Tim3 binding to galectin-9 stimulates antimicrobial immunity

T cell immunoglobulin and mucin domain 3 (Tim3) is a negative regulatory molecule that inhibits effector T(H)1-type responses. Such inhibitory signals prevent unintended tissue inflammation, but can be detrimental if they lead to premature T cell exhaustion. Although the role of Tim3 in autoimmunity has been extensively studied, whether Tim3 regulates antimicrobial immunity has not been explored. Here, we show that Tim3 expressed on T(H)1 cells interacts with its ligand, galectin-9 (Gal9), which is expressed by Mycobacterium tuberculosis-infected macrophages to restrict intracellular bacterial growth. Tim3-Gal9 interaction leads to macrophage activation and stimulates bactericidal activity by inducing caspase-1-dependent IL-1β secretion. We propose that the T(H)1 cell surface molecule Tim3 has evolved to inhibit growth of intracellular pathogens via its ligand Gal9, which in turn inhibits expansion of effector T(H)1 cells to prevent further tissue inflammation.     

Development of new strategies to prevent type 1 diabetes: the role of animal models

Type 1 diabetes is an immune‐mediated disease typically preceded by a long preclinical stage during which a growing number of islet‐cell‐specific autoantibodies appear in the serum. Although antigen‐specific T lymphocytes and cytokines rather than these autoantibodies are the likely executors of β‐cell‐destruction, these autoantibodies reflect the existence of autoimmunity that targets islet β‐cells. Abrogation of this autoimmunity during the preclinical stage would be the key to the prevention of type 1 diabetes. However, the quest of protecting islet‐cells from the immune attack requires detailed knowledge of mechanisms that control islet‐inflammation and β‐cell‐destruction, and of mechanisms that control immune tolerance to peripheral self‐antigens in general. This knowledge can only be obtained through further innovative research in experimental animal models. In this review, we will first examine how research in non‐obese diabetic mice has already led to promising new strategies of diabetes prevention now being tested in human clinical trials. Thereafter, we will discuss how recent advances in understanding the mechanisms that control immune response to peripheral self‐antigens such as β‐cell antigens may help to develop even more selective and effective strategies to prevent diabetes in the future.     

American council on ECP (ACE): Why now?

Stimulated by the scientific progress in deciphering the principal elements contributing to the clinical efficacy of extracorporeal photochemotherapy (ECP), the American Council on ECP (ACE) was formed, under the auspices of the American Society for Apheresis (ASFA), to develop a field‐guiding Consensus Report. ACE is composed of thirty nationally recognized ECP experts, clinically spanning cancer, transplantation, and autoimmunity and scientifically bridging immunology, bioengineering, and hematology. The two‐day meeting took place in Manhattan, April 13‐14, 2017, and unanimous consensus on nine pivotal points is herein reported. (1) ECP's clinical evolution must now enter a scientifically driven phase. (2) ECP is currently a bidirectional therapy, both immunizing and tolerizing simultaneously, via a single one‐size‐fits‐all inflexible medical device. (3) To preclude inadvertent tolerization in the cancer setting, or immunization in the transplant rejection setting, polarization of ECP to either immunization or tolerization mode to match the clinical need is now possible and necessary. (4) Cutaneous T cell lymphoma (CTCL) is a genetically driven cancer, whose response to ECP is due to enhanced anti‐cancer immunity. (5) ECP is a dendritic antigen‐presenting cell (DC) based therapy. (6) ECP's efficacy can now be tested in a broad array of cancers. (7) ECP's capacity to tolerize to allotransplants via processing of donor leukocytes merits expedited human investigation. (8) UVA‐8‐MOP‐impacted ECP‐induced DC are potent antigen‐specific tolerizing agents, while UVA‐8‐MOP(8‐Methoxypsoralen)‐spared ECP‐induced DC are potent antigen‐specific immunizing agents. (9) Six pilot clinical trial areas (CTCL, graft‐vs.‐host disease, ovarian carcinoma, anti‐graft cytotoxic antibodies, pemphigus vulgaris, and haplotype mismatched stem cell transplants) are advised. ACE will be an ongoing advisory group for the field, with the goal of overseeing coordinated clinical and fundamental research efforts.     

Extracorporeal photopheresis in pediatric patients: Practical and technical considerations

In adults, extracorporeal photopheresis (ECP) is widely utilized for a variety of indications, most commonly cutaneous T‐cell lymphoma, acute or chronic graft‐versus‐host disease (GVHD), solid organ transplant rejection, and other autoimmune and T‐cell‐mediated disorders. In pediatric patients, the majority of case series and reports have focused on its use in the management of acute and chronic GVHD. Currently utilized ECP technologies were designed for adult patients and there are several challenges in adapting these technologies for use in children. In our review, we focus on practical considerations and procedural modifications for ECP use in pediatric patients, with special attention to patient safety.     

A therapeutic cancer vaccine delivers antigens and adjuvants to lymphoid tissues using genetically modified T cells

Therapeutic vaccines that augment T cell responses to tumor antigens have been limited by poor potency in clinical trials. In contrast, the transfer of T cells modified with foreign transgenes frequently induces potent endogenous T cell responses to epitopes in the transgene product, and these responses are undesirable, because they lead to rejection of the transferred T cells. We sought to harness gene-modified T cells as a vaccine platform and developed cancer vaccines composed of autologous T cells modified with tumor antigens and additional adjuvant signals (Tvax). T cells expressing model antigens and a broad range of tumor neoantigens induced robust and durable T cell responses through cross-presentation of antigens by host DCs. Providing Tvax with signals such as CD80, CD137L, IFN-β, IL-12, GM-CSF, and FLT3L enhanced T cell priming. Coexpression of IL-12 and GM-CSF induced the strongest CD4⁺ and CD8⁺ T cell responses through complimentary effects on the recruitment and activation of DCs, mediated by autocrine IL-12 receptor signaling in the Tvax. Therapeutic vaccination with Tvax and adjuvants showed antitumor activity in subcutaneous and metastatic preclinical mouse models. Human T cells modified with neoantigens readily activated specific T cells derived from patients, providing a path for clinical translation of this therapeutic platform in cancer.     

Targeted Inhibition of Prostate Cancer Metastases with an RNA Aptamer to Prostate-specific Membrane Antigen

Cell-targeted therapies (smart drugs), which selectively control cancer cell progression with limited toxicity to normal cells, have been developed to effectively treat some cancers. However, many cancers such as metastatic prostate cancer (PC) have yet to be treated with current smart drug technology. Here, we describe the thorough preclinical characterization of an RNA aptamer (A9g) that functions as a smart drug for PC by inhibiting the enzymatic activity of prostate-specific membrane antigen (PSMA). Treatment of PC cells with A9g results in reduced cell migration/invasion in culture and metastatic disease in vivo. Importantly, A9g is safe in vivo and is not immunogenic in human cells. Pharmacokinetic and biodistribution studies in mice confirm target specificity and absence of non-specific on/off-target effects. In conclusion, these studies provide new and important insights into the role of PSMA in driving carcinogenesis and demonstrate critical endpoints for the translation of a novel RNA smart drug for advanced stage PC.     

Regulation of immunity by lysosphingolipids and their G protein-coupled receptors

T and B lymphocytes, as well as endothelial cells, express distinctive profiles of G protein-coupled receptors for sphingosine 1-phosphate, which is a major regulator of T cell development, B and T cell recirculation, tissue homing patterns, and chemotactic responses to chemokines. The capacity of drugs that act on type 1 sphingosine 1-phosphate receptors to suppress organ graft rejection in humans and autoimmunity in animal models without apparent impairment of host defenses against infections suggests that this system is a promising target for new forms of immunotherapy.     

Mesenchymal cells inhibit expansion but not cytotoxicity exerted by gamma–delta T cells

Background Multipotent mesenchymal stromal cells (MSCs) exert a relevant immunosuppressive activity by inhibiting T‐ and B‐lymphocytes, natural killer (NK) cells and dendritic cell expansion. Nevertheless, a possible activity on gamma/delta T cells has still not been evaluated. Gamma–delta T lymphocytes play an important role in the control of cancer and they have been shown to be implicated in graft‐vs.‐host disease. Thus, modulation of activation and proliferation of these cells could be relevant for therapeutic purposes. Materials and methods Peripheral blood mononuclear cells from 21 healthy donors were used as source for gamma–delta T cells, expanded in presence of 10 IU mL^?1 interleukin‐2 (IL‐2) and 1 μM zoledronate. MSCs were recovered from patients undergoing routine total hip replacement surgery, and characterised by flow cytometry. Cytotoxicity on multiple myeloma and melanoma cell lines was assessed by measuring dilution of the carboxyfluorescein diacetate succinimydylester dye (CFSE). Gamma–delta T cells were then incubated with MSCs in contact cultures, and with addition of MSC‐conditioned medium. Results In this article we confirmed that (1) in vitro expanded gamma–delta T cells play a significant anti‐proliferative effect on multiple myeloma and melanoma cells and (2) multipotent mesenchymal stromal cells effectively suppress the ex vivo expansion of T cells carrying a specific T‐cell receptor gene (TCR) rearrangement, Vgamma9/Vdelta2, induced by the combination of IL‐2 and zoledronate, without interfering with their cytotoxic activity. Discussion These findings contribute to explain the activity of ex vivo expanded mesenchymal cells, suggesting that MSCs would interact with gamma–delta T lymphocytes. Conclusion This effect could be relevant in separating graft‐vs.‐host from the graft‐vs.‐tumour effect, especially considering the possibility of modulating T‐lymphocytes activity by the immunomodulating drugs now available.     

How do i participate in T‐cell immunotherapy?

T cells play a key role in the adaptive immune response, and the ability to manipulate T cells for therapeutic uses has advanced in the past decade. Infusion of expanded or engineered T cells can potentially be used to treat cancer, viral infections, graft‐versus‐host disease, and organ transplant rejection. The role that blood banks play in the manufacture and distribution of T‐cell therapeutics is still being defined. Given the regulatory framework of blood banks, they are well positioned to collect raw material for manufacture of T‐cell therapies and to distribute finished product to hospitals in support of clinical trials or eventually for licensed products. A deeper level of involvement in manufacture of T‐cell therapeutics is also possible, although that requires more substantial investment in physical facilities and personnel with the regulatory and scientific expertise to prepare and produce cellular therapy products. Examples of physical infrastructure needed would be a laboratory with a clean room for culture of T cells, specialized equipment for expansion of the cells, and adequate administrative and storage support space. Processes that would need to be developed to produce T‐cell therapeutics would include development of standard operating procedures and an appropriate quality assurance program. As blood banks consider supporting this novel class of therapies, they will need to weigh capital and expertise requirements with the benefits of providing a novel therapy and the potential of growth for their operations.     

Anti-CD4 abrogates rejection and reestablishes long-term tolerance to syngeneic newborn hearts grafted in mice chronically infected with Trypanosoma cruzi

The contribution of autoimmunity in the genesis of chronic Chagas' heart pathology is not clear. In the present study, we show that: (a) BALB/c mice chronically infected with Trypanosoma cruzi reject syngeneic newborn hearts; (b) in vivo treatment with anti-CD4 but not anti-CD8 monoclonal antibodies (mAbs) abrogates rejection; (c) CD4+ T cells from chronically infected mice proliferate in vitro to syngeneic myocardium antigens and induce heart graft destruction when injected in situ; (d) anti-CD4 treatment of chronically infected mice establishes long-term tolerance to syngeneic heart grafts; and (e) the state of tolerance is related to in vitro and in vivo unresponsiveness of the CD4+ T cells. These findings allow us to suggest that autoimmunity is the major mechanism implicated in the rejection of syngeneic heart tissues grafted into the pinna of the ear of mice chronically infected with T. cruzi. The similarity of the lesions to those found in humans suggests that autoimmunity is involved in the pathogenesis of chagasic cardiomyopathy in humans. Moreover, this could imply therapeutic strategies by reestablishing long-term tissue-specific tolerance with anti-CD4 mAb treatment, mediating anergy, or deleting the responder CD4+ T cells to heart tissue antigens.     

Triptan drugs, natural killer cell cytotoxicity, and neutrophils pro-matrix metalloproteinase-9 secretion

Objective.— To study the effect of various triptan‐like drugs, eg, avitriptan, naratriptan, and sumatriptan, as well as the benzopyran alnitidan, on the natural killer cell (NKC) activity of peripheral blood mononuclear cell (PBMC) samples and highly purified NKC (HPNKC) preparations. We also examined the possible role of these agents as immunomodulators by studying their effect upon the in vitro secretion of pro‐matrix metalloproteinase‐9 (pMMP‐9) from whole blood and purified neutrophils samples. Background.— The pharmacological profile of a large number of triptan‐like compounds has been extensively studied. However, relatively little is known of their interactions with cellular components of the immune system. Methods.— Blood was obtained from nonsmoking, drug‐free healthy individuals from the Blood Bank of the University of Chile main Clinical Hospital (J.J.A.). PBMC were separated by centrifugation and HPNKC acquired by an immunomagnetic isolation procedure. NKC cytotoxicity was assayed using ⁵¹Cr‐labeled K‐562 cells as target. Addition of drugs and of effector cells (30 : 1, 50 : 1, and 70 : 1 ratio for PBMCs, and 5 : 1 for HPNKCs) was followed by incubation. Paired Student's t‐test (2‐tailed) was used to determine the significance of the specific ⁵¹Cr release in controls vs drug‐treated samples. Aliquots of whole blood or purified neutrophils were added test drug, incubated, centrifuged, and the supernatant analyzed by gelatine zymography. Gelatinolytic activity was visualized, and a digested zone at MW 92 kD indicated presence of pMMP‐9. Area of proteolysis was estimated by densitometry; prestained standards were used to assess pMMP‐9 molecular weight. Results.— Peripheral blood mononuclear cell's NKC cytotoxicity was consistently decreased after incubation with each and every one of the drugs tested. This result, observed for the 3 effector : target (E : T) cell ratios used, was relatively similar among the various compounds studied, and reached statistical significance only at E : T 70 : 1. Similar drug treatment failed, however, to produce significant changes in the cytotoxicity of HPNKC preparations, suggesting that modulation of the PBMC's NKC activity and that of HPNKC samples require different kinds of cell's derived signal. Incubation with either of the drugs tested failed to significantly alter (basal) nonstimulated pMPP‐9 secretion by whole blood samples. However, basal pMMP‐9 secretion by purified neutrophil preparations was significantly inhibited by alnitidan and sumatriptan, and not affected by naratriptan. Conclusions.— Various drugs with a triptan‐like chemical structure interact with cellular components of the innate immune system, resulting in an apparent indirect inhibition of NKC activity and direct inhibition of neutrophils pMMP‐9 secretion. These results suggest that they may play a positive role in decreasing the severity of inflammatory processes. Whether this effect is part of triptans antimigraine mechanism of action, or just an added beneficial effect of their use for the reversal treatment of migraine headaches remains to be explored.     

Photopheresis therapy for problematic renal allograft rejection

Background: Photopheresis is an immunomodulatory therapy for the treatment of T cell‐mediated disorders. It has been used for rejection prophylaxis in cardiac transplantation, adjuvant treatment of bronchiolitis obliterans in lung transplantation, treatment of graft verse host disease, and in a small number of cases, for treatment of acute rejection in renal transplantation. Little is known of long‐term outcomes following the use of photopheresis in solid organ transplantation. Methods: We report prospective follow‐up of our consecutive experience of the use of photopheresis as adjuvant/salvage therapy for problematic rejection in patients undergoing renal transplantation. Transplant graft survival, infective and malignant outcomes were reported. Results: A cohort of 10 renal transplants recipients received photopheresis therapy for therapy‐resistant rejection. Conventional therapy included an average of 6.2 g pulse methyl‐prednisolone and 17.1 days antilymphocyte therapy. The cohort received additional photopheresis therapy when the unresponsive nature of their rejections raised concerns of graft loss. Median follow‐up censored for patient loss was 66.7 months following photopheresis commencement. Rejection resolved in association with photopheresis use in all 10 patients. Six patients continued to have stable graft function (median serum creatinine: 191.5 μmol/L) at a median follow‐up of 71.0 months. There has been one patient death from sepsis and two from malignancy with functioning grafts while one graft has been lost to disease recurrence. Conclusion: Photopheresis may have a role as an adjuvant or salvage antirejection therapy in solid organ transplantation. Furthermore, evaluation in randomized controlled clinical trials is required to evaluate its potential. J. Clin. Apheresis, 2009. © 2009 Wiley‐Liss, Inc.     

Raising the Roof: The Preferential Pharmacological Stimulation of Th1 and Th2 Responses Mediated by NKT Cells

Natural killer T (NKT) cells serve as a bridge between the innate and adaptive immune systems, and manipulating their effector functions can have therapeutic significances in the treatment of autoimmunity, transplant biology, infectious disease, and cancer. NKT cells are a subset of T cells that express cell‐surface markers characteristic of both natural killer cells and T cells. These unique immunologic cells have been demonstrated to serve as a link between the innate and adaptive immune systems through their potent cytokine production following the recognition of a range of lipid antigens, mediated through presentation of the major histocompatibility complex (MHC) class I like CD1d molecule, in addition to the NKT cell's cytotoxic capabilities upon activation. Although a number of glycolipid antigens have been shown to complex with CD1d molecules, most notably the marine sponge derived glycolipid alpha‐galactosylceramide (α‐GalCer), there has been debate as to the identity of the endogenous activating lipid presented to the T‐cell receptor (TCR) via the CD1d molecule on antigen‐presenting cells (APCs). This review aims to survey the use of pharmacological agents and subsequent structure–activity relationships (SAR) that have given insight into the binding interaction of glycolipids with both the CD1d molecules as well as the TCR and the subsequent immunologic response of NKT cells. These studies not only elucidate basic binding interactions but also pave the way for future pharmacological modulation of NKT cell responses.     

Second class minors: molecular identification of the autosomal H46 histocompatibility locus as a peptide presented by major histocompatibility complex class II molecules

CD4 T cells regulate immune responses that cause chronic graft rejection and graft versus host disease but their target antigens remain virtually unknown. We developed a new method to identify CD4 T cell-stimulating antigens. LacZ-inducible CD4 T cells were used as a probe to detect their cognate peptide/MHC II ligand generated in dendritic cells fed with Escherichia coli expressing a library of target cell genes. The murine H46 locus on chromosome 7 was thus found to encode the interleukin 4-induced IL4i1 gene. The IL4i1 precursor contains the HAFVEAIPELQGHV peptide which is presented by A(b) major histocompatibility complex class II molecule via an endogenous pathway in professional antigen presenting cells. Both allelic peptides bind A(b) and a single alanine to methionine substitution at p2 defines nonself. These results reveal novel features of H loci that regulate CD4 T cell responses as well as provide a general strategy for identifying elusive antigens that elicit CD4 T cell responses to tumors or self-tissues in autoimmunity.     

Systemic IFN-β gene therapy results in long-term survival in mice with established colorectal liver metastases

Most patients succumbing to colorectal cancer fail with liver-predominant metastases. To make a clinical impact in this disease, a systemic or whole-liver therapy may be required, whereas most cancer gene therapy approaches are limited in their ability to treat beyond local disease. As a preclinical model for cancer gene therapy, recombinant adenovirus containing the human IFN-beta (hIFN-beta) cDNA was delivered systemically in nude mouse xenograft models of human colorectal cancer liver metastases. The vector targeted hepatocytes that produced high levels of hIFN-beta in the liver, resulting in a profound apoptotic response in the tumors and significant tumor regression. hIFN-beta gene therapy not only resulted in improved survival and long-term cure in a micrometastatic model, but provided similar benefits in a clinically relevant gross disease model. A similar recombinant adenovirus containing the murine IFN-beta (mIFN-beta) cDNA also resulted in a therapeutic response and improved survival in syngeneic mouse models of colorectal cancer liver metastases. Depletion studies demonstrate a contribution of natural killer cells to this therapeutic response. The toxicity of an adenoviral vector expressing murine IFN-beta in a syngeneic model is also presented. These encouraging results warrant further investigation of the use of cancer gene therapy for targeting metastatic disease.     

Src inhibitors in the treatment of metastatic bone disease: rationale and clinical data

Src is a nonreceptor tyrosine kinase essential for the activation of osteoclasts, the cells that degrade bone. Src also regulates normal cell functions, cancer cell growth and metastasis to organs, including bone where tumor cells induce bone destruction by osteoclasts. Src inhibitors prevent bone destruction and tumor cell growth in animal models of metastatic bone disease, and some are being investigated in clinical trials, particularly in patients with prostate cancer, which has high bone metastatic potential. Here, we review how Src regulates osteoclast formation, activation and survival and the results of preclinical and clinical trials of Src inhibitors, which show some promise in inhibiting the effects of tumor cells on the skeleton.     

Antigen-specific precursor frequency impacts T cell proliferation, differentiation, and requirement for costimulation

After a brief period of antigenic stimulation, T cells become committed to a program of autonomous expansion and differentiation. We investigated the role of antigen-specific T cell precursor frequency as a possible cell-extrinsic factor impacting T cell programming in a model of allogeneic tissue transplantation. Using an adoptive transfer system to incrementally raise the precursor frequency of antigen-specific CD8(+) T cells, we found that donor-reactive T cells primed at low frequency exhibited increased cellular division, decreased development of multifunctional effector activity, and an increased requirement for CD28- and CD154-mediated costimulation relative to those primed at high frequency. The results demonstrated that recipients with low CD4(+) and CD8(+) donor-reactive T cell frequencies exhibited long-term skin graft survival upon CD28/CD154 blockade, whereas simultaneously raising the frequency of CD4(+) T cells to approximately 0.5% and CD8(+) T cells to approximately 5% precipitated graft rejection despite CD28/CD154 blockade. Antigenic rechallenge of equal numbers of cells stimulated at high or low frequency revealed that cells retained an imprint of the frequency at which they were primed. These results demonstrate a critical role for initial precursor frequency in determining the CD8(+) T cell requirement for CD28- and CD154-mediated costimulatory signals during graft rejection.     

MERTK on mononuclear phagocytes regulates T cell antigen recognition at autoimmune and tumor sites

Understanding mechanisms of immune regulation is key to developing immunotherapies for autoimmunity and cancer. We examined the role of mononuclear phagocytes during peripheral T cell regulation in type 1 diabetes and melanoma. MERTK expression and activity in mononuclear phagocytes in the pancreatic islets promoted islet T cell regulation, resulting in reduced sensitivity of T cell scanning for cognate antigen in prediabetic islets. MERTK-dependent regulation led to reduced T cell activation and effector function at the disease site in islets and prevented rapid progression of type 1 diabetes. In human islets, MERTK-expressing cells were increased in remaining insulin-containing islets of type 1 diabetic patients, suggesting that MERTK protects islets from autoimmune destruction. MERTK also regulated T cell arrest in melanoma tumors. These data indicate that MERTK signaling in mononuclear phagocytes drives T cell regulation at inflammatory disease sites in peripheral tissues through a mechanism that reduces the sensitivity of scanning for antigen leading to reduced responsiveness to antigen.     

Going both ways: immune regulation via CD1d-dependent NKT cells

NKT cells are a unique T lymphocyte sublineage that has been implicated in the regulation of immune responses associated with a broad range of diseases, including autoimmunity, infectious diseases, and cancer. In stark contrast to both conventional T lymphocytes and other types of Tregs, NKT cells are reactive to the nonclassical class I antigen-presenting molecule CD1d, and they recognize glycolipid antigens rather than peptides. Moreover, they can either up- or downregulate immune responses by promoting the secretion of Th1, Th2, or immune regulatory cytokines. This review will explore the diverse influences of these cells in various disease models, their ability to suppress or enhance immunity, and the potential for manipulating these cells as a novel form of immunotherapy.     

Progress and challenges in the development of a cell‐based therapy for hemophilia A

Hemophilia A results from an insufficiency of factor VIII (FVIII). Although replacement therapy with plasma‐derived or recombinant FVIII is a life‐saving therapy for hemophilia A patients, such therapy is a life‐long treatment rather than a cure for the disease. In this review, we discuss the possibilities, progress, and challenges that remain in the development of a cell‐based cure for hemophilia A. The success of cell therapy depends on the type and availability of donor cells, the age of the host and method of transplantation, and the levels of engraftment and production of FVIII by the graft. Early therapy, possibly even prenatal transplantation, may yield the highest levels of engraftment by avoiding immunological rejection of the graft. Potential cell sources of FVIII include a specialized subset of endothelial cells known as liver sinusoidal endothelial cells (LSECs) present in the adult and fetal liver, or patient‐specific endothelial cells derived from induced pluripotent stem cells that have undergone gene editing to produce FVIII. Achieving sufficient engraftment of transplanted LSECs is one of the obstacles to successful cell therapy for hemophilia A. We discuss recent results from transplants performed in animals that show production of functional and clinically relevant levels of FVIII obtained from donor LSECs. Hence, the possibility of treating hemophilia A can be envisioned through persistent production of FVIII from transplanted donor cells derived from a number of potential cell sources or through creation of donor endothelial cells from patient‐specific induced pluripotent stem cells.