The Neuregulin-1 (Nrg1) signaling pathway has been widely implicated in many aspects of heart development including cardiac trabeculation. Cardiac trabeculation is an important morphogenetic process where clusters of ventricular cardiomyocytes extrude and expand into the lumen of the ventricular chambers. In mouse, Nrg1 isoforms containing an immunoglobulin-like (IgG) domain are essential for cardiac trabeculation through interaction with heterodimers of the epidermal growth factor-like (EGF-like) receptors ErbB2/ErbB4. Recent reports have underscored the importance of Nrg1 signaling in cardiac homeostasis and disease, however, placental development has precluded refined evaluation of the role of this pathway in mammals. ErbB2 has been shown to have a developmentally conserved role in cardiac trabeculation in zebrafish, a vertebrate model organism with completely external development, but the requirement for Nrg1 has not been examined. We found that among the multiple Nrg1 isoforms, the IgG domain-containing, type I Nrg1 (nrg1-I) is the only isoform detectable in the heart. Then, using CRISPR/Cas9 gene editing, we targeted the IgG domain of Nrg1 to produce novel alleles, nrg1nc28 and nrg1nc29, encoding nrg1-I and nrg1-II truncations. Our results indicated that zebrafish deficient for nrg1-I developed trabeculae in an ErbB2-dependent manner. Further, these mutants survive to reproductive adulthood with no overt cardiovascular defects. We also found that additional EGF-like ligands were expressed in the zebrafish heart during development of trabeculae. Together, these results suggest that Nrg1 is not the primary effector of trabeculation and/or that other EGF-like ligand(s) activates the ErbB2/ErbB4 pathway, either through functioning as the primary ligand or acting in a redundant manner. Overall, our work provides an example of cross-species differences in EGF family member requirements for an evolutionary conserved process.

The Neuregulin‐1 (Nrg1)/ErbB pathway plays multiple, critical roles in early cardiac and nervous system development and has been implicated in both heart and nerve repair processes. However, the early embryonic lethality of mouse Nrg1 mutants precludes an analysis of Nrg1's function in later cardiac development and homeostasis. In this study, we generated a novel nrg1 null allele targeting all known isoforms of nrg1 in zebrafish and examined cardiac structural and functional parameters throughout development. We found that zebrafish nrg1 mutants instead survived until young adult stages when they exhibited reduced survivorship. This coincided with structural and functional defects in the developing juvenile and young adult hearts, as demonstrated by reduced intracardiac myocardial density, cardiomyocyte cell number, swimming performance and dysregulated heartbeat. Interestingly, nrg1 mutant hearts were missing long axons on the ventricle surface by standard length (SL) 5 mm, which preceded juvenile and adult cardiac defects. Given that the autonomic nervous system normally exerts fine control of cardiac output through this nerve plexus, these data suggest that Nrg1 may play a critical role in establishing the cardiac nerve plexus such that inadequate innervation leads to deficits in cardiac maturation, function and survival.

Genetic engineering of allogeneic cell therapeutics that fully prevents rejection by a recipient’s immune system would abolish the requirement for immunosuppressive drugs or encapsulation and support large-scale manufacturing of off-the-shelf cell products. Previously, we generated mouse and human hypoimmune pluripotent (HIP) stem cells by depleting HLA class I and II molecules and overexpressing CD47 (B2M−/−CIITA−/−CD47+). To determine whether this strategy is successful in non-human primates, we engineered rhesus macaque HIP cells and transplanted them intramuscularly into four allogeneic rhesus macaques. The HIP cells survived unrestricted for 16 weeks in fully immunocompetent allogeneic recipients and differentiated into several lineages, whereas allogeneic wild-type cells were vigorously rejected. We also differentiated human HIP cells into endocrinologically active pancreatic islet cells and showed that they survived in immunocompetent, allogeneic diabetic humanized mice for 4 weeks and ameliorated diabetes. HIP-edited primary rhesus macaque islets survived for 40 weeks in an allogeneic rhesus macaque recipient without immunosuppression, whereas unedited islets were quickly rejected.

Regulatory T-cells (Treg) depend on signals from IL2 and their endogenous T-cell receptors to survive, proliferate, and maintain suppressive activity. We have developed a strategy for engineering effector CD4 T-cells into edited, regulatory-like T-cells (edTregs) for treatment of autoimmune disease. edTregs contain a rapamycin-activated synthetic IL2 receptor (designated a chemical-induced signaling complex or CISC) for use in selective cell manufacturing and in vivo trophic support. Our strategy uses gene editing to integrate an MND/ CISC expression cassette into the native FOXP3 locus, resulting in the CISC system cis-linked to expression of the native FOXP3 gene. The resulting high-level and stable expression of FOXP3 converts peripheral T-cells to edTregs with immunosuppressive activity. Cis-linked expression of the CISC system allows for selective cell expansion and in vivo support using rapamycin. Using an optimized protocol, we obtained efficient HDR rates across cells from multiple healthy donors. Edited cells were enriched to >90% purity and expanded 20-50-fold over a 10 day period of culture in rapamycin. Importantly, we demonstrated sustained in vivo suppressive activity of edTregs in a xeno-GvHD mouse model, and successful trophic support of these edTregs by rapamycin (via the CISC) in the absence of effector CD4 T-cells. Along with preliminary data showing successful editing of CD4-positive T-cells from auto-immune disease patients, our data provide pre-clinical proof-of-concept data supporting clinical use of CISC-edTreg in conjunction with rapamycin support for therapy of autoimmune disease. Disclosures Uenishi: Casebia Therapeutics: Employment. Mallari:Casebia Therapeutics: Employment. Gamboa:Casebia Therapeutics: Employment. Boucher:Casebia Therapeutics LLc: Employment. Chin:Casebia Therapeutics LLc: Employment. Aeran:Casebia Therapeutics: Employment. Wodziak:Casebia Therapeutics: Employment. Gebremeskel:Casebia Therapeutics: Employment. Vo:Casebia Therapeutics: Employment. Ito:Casebia Therapeutics: Employment. Patel:Casebia Therapeutics: Employment. Abe:Casebia Therapeutics: Employment. Stankovich:Casebia Therapeutics LLc: Employment. Torgerson:Shire: Consultancy; CSL Behring: Consultancy; ADMA Biosciences: Consultancy; UCB: Consultancy. Scharenberg:Generation Bio: Equity Ownership; Casebia Therapeutics LLc: Employment, Equity Ownership; Alpine Biosciences: Consultancy, Equity Ownership. Cost:Casebia Therapeutics: Employment.

No abstract

Auto-reactive antibody production by plasma cells is the direct cause of many auto-immune diseases. In such cases elimination of plasma cells would ameliorate the disease. Chimeric antigen receptor T (CAR-T) cells with cytotoxicity toward cells expressing B-cell maturation antigen (BCMA) have shown remarkable promise for the treatment of multiple myeloma, a plasma cell neoplasm. Elimination of non-malignant plasma cells is a side-effect of anti-BCMA CAR-T treatment of multiple myeloma, suggesting the use of these anti-BCMA CAR T cells for auto-immune indications. Unfortunately, CAR-T administration requires use of lymphodepletion to achieve efficient cell engraftment, and is often accompanied by cytokine release syndrome (CRS), a potentially life-threatening side-effect. As lymphodepletion and CRS pose morbidity/mortality risks that are unacceptable for therapy of many auto-immune diseases, we have utilized CRISPR-Cas9 gene editing to develop a controllable CAR-T cell platform that provides for (1) engraftment with non-cytotoxic transient immunosuppression; and (2) small-molecule dependent CAR T-cell expansion. We have implemented this platform using a unique dual targeting approach in which a BCMA CAR transgene is integrated into the TRAC locus, and additional payloads are integrated into a second locus, thus also enabling an allogeneic manufacturing process. Transgene integration occurred in >50% of cells individually with several percent of cells targeted at two loci. TRAC-targeted, anti-BCMA CAR T cells demonstrated CAR-dependent, target-cell-BCMA-dependent cytotoxicity towards both high-BCMA- and low-BCMA-expressing cell lines and in multiple myeloma cells xenografted into NSG mice. Drug-regulation properties and immunosuppression resistance are the subject of ongoing experiments. Anti-BCMA CAR T cells that are chemically controlled, incapable of graft-versus-host disease, and insensitive to immunosuppression may be an attractive treatment option a variety of antibody-mediated auto-immune conditions. Disclosures Rajavel: Casebia Therapeutics: Employment. Ito:Casebia Therapeutics: Employment. Abe:Casebia Therapeutics: Employment. Guerrero:Casebia Therapeutics: Employment. Uenishi:Casebia Therapeutics: Employment. Scharenberg:Casebia Therapeutics: Employment; Generation Bio: Equity Ownership; Alpine Immune Sciences: Equity Ownership. Cost:Casebia Therapeutics: Employment.