Application of induced pluripotent stem cells to primary immunodeficiency diseases
2019; Elsevier BV; Volume: 71; Linguagem: Inglês
10.1016/j.exphem.2019.01.005
ISSN1873-2399
AutoresPeter Karagiannis, Shinya Yamanaka, Megumu K. Saito,
Tópico(s)Neurogenetic and Muscular Disorders Research
Resumo•Induced pluripotent stem cells (iPSCs) can provide an indefinite supply of patient hematopoietic cells.•Patient iPSC models have revealed molecular causes for several primary immunodeficiency diseases (PIDs).•The function of PID iPSC models has not been tested in animal models. Primary immunodeficiency diseases (PIDs) are a heterogeneous group of rare immune disorders with genetic causes. Effective treatments using hematopoietic stem cells or pharmaceutical agents have been around for decades. However, for many patients, these treatment options are ineffective, partly because the rarity of these PIDs complicates the diagnosis and therapy. Induced pluripotent stem cells (iPSCs) offer a potential solution to these problems. The proliferative capacity of iPSCs allows for the preparation of a large, stable supply of hematopoietic cells with the same genome as the patient, allowing for new human cell models that can trace cellular abnormalities during the pathogenesis and lead to new drug discovery. PID models using patient iPSCs have been instrumental in identifying deviations in the development or function of several types of immune cells, revealing new molecular targets for experimental therapies. These models are only in their early stages and for the most part have recapitulated results from existing models using animals or primary cells. However, iPSC-based models are being used to study complex diseases of other organs, including those with multigenic causes, suggesting that advances in differentiation processes will expand iPSC-based models to complex PIDs as well. Primary immunodeficiency diseases (PIDs) are a heterogeneous group of rare immune disorders with genetic causes. Effective treatments using hematopoietic stem cells or pharmaceutical agents have been around for decades. However, for many patients, these treatment options are ineffective, partly because the rarity of these PIDs complicates the diagnosis and therapy. Induced pluripotent stem cells (iPSCs) offer a potential solution to these problems. The proliferative capacity of iPSCs allows for the preparation of a large, stable supply of hematopoietic cells with the same genome as the patient, allowing for new human cell models that can trace cellular abnormalities during the pathogenesis and lead to new drug discovery. PID models using patient iPSCs have been instrumental in identifying deviations in the development or function of several types of immune cells, revealing new molecular targets for experimental therapies. These models are only in their early stages and for the most part have recapitulated results from existing models using animals or primary cells. However, iPSC-based models are being used to study complex diseases of other organs, including those with multigenic causes, suggesting that advances in differentiation processes will expand iPSC-based models to complex PIDs as well. Primary immunodeficiency diseases (PIDs) describe a group of clinically and genetically heterogeneous disorders that afflict lymphoid and myeloid lineages. PIDs have been recognized for a century, but the first molecular cause was not reported until 1972, when scientists realized that a child with severe combined immune deficiency (SCID) completely lacked adenosine deaminase, eventually leading to enzyme replacement therapy [1Giblett ER Anderson JE Cohen F et al.Adenosine-deaminase deficiency in two patients with severely impaired cellular immunity.Lancet. 1972; 2: 1067-1069Abstract PubMed Scopus (1164) Google Scholar, 2Ochs HD Petroni D From clinical observations and molecular dissection to novel therapeutic strategies for primary immunodeficiency disorders.Am J Med Genet A. 2018; 176: 784-803Crossref PubMed Scopus (11) Google Scholar]. There are now a number of therapeutic options for PIDs, including cytokine-based strategies, gene therapies, and hematopoietic stem cell (HSC) transplantation [3Gatti RA Meuwisse Hj Allen HD et al.Immunological reconstitution of sex-linked lymphopenic immunological deficiency.Lancet. 1968; 2: 1366-1369Abstract PubMed Google Scholar, 4Marciano BE Holland SM Primary immunodeficiency diseases: current and emerging therapeutics.Front Immunol. 2017; 8: 937Crossref PubMed Scopus (33) Google Scholar, 5Thrasher AJ Williams DA Evolving gene therapy in primary immunodeficiency.Mol Ther. 2017; 25: 1132-1141Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar]. Mutations in more than 300 genes have been associated with PIDs, but estimates assume thousands more are still to be identified [6Itan Y Casanova JL Novel primary immunodeficiency candidate genes predicted by the human gene connectome.Front Immunol. 2015; 6: 142Crossref PubMed Scopus (41) Google Scholar]. Although most categorized PIDs are monogenic, advanced diagnostics are revealing that multigenic factors and somatic mosaicisms are also contributing factors. The rates of PIDs vary, with frequencies approaching as low as one in a million, and approximately 20% of PID cases were originally reported in single patients [7Casanova JL Conley ME Seligman SJ et al.Guidelines for genetic studies in single patients: lessons from primary immunodeficiencies.J Exp Med. 2014; 211: 2137-2149Crossref PubMed Scopus (166) Google Scholar, 8Fang M Abolhassani H Lim CK et al.Next generation sequencing data analysis in primary immunodeficiency disorders: future directions.J Clin Immunol. 2016; 36: 68-75Crossref PubMed Scopus (52) Google Scholar]. Reduced costs and increased speeds have made next-generation sequencing (NGS) the standard for PID diagnosis; however, a considerable number of patients with unknown genetic etiology cannot be diagnosed due to the rarity of patients or the nature of the mutation (e.g., deep intronic mutations) [9Boisson B Honda Y Ajiro M et al.Rescue of recurrent deep intronic mutation underlying cell type-dependent quantitative NEMO deficiency.J Clin Invest. 2019; 129: 15Google Scholar]. Furthermore, findings should be confirmed with cell assays, which can be difficult to establish using primary hematopoietic cells due to the patient's condition. The result is delayed diagnosis, which complicates treatment and worsens morbidity and mortality. Induced pluripotent stem cells (iPSCs) provide a new model for studying these challenging PIDs. iPSCs are somatic cells reprogrammed to the pluripotent state, thus making it possible to prepare an indefinite number of cells for disease study even in circumstances when cell accessibility is difficult or only few patients are available. Importantly, these reprogrammed cells share the same genome of inaccessible primary cells. The result is new understanding of the disease pathogenesis and new molecular targets for treatment. Indeed, iPSC models have already been constructed for several PIDs, either affirming or challenging current theories about the molecular disorders contributing to the disease. PIDs are a wide class and primarily associated with mutations that disrupt the development or function of leukocytes, but also with inborn errors of metabolism [10Parvaneh N Quartier P Rostami P et al.Inborn errors of metabolism underlying primary immunodeficiencies.J Clin Immunol. 2014; 34: 753-771Crossref PubMed Scopus (18) Google Scholar]. Depending on the severity, patients can show vulnerability to a whole range of infections (e.g., IL2RG mutations in SCID) or in some cases to just a few viruses (e.g., TLR3 mutations in herpes simplex encephalitis) [11Fodil N Langlais D Gros P Primary immunodeficiencies and inflammatory disease: a growing genetic intersection.Trends Immunol. 2016; 37: 126-140Abstract Full Text Full Text PDF PubMed Scopus (37) Google Scholar]. Diagnostics include functional cell assays and genomic screenings. Complicating treatment is that any given PID can be heterogeneous and have mutations in dozens of genes without any specific set appearing causative [12Walkovich K Connelly JA Primary immunodeficiency in the neonate: early diagnosis and management.Semin Fetal Neonatal Med. 2016; 21: 35-43Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar]. Some patients are at extreme risk even from birth. The continuing reduction of NGS costs has made newborn screenings a standard option in suspected cases even when there is no family history [13Pavey AR Bodian DL Vilboux T et al.Utilization of genomic sequencing for population screening of immunodeficiencies in the newborn.Genet Med. 2017; 19: 1367-1375Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar]. Indeed, NGS has revealed that PIDs, which were once considered an exclusively Mendelian and monogenic family, are far more heterogeneous and include many multigenic and somatic factors [14Seleman M Hoyos-Bachiloglu R Geha RS et al.Uses of next-generation sequencing technologies for the diagnosis of primary immunodeficiencies.Front Immunol. 2017; 8: 847Crossref PubMed Scopus (46) Google Scholar]. However, despite these advances, several patients escape positive diagnosis. In these cases, when a PID is suspected but no clear genetic cause is found, autologous iPSCs should be considered. Using iPSCs from patients, scientists have gained new insights on how different cell types are affected by a PID and the developmental stage in which the disease phenotype emerges [15Menon T Firth AL Scripture-Adams DD et al.Lymphoid regeneration from gene-corrected SCID-X1 subject-derived iPSCs.Cell Stem Cell. 2015; 16: 367-372Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar, 16Zimmer B Ewaleifoh O Harschnitz O et al.Human iPSC-derived trigeminal neurons lack constitutive TLR3-dependent immunity that protects cortical neurons from HSV-1 infection.Proc Natl Acad Sci U S A. 2018; 115: E8775-E8782Crossref PubMed Scopus (49) Google Scholar]. iPSCs describe the reprogramming of somatic cells into an embryonic stem cell (ESC)-like state. ESCs are pluripotent and can replicate indefinitely. They and, by extension, iPSCs can model the development of all three germ layers, including all stages of hematopoiesis [17Wahlster L Daley GQ Progress towards generation of human haematopoietic stem cells.Nat Cell Biol. 2016; 18: 1111-1117Crossref PubMed Scopus (53) Google Scholar]. Exploiting these features, researchers have induced iPSCs to differentiate into an assortment of hematopoietic cells [18Karagiannis P Takahashi K Saito M et al.Induced pluripotent stem cells and their use in human models of disease and development.Physiol Rev. 2019; 99: 79-114Crossref PubMed Scopus (134) Google Scholar]. The first iPSCs were generated by exogenously expressing a master set of transcription factors (Oct3/4, Sox2, Klf4, and c-Myc) [19Takahashi K Tanabe K Ohnuki M et al.Induction of pluripotent stem cells from adult human fibroblasts by defined factors.Cell. 2007; 131: 861-872Abstract Full Text Full Text PDF PubMed Scopus (14786) Google Scholar, 20Takahashi K Yamanaka S Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors.Cell. 2006; 126: 663-676Abstract Full Text Full Text PDF PubMed Scopus (18636) Google Scholar]. Since the original iPSC studies, this master set has been used to prepare iPSCs from multiple types of somatic cells from multiple types of species, confirming universality of the reprogramming mechanism. Just as there are species differences in embryonic and hematopoietic development, there are species differences in ESCs and iPSCs (collectively, pluripotent stem cells, or PSCs), namely, the quality of the pluripotency. Human PSCs have primed pluripotency, whereas mouse PSCs have naïve pluripotency [21Nichols J Smith A Naive and primed pluripotent states.Cell Stem Cell. 2009; 4: 487-492Abstract Full Text Full Text PDF PubMed Scopus (1261) Google Scholar]. The different states describe the stability of the pluripotency and have implications on the creation of chimeric animals. Researchers have managed to reset primed human iPSCs to the naïve state, but the chimeric potential of these cells has never been confirmed and, unlike mouse PSCs, no naïve human PSCs have been generated without first acquiring the primed state [22Takashima Y Guo G Loos R et al.Resetting transcription factor control circuitry toward ground-state pluripotency in human.Cell. 2014; 158: 1254-1269Abstract Full Text Full Text PDF PubMed Scopus (597) Google Scholar, 23Theunissen TW Powell BE Wang H et al.Systematic identification of culture conditions for induction and maintenance of naive human pluripotency.Cell Stem Cell. 2014; 15: 471-487Abstract Full Text Full Text PDF PubMed Scopus (533) Google Scholar]. The pluripotency state is considered a key determinant for modeling early development. Therefore, although hematopoietic cells have been successfully generated from human primed PSCs, the quality of the cells may be improved if naïve PSCs are the starting source. Aside from the development potential of iPSCs, they provide a unique model that can recapitulate disease phenotypes in vitro. Within 2 years of the first human iPSC report, scientists confirmed that patient cells can be reprogrammed to iPSCs, which were used to study the disease pathogenesis [24Dimos JT Rodolfa KT Niakan KK et al.Induced pluripotent stem cells generated from patients with ALS can be differentiated into motor neurons.Science. 2008; 321: 1218-1221Crossref PubMed Scopus (1598) Google Scholar, 25Lee G Papapetrou EP Kim H et al.Modelling pathogenesis and treatment of familial dysautonomia using patient-specific iPSCs.Nature. 2009; 461: 402-406Crossref PubMed Scopus (707) Google Scholar]. Moreover, patient iPSCs are the basis for several clinical cell therapies and drug studies (Table 1). Not included in these lists is an iPSC model that identified a candidate neutrophil elastase inhibitor that could recover mature neutrophils from patients with severe congenital neutropenia (SCN) and who are unresponsive to alternative treatments [26Makaryan V Kelley ML Fletcher B et al.Elastase inhibitors as potential therapies for ELANE-associated neutropenia.J Leukoc Biol. 2017; 102: 1143-1151Crossref PubMed Scopus (19) Google Scholar]. Important from an industry perspective, some of these drug candidates have come not from drug discovery, but rather from drug repositioning, which is estimated to lower the cost and time to approval by one-third [27Karagiannis P Onodera A Yamanaka S New models for therapeutic innovation from japan.EBioMedicine. 2017; 18: 3-4Abstract Full Text Full Text PDF PubMed Scopus (4) Google Scholar].Table 1iPSCs in the clinical settingDiseaseType of TherapyStatusiPSC-based cell therapiesAge-related macular degeneration 73Mandai M Watanabe A Kurimoto Y et al.Autologous induced stem-cell-derived retinal cells for macular degeneration.N Engl J Med. 2017; 376: 1038-1046Crossref PubMed Scopus (794) Google ScholarAutologous and allogeneic transplantation of iPSC-based product<10 patients have received transplantation of retinal epithelial cellsAplastic anemia with platelet refractoriness 64Ito Y Nakamura S Sugimoto N et al.Turbulence activates platelet biogenesis to enable clinical scale ex vivo production.Cell. 2018; 174: 636-648.e18Abstract Full Text Full Text PDF PubMed Scopus (158) Google ScholarAutologous transfusion of iPSC-derived plateletsSingle patient has been recruited; awaiting regulatory approvalHeart failure 74Miyagawa S Sawa Y Building a new strategy for treating heart failure using induced pluripotent stem cells.J Cardiol. 2018; 72: 445-448Abstract Full Text Full Text PDF PubMed Scopus (18) Google ScholarAllogeneic transplantation of iPSC-based productPatient recruitmentParkinson's disease 75Kikuchi T Morizane A Doi D et al.Human iPS cell-derived dopaminergic neurons function in a primate Parkinson's disease model.Nature. 2017; 548: 592-596Crossref PubMed Scopus (373) Google ScholarAllogeneic transplantation of iPSC-based productFirst operation was done in November 2018Spinal cord therapy 76Nagoshi N Okano H iPSC-derived neural precursor cells: potential for cell transplantation therapy in spinal cord injury.Cell Mol Life Sci. 2018; 75: 989-1000Crossref PubMed Scopus (47) Google ScholarAllogeneic transplantation of iPSC-based productApproval received from university board of ethics; approval from the Japan national regulatory body is expectedDrug trials based on iPSC patient modelsAmyotrophic lateral sclerosis 77McNeish J Gardner JP Wainger BJ et al.From dish to bedside: lessons learned while translating findings from a stem cell model of disease to a clinical trial.Cell Stem Cell. 2015; 17: 8-10Abstract Full Text Full Text PDF PubMed Scopus (59) Google ScholarDrug (ergobine)Phase IIFibrodysplasia ossifcans progressiva 78Hino K Horigome K Nishio M et al.Activin-A enhances mTOR signaling to promote aberrant chondrogenesis in fibrodysplasia ossificans progressiva.J Clin Invest. 2017; 127: 3339-3352Crossref PubMed Scopus (96) Google ScholarDrug (rapamycin)<20 patients have received the drug in double-blind studyProgressive supernuclear palsy 79Bright J Hussain S Dang V et al.Human secreted tau increases amyloid–beta production.Neurobiol Aging. 2015; 36: 693-709Crossref PubMed Scopus (160) Google ScholarDrug (BMS-986168)Phase IISpinal muscular atrophy 80Naryshkin NA Weetall M Dakka A et al.Motor neuron disease. SMN2 splicing modifiers improve motor function and longevity in mice with spinal muscular atrophy.Science. 2014; 345: 688-693Crossref PubMed Scopus (364) Google ScholarDrug (RG7800)Terminated after Phase I Open table in a new tab Accordingly, several patient iPSC models have been made to investigate blood diseases, including those causing bone marrow failure, anemia, and leukemia [28Dolatshad H Tatwavedi D Ahmed D et al.Application of induced pluripotent stem cell technology for the investigation of hematological disorders.Adv Biol Regul. 2019; 71: 19-33Google Scholar]. These studies have not yet led to clinical application, but they have revealed insights about which developmental stage the disease first manifests. For example, reprogramming cells from Fanconi anemia patients identified the disturbed differentiation capacity associated with the disease to occur as early as the hemoangiogenic progenitor stage, biasing cells to differentiate away from hematopoietic lineages and toward endothelial lineages [29Suzuki NM Niwa A Yabe M et al.Pluripotent cell models of fanconi anemia identify the early pathological defect in human hemoangiogenic progenitors.Stem Cells Transl Med. 2015; 4: 333-338Crossref PubMed Scopus (25) Google Scholar]. Another study using iPSCs from Diamond–Blackfan anemia patients found that erythropoiesis could be enhanced by a small chemical that induced autophagy via ATG5, a molecule required for autophagosome formation [30Doulatov S Vo LT Macari ER et al.Drug discovery for Diamond–Blackfan anemia using reprogrammed hematopoietic progenitors.Sci Transl Med. 2017; 9: eaah5645Crossref PubMed Scopus (70) Google Scholar]. Another SCN study found that the efficiency of neutrophil differentiation from patient iPSCs with a mutation in HAX1 was 25% that of healthy donor cells [31Morishima T Watanabe K Niwa A et al.Genetic correction of HAX1 in induced pluripotent stem cells from a patient with severe congenital neutropenia improves defective granulopoiesis.Haematologica. 2014; 99: 19-27Crossref PubMed Scopus (44) Google Scholar]. Instead, the differentiation tended to arrest at the myeloid progenitor stage and showed a higher propensity for apoptosis, consistent with the abnormal granulopoiesis seen in the disease. The transduction of HAX1 by lentivirus recovered the low neutrophil count. Fortunately, we have had exceptional access to consenting patients suffering from rare PIDs, allowing us to reprogram their cells and build models to examine monocyte and macrophage development. The findings from these investigations have confirmed other models or revealed previously unknown molecular causes (see below for examples). Mutations to NOD2 are the cause of Blau syndrome, a congenital monogenic granulomatosis. NOD2 is a receptor that upon binding to muramyl dipeptide (MDP) activates the nuclear factor-kappa beta (NF-κB) pathway, upregulating cytokines and chemokines [32Girardin SE Boneca IG Viala J et al.Nod2 is a general sensor of peptidoglycan through muramyl dipeptide (MDP) detection.J Biol Chem. 2003; 278: 8869-8872Crossref PubMed Scopus (1892) Google Scholar, 33Inohara N Ogura Y Fontalba A et al.Host recognition of bacterial muramyl dipeptide mediated through NOD2. Implications for Crohn's disease.J Biol Chem. 2003; 278: 5509-5512Crossref PubMed Scopus (1392) Google Scholar]. We reprogrammed cells from two NOD2 patients with the R334W mutation. In one group of iPSCs, the mutation was corrected by gene editing. In addition, cells from a healthy donor were reprogrammed with the mutation knocked in. Assays revealed distinctive responses by iPSC-derived macrophages to interferon-gamma (IFN-γ) stimulation based on the mutation [34Takada S Kambe N Kawasaki Y et al.Pluripotent stem cell models of Blau syndrome reveal an IFN-gamma-dependent inflammatory response in macrophages.J Allergy Clin Immunol. 2018; 141: 339-349.e311Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar]. In all cases, IFN-γ stimulation upregulated NOD2 expression, indicating a priming role. However, only in cells derived from mutant iPSCs did IFN-γ alone activate NF-κB (Figure 1A ). In the corrected case, MDP binding was required after the IFN-γ priming signal, suggesting that targeting IFN-γ could have therapeutic benefit. These results were confirmed in primary patient macrophages. Neonatal-onset multisystem inflammatory disease (NOMID), or chronic infantile neurologic, cutaneous and arthritis (CINCA), is the most clinically severe form of cryopyrin-associated periodic syndrome. The autoinflammation primarily affects the nerves, skin, and joints, and patients will develop sensory problems due to meningitis, rashes, and joint deformities. The majority of cases are associated with a mutation in the NLRP3 gene, which causes excessive secretion of interleukin-1 beta (IL-1β) by monocytes [35Tanaka N Izawa K Saito MK et al.High incidence of NLRP3 somatic mosaicism in patients with chronic infantile neurologic, cutaneous, articular syndrome: results of an International Multicenter Collaborative Study.Arthritis Rheum. 2011; 63: 3625-3632Crossref PubMed Scopus (210) Google Scholar, 36Goldbach-Mansky R Current status of understanding the pathogenesis and management of patients with NOMID/CINCA.Curr Rheumatol Rep. 2011; 13: 123-131Crossref PubMed Scopus (101) Google Scholar]. Dysfunction in the NLRP3 inflammasome is associated with several metabolic diseases such as gout and obesity, and many clinical therapies target the excessive IL-1β or the NLRP3 complex [37Shao BZ Xu ZQ Han BZ et al.NLRP3 inflammasome and its inhibitors: a review.Front Pharmacol. 2015; 6: 262Crossref PubMed Scopus (474) Google Scholar]. However, a large minority of NOMID patients do not express a pathological mutation in NLRP3, instead showing somatic mosaicism. One such case was shown in a single Japanese patient with a mutation in NLRC4 [38Kawasaki Y Oda H Ito J et al.Identification of a high-frequency somatic NLRC4 mutation as a cause of autoinflammation by pluripotent cell-based phenotype dissection.Arthritis Rheumatol. 2017; 69: 447-459Crossref PubMed Scopus (76) Google Scholar]. Interest in this gene has risen in recent years due to its discovered role in several autoinflammatory syndromes [39Canna SW de Jesus AA Gounil S et al.An activating NLRC4 inflammasome mutation causes autoinflammation with recurrent macrophage activation syndrome.Nat Genet. 2014; 46: 1140-1146Crossref PubMed Scopus (442) Google Scholar, 40Kitamura A Sasaki Y Abe T et al.An inherited mutation in NLRC4 causes autoinflammation in human and mice.J Exp Med. 2014; 211: 2385-2396Crossref PubMed Scopus (184) Google Scholar, 41Romberg N Al Moussawi K Nelson-Williams C et al.Mutation of NLRC4 causes a syndrome of enterocolitis and autoinflammation.Nat Genet. 2014; 46: 1135-1139Crossref PubMed Scopus (317) Google Scholar]. Fibroblasts from the NOMID patient were reprogrammed into iPSCs and then differentiated into monocytes. Consistent with NOMID symptoms, the iPSC-derived monocytes secreted IL-1β without a secondary signal. Interestingly, activation absent the secondary signal was true of only some iPSC clones despite all being made from the same patient (Figure 1B). Whole-exome sequence analysis of the two clone types revealed a somatic mosaicism of the NLRC4 mutation T177A as causative. Correcting the mutation by gene editing resulted in monocytes that behaved normally. Many NOMID patients are diagnosed without identifying causal mutations and somatic mutations can occur at frequencies below the detection limit of NGS systems, reiterating the benefits of iPSCs for rare PIDs [42Hoffman HM Broderick L Editorial: it just takes one: somatic mosaicism in autoinflammatory disease.Arthritis Rheumatol. 2017; 69: 253-256Crossref PubMed Scopus (13) Google Scholar]. Nakajo–Nishimura syndrome (NNS) is an autosomal disorder caused by mutations in PSMB8, which encodes for β5i protein, one of three subunits specialized for the immunoproteosome [43Arima K Kinoshita A Mishima H et al.Proteasome assembly defect due to a proteasome subunit beta type 8 (PSMB8) mutation causes the autoinflammatory disorder, Nakajo–Nishimura syndrome.Proc Natl Acad Sci U S A. 2011; 108: 14914-14919Crossref PubMed Scopus (224) Google Scholar, 44Murata S Yashiroda H Tanaka K Molecular mechanisms of proteasome assembly.Nat Rev Mol Cell Biol. 2009; 10: 104-115Crossref PubMed Scopus (395) Google Scholar]. Point mutations in this gene are associated with phenotypes beyond autoimmune symptoms, including muscle atrophy and lipodystrophy [45Agarwal AK Xing C DeMartino GN et al.PSMB8 encoding the beta5i proteasome subunit is mutated in joint contractures, muscle atrophy, microcytic anemia, and panniculitis–induced lipodystrophy syndrome.Am J Hum Genet. 2010; 87: 866-872Abstract Full Text Full Text PDF PubMed Scopus (243) Google Scholar, 46Kitamura A Maekawa Y Uehara H et al.A mutation in the immunoproteasome subunit PSMB8 causes autoinflammation and lipodystrophy in humans.J Clin Invest. 2011; 121: 4150-4160Crossref PubMed Scopus (206) Google Scholar]. NNS patients are susceptible to rashes and skin eruptions and are usually treated with corticosteroids, but this therapy does not ameliorate the lipodystrophy [47Kunimoto K Kimura A Uede K et al.A new infant case of Nakajo–Nishimura syndrome with a genetic mutation in the immunoproteasome subunit: an overlapping entity with JMP and CANDLE syndrome related to PSMB8 mutations.Dermatology. 2013; 227: 26-30Crossref PubMed Scopus (21) Google Scholar]. In NNS, the upregulation of proinflammatory factors is attributed to the p38 mitogen-activated protein kinase (MAPK) pathway. As expected, myeloid cells differentiated from patient iPSCs showed reduced immunoproteasome activity, higher production of reactive oxygen species, and increased production of IL-6, MCP-1, and IP-10, cytokines and chemokines that are associated with the disease [48Honda-Ozaki F Terashima M Niwa A et al.Pluripotent stem cell model of Nakajo–Nishimura syndrome untangles proinflammatory pathways mediated by oxidative stress.Stem Cell Reports. 2018; 10: 1835-1850Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar]. Furthermore, myeloid cells from patient and isogenic control iPSCs differed in that the mutant types showed evidence of being in a primed state even absent a stimulus (Figure 1C). Application of a p38 MAPK inhibitor to the cells suppressed the secretion of IL-6, MCP-1, and IP-10 in a dose-dependent manner, demonstrating how patient iPSCs in combination with gene editing for the generation of isogenic controls could contribute to drug discovery for PIDs. Some PIDs associated with mutations in proteasome dysfunctions, like those seen with PSMB8 mutations, are multigenic [49Brehm A Liu Y Sheikh A et al.Additive loss-of-function proteasome subunit mutations in CANDLE/PRAAS patients promote type I IFN production.J Clin Invest. 2015; 125: 4196-4211Crossref PubMed Scopus (179) Google Scholar]. Such diseases have proven a degree more difficult to study with iPSCs. However, success has been reported with complex disorders such as autism or idiopathic conditions such as amyotrophic lateral sclerosis, suggesting that a combination of iPSCs with other biotechnologies such as gene editing could lead to major breakthroughs for this category of PIDs [50Marchetto MC Belinson H Tian Y et al.Altered proliferation and networks in neural cells derived from idiopathic autistic individuals.Mol Psychiatry. 2017; 22: 820-835Crossref PubMed Scopus (231) Google Scholar, 51Imamura K Izumi Y Watanabe A et al.The Src/c-Abl pathway is a potential therapeutic target in amyotrophic lateral sclerosis.Sci Transl Med. 2017; 9: eaaf3962Crossref PubMed Scopus (134) Google Scholar]. Additionally, some PIDs are attributed to epigenetic alterations without any known genetic origin [52Campos-Sanchez E Martinez-Cano J Del Pino Molina L et al.Epigenetic deregulation in human primary immunodeficiencies.Trends Immunol. 2019; 40: 49-65Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar]. Cell reprogramming involves epigenetic resetting without changes to the genome and studies have shown how cell reprogramming in vivo can be used to study epigenetic causes in solid cancers [53Sogabe Y Seno H Yamamoto T et al.Unveiling epigenetic regulation in cancer, aging, and rejuvenation with in vivo reprogramming technology.Cancer Sci. 2018; 109: 2641-2650Crossref PubMed Scopus (9) Google Scholar]. Human iPSCs only recently reached their second decade and current disease models for PIDs could be viewed as a first gener
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