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Background aim X-linked MAGT1 deficiency with increased susceptibility to EBV-infection and N-linked glycosylation defect' (XMEN) disease is caused by mutations in the magnesium transporter 1 (MAGT1) gene. Loss of MAGT1 function results in a glycosylation defect that abrogates expression of key immune proteins such as the NKG2D receptor on CD8+ T and NK cells, which is critical for the recognition and killing of virus-infected and transformed cells, a biomarker for MAGT1 function. Patients with XMEN disease frequently have increased susceptibility to EBV infections and EBV-associated B cell malignancies, for which no specific treatment options are currently available. Experimental transfer of donor EBV-specific cytotoxic T cells may be beneficial but carries the risks of eliciting alloimmune responses. An approach for cell therapy to address viral infections and associated complications that avoids the risks of alloimmunity is needed. Methods Here the authors assess the feasibility and efficiency of correcting autologous lymphocytes from XMEN patients by MAGT1 mRNA electroporation (EP) that avoids genomic integration and can be scaled for clinical application. Results and conclusions Restoration of NKG2D expression was demonstrated in XMEN patient lymphocytes after MAGT1 mRNA electroporation that reach healthy donor levels in CD8+ T and NK cells at 1-2 days after EP. NKG2D expression persisted at ∼50% for 2 weeks after EP. Functionally, mRNA-correction of XMEN NK cells rescued cytotoxic activity also to healthy donor NK cell level. The restored NKG2D receptor expression and function were unaffected by cryopreservation, which will make feasible repeat infusions of MAGT1 mRNA-corrected autologous XMEN CD8+ T and NK cells for potential short term therapy for XMEN patients without the risks of alloimmunization.

Introduction 'X-linked immunodeficiency with magnesium defect, Epstein-Barr virus (EBV) infection, and neoplasia' (XMEN) disease is a primary immunodeficiency disease caused by loss-of-function mutations in the MAGT1 gene encoding for the magnesium transporter 1. This leads to the absence of expression of the "Natural-Killer Group 2, member D" (NKG2D) receptor in natural killer (NK) and CD8+ T cells, which is essential for their antiviral and antitumoral cytotoxic activity. In consequence, XMEN patients develop chronic EBV infections and EBV-related lymphoproliferative disorders. Allogeneic bone marrow transplant has been associated with significant mortality, and there are no other effective treatments. In that context, we aimed at developing two complementary approaches to treat XMEN patients: 1) Adoptive transfer of XMEN T/NK cells corrected by transient mRNA therapy or longer-lasting gene editing therapy in order to control infections, and 2) Transplantation of gene-edited CD34+ cells in order to permanently restore production of functional immune cells. Material and methods CD34+ cells and PBMCs were collected from XMEN patients and healthy donors (HD) (NIH Protocol 94-I-073). For mRNA therapy, we expanded T cells with anti-CD3/anti-CD28 beads in RPMI + 10% serum supplemented with 200 IU/mL IL2 for 5-7 days and NK cells with 100 IU/mL IL2 and 10 ng/mL IL15 in culture with K562-mb15-41BBL for 10-15 days. Both XMEN T and NK cells were electroporated (EP) with MAGT1 mRNA and cultured for up to 28 days. For gene editing, XMEN CD34+ or stimulated T cells were electroporated with Cas9 mRNA and sgRNA; a rAAV6 donor encoding for the codon-optimized MAGT1 cDNA was added after EP. Two days post-EP, CD34+ cells were differentiated into NK cells for 35 days in vitro. Results MAGT1 mRNA-based therapy. We first showed a restored MAGT1 expression by western blot at 6h and 24h post-EP of the MAGT1 mRNA. In consequence, NKG2D expression analyzed by flow cytometry was restored in expanded CD8+ T and NK cells starting within the 6h post-EP (20-40%), with a peak at 48h (>85%) and a progressive decrease of the expression over time (still 40% and 75%, respectively, of CD8+ T and NK cells of cells at day 14 post-EP respectively). The cytotoxic activity of mRNA-corrected XMEN NK cells was analyzed by culture with K562 target cells at several effector:target (E:T) ratios and shown to be restored at a level similar to HD NK cells (mRNA-treated: 66.7% ±5.8%; HD: 67.8% ±5.9% at E:T 2:1 ratio) compared to untreated cells (49.0% ±7.2%) (Fig 1a). Anticipating the potential use of these cells for repeated infusions as a treatment modality to control infections, we demonstrated that MAGT1 mRNA-corrected CD8+ T and NK cells that have been cryopreserved and thawed exhibit the same NKG2D expression kinetics following thaw and culture. Gene editing therapy. XMEN CD34+ cells electroporated with Cas9 mRNA and a sgRNA targeting exon 1 of MAGT1 gene showed an in vitro average integration rate of the MAGT1 cDNA AAV donor of 35.6% (range: 33.8-41.9%). The NKG2D expression in AAV-treated CD34+-derived NK cells was approximatively of 23% (range: 14.2-27.9%). Interestingly, their cytotoxic activity was similar to the level of NKG2D expression (23.1% ±4.3%), significantly higher than in untreated cells (9.7% ±2.8%) (Fig 1b). Similar rates of targeted integration and NKG2D expression were also obtained in AAV-treated CD8+ T cells. Conclusion For the first time, we demonstrate the efficiency of two approaches for development of potential cell therapy treatments of XMEN patients. MAGT1 mRNA electroporation can restore efficient transient expression of NKG2D in CD8+ T and NK cells, thus fully restoring the cytotoxic activity of NK cells. In addition, cells electroporated with MAGT1 mRNA can be cryopreserved, thus allowing repeated infusions. In parallel, we showed that efficient targeted insertion can be achieved in CD8+ T cells and CD34+ cells by using an AAV donor although the level of NKG2D expression is lower. Optimizations are currently ongoing in order to reach higher levels of correction. Both approaches could be combined in order to propose a new therapeutic strategy for the treatment of XMEN patients: repetitive adoptive transfer of mRNA-corrected autologous T/NK cells for the prevention or control of intractable infections, and transplantation of gene-edited CD34+ cells for the definitive treatment of these patients. Disclosures Meis: CELLSCRIPT, LLC: Employment. Li:MaxCyte, Inc: Employment. Allen:MaxCyte, Inc: Employment. Clark:CELLSCRIPT, LLC: Employment. Dahl:CELLSCRIPT, LLC: Other: Owner and officer.

Lentivector mediated gene transfer into hematopoietic stem/progenitor cells and T cells has resulted in long-term stable integration of transgenes and significant clinical benefits in many diseases. We previously reported (De Ravin et al Sci Transl Med. 2016) early outcome data for 5 patients with X-linked severe combined immunodeficiency (X-SCID) enrolled in a first-in-human lentivector gene therapy clinical trial (NCT03315078) as salvage therapy for older children and young adults who had received prior haplo-identical hematopoietic stem cell transplantation (HSCT) as infants without chemotherapy-based conditioning. Lymphocyte-depleted haplo-identical stem cell transplant in X-SCID infants without conditioning generally results in only a T-cell engraftment that may also decline over time which, combined with B- and NK-cell dysfunction, may result in the progression of multi-system clinical problems (bronchiectasis, infections, gastrointestinal malabsorption, failure to grow, immune dysregulation). By 2016 three additional patients were treated and the cohort of 8 patients have now been followed for 3 to 7 years (Cohort A), where we observed gradual clinical benefit in the clearance of chronic norovirus and associated improved abdominal complaints, malabsorption, and growth and IgG production. Four patients were able to cease immunoglobulin replacement therapy. Despite these encouraging results, the relatively inefficient transduction of hematopoietic stem/progenitor cells (HSPCs) required large quantities of vector, and resulted in relatively low vector copy number in myeloid cells in some patients, with delayed immune cell recovery and persistent clinical disease especially in the last patient treated, P8. To address this, we developed a refined enhanced transduction (ET) procedure consisting of a single overnight transduction after 48hours pre-stimulation in cytokines (Stem cell factor, Thrombopoietin, Flt3-ligand; 100ng/mL) and incorporated transduction enhancers LentiBoost 1:100 and dimethyl prostaglandin 2 (dmPGE2; 1mM) and recently treat 6 patients, including re-treatment of P8 (Cohort B). Here we compared the early outcomes from Cohort B patients who received autologous CD34+ HSPCs processed with the enhanced transduction (ET) procedure. These patients (aged 12 to 36 yo) had significant problems with donor T cell infiltration of liver, bone marrow and kidneys, and near absent B and NK cells. Cryopreserved G-CSF/plerixafor mobilized peripheral blood CD34+ HSPCs (5x106/kg to 28x106/kg) were transduced by the ET process at 5% vector concentration, compared to previous method without transduction enhancers of two daily transductions at 20-30% final vector concentration, representing a 10-12 fold reduction in vector used. Colony forming unit assays showed 78%-92% versus 17%-58% vector-positive clones in Cohort B compared with Cohort A, with VCN of 1.5-12 copies (Cohort B), compared with 0.06 to 0.5 copies in Cohort A. At one month following infusion of gene corrected cell product, we isolated peripheral blood CD14+ myeloid cells as indication of early marrow output from engrafted HSPCs, and observed VCN of 1 to 4 copies (P9-12 and re-treat P8), a ≥10x increase from Cohort A (0.04 to 0.23) at same early time point after infusion (Fig 1). In addition to earlier clinical improvement (abdominal complaints, appetite, growth), there was also an early appearance of B and NK cells (Fig. 2) at much higher levels in Cohort B than previously observed even at years after treatment in Cohort A. In conclusion, we observed significantly improved measures of early clinical outcomes from lentivector gene therapy of older children and young adults with X-SCID using enhanced transduction procedure with addition of LentiBoost and dmPGE2, that achieves much greater transduction efficiencies with >10 fold less vector, and results in faster immune reconstitution and more significant clinical benefit by 3 months. The patients are monitored closely for potential risks from higher VCNs that may be balanced by reduced selection pressure due to the greater numbers of gene corrected clones. Figure Disclosures Puck: NIAID: Research Funding; Pfeizer: Other: spouse serves on Rare Disease Advisory Board; Invitae: Other: spouse employment. Cowan:bluebird bio: Consultancy; Homology Medicine: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; UpToDate: Honoraria; California Institute Of Regenerative Medicine: Research Funding; NIH NIAD: Research Funding; Rocket Pharma: Consultancy; Leadiant: Consultancy. Mamcarz:ASSISI Foundation of Memphis: Research Funding; MBIO: Other: St. Jude Children's Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy; California Institute of Regenerative Medicine: Research Funding; NHLBI: Research Funding; UpToDate: Honoraria; American Lebanese Syrian Associated Charities: Research Funding. Gottschalk:Patents and patent applications in the fields of T-cell & Gene therapy for cancer: Patents & Royalties; California Institute for Regenerative Medicine: Research Funding; NHLBI: Research Funding; America Lebanese Syrian Associated Charities: Research Funding; TESSA Therapeutics: Other: Research Collaboration; ViraCyte: Consultancy; MBIO: Other: St. Jude Children's Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy; Sanofi: Honoraria; Tidal: Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy; EMD Serono: Honoraria; ASSISI fundation of Memphis: Research Funding; Inmatics: Membership on an entity's Board of Directors or advisory committees. Meagher:MBIO: Other: St. Jude Children's Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy.

There is a paucity of data on the effect of multimorbidity on early (≤ 1-year) mortality in older adults after permanent pacemaker placement (PPM) implantation. Observational retrospective study from 2008 to 2015, within an integrated healthcare delivery system to assess the association of the

Background: T-wave alternans (TWA) is a promising electrocardiogram (ECG) predictor of sudden cardiac arrest, yet needs specialized recordings for conventional spectral analysis. Modified moving average (MMA) analysis is a new approach that can measure TWA from routine ECGs, thus widening its applicability. However, MMA-TWA has not been calibrated against spectral TWA nor outcome in high risk patients. We hypothesized that spectral and MMA-TWA would both predict arrhythmia-free survival on long-term prospective follow-up. Methods and Results: In 41 patients with left ventricular systolic dysfunction (ejection fraction 31 ± 13%), we studied TWA simultaneously using spectral and MMA during pacing (< 110 beats/min). MMA amplified TWA over spectral analyses (13.0 ± 8.28 μV vs 1.96 ± 5.15 μV, P < 0.001). On 542 ± 311 days' follow-up, from clinic visits, telephonic interviews, and device interrogations, there were 11 deaths or sustained ventricular arrhythmias (‘events’). Positive spectral TWA (≥1.9 μV) identified patients with from those without events (P = 0.02). Receiver-operating characteristics for MMA-TWA showed that the cutpoint ≥ 10.75 μV was optimal for the combined endpoint. Kaplan-Meier analysis using this MMA-TWA cutpoint trended to predict events (P = 0.06), while MMA combined with spectral TWA identified events (P = 0.01). Conclusions: MMA amplifies TWA compared to traditional spectral analyses, but both likely reflect similar pathophysiology. Validation in larger populations will enable MMA-TWA to be widely applied to stratify risk for sudden cardiac arrest.

Introduction: The causes of transcristal conduction (TC) in patients with atrial flutter (AFL) are unknown. Methods and Results: In two groups of patients referred for AFL ablation, 36 had cavotricuspid isthmus (CTI) dependent flutter (Group I) and 24 had lower (n = 21) or upper loop reentry (n = 5) (Group II). After ablation, isthmus block was evaluated by pacing from the coronary sinus (CS) and low lateral right atrium and by alternative techniques, including mapping with electrodes spanning the CTI or electroanatomic mapping. After bidirectional CTI block was verified, 21/36 (58%) in Group I showed TC with CS pacing, including low TC in 16 (including 11 showing “pseudo” CTI conduction), higher TC in 6 and multiple breaks in 3. However, 8 with low TC during CS pacing showed unidirectional block by pacing outside of the CS os. Twelve (50%) in Group II had TC during CS pacing after bidirectional CTI block, with low TC in 5 (2 mimicking residual CTI conduction) and higher breaks in 9. There was no significant difference in the incidence of TC during CS pacing after CTI block between groups. In seven autopsied hearts, the muscle orientation between the proximal CS musculature and Eustachian ridge were examined. Muscular connections between the CS and Eustachian ridge coursing toward the orifice of inferior vena cava were found in one of the hearts. Conclusions: It is concluded that in patients with bidirectional CTI block, pacing from the CS may be associated with TC mimicking a conduction leak through the isthmus. Pacing just outside the CS os helps distinguish pseudo from true isthmus block.

There is a paucity of data on cardiovascular outcomes in patients with end-stage renal disease (ESRD) after implantation of an implantable cardiac defibrillator (ICD) or cardiac resynchronization therapy (CRT). We enrolled 7,825 Kaiser Permanente members across 6 geographical regions of the United

Background: Abnormal heart rate turbulence (HRT) reflects autonomic derangements predicting all-cause mortality, yet has riot been shown to predict ventriculor arrhythmias in at-risk patients. We hypothesized that HRT at programmed ventricular stimulation (PVS) would predict arrhythmia initiation in patients with left ventriculor dysfunction. Methods: We studied 27 patients with coronary disease, left ventricular ejection fraction (LVEF) 26.7 +/- 9.1%, and plasma B-type natriuretic peptide (BNP) 461 +/- 561 pg/mL. Prior to arrhythmia induction at PVS, we measured sinus cycles after spontaneous or paced premature ventricular contractions (PVCs) for turbulence onset (TO; % cycle length change following PVC) and slope (TS; greatest slope of return to baseline cycle). T-wave alternans (TWA) was also measured during atrial pacing. Results: At PVS, abnormal TO (>= 0%) predicted inducible ventricular tachycardia (VT; n = 10 patients; P < 0.05). TO was greater in inducible than in noninducible patients (2.3 +/- 3.1% vs -0.02 +/- 2.8%, P < 0.05) and correlated with LVEF (P < 0.05) but not with BNP. TS did not differ between groups. Conversely, ambulatory HRT differed significantly from HRT at PVS (TO -0.55 +/- 1.08% vs 0.85 +/- 3.02%, P < 0.05; TS 2.63 +/- 2.09 ms/RR vs 8.70 +/- 6.56 ms/RR, P < 0.01), and did not predict inducible VT but trended (P = 0.05) to predict sustained VT on 739 179 days follow-up. TWA predicted inducible (P < 0.05) and spontaneous (P = 0.0001) VT but did not co-migrate with HRT. Conclusions: Abnormal HRT measured at PVS predicted the induction of sustained ventricular arrhythmias in patients with ischemic cardiomyopathy. However, HRT at PVS did not correlate with ambulatory HRT nor with TWA, both of which predicted spontaneous ventricular arrhythmias. Thus, HRT may reflect the influence of autonomic milieu on arrhythmic susceptibility and is likely complementary to traditional arrhythmic indices.