with cells that integrate and function optimally. The capacity of pluripotent stem cells to produce unlimited numbers of differentiated cells is of considerable therapeutic interest, with several clinical trials underway. However, the host immune response represents an important barrier to clinical translation. Here we describe the role of the host innate and adaptive immune responses as triggers of allogeneic graft rejection. We discuss how the immune response is determined by the cellular therapy. Additionally, we describe the range of available in vitro and in vivo experimental approaches to examine the immunogenicity of cellular therapies, and finally we review potential strategies to ameliorate immune rejection. In conclusion, we advocate establishment of platforms that bring together the multidisciplinary expertise and infrastructure necessary to comprehensively investigate the immunogenicity of cellular therapies to ensure their clinical safety and efficacy.

Advances in Genome Editing and Application to the Generation of Genetically Modified Rat Models

The rat has been extensively used as a small animal model. Many genetically engineered rat models have emerged in the last two decades, and the advent of gene-specific nucleases has accelerated their generation in recent years. This review covers the techniques and advances used to generate genetically engineered rat lines and their application to the development of rat models more broadly, such as conditional knockouts and reporter gene strains. In addition, genome-editing techniques that remain to be explored in the rat are discussed. The review also focuses more particularly on two areas in which extensive work has been done: human genetic diseases and immune system analysis. Models are thoroughly described in these two areas and highlight the competitive advantages of rat models over available corresponding mouse versions. The objective of this review is to provide a comprehensive description of the advantages and potential of rat models for addressing specific scientific questions and to characterize the best genome-engineering tools for developing new projects.

Development of LT-HSC-Reconstituted Non-Irradiated NBSGW Mice for the Study of Human Hematopoiesis In Vivo

Humanized immune system (HIS) mouse models are useful tools for the in vivo investigation of human hematopoiesis. However, the majority of HIS models currently in use are biased towards lymphocyte development and fail to support long-term multilineage leucocytes and erythrocytes. Those that achieve successful multilineage reconstitution often require preconditioning steps which are expensive, cause animal morbidity, are technically demanding, and poorly reproducible. In this study, we address this challenge by using HSPC-NBSGW mice, in which NOD,B6.SCID IL-2rγ-/-KitW41/W41 (NBSGW) mice are engrafted with human CD133+ hematopoietic stem and progenitor cells (HSPCs) without the need for preconditioning by sublethal irradiation. These HSPCs are enriched in long-term hematopoietic stem cells (LT-HSCs), while NBSGW mice are permissive to human hematopoietic stem cell (HSC) engraftment, thus reducing the cell number required for successful HIS development. B cells reconstitute with the greatest efficiency, including mature B cells capable of class-switching following allogeneic stimulation and, within lymphoid organs and peripheral blood, T cells at a spectrum of stages of maturation. In the thymus, human thymocytes are identified at all major stages of development. Phenotypically distinct subsets of myeloid cells, including dendritic cells and mature monocytes, engraft to a variable degree in the bone marrow and spleen, and circulate in peripheral blood. Finally, we observe human erythrocytes which persist in the periphery at high levels following macrophage clearance. The HSPC-NBSGW model therefore provides a useful platform for the study of human hematological and immunological processes and pathologies.

Genetic engineering of human and mouse CD4+ and CD8+ Tregs using lentiviral vectors encoding chimeric antigen receptors

The last decade has seen a significant increase of cell therapy protocols using effector T cells (Teffs) in particular, but also, more recently, non-engineered and expanded polyclonal regulatory T cells (Tregs) to control pathological immune responses such as cancer, autoimmune diseases, or transplantation rejection. However, limitations, such as stability, migration, and specificity of the cell products, have been seen. Thus, genetic engineering of these cell subsets is expected to provide the next generation of T cell therapy products. Lentiviral vectors are commonly used to modify Teffs; however, Tregs are more sensitive to mechanical stress and require specific culture conditions. Also, there is a lack of reproducible and efficient protocols to expand and genetically modify Tregs without affecting their growth and function. Due to smaller number of cells and poorer viability upon culture in vitro, mouse Tregs are more difficult to transduce and amplify in vitro than human Tregs. Here we propose a step-by-step protocol to produce both human and mouse genetically modified CD8⁺ and CD4⁺ Tregs in sufficient amounts to assess their therapeutic efficacy in humanized immunocompromised mouse models and murine models of disease and to establish pre-clinical proofs of concept. We report, for the first time, an efficient and reproducible method to isolate Tregs from human blood or mouse spleen, transduce with a lentiviral vector, and culture, in parallel, CD8⁺ and CD4⁺ Tregs while preserving their function. Beyond chimeric antigen receptor (CAR)-Treg cell therapy, this protocol will promote the development of potential new engineered T cell therapies to treat autoimmune diseases and transplantation rejection.

Super-Treg: Toward a New Era of Adoptive Treg Therapy Enabled by Genetic Modifications

Regulatory Tcells (Treg) are essential components of peripheral immune homeostasis. Adoptive Treg cell therapy has shown efficacy in a variety of immune-mediated diseases in preclinical studies and is now moving from phase I/IIa to larger phase II studies aiming to demonstrate efficacy. However, hurdles such as in vivo stability and efficacy remain to be addressed. Nevertheless, preclinical models have shown that Treg function and specificity can be increased by pharmacological substances or gene modifications, and even that conventional T cells can be converted to Treg potentially providing new sources of Treg and facilitating Treg cell therapy. The exponential growth in genetic engineering techniques and their application to T cells coupled to a large body of knowledge on Treg open numerous opportunities to generate Treg with "superpowers". This review summarizes the genetic engineering techniques available and their applications for the next-generation of Super-Treg with increased function, stability, redirected specificity and survival.

The Tumor Milieu Promotes Functional Human Tumor-Resident Plasmacytoid Dendritic Cells in Humanized Mouse Models

Particular interest to harness the innate immune system for cancer immunotherapy is fueled by limitations of immune checkpoint blockade. Plasmacytoid dendritic cells (pDC) are detected in a variety of solid tumors and correlate with poor clinical outcome. Release of type I interferons in response to toll-like-receptor (TLR)7 and TLR9 activation is the pDC hallmark. Mouse and human pDC differ substantially in their biology concerning surface marker expression and cytokine production. Here, we employed humanized mouse models (HIS) to study pDC function. We performed a comprehensive characterization of transgenic, myeloid-enhanced mouse strains (NOG-EXL and NSG-SGM3) expressing human interleukin-3 (hIL-3) and granulocyte-macrophage colony stimulating factor (GM-CSF) using identical humanization protocols. Only in HIS-NOG-EXL mice sufficient pDC infiltration was detectable. Therefore, we selected this strain for subsequent tumor studies. We analyzed pDC frequency in peripheral blood and tumors by comparing HIS-NOG-EXL with HIS-NOG mice bearing three different ovarian and breast tumors. Despite the substantially increased pDC numbers in peripheral blood of HIS-NOG-EXL mice, we detected TLR7/8 agonist responsive and thus functional pDCs only in certain tumor models independent of the mouse strain employed. However, HIS-NOG-EXL mice showed in general a superior humanization phenotype characterized by reconstitution of different myeloid subsets, NK cells and B cells producing physiologic IgG levels. Hence, we provide first evidence that the tumor milieu but not genetically introduced cytokines defines intratumoral (i.t.) frequencies of the rare pDC subset. This study provides model systems to investigate in vivo pro- and anti-tumoral human pDC functions.