Genome editing of donor-derived T-cells to generate allogenic chimeric antigen receptor-modified T cells: Optimizing αß T cell-depleted haploidentical hematopoietic stem cell transplantation.

Allogeneic hematopoietic stem cell transplantation is an effective therapy for high-risk leukemias. In children, graft manipulation based on the selective removal of aß T cells and B cells has been shown to reduce the risk of acute and chronic graft-versus-host disease, thus allowing the use of haploidentical donors which expands the population of recipients in whom allogeneic hematopoietic stem cell transplantation can be used. Leukemic relapse, however, remains a challenge. T cells expressing chimeric antigen receptors can potently eliminate leukemia, including those in the central nervous system. We hypothesized that by engineering the donor aß T cells that are removed from the graft by genome editing to express a CD19-specific chimeric antigen receptor, while simultaneously inactivating the T-cell receptor, we could create a therapy that enhances the anti-leukemic efficacy of the stem cell transplant without increasing the risk of graft-versus-host disease. Using genome editing with Cas9 ribonucleoprotein and adeno-associated virus serotype 6, we integrated a CD19-specific chimeric antigen receptor inframe into the TRAC locus. More than 90% of cells lost T-cell receptor expression, while >75% expressed the chimeric antigen receptor. The initial product was further purified with less than 0.05% T-cell receptorpositive cells remaining. In vitro, the chimeric antigen receptor T cells efficiently eliminated target cells and produced high cytokine levels when challenged with CD19+ leukemia cells. In vivo, the gene-modified T cells eliminated leukemia without causing graft-versus-host disease in a xenograft model. Gene editing was highly specific with no evidence of off-target effects. These data support the concept that the addition of aß T-cell-derived, genome-edited T cells expressing CD19-specific chimeric antigen receptors could enhance the anti-leukemic efficacy of aß T-celldepleted haploidentical hematopoietic stem cell transplantation without increasing the risk of graft-versus-host disease.

IPEX due to an exon 7 skipping FOXP3 mutation with autoimmune diabetes mellitus cured by selective TReg cell engraftment.

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare inherited disorder leading to severe organ-specific autoimmunity. IPEX is caused by hemizygous mutations in FOXP3, which codes for a master transcription factor of regulatory T (TReg) cell development and function. We describe a four-year-old boy with typical but slightly delayed-onset of IPEX with autoimmune diabetes mellitus, enteropathy, hepatitis and skin disease. We found the unreported FOXP3 splice site mutation c.816+2T>A that leads to the loss of leucine-zipper coding exon 7. RNA-Seq revealed that FOXP3Δ7 leads to differential expression of FOXP3 regulated genes. After myeloablative conditioning the patient underwent allogeneic HSCT from a matched unrelated donor. HSCT led to the resolution of all IPEX symptoms including insulin requirement despite persisting autoantibody levels. After initial full donor engraftment nearly complete autologous reconstitution was documented, but donor-derived TReg cells persisted with a lineage-specific chimerism of >70% and the patient remained in clinical remission.

Maturation of Platelet Function During Murine Fetal Development In Vivo.

OBJECTIVE: Platelet function has been intensively studied in the adult organism. However, little is known about the function and hemostatic capacity of platelets in the developing fetus as suitable in vivo models are lacking. APPROACH AND RESULTS: To examine fetal platelet function in vivo, we generated a fetal thrombosis model and investigated light/dye-induced thrombus formation by intravital microscopy throughout gestation. We observed that significantly less and unstable thrombi were formed at embryonic day (E) 13.5 compared with E17.5. Flow cytometry revealed significantly lower platelet counts in E13.5 versus E17.5 fetuses versus adult controls. In addition, fetal platelets demonstrated changed activation responses of surface adhesion molecules and reduced P-selectin content and mobilization. Interestingly, we also measured reduced levels of the integrin-activating proteins Kindlin-3, Talin-1, and Rap1 during fetal development. Consistently, fetal platelets demonstrated diminished spreading capacity compared with adults. Transfusion of adult platelets into the fetal circulation led to rapid platelet aggregate formation even in young fetuses. Yet, retrospective data analysis of a neonatal cohort demonstrated no correlation of platelet transfusion with closure of a persistent ductus arteriosus, a process reported to be platelet dependent. CONCLUSIONS: Taken together, we demonstrate an ontogenetic regulation of platelet function in vivo with physiologically low platelet numbers and hyporeactivity early during fetal development shedding new light on hemostatic function during fetal life.

Reduced toxicity, myeloablative HLA-haploidentical hematopoietic stem cell transplantation with post-transplantation cyclophosphamide for sickle cell disease.

Allogeneic hematopoietic stem cell transplantation (HSCT) offers the possibility of cure for sickle cell disease (SCD) patients. Unfortunately, the probability of finding an HLA-matched donor for SCD patients is low. HSCT from HLA-haploidentical donors using reduced intensity conditioning, unmanipulated bone marrow and post-transplantation cyclophosphamide (ptCy) has resulted in negligible toxicity but high rates of graft rejection. We hypothesized that combining ptCy with a myeloablative reduced toxicity conditioning including serotherapy to increase immune ablation would allow for better engraftment. In a pilot approach, we treated three patients with SCD (5, 8, and 20 years old) lacking a matched donor. All patients had severe disease-related complications despite standard treatment. They received unmanipulated bone marrow from parental HLA-haploidentical donors. Conditioning consisted of alemtuzumab 0.2 mg/kg/day on days -9 and -8, fludarabine 30 mg/m2/day on days -7 to -3, treosulfan 14 g/m2/day on days -7 to -5, thiotepa 2 × 5 mg/kg/day on day -4, and cyclophosphamide 14.5 mg/kg/day on days -3 and -2. GVHD prophylaxis was performed using cyclophosphamide 2 × 50 mg/kg on days +3 and +4 and mycophenolate mofetil, tacrolimus from day +5. After a follow-up of 11, 14, and 30 months, all three patients are alive and well, off immunosuppression, and without symptoms of SCD. One patient experienced mild skin GVHD grade I, none showed chronic GVHD. Asymptomatic CMV reactivation was seen in two patients. HLA-haploidentical HSCT can extend the donor pool for patients with SCD. Whether intensification of the conditioning regimen and intensive immunosuppression leads to improvement in engraftment rates while still allowing a favorable toxicity profile deserves further investigation.

Impairment of endothelial progenitor cell function and vascularization capacity by aldosterone in mice and humans.

AIMS: Hyperaldosteronism is associated with vascular injury and increased cardiovascular events. Bone marrow-derived endothelial progenitor cells (EPCs) play an important role in endothelial repair and vascular homeostasis. We hypothesized that hyperaldosteronism impairs EPC function and vascularization capacity in mice and humans. METHODS AND RESULTS: We characterized the effects of aldosterone and mineralocorticoid receptor (MR) blockade on EPC number and function as well as vascularization capacity and endothelial function. Treatment of human EPC with aldosterone induced translocation of the MR and impaired multiple cellular functions of EPC, such as differentiation, migration, and proliferation in vitro. Impaired EPC function was rescued by pharmacological blockade or genetic ablation of the MR. Aldosterone protein kinase A (PKA) dependently increased reactive oxygen species formation in EPC. Aldosterone infusion in mice impaired EPC function, EPC homing to vascular structures and vascularization capacity in a MR-dependent but blood pressure-independent manner. Endothelial progenitor cells from patients with primary hyperaldosteronism compared with controls of similar age displayed reduced migratory potential. Impaired EPC function was associated with endothelial dysfunction. MR blockade in patients with hyperaldosteronism improved EPC function and arterial stiffness. CONCLUSION: Endothelial progenitor cells express a MR that mediates functional impairment by PKA-dependent increase of reactive oxygen species. Normalization of EPC function may represent a novel mechanism contributing to the beneficial effects of MR blockade in cardiovascular disease prevention and treatment.

Reengineering Ponatinib to Minimize Cardiovascular Toxicity.

Small molecule tyrosine kinase inhibitors (TKI) have revolutionized cancer treatment and greatly improved patient survival. However, life-threatening cardiotoxicity of many TKIs has become a major concern. Ponatinib (ICLUSIG) was developed as an inhibitor of the BCR-ABL oncogene and is among the most cardiotoxic of TKIs. Consequently, use of ponatinib is restricted to the treatment of tumors carrying T315I-mutated BCR-ABL, which occurs in chronic myeloid leukemia (CML) and confers resistance to first- and second-generation inhibitors such as imatinib and nilotinib. Through parallel screening of cardiovascular toxicity and antitumor efficacy assays, we engineered safer analogs of ponatinib that retained potency against T315I BCR-ABL kinase activity and suppressed T315I mutant CML tumor growth. The new compounds were substantially less toxic in human cardiac vasculogenesis and cardiomyocyte contractility assays in vitro. The compounds showed a larger therapeutic window in vivo, leading to regression of human T315I mutant CML xenografts without cardiotoxicity. Comparison of the kinase inhibition profiles of ponatinib and the new compounds suggested that ponatinib cardiotoxicity is mediated by a few kinases, some of which were previously unassociated with cardiovascular disease. Overall, the study develops an approach using complex phenotypic assays to reduce the high risk of cardiovascular toxicity that is prevalent among small molecule oncology therapeutics. SIGNIFICANCE: Newly developed ponatinib analogs retain antitumor efficacy but elicit significantly decreased cardiotoxicity, representing a therapeutic opportunity for safer CML treatment.

Metabolic engineering generates a transgene-free safety switch for cell therapy.

Safeguard mechanisms can ameliorate the potential risks associated with cell therapies but currently rely on the introduction of transgenes. This limits their application owing to immunogenicity or transgene silencing. We aimed to create a control mechanism for human cells that is not mediated by a transgene. Using genome editing methods, we disrupt uridine monophosphate synthetase (UMPS) in the pyrimidine de novo synthesis pathway in cell lines, pluripotent cells and primary human T cells. We show that this makes proliferation dependent on external uridine and enables us to control cell growth by modulating the uridine supply, both in vitro and in vivo after transplantation in xenograft models. Additionally, disrupting this pathway creates resistance to 5-fluoroorotic acid, which enables positive selection of UMPS-knockout cells. We envision that this approach will add an additional level of safety to cell therapies and therefore enable the development of approaches with higher risks, especially those that are intended for limited treatment durations.

Tuning the Antigen Density Requirement for CAR T-cell Activity.

Insufficient reactivity against cells with low antigen density has emerged as an important cause of chimeric antigen receptor (CAR) T-cell resistance. Little is known about factors that modulate the threshold for antigen recognition. We demonstrate that CD19 CAR activity is dependent upon antigen density and that the CAR construct in axicabtagene ciloleucel (CD19-CD28ζ) outperforms that in tisagenlecleucel (CD19-4-1BBζ) against antigen-low tumors. Enhancing signal strength by including additional immunoreceptor tyrosine-based activation motifs (ITAM) in the CAR enables recognition of low-antigen-density cells, whereas ITAM deletions blunt signal and increase the antigen density threshold. Furthermore, replacement of the CD8 hinge-transmembrane (H/T) region of a 4-1BBζ CAR with a CD28-H/T lowers the threshold for CAR reactivity despite identical signaling molecules. CARs incorporating a CD28-H/T demonstrate a more stable and efficient immunologic synapse. Precise design of CARs can tune the threshold for antigen recognition and endow 4-1BBζ-CARs with enhanced capacity to recognize antigen-low targets while retaining a superior capacity for persistence. SIGNIFICANCE: Optimal CAR T-cell activity is dependent on antigen density, which is variable in many cancers, including lymphoma and solid tumors. CD28ζ-CARs outperform 4-1BBζ-CARs when antigen density is low. However, 4-1BBζ-CARs can be reengineered to enhance activity against low-antigen-density tumors while maintaining their unique capacity for persistence.This article is highlighted in the In This Issue feature, p. 627.

Author Correction: Gene correction for SCID-X1 in long-term hematopoietic stem cells.

The original version of this Article omitted the following from the Acknowledgements: "G.B. acknowledges the support from the Cancer Prevention and Research Institute of Texas (RR140081 and RR170721)."This has now been corrected in both the PDF and HTML versions of the Article.

Highly Efficient and Marker-free Genome Editing of Human Pluripotent Stem Cells by CRISPR-Cas9 RNP and AAV6 Donor-Mediated Homologous Recombination.

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

Gene correction for SCID-X1 in long-term hematopoietic stem cells.

Gene correction in human long-term hematopoietic stem cells (LT-HSCs) could be an effective therapy for monogenic diseases of the blood and immune system. Here we describe an approach for X-linked sSevere cCombined iImmunodeficiency (SCID-X1) using targeted integration of a cDNA into the endogenous start codon to functionally correct disease-causing mutations throughout the gene. Using a CRISPR-Cas9/AAV6 based strategy, we achieve up to 20% targeted integration frequencies in LT-HSCs. As measures of the lack of toxicity we observe no evidence of abnormal hematopoiesis following transplantation and no evidence of off-target mutations using a high-fidelity Cas9 as a ribonucleoprotein complex. We achieve high levels of targeting frequencies (median 45%) in CD34+ HSPCs from six SCID-X1 patients and demonstrate rescue of lymphopoietic defect in a patient derived HSPC population in vitro and in vivo. In sum, our study provides specificity, toxicity and efficacy data supportive of clinical development of genome editing to treat SCID-Xl.

Author Correction: Gene correction for SCID-X1 in long-term hematopoietic stem cells.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A high-fidelity Cas9 mutant delivered as a ribonucleoprotein complex enables efficient gene editing in human hematopoietic stem and progenitor cells.

Translation of the CRISPR-Cas9 system to human therapeutics holds high promise. However, specificity remains a concern especially when modifying stem cell populations. We show that existing rationally engineered Cas9 high-fidelity variants have reduced on-target activity when using the therapeutically relevant ribonucleoprotein (RNP) delivery method. Therefore, we devised an unbiased bacterial screen to isolate variants that retain activity in the RNP format. Introduction of a single point mutation, p.R691A, in Cas9 (high-fidelity (HiFi) Cas9) retained the high on-target activity of Cas9 while reducing off-target editing. HiFi Cas9 induces robust AAV6-mediated gene targeting at five therapeutically relevant loci (HBB, IL2RG, CCR5, HEXB, and TRAC) in human CD34+ hematopoietic stem and progenitor cells (HSPCs) as well as primary T cells. We also show that HiFi Cas9 mediates high-level correction of the sickle cell disease (SCD)-causing p.E6V mutation in HSPCs derived from patients with SCD. We anticipate that HiFi Cas9 will have wide utility for both basic science and therapeutic genome-editing applications.

Organic nitrates differentially modulate circulating endothelial progenitor cells and endothelial function in patients with symptomatic coronary artery disease.

Symptomatic coronary artery disease (CAD) is usually treated with organic nitrates. Endothelial progenitor cells (EPCs) are a circulating cell population participating in vascular homeostasis in a nitric oxide-dependent manner. We investigated the effects of the nitric oxide donors isosorbide dinitrate (ISDN) and pentaerythritol tetranitrate (PETN) on EPC and endothelial function in patients with symptomatic CAD. We randomized 36 patients with angiographically proven CAD to treatment with either ISDN (40 mg retarded release orally two times per day; n = 18) or PETN (80 mg orally two times per day; n = 18) for 14 days (clinical trial number: NCT01030367). PETN treatment substantially increased numbers of circulating CD34(+)/KDR(+) EPCs (p = 0.02), whereas no effects were observed in patients treated with ISDN. EPC function assessed by formation of endothelial colonies was enhanced by twofold (p = 0.04) in patients treated with PETN. No changes were observed after ISDN treatment. Endothelial function, assessed by peripheral arterial tonometry, remained unchanged during PETN treatment, but was significantly impaired in patients treated with ISDN. Treatment of symptomatic CAD patients with PETN for 14 days significantly increased levels of circulating EPC and improved markers for EPC function, whereas ISDN was without effects on EPCs and worsened endothelial function.