Human CD59 Research Articles

ADG153, an Anti-CD47 Monoclonal Antibody Prodrug, Has Strong In Vivo Anti-Tumor Activity, Minimal RBC-Related and Antigen Sink Liabilities, and Extended Half Life in Comparison with Benchmark Clinical Antibodies of the Same IgG Subclass

Binding of the CD47 membrane protein, overexpressed on many tumor types, to the SIRPα inhibitory receptor on myeloid cells results in the inhibition of the activation of macrophages and other phagocytes against tumors. Therapies targeting the CD47/SIRPα axis have shown success in various preclinical models and are now in clinical trials for both solid and hematologic malignancies. Although anti-CD47 therapies have demonstrated promising clinical activities, the expression of CD47 on many different normal human cell types, including red blood cells (RBCs), serves as a large antigen sink for anti-CD47 antibodies. Blocking CD47 on RBCs, such as by magrolimab (Hu5F9), has led to transient anemia, requiring step-up dosing in the clinic.To circumvent these challenges, we developed ADG153, a fully human anti-CD47 SAFEbody masked by conditionally activable peptides. In normal tissues, the SAFEbody masking moiety can function to block ADG153 from binding to CD47; however, in an activable condition such as the tumor microenvironment where protease activity has been reported to be elevated, the masked antibody can be activated, enabling the activated ADG153 antibody to bind to and inhibit CD47 function on tumor cells.For head-to-head comparisons, in vitro studies were performed to compare the activity of Hu5F9 and unmasked ADG153 parental antibody of the IgG4 isotype. Both antibodies (1) blocked human SIRPα from binding to human CD47, (2) had similar potencies for binding to human CD47 protein, CD47-positive tumor cell lines, and human RBCs, and (3) induced macrophage phagocytosis. In contrast, the masked ADG153 SAFEbody demonstrated significantly reduced activities (>450-fold) in the same in vitro assays, showing strong masking efficiencies. Unlike Hu5F9, both the ADG153 parental and SAFEbody molecules did not cause in vitro human RBC hemagglutination.Although the ADG153 SAFEbody had significantly reduced binding to CD47 in vitro as expected, it demonstrated strong anti-tumor activity in in vivo mouse tumor models. In both the disseminated and subcutaneous CD47-positive Raji tumor models, the ADG153 SAFEbody of the IgG4 isotype showed similar anti-tumor activities to Hu5F9. However, in exploratory toxicology studies in cynomolgus monkeys, the ADG153 SAFEbody showed significantly less decreases than Hu5F9 in RBCs, hemoglobin, and hematocrit. Hu5F9 at 10 mg/kg caused ~49% maximum decrease in RBCs, while ADG153 SAFEbody at 60 mg/kg showed ~23% maximum decrease in RBCs (Panel A). Pharmacokinetic (PK) studies of single intravenous dose ADG153 SAFEbody compared to Hu5F9 in monkeys demonstrated ~8-fold longer apparent half-life and ~9-fold higher Area Under the Curve at 10 mg/kg (Panel B). Collectively, ADG153 SAFEbody is a differentiated anti-CD47 antibody that has strong in vivo anti-tumor activity with reduced RBC-related and antigen sink liabilities and favorable PK properties. This preclinical profile with an enhanced therapeutic index provides a strong rationale for advancing ADG153 SAFEbody into clinical development. [Display omitted] DisclosuresCai: Adagene Inc.: Current Employment, Current equity holder in publicly-traded company. Nguyen: Adagene Inc.: Current Employment, Current equity holder in publicly-traded company; Sparcbio, LLC: Ended employment in the past 24 months. Zheng: Adagene Inc.: Current Employment, Current equity holder in publicly-traded company; Janssen Pharmaceuticals: Ended employment in the past 24 months. Shi: Adagene Inc.: Current Employment, Current equity holder in publicly-traded company. Liu: Adagene Inc.: Current Employment, Current equity holder in publicly-traded company. Li: Adagene Inc.: Current Employment, Current equity holder in publicly-traded company. Du: Adagene Inc.: Current Employment, Current equity holder in publicly-traded company. Luo: Adagene Inc.: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees. Xu: Adagene Inc.: Current Employment, Current equity holder in publicly-traded company; Bristol Myers Squibb: Current equity holder in publicly-traded company, Ended employment in the past 24 months.

An oncolytic virus expressing a full-length antibody enhances antitumor innate immune response to glioblastoma

Oncolytic herpes simplex virus-1 is capable of lysing tumor cells while alerting the immune system. CD47, in collaboration with SIRPα, represents an important immune checkpoint to inhibit phagocytosis by innate immune cells. Here we show locoregional control of glioblastoma by an oncolytic herpes virus expressing a full-length anti(α)-human CD47 IgG1 or IgG4 antibody. The antibodies secreted by the virus-infected glioblastoma cells block the CD47 ‘don’t eat me’ signal irrespective of the subclass; however, αCD47-IgG1 has a stronger tumor killing effect than αCD47-IgG4 due to additional antibody-dependent cellular phagocytosis by macrophages and antibody-dependent cellular cytotoxicity by NK cells. Intracranially injected αCD47-IgG1-producing virus continuously releases the respective antibody in the tumor microenvironment but not into systemic circulation; additionally, αCD47-IgG1-producing virus also improves the survival of tumor-bearing mice better than control oncolytic herpes virus combined with topical αCD47-IgG1. Results from immunocompetent mouse tumor models further confirm that macrophages, and to a lesser extent NK cells, mediate the anti-tumor cytotoxicity of antibody-producing oncolytic herpesviruses. Collectively, oncolytic herpes simplex virus-1 encoding full-length antibodies could improve immune-virotherapy for glioblastoma.

Expression of human CD47 in pig glomeruli prevents proteinuria and prolongs graft survival following pig-to-baboon xenotransplantation.

Nephrotic syndrome is a common complication of pig-to-baboon kidney xenotransplantation (KXTx) that adversely affects outcomes. We have reported that upregulation of CD80 and down-regulation of SMPDL-3b in glomeruli have an important role in the development of proteinuria following pig-to-baboon KXTx. Recently we found induced expression of human CD47 (hCD47) on endothelial cells and podocytes isolated from hCD47 transgenic (Tg) swine markedly reduced phagocytosis by baboon and human macrophages. These observations led us to hypothesize that transplanting hCD47 Tg porcine kidneys could overcome the incompatibility of the porcine CD47-baboon SIRPα interspecies ligand-receptor interaction and prevent the development of proteinuria following KXTx. Ten baboons received pig kidneys with vascularized thymic grafts (n=8) or intra-bone bone marrow transplants (n=2). Baboons were divided into three groups (A, B, and C) based on the transgenic expression of hCD47 in GalT-KO pigs. Baboons in Group A received kidney grafts with expression of hCD47 restricted to glomerular cells (n=2). Baboons in Group B received kidney grafts with high expression of hCD47 on both glomerular and tubular cells of the kidneys (n=4). Baboons in Group C received kidney grafts with low/no glomerular expression of hCD47, and high expression of hCD47 on renal tubular cells (n=4). Consistent with this hypothesis, GalT-KO/hCD47 kidney grafts with high expression of hCD47 on glomerular cells developed minimal proteinuria. However, high hCD47 expression in all renal cells including renal tubular cells induced an apparent destructive inflammatory response associated with upregulated thrombospondin-1. This response could be avoided by a short course of weekly anti-IL6R antibody administration, resulting in prolonged survival without proteinuria (mean 170.5 days from 47.8 days). Data showed that transgenic expression of hCD47 on glomerular cells in the GalT-KO donor kidneys can prevent xenograft nephropathy, a significant barrier for therapeutic applications of xenotransplantation. The ability to prevent nephrotic syndrome following KXTx overcomes a critical barrier for future clinical applications of KXTx.

Profiling Human CD55 Transgene Performance Assist in Selecting Best Suited Specimens and Tissues for Swine Organ Xenotransplantation.

Simple SummaryThe unbalance between availability and needs of human organs has drawn researchers’ attention to xenotransplantation as an option to cope with this shortage. Pig organs have received substantial attention for being comparable to human’s; nevertheless, compatibility constrains still block clinical applications. Transgenesis of human complement regulatory proteins, including the CD55 gene and its product the decay-accelerating factor (DAF), has been proposed to overcome xenorejection. This line of research has obtained interesting results along the years; however, most works assessing the impact of this strategy for xenotransplantation are limited to analyzing gene expression and assessing resistance to conventional serum challenge hemolysis assays, which provide somewhat reduced information prior to surgery. In this work, we tried to expand the analysis of the hCD55 transgene performance beyond common practice and into a better molecular understanding of its impact in xenotransplantation. We determined hCD55 gene expression, as well as hDAF protein presence, in different organs from five transgenic pigs, comparing readings from organs worthy for transplantation and other non-valuable organs and tissues. We also assessed the ability of transgenic cells, compared to non-transgenic, to withstand hemolysis and cytolysis. Finally, we made an effort to establish potential correlations between the hCD55 mRNA and hDAF protein levels detected.Xenotransplantation of pig organs receives substantial attention for being comparable to human’s. However, compatibility constraints involving hyper-acute rejection (HAR) still block clinical applications. Transgenesis of human complement regulatory proteins has been proposed to overcome xenorejection. Pigs expressing human-CD55 have been widely tested in experimental surgery. Still, no standardized method has been developed to determine tissue expression of human decay-accelerating factor (DAF), hCD55’s product, or to predict the ability to overpass HAR. Here we describe objective procedures addressing this need. Organs and tissues from five hCD55 transgenic pigs were collected and classified according to their xenotransplantation value. The ability to overcome HAR was assessed by classical complement pathway hemolysis assays. Quantitative PCR mRNA expression and Western blot protein level studies were performed. Real-time cytotoxicity assays (RTCA) on fibroblast cultures exposed to baboon and human sera informed on longer-term rejection dynamics. While greater hCD55/DAF expression correlated with better performance, the results obtained varied among specimens. Interestingly, the individual with highest mRNA and protein levels showed positive feedback for hCD55 transcript after challenge with human and baboon sera. Moreover, hCD55 expression correlated to DAF levels in the liver, lung and intestine, but not in the heart. Moreover, we found significant correlations among valuable and non-valuable tissues. In sum, the methodology proposed allows us to characterize the hCD55 transgene functioning and performance. Moreover, the correlations found could allow us to predict hCD55/DAF expression in surrogate tissues, thus eliminating the need for direct biopsies, resulting in preservation of organ integrity before xenotransplantation.

Abstract 502: In vitro characterization of antibodies targeting the SIRPα-CD47 phagocytosis checkpoint using tumor-associated macrophages from HuGEMM™ mice

Abstract Introduction: The signal-regulatory protein SIRPα-CD47 pathway is a phagocytosis checkpoint for macrophages and other innate immune cells. Tumor cells ubiquitously express CD47, and blocking SIRPα-CD47 interactions has been shown to promote cancer cell elimination by macrophage phagocytosis. The impact of SIRPα-CD47 blockade may be further improved by targeting prophagocytic receptors (Fc receptors) to enhance phagocytosis for anti-CD47 antibodies. Tumor-associated macrophages (TAMs) are the most abundant innate immune cells in late-stage tumors. Currently, drug development targeting CD47-SIRPα is rapidly growing, requiring robust in vitro macrophage/tumor cell co-culture assays to evaluate new agents targeting this pathway. Here, we report on the use of macrophages from an engineered mouse model expressing human SIRPα, which may serve as a good tool to test drug candidates. Methods: We have developed and characterized the human CD47 and SIRPα double knock-in mouse model (CD47/SIRPα HuGEMM) via CRISPR/Cas9 targeting. To characterize the effects of anti-human CD47 antibodies on phagocytosis and tumor cell killing, TAMs were isolated from tumor-bearing HuGEMM mice for in vitro macrophage/tumor cell co-culture. Results: Human CD47 expressing tumor cells, such as murine MC38-hCD47 and human Jurkat cells, were labeled with CFSE and used as target cells for antibody-dependent cellular phagocytosis (ADCP) and tumor cell death. The percentage of CFSE-positive among macrophages, and the percentage of dead cells among CFSE-positive tumor cell death, were measured by flow cytometry. We observed significant ADCP effects by TAM and killing of tumor cells after in vitro anti-CD47 antibody treatment. The contribution to ADCP by SIRPα-CD47 blockade and/or Fc effector function of antibodies was further investigated. We also evaluated the effect of SIRPα-CD47 blockade on the modulation of TAM phenotypes. Conclusion: Our data show that the CD47/SIRPα HuGEMM system provides an excellent tool for in vitro functional assays for drug candidates targeting the SIRPα-CD47 pathway, to evaluate the effect on ADCP by macrophages, activation of macrophages, and overall tumor cell death. Citation Format: Xuefei Yan, Hongjuan Zhang, Yi Liu, Yahong Zhang, Lei Zheng, Mingfa Zang, Annie Xiaoyu An, kevin Qijin Xu, Davy Ouyang, Henry Li, Yujun Huang. In vitro characterization of antibodies targeting the SIRPα-CD47 phagocytosis checkpoint using tumor-associated macrophages from HuGEMM™ mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 502.

Abstract 496: Humanized SIRPA and double humanized SIRPA/CD47 B-NDG mouse models are promising tools for anti-SIRPα antibody in vivo efficacy studies

Abstract The CD47/Signal regulatory protein α (SIRPα) axis regulates myeloid cell activation and functions as a crucial myeloid specific immune checkpoint. CD47 is highly expressed on many different types of cancer and upon binding with SIRPα which is abundantly expressed on myeloid cells, transduces inhibitory signals that protect cancer cells from phagocytosis by macrophages and other myeloid cells. Therefore, antibodies that block CD47 and SIRPα binding become encouraging tools for cancer immunotherapy. Biocytogen developed humanized SIRPα B-NDG mice and double humanized SIRPα/CD47 B-NDG mice to provide solid platforms for in vivo efficacy assessment of SIRPα antibodies with or without other immune checkpoint regulators. These mice have a B-NDG mouse background (completely lacking mature T, B and NK cells and were deficient in cytokine signaling) and express human SIRPα protein only or with human CD47 IgV domain and no mouse counterpart expressed. Raji-Luc cells were injected into these mouse models for tumor xenografting and anti-tumor efficacy of anti SIRPα antibody in combination with other antibodies was evaluated. The results showed that the combination of antibodies could effectively control tumor growth in the two mouse models. In addition, B-NDG hSIRPα/hCD47 mice can be used for toxicity assessment for SIRPα or CD47 antibodies. In summary, both B-NDG hSIRPA and B-NDG hSIRPA/hCD47 mice are promising models for preclinical in vivo evaluation of SIRPα antibodies and combined therapy. Citation Format: Yuting Hu, Lei Zhao, Yujie Liu, Li Hui, Zhaoxue (Luke) Yu. Humanized SIRPA and double humanized SIRPA/CD47 B-NDG mouse models are promising tools for anti-SIRPα antibody in vivo efficacy studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 496.

Abstract 1611: A novel anti-human CD47 antibody prodrug as cancer therapeutics to lower on-target side effects

Abstract CD47 is highly expressed in many types of cancers, including human acute myeloid leukemia (AML), non-Hodgkin's lymphoma (NHL), and solid tumors such as small-cell lung cancer (SCLC). Binding of CD47 to its receptor, SIRPα, on macrophages leads to inhibition of macrophage activation and phagocytosis. CD47 overexpression is one of the mechanisms cancer cells employ to evade immune surveillance and correlates with poor prognosis in cancers. Several strategies have been used to block CD47 binding to SIRPα, including anti-CD47 blocking antibodies and SIRPα-Fc fusion proteins. However, since CD47 is also expressed on normal cells, a major concern is that anti-CD47 antibodies could also cause on-target side effects, such as red blood cell hemagglutination and anemia. We have identified a panel of high affinity anti-human CD47 blocking antibodies. The lead antibodies bound to human CD47 with sub-nanomolar affinities and displayed a range of activities in blocking CD47:SIRPα interaction. These antibodies showed robust activities in stimulating macrophage-mediated phagocytosis of cancer cells. To minimize the on-target side effects of anti-CD47 antibodies, we have taken an antibody prodrug approach in which the antibody is inactive for normal cells while it becomes functional in the tumor microenvironment enriched with proteases. By screening a phage peptide library, we identified peptides that specifically block the anti-CD47 antibody binding activity. These peptides were fused to the humanized anti-CD47 antibody via a linker containing protease substrate sequences to derive the anti-CD47 antibody prodrug. We demonstrated that the anti-CD47 antibody prodrug lacked CD47 binding activity and was unable to block CD47:SIRPα interaction. Upon cleavage of the anti-CD47 antibody prodrug with proteases, the antibody regained full activities in both CD47 binding and blocking CD47:SIRPα interaction. Importantly, we showed that the anti-CD47 antibody prodrug had minimal hemagglutination and RBC binding activities. These data suggest that the novel anti-CD47 antibody prodrug is a promising candidate for the next generation anti-CD47 therapeutics with improved safety profile. Citation Format: Richard Zhang, Hunter Drobenaire, Huey Li, Veronica Pizzarella, Haishan Lin. A novel anti-human CD47 antibody prodrug as cancer therapeutics to lower on-target side effects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1611.

HMBD004, a Novel Anti-CD47xCD33 Bispecific Antibody Displays Potent Anti-Tumor Effects in Pre-Clinical Models of AML

CD47 is the “don't-eat-me” signal and is ubiquitously expressed on normal cells where binding to SIRPalpha on macrophages inhibits phagocytosis. CD47 is commonly over-expressed in tumors where it correlates with immune evasion and poor prognosis. Blocking CD47-SIRPalpha interaction restores macrophage phagocytosis of tumor cells and anti-CD47 mAbs have shown anti-tumor efficacy in mouse models of solid tumors and hematological malignancies. Nevertheless, the widespread expression of CD47 decreases the bioavailability of anti-CD47 mAbs at the tumor due to antigen sink effects, and also risks off-target toxicities, most significantly from cross-linking of erythrocytes that show high expression of CD47. Therefore, increasing the specificity for binding CD47, and inhibiting the interaction with SIRPalpha, to tumor cells alone should increase the efficacy and safety of anti-CD47 therapy.CD33 is expressed on myeloid cells, but is highly over-expressed in 90% of AML patients, where it marks leukemic blast cells. The safety of CD33 as an antibody target for directing effector molecules to tumor cells has been convincingly demonstrated by the efficacy of gemtuzumab ozogamicin (Mylotarg), an antibody-drug conjugate (ADC) that binds CD33 with high affinity, in the treatment of relapsed AML. However, ADCs are notable for their significant risk of toxicities, and gemtuzumab ozogmicin was withdrawn for this reason in 2010. Still, other companies continue development on next generation anti-CD33 ADCs, e.g. vadastuximab talirine.Hummingbird Bioscience has used its proprietary Rational Antibody Development Platform for the design and development of novel therapeutic antibodies against CD47. Computational sequence and structural analyses predicted a highly specific surface epitope, with strong antigenicity and good safety profile, where antibody binding would inhibit binding to SIRPalpha. Subsequently, an in-house mouse immunization and screening strategy efficiently yielded a monoclonal antibody (mAb, 11a1) that bound with low nM (KD 5 nM) affinity and high specificity to the desired epitope on human CD47. In vitro, 11a1 demonstrated 100% inhibition of SIRPalpha binding at 1 nM, and potently induced phagocytosis of Raji cells by isolated macrophages.11a1 was subsequently humanized by CDR grafting and back-mutation, and the resulting humanized mAb maintained high affinity binding to CD47. Hummingbird Bioscience then constructed a bispecific anti-CD47xCD33 antibody (bsAb), based on a standard 1+1 IgG format, with a humanized anti-CD47 variable domain as an effector arm and the gemtuzumab variable domain as an anti-CD33 specificity arm. This bsAb (HMBD004) maintained the potent inhibition of SIRPalpha binding and induction of phagocytosis but, unlike many CD47 mAbs, caused negligible hemagglutination (i.e. cross-linking) of erythrocytes in vitro . Furthermore, HMBD004 showed preferential sorting of CD47+ CD33+ cells during FACS of mixed populations of CD47+ cells. Finally, in vivo CDX mouse models of AML were established by engrafting NCr nude mice with the CD47+ CD33+ AML cell line, HL-60, via subcutaneous implantation. Treatment of these mice with HMBD004 showed a significant decrease in tumor burden and increased PFS.Together, these data highlight the benefit of using CD33 binding to enhance the specificity, efficacy and safety of anti-CD47 antibody therapy in AML. Hummingbird Bioscience is currently advancing HMBD004 towards the clinic in 2018. DisclosuresNo relevant conflicts of interest to declare.

ALX148 Is a High Affinity Sirpα Fusion Protein That Blocks CD47, Enhances the Activity of Anti-Cancer Antibodies and Checkpoint Inhibitors, and Has a Favorable Safety Profile in Preclinical Models

CD47 is a widely expressed cell surface protein thought to function as an immune checkpoint in cancer. CD47 binds SIRPα on myeloid cells, suppressing tumor cell phagocytosis and other innate immune functions. CD47-SIRPα signaling has also been implicated in the suppression of adaptive antitumor responses, but the relevant cellular functions have yet to be elucidated. Abundant CD47 expression has been observed in tumors and may aid tumor cells in the evasion of immune surveillance.Therapeutic blockade of the CD47 pathway may stimulate antitumor immunity and improve cancer therapy. To this end, the novel CD47-blocking molecule ALX148 was generated by fusing a modified SIRPα N-terminal D1 domain to an inactive Fc. Surface plasmon resonance analysis demonstrated that ALX148 binds human and murine CD47 with high affinity, with respective KDs of 0.14 nM and 12 nM. ALX148 also bound multiple CD47-expressing cell populations in flow cytometry assays. ALX148 blocks the interaction between CD47 and wild type SIRPα, enhancing antibody-dependent phagocytosis of hematologic tumor cell lines by daratumumab, rituximab, and obinutuzumab.ALX148 increased the efficacy of antibodies targeting hematologic tumors, such as rituximab and obinutuzumab, in xenograft models of hematologic malignancies. Because ALX148 also binds murine CD47 with high affinity, syngeneic tumor models were used to examine the activity of ALX148 in the context of an intact immune system. ALX148 enhanced the antitumor activities of checkpoint inhibitors. Specifically, the immune response induced by ALX148 bridged innate and adaptive immune responses. ALX148 stimulated antitumor properties of innate immune cells, promoting dendritic cell activation and a shift of tumor associated macrophages toward a proinflammatory phenotype. ALX148 in combination with checkpoint inhibitors caused increased cytotoxic T cell infiltrates, with greater CD8 to Treg ratios, and greater amounts of interferon gamma production by T cells in both tumors and the spleen. These findings reveal multiple mechanisms by which adaptive immunity is stimulated by CD47 blockade.Notably, ALX148 had no adverse effect on CD47-expressing red blood cells and platelets. In vitro, ALX148 did not induce erythrocyte hemagglutination. In non-human primate toxicology studies, ALX148 multi-dose administration was well tolerated and did not affect levels of circulating red blood cells, white blood cells, or platelets. This is in contrast to other published CD47-blocking molecules, which have caused anemia and thrombocytopenia in preclinical and clinical studies. Thus, ALX148 may have minimal hematologic toxicity in humans.ALX148 enhances adaptive and innate immune responses, demonstrates enhanced preclinical anti-tumor activity in combination with multiple standard of care cancer therapies, and is well tolerated. It is currently being investigated in a first-in-patient, phase 1 dose escalation/expansion, multi-center study in patients with advanced solid tumors and lymphoma. (NCT03013218). DisclosuresKauder:Alexo Therapeutics: Employment. Kuo:Alexo Therapeutics: Employment. Chen:Alexo Therapeutics: Employment. Harrabi:Alexo Therapeutics: Employment. Rocha:Alexo Therapeutics: Employment. Doyle:Alexo Therapeutics: Employment. Bollini:Alexo Therapeutics: Employment. Han:Alexo Therapeutics: Employment. Sangalang:Novartis: Employment; Alexo Therapeutics: Employment. Sim:Alexo Therapeutics: Employment. Randolph:VenBio: Consultancy; Carrick Therapeutics: Membership on an entity's Board of Directors or advisory committees; Alexo Therapeutics: Employment. Pons:Alexo Therapeutics: Employment, Equity Ownership. Wan:Alexo Therapeutics: Employment; Pfizer: Equity Ownership.

Liver-Directed Gene Therapy for Hemophilia B with Immune Stealth Lentiviral Vectors

Gene therapy is rapidly gaining renewed interest and is emerging as a realistic treatment option for several genetic and acquired diseases. Underlying this success is the development of improved gene transfer vectors. Among them, lentiviral vectors (LV) are emerging as versatile vehicles of relatively large capacity for stable transgene integration in the genome of target cells. Over the past years, we developed LV that achieve stable transgene expression in the liver and establish correction of hemophilia, in mouse and dog models of the disease, upon systemic administration. These LV are designed to stringently target transgene expression to hepatocytes through transcriptional and microRNA-mediated regulation. We previously evaluated portal vein administration of LV expressing canine factor IX (FIX) in 3 adult hemophilia B dogs and reported stable multiyear reconstitution of FIX activity up to 1 % of normal. We have more recently treated 4 dogs as pups (2-4 months of age) by peripheral vein administration of escalating doses of LV (5 to 10e9 T.U./kg) expressing a hyper-functional canine FIX and achieved reconstitution of FIX activity up to 32% of normal at the highest dose tested. We then modified the vector envelope by changing the protein composition of the producer cell plasma membrane through genome editing to reduce immunogenicity of LV particles. First, we performed genetic disruption of the β-2 microglobulin (B2M) gene, a required component for the assembly and trafficking of all class-I major histocompatibility complexes (MHC-I) to the plasma membrane in LV producer cells, exploiting the RNA-guided Cas9 nuclease. The resulting B2M-negative cells were devoid of surface-exposed MHC-I and produced MHC-free LVs. These LVs retain their infectivity on all tested cells in vitro and efficiently transduced the mouse liver upon intravenous administration. These MHC-free LVs showed significantly reduced immunogenicity in a T-cell activation assay performed on human primary T cells co-cultured with autologous monocytes exposed to LV, from several healthy donors, suggesting that conventional MHC-bearing LV may trigger allogeneic immune responses. Secondly, we generated LV with increasedlevels of CD47, a phagocytosis inhibitor, on the vector surface (CD47high LV), which show substantially decreased uptake by human macrophages in vitro . In order to evaluate the role of CD47 in LV biodistribution upon in vivo administration we took advantage of the non-obese diabetic (NOD) mouse model whose SIRPα (the CD47 receptor) is known to have high affinity for the human CD47. In this setting, CD47 proved to be a key player in reducing phagocytosis of LV, decreasing the inflammatory cytokine response following their administration, and increasing hepatocyte transduction and FIX output. We have now administered MHC-free or MHC-free/CD47high LV to 6 non-human primates (NHP, 3 for each LV version). We chose Macaca nemestrina as recipient, because of the lower restriction to HIV infection than other NHP species. Administration of 7.5e9 T.U./kg LV via peripheral vein was well tolerated, without significant elevation of serum aminotransferases or body temperature and only caused a transient self-limiting leukopenia. Remarkably, human-specific FIX activity reached up to 300% of normal and was nearly 3-fold higher in the CD47high-LV treated animals, showing a much more favorable LV dose-response than observed in mice and dogs. Upon necropsy, we measured vector copies in liver, spleen and major organs of treated animals and found between 0.5 and 1.5 LV copies in the liver accounting for 80-90% of all the retrieved LV copies, showing selective targeting and efficient gene transfer to the liver by LV in NHP. Overall, our studies support the efficacy and safety of these immune-stealth LV in NHP and position them to address some of the outstanding challenges in liver-directed gene therapy for hemophilia and conceivably other diseases. DisclosuresLiu:Bioverativ: Employment, Other: Shareholder. Peters:Bioverativ: Employment, Other: Shareholder.

ASK1 Activation in Platelets By Oxidized LDL Is Independent of CD36

Oxidized low-density lipoprotein (oxLDL) is a major contributor to platelet hyper-activation in hyperlipidemic conditions. OxLDL induces a prothrombotic phenotype by sensitizing the platelets for activation. Several receptors have been identified for oxLDL on platelets, but majority of the studies were focused on CD36. OxLDL binding to CD36 results in activation of multiple signaling molecules including Src family kinases (SFKs), Vav 1&3, JNK2, ERK5, and reactive oxygen species (ROS). The mechanism(s) by which oxLDL sensitizes platelets for activation is poorly understood. We have recently identified Apoptosis Signal Regulating Kinase 1 (ASK1), a MAP kinase kinase kinase, in platelets. Here, we show that in human platelets ASK1 is activated by oxLDL as determined by its activation-specific phosphorylation on T845. ASK1 activation was evident with oxLDL concentrations as low as 10μg/ml, with maximal activation observed with 100μg/ml. In contrast, native LDL (nLDL, 10-200μg/ml) failed to stimulate ASK1 activation. The activation of ASK1 was rapid peaking at 1 minute and returning to base line by 5 minutes. To determine if ROS is responsible for the activation of ASK1, we pretreated platelets with MnTMPyP, a ROS scavenger. MnTMPyP failed to inhibit the activation of ASK1 induced by oxLDL. To determine the mechanism by which oxLDL induces ASK1 activation, we pretreated platelets with 10μM each of pharmacological inhibitors, PP2 for SFKs, Y27632 for Rho kinase, bisindolylmaleimide for PKC, LY294002 for PI3 Kinase, U73122 for PLC, and 25μM of BAPTA-AM to chelate calcium. We found that platelets pretreated with U73122 and BAPTA-AM abolished oxLDL induced ASK1 activation, whereas others had no effect suggesting that ASK1 is activated in a calcium-dependent manner. To investigate the role of CD36 in oxLDL induced ASK1 activation, we used FA6-152, a function-blocking antibody for human CD36, and murine CD36nullplatelets. Interestingly, either blocking or lack of CD36 had no effect on oxLDL-induced ASK1/p38 activation suggesting that CD36 is not involved in oxLDL induced ASK1 activation. To determine if ASK1 play a role in oxLDL-induced sensitization of platelets for activation, we treated platelets with GS-4997, a specific ASK1 inhibitor, before stimulating them with ADP and oxLDL. ADP (10µM) or oxLDL (100µg/ml), showed no aggregation, but combination of oxLDL and ADP showed robust aggregation of vehicle-treated platelets. However, pretreatment of platelets with GS-4997 significantly inhibited oxLDL-induced potentiation of ADP-induced platelet aggregation suggesting that ASK1 plays a role in platelet activation under hyperlipidemic conditions. DisclosuresNo relevant conflicts of interest to declare.

CD36 Ectodomain Detects Apoptosis in Mammalian Cells.

The cells that undergo apoptosis show phosphatidylserine (PS) on the cell membrane. The fluorescently labeled hCD36_ecto is staining and detecting apoptotic cells in a flow-based assay with several advantages over Annexin V. The human CD36 ectodomain (hCD36_ecto) is stable for a range of temperatures and experimental conditions and doesn't require Ca2+ for detecting apoptosis and specific towards PS compared to other lipids. The blocking with unlabeled hCD36_ecto reduces the staining of Annexin V-FITC for apoptotic cells, whereas R63A does not affect the binding of Annexin V- FITC to apoptotic cells. It indicates the role of CD36-PS interaction in detecting apoptotic cells. Dual-staining with hCD36_ecto-FITC/PI is universally detecting apoptosis in different nucleated cells or eryptosis in non-nucleated RBCs. Hence, our study highlights the utility of CD36 as a probe to detect apoptosis in mammalian cells. It might be a robust, economical reagent for the scientific community to facilitate their research.

Xenotransplantation Is the Future of Pediatric Cardiac Surgery

Norman Shumway coined the aphorism that “xenotransplantation is the future of transplantation, and always will be.” In this issue of The Annals of Thoracic Surgery, Cleveland and colleagues1 from the University of Alabama give us a glimpse of this future. Nonhuman primates survived for up to 241 days after orthotopic cardiac xenotransplantation from alpha 1-3 galactosyltransferase gene knockout swine expressing human complement regulatory protein CD46 and human thrombomodulin using a clinically feasible immunosuppression regime.

The Genetically Engineered Heart as a Bridge to Allotransplantation in Infants Just Around the Corner?

BackgroundMortality for infants on the heart transplant waitlist remains unacceptably high, and available mechanical circulatory support is suboptimal. Our goal is to demonstrate the feasibility of utilizing genetically engineered pig (GEP) heart as a bridge to allotransplantation by transplantation of a GEP heart in a baboon. MethodsFour baboons underwent orthotopic cardiac transplantation from GEP donors. All donor pigs had galactosyl-1,3-galactose knocked out. Two donor pigs had human complement regulatory CD55 transgene and the other 2 had human complement regulatory CD46 and thrombomodulin. Induction immunosuppression included thymoglobulin, and anti-CD20. Maintenance immunosuppression was rapamycin, anti-CD-40, and methylprednisolone. One donor heart was preserved with University of Wisconsin solution and the other three with del Nido solution. ResultsAll baboons weaned from cardiopulmonary bypass. B217 received a donor heart preserved with University of Wisconsin solution. Ventricular arrhythmias and depressed cardiac function resulted in early death. All recipients of del Nido preserved hearts easily weaned from cardiopulmonary bypass with minimal inotropic support. B15416 and B1917 survived for 90 days and 241 days, respectively. Histopathology in B15416 revealed no significant myocardial rejection but cellular infiltrate around Purkinje fibers. Histopathology in B1917 was consistent with severe rejection. B37367 had uneventful transplant but developed significant respiratory distress with cardiac arrest. ConclusionsSurvival of B15416 and B1917 demonstrates the feasibility of pursuing additional research to document the ability to bridge an infant to cardiac allotransplant with a GEP heart.

Novel Pharmaceutical Strategy for Selective Abrogation of TSP1-Induced Vascular Dysfunction by Decoy Recombinant CD47 Soluble Receptor in Prophylaxis and Treatment Models.

Elevated thrombospondin 1 (TSP1) is a prevalent factor, via cognate receptor CD47, in the pathogenesis of cardiovascular conditions, including ischemia-reperfusion injury (IRI) and pulmonary arterial hypertension (PAH). Moreover, TSP1/CD47 interaction has been found to be associated with platelet hyperaggregability and impaired nitric oxide response, exacerbating progression in IRI and PAH. Pathological TSP1 in circulation arises as a target of our novel therapeutic approach. Our “proof-of-concept” pharmacological strategy relies on recombinant human CD47 peptide (rh-CD47p) as a decoy receptor protein (DRP) to specifically bind TSP1 and neutralize TSP1-impaired vasorelaxation, strongly implicated in IRI and PAH. The binding of rh-CD47p and TSP1 was first verified as the primary mechanism via Western blotting and further quantified with modified ELISA, which also revealed a linear molar dose-dependent interaction. Ex vivo, pretreatment protocol with rh-CD47p (rh-CD47p added prior to TSP1 incubation) demonstrated a prophylactic effect against TSP1-impairment of endothelium-dependent vasodilation. Post-treatment set-up (TSP1 incubation prior to rh-CD47p addition), mimicking pre-existing excessive TSP1 in PAH, reversed TSP1-inhibited vasodilation back to control level. Dose titration identified an effective molar dose range (approx. ≥1:3 of tTSP1:rh-CD47p) for prevention of/recovery from TSP1-induced vascular dysfunction. Our results indicate the great potential for proposed novel decoy rh-CD47p-therapy to abrogate TSP1-associated cardiovascular complications, such as PAH.

Bile acid-activated macrophages promote biliary epithelial cell proliferation through integrin αvβ6 upregulation following liver injury.

Cholangiopathies caused by biliary epithelial cell (BEC) injury represent a leading cause of liver failure. No effective pharmacologic therapies exist, and the underlying mechanisms remain obscure. We aimed to explore the mechanisms of bile duct repair after targeted BEC injury. Injection of intermedilysin into BEC-specific human CD59 (hCD59) transgenic mice induced acute and specific BEC death, representing a model to study the early signals that drive bile duct repair. Acute BEC injury induced cholestasis followed by CCR2+ monocyte recruitment and BEC proliferation. Using microdissection and next-generation RNA-Seq, we identified 5 genes, including Mapk8ip2, Cdkn1a, Itgb6, Rgs4, and Ccl2, that were most upregulated in proliferating BECs after acute injury. Immunohistochemical analyses confirmed robust upregulation of integrin αvβ6 (ITGβ6) expression in this BEC injury model, after bile duct ligation, and in patients with chronic cholangiopathies. Deletion of the Itgb6 gene attenuated BEC proliferation after acute bile duct injury. Macrophage depletion or Ccr2 deficiency impaired ITGβ6 expression and BEC proliferation. In vitro experiments revealed that bile acid-activated monocytes promoted BEC proliferation through ITGβ6. Our data suggest that BEC injury induces cholestasis, monocyte recruitment, and induction of ITGβ6, which work together to promote BEC proliferation and therefore represent potential therapeutic targets for cholangiopathies.

Microglial trogocytosis and the complement system regulate axonal pruning in vivo.

Partial phagocytosis-called trogocytosis-of axons by microglia has been documented in ex vivo preparations but has not been directly observed in vivo. The mechanisms that modulate microglial trogocytosis of axons and its function in neural circuit development remain poorly understood. Here, we directly observe axon trogocytosis by microglia in vivo in the developing Xenopus laevis retinotectal circuit. We show that microglia regulate pruning of retinal ganglion cell axons and are important for proper behavioral response to dark and bright looming stimuli. Using bioinformatics, we identify amphibian regulator of complement activation 3, a homolog of human CD46, as a neuronally expressed synapse-associated complement inhibitory molecule that inhibits trogocytosis and axonal pruning. Using a membrane-bound complement C3 fusion protein, we demonstrate that enhancing complement activity enhances axonal pruning. Our results support the model that microglia remodel axons via trogocytosis and that neurons can control this process through expression of complement inhibitory proteins.

Coagulation, inflammation, and CD46 transgene expression in neonatal porcine islet xenotransplantation.

Thrombosis is a known consequence of intraportal islet transplantation, particularly for xenogeneic islets. To define the origins of thrombosis after islet xenotransplantation and relate it to early inflammation, we examined porcine islets transplanted into non-human primates using a dual-transplant model to directly compare islet characteristics. α1,3-Galactosyltransferase gene-knockout (GTKO) islets with and without expression of the human complement regulatory transgene CD46 (hCD46) were studied. Biologically inert polyethylene microspheres were used to examine the generic pro-thrombotic effects of particle embolization. Immunohistochemistry was performed 1 and 24hours after transplantation. Xeno-islet transplantation activated both extrinsic and intrinsic coagulation pathways. The intrinsic pathway was also initiated by microsphere embolization, while extrinsic pathway tissue factor (TF) and platelet aggregation were more specific to engrafted islets. hCD46 expression significantly reduced TF, platelet, fibrin, and factor XIIIa accumulation in and around islets but did not alter intrinsic factor activation. Layers of TF+ cells emerged around islets within 24hours, particularly co-localized with vimentin, and identified as CD3+ and CD68+ cells inflammatory cells. These findings detail the origins of thrombosis following islet xenotransplantation, relate it to early immune activation, and suggest a role for transgenic hCD46 expression in its mitigation. Layers of TF-positive inflammatory cells and fibroblasts around islets at 24hours may have important roles in the progressive events of thrombosis, inflammatory cell recruitment, rejection, and the ultimate outcome of transplanted grafts. These suggest that the strategies targeting these elements could yield more progress toward successful xenogeneic islet engraftment and survival.

Sulfated Polysaccharides from Macroalgae Are Potent Dual Inhibitors of Human ATP-Hydrolyzing Ectonucleotidases NPP1 and CD39

Extracellular ATP mediates proinflammatory and antiproliferative effects via activation of P2 nucleotide receptors. In contrast, its metabolite, the nucleoside adenosine, is strongly immunosuppressive and enhances tumor proliferation and metastasis. The conversion of ATP to adenosine is catalyzed by ectonucleotidases, which are expressed on immune cells and typically upregulated on tumor cells. In the present study, we identified sulfopolysaccharides from brown and red sea algae to act as potent dual inhibitors of the main ATP-hydrolyzing ectoenzymes, ectonucleotide pyrophosphatase/phosphodiesterase-1 (NPP1) and ecto-nucleoside triphosphate diphosphohydrolase-1 (NTPDase1, CD39), showing nano- to picomolar potency and displaying a non-competitive mechanism of inhibition. We showed that one of the sulfopolysaccharides tested as a representative example reduced adenosine formation at the surface of the human glioblastoma cell line U87 in a concentration-dependent manner. These natural products represent the most potent inhibitors of extracellular ATP hydrolysis known to date and have potential as novel therapeutics for the immunotherapy of cancer.

Structural basis for tuning activity and membrane specificity of bacterial cytolysins

Cholesterol-dependent cytolysins (CDCs) are pore-forming proteins that serve as major virulence factors for pathogenic bacteria. They target eukaryotic cells using different mechanisms, but all require the presence of cholesterol to pierce lipid bilayers. How CDCs use cholesterol to selectively lyse cells is essential for understanding virulence strategies of several pathogenic bacteria, and for repurposing CDCs to kill new cellular targets. Here we address that question by trapping an early state of pore formation for the CDC intermedilysin, bound to the human immune receptor CD59 in a nanodisc model membrane. Our cryo electron microscopy map reveals structural transitions required for oligomerization, which include the lateral movement of a key amphipathic helix. We demonstrate that the charge of this helix is crucial for tuning lytic activity of CDCs. Furthermore, we discover modifications that overcome the requirement of cholesterol for membrane rupture, which may facilitate engineering the target-cell specificity of pore-forming proteins.