Membrane cofactor protein (MCP; CD46) expression in transgenic mice

Peak transgene expression after intramuscular immunization of mice with adenovirus 26-based vector vaccines correlates with transgene-specific adaptive immune responses

Non-replicating adenovirus-based vectors have been broadly used for the development of prophylactic vaccines in humans and are licensed for COVID-19 and Ebola virus disease prevention. Adenovirus-based vectored vaccines encode for one or more disease specific transgenes with the aim to induce protective immunity against the target disease. The magnitude and duration of transgene expression of adenovirus 5- based vectors (human type C) in the host are key factors influencing antigen presentation and adaptive immune responses. Here we characterize the magnitude, duration, and organ biodistribution of transgene expression after single intramuscular administration of adenovirus 26-based vector vaccines in mice and evaluate the differences with adenovirus 5-based vector vaccine to understand if this is universally applicable across serotypes. We demonstrate a correlation between peak transgene expression early after adenovirus 26-based vaccination and transgene-specific cellular and humoral immune responses for a model antigen and SARS-CoV-2 spike protein, independent of innate immune activation. Notably, the memory immune response was similar in mice immunized with adenovirus 26-based vaccine and adenovirus 5-based vaccine, despite the latter inducing a higher peak of transgene expression early after immunization and a longer duration of transgene expression. Together these results provide further insights into the mode of action of adenovirus 26-based vector vaccines.

CD46 expression in the central nervous system of male and female pubescent mice

CD46 is a complementary regulatory protein ubiquitously expressed in human cells, controlling complement system activation. CD46 has further been identified to have several other functions including regulatory T cell induction and intestinal epithelial (IEC) barrier regulation. Activation of CD46 in the IEC can impact intestinal barrier permeability and immune system functioning. CD46 has only been identified in the spermatozoa and retina of mice. In other murine cells, the homologue CRRY is identified to function as the complementary regulator. Due to the identification of CRRY across other wild-type mouse cells and the development of mouse strains transgenic for human CD46, no recent research has been conducted to determine if CD46 is present in non-transgenic mouse strains. Therefore, the current study investigated if CD46 is expressed in the substantia nigra (SN) and caudate putamen (CP) of pubescent CD1 mice and examined the acute effects of pubertal antimicrobial and lipopolysaccharide (LPS) treatment on CD46 expression in the brain. As of 5 weeks of age, mice were administered mixed antimicrobial solution or water with oral gavage twice daily for 7 days. At 6 weeks of age, mice received an intraperitoneal injection of LPS or saline. Mice were euthanized 8 h post-injection and brain samples were collected. Our results indicate that pubescent CD-1 mice express CD46 in the SN and CP. However, LPS-treated mice displayed significantly less CD46 expression in the SN in comparison to saline-treated mice. Furthermore, males displayed more CD46 in the CP compared to females, regardless of LPS and antimicrobial treatments. Our data suggest CD46 is present in CD1 mice and that LPS and antimicrobial treatments impact CD46 protein expression in a sex-dependent manner. These results have important implications for the expression of CD46 in the mouse brain and the understanding of its role in immune system regulation.

A novel humanized tri-receptor transgenic mouse model of HAdV infection and pathogenesis

Human adenovirus (HAdV) is a highly virulent respiratory pathogen that poses clinical challenges in terms of diagnostics and treatment. Currently, no effective therapeutic drugs or prophylactic vaccines are available for HAdV infections. One factor contributing to this deficiency is that existing animal models, including wild-type and single-receptor transgenic mice, are unsuitable for HAdV proliferation and pathology testing. In this study, a tri-receptor transgenic mouse model expressing the three best-characterized human cellular receptors for HAdV (hCAR, hCD46, and hDSG2) was generated and validated via analysis of transgene insertion, receptor mRNA expression, and protein abundance distribution. Following HAdV-7 infection, the tri-receptor mice exhibited high transcription levels at the early and late stages of the HAdV gene, as well as viral protein expression. Furthermore, the tri-receptor mice infected with HAdV exhibited dysregulated cytokine responses and multiple tissue lesions. This transgenic mouse model represents human HAdV infection and pathogenesis with more accuracy than any other reported animal model. As such, this model facilitates the comprehensive investigation of HAdV pathogenesis as well as the evaluation of potential vaccines and therapeutic modalities for HAdV.

Development and evaluation of helper dependent adenoviral vectors for inner ear gene delivery

Viral vector gene therapy is an attractive strategy to treat hearing loss. Since hearing loss is due to a variety of pathogenic signaling cascades in distinct cells, viral vectors that can express large or multiple genes in a cell-type specific manner are needed. Helper-dependent adenoviral vectors (HdAd) are safe viral vectors with a large packaging capacity (-36 kb). Despite the potential of HdAd, its use in the inner ear is largely unexplored. Therefore, to evaluate the utility of HdAd for inner ear gene therapy, we created two HdAd vectors that use distinct cellular receptors for transduction: HdAd Serotype Type 5 (HdAd5), the Coxsackie-Adenovirus Receptor (CAR) and a chimeric HdAd 5/35, the human CD46+ receptor (hCD46). We delivered these vectors through the round window (RW) or scala media in CBA/J, C57Bl6/J and hCD46 transgenic mice. Immunostaining in conjunction with confocal microscopy of cochlear sections revealed that multiple cell types were transduced using HdAd5 and HdAd 5/35 in all mouse models. Delivery of HdAd5 via RW in the C57Bl/6 J or CBA/J cochlea resulted in transduced mesenchymal cells of the peri‑lymphatic lining and modiolar region while scala media delivery resulted in transduction of supporting cells and inner hair cells. Hd5/35 transduction was CD46 dependent and RW delivery of HdAd5/35 in the hCD46 mouse model resulted in a similar transduction pattern as HdAd5 in the peri‑lymphatic lining and modiolar region in the cochlea. Our data indicate that HdAd vectors are promising vectors for use in inner ear gene therapy to treat some causes of hearing loss.

Engineering Human Pluripotent Stem Cell Lines to Evade Xenogeneic Transplantation Barriers

Allogeneic human pluripotent stem cell (hPSC)-derived cells and tissues for therapeutic transplantation must necessarily overcome immunological rejection by the recipient. To define these barriers and to create cells capable of evading rejection for preclinical testing in immunocompetent mouse models, we genetically ablated β2m, Tap1, Ciita, Cd74, Mica, and Micb to limit expression of HLA-I, HLA-II, and natural killer cell activating ligands in hPSCs. Though these and even unedited hPSCs readily formed teratomas in cord blood-humanized immunodeficient mice, grafts were rapidly rejected by immunocompetent wild-type mice. Transplantation of these cells that also expressed covalent single chain trimers of Qa1 and H2-Kb to inhibit natural killer cells and CD55, Crry, and CD59 to inhibit complement deposition led to persistent teratomas in wild-type mice. Expression of additional inhibitory factors such as CD24, CD47, and/or PD-L1 had no discernible impact on teratoma growth or persistence. Transplantation of HLA-deficient hPSCs into mice genetically deficient in complement and depleted of natural killer cells also led to persistent teratomas. Thus, T cell, NK cell, and complement evasion are necessary to prevent immunological rejection of hPSCs and their progeny. These cells and versions expressing human orthologs of immune evasion factors can be used to refine tissue- and cell type-specific immune barriers, and to conduct preclinical testing in immunocompetent mouse models.

HDAd6/35++ - A new helper-dependent adenovirus vector platform for in vivo transduction of hematopoietic stem cells

In previous studies, we achieved safe and efficient in vivo hematopoietic stem cell (HSC) transduction in mobilized mice and macaques with intravenously injected helper-dependent adenovirus HDAd5/35++ vectors. These vectors are derivatives of serotype Ad5-containing CD46-affinity enhanced Ad35 fiber knob domains. Considering the impact of anti-Ad5/HDAd5/35++ neutralizing serum antibodies present in the human population, we generated HSC-retargeted HDAd6/35++ vectors derived from serotype 6. We found a lower prevalence and titers of serum anti-HDAd6/35++ in human samples compared with HDAd5/35++. HDAd6/35++ vectors efficiently transduced human and rhesus CD34+ cells in vitro. Intravenous injection of HDAd5/35++-GFP or HDAd6/35++-GFP vectors after G-CSF/AMD3100 mobilization of mice with established human hematopoiesis or human CD46 transgenic mice resulted in comparable GFP marking rates in HSCs in the bone marrow and spleen. In long-term in vivo HSC transduction and selection studies with integrating vectors, stable GFP expression in >75% of PBMCs was show for both vectors. In contrast with HDAd5/35++, undesired transduction of hepatocytes was minimal with HDAd6/35++. Furthermore, HDAd6/35++ allowed for efficient in vivo HSC transduction in Ad5-pre-immune mice. These features, together with the straightforward production of HDAd6/35++ vectors at high yield, make this new HDAd vector platform attractive for clinical translation of the in vivo approach.

In vivo HSC prime editing rescues sickle cell disease in a mouse model

Sickle cell disease (SCD) is a monogenic disease caused by a nucleotide mutation in the β-globin gene. Current gene therapy studies are mainly focused on lentiviral vector-mediated gene addition or CRISPR/Cas9-mediated fetal globin reactivation, leaving the root cause unfixed. We developed a vectorized prime editing system that can directly repair the SCD mutation in hematopoietic stem cells (HSCs) in vivo in a SCD mouse model (CD46/Townes mice). Our approach involved a single intravenous injection of a nonintegrating, prime editor-expressing viral vector into mobilized CD46/Townes mice and low-dose drug selection in vivo. This procedure resulted in the correction of ∼40% of βS alleles in HSCs. On average, 43% of sickle hemoglobin was replaced by adult hemoglobin, thereby greatly mitigating the SCD phenotypes. Transplantation in secondary recipients demonstrated that long-term repopulating HSCs were edited. Highly efficient target site editing was achieved with minimal generation of insertions and deletions and no detectable off-target editing. Because of its simplicity and portability, our in vivo prime editing approach has the potential for application in resource-poor countries where SCD is prevalent.

Stable HIV decoy receptor expression after in vivo HSC transduction in mice and NHPs: Safety and efficacy in protection from SHIV

We aim to develop an in vivo hematopoietic stem cell (HSC) gene therapy approach for persistent control/protection of HIV-1 infection based on the stable expression of a secreted decoy protein for HIV receptors CD4 and CCR5 (eCD4-Ig) from blood cells. HSCs in mice and a rhesus macaque were mobilized from the bone marrow and transduced by an intravenous injection of HSC-tropic, integrating HDAd5/35++ vectors expressing rhesus eCD4-Ig. In vivo HSC transduction/selection resulted in stable serum eCD4-Ig levels of ∼100 μg/mL (mice) and >20 μg/mL (rhesus) with half maximal inhibitory concentrations (IC50s) of 1 μg/mL measured by an HIV neutralization assay. After simian-human-immunodeficiency virus D (SHIV.D) challenge of rhesus macaques injected with HDAd-eCD4-Ig or a control HDAd5/35++ vector, peak plasma viral load levels were ∼50-fold lower in the eCD4-Ig-expressing animal. Furthermore, the viral load was lower in tissues with the highest eCD4-Ig expression, specifically the spleen and lymph nodes. SHIV.D challenge triggered a selective expansion of transduced CD4+CCR5+ cells, thereby increasing serum eCD4-Ig levels. The latter, however, broke immune tolerance and triggered anti-eCD4-Ig antibody responses, which could have contributed to the inability to eliminate SHIV.D. Our data will guide us in the improvement of the in vivo approach. Clearly, our conclusions need to be validated in larger animal cohorts.

A Renaissance for Oncolytic Adenoviruses?

In the 1990s, adenovirus became one of the first virus types to be genetically engineered to selectively destroy cancer cells. In the intervening years, the field of "oncolytic viruses" has slowly progressed and culminated in 2015 with the FDA approval of Talimogene laherparepvec, a genetically engineered herpesvirus, for the treatment of metastatic melanoma. Despite the slower progress in translating oncolytic adenovirus to the clinic, interest in the virus remains strong. Among all the clinical trials currently using viral oncolytic agents, the largest proportion of these are using recombinant adenovirus. Many trials are currently underway to use oncolytic virus in combination with immune checkpoint inhibitors (ICIs), and early results using oncolytic adenovirus in this manner are starting to show promise. Many of the existing strategies to engineer adenoviruses were designed to enhance selective tumor cell replication without much regard to interactions with the immune system. Adenovirus possesses a wide range of viral factors to attenuate both innate anti-viral pathways and immune cell killing. In this review, we summarize the strategies of oncolytic adenoviruses currently in clinical trials, and speculate how the mutational backgrounds of these viruses may impact upon the efficacy of these agents in oncolytic and immunotherapy. Despite decades of research on human adenoviruses, the interactions that these viruses have with the immune system remains one of the most understudied aspects of the virus and needs to be improved to rationally design the next generation of engineered viruses.

In vivo base editing by a single i.v. vector injection for treatment of hemoglobinopathies

Individuals with β-thalassemia or sickle cell disease and hereditary persistence of fetal hemoglobin (HPFH) possessing 30% fetal hemoglobin (HbF) appear to be symptom free. Here, we used a nonintegrating HDAd5/35++ vector expressing a highly efficient and accurate version of an adenine base editor (ABE8e) to install, in vivo, a -113 A>G HPFH mutation in the γ-globin promoters in healthy CD46/β-YAC mice carrying the human β-globin locus. Our in vivo hematopoietic stem cell (HSC) editing/selection strategy involves only s.c. and i.v. injections and does not require myeloablation and HSC transplantation. In vivo HSC base editing in CD46/β-YAC mice resulted in > 60% -113 A>G conversion, with 30% γ-globin of β-globin expressed in 70% of erythrocytes. Importantly, no off-target editing at sites predicted by CIRCLE-Seq or in silico was detected. Furthermore, no critical alterations in the transcriptome of in vivo edited mice were found by RNA-Seq. In vitro, in HSCs from β-thalassemia and patients with sickle cell disease, transduction with the base editor vector mediated efficient -113 A>G conversion and reactivation of γ-globin expression with subsequent phenotypic correction of erythroid cells. Because our in vivo base editing strategy is safe and technically simple, it has the potential for clinical application in developing countries where hemoglobinopathies are prevalent.

Safe and efficient in vivo hematopoietic stem cell transduction in nonhuman primates using HDAd5/35++ vectors

We tested a new in vivo hematopoietic stem cell (HSC) transduction/selection approach in rhesus macaques using HSC-tropic, integrating, helper-dependent adenovirus vectors (HDAd5/35++) designed for the expression of human γ-globin in red blood cells (RBCs) to treat hemoglobinopathies. We show that HDAd5/35++ vectors preferentially transduce HSCs in vivo after intravenous injection into granulocyte colony-stimulating factor (G-CSF)/AMD3100-mobilized animals and that transduced cells return to the bone marrow and spleen. The approach was well tolerated, and the activation of proinflammatory cytokines that are usually associated with intravenous adenovirus vector injection was successfully blunted by pre-treatment with dexamethasone in combination with interleukin (IL)-1 and IL-6 receptor blockers. Using our MGMT^P140K-based in vivo selection approach, γ-globin⁺ RBCs increased in all animals with levels up to 90%. After selection, the percentage of γ-globin⁺ RBCs declined, most likely due to an immune response against human transgene products. Our biodistribution data indicate that γ-globin⁺ RBCs in the periphery were mostly derived from mobilized HSCs that homed to the spleen. Integration site analysis revealed a polyclonal pattern and no genotoxicity related to transgene integrations. This is the first proof-of-concept study in nonhuman primates to show that in vivo HSC gene therapy could be feasible in humans without the need for high-dose chemotherapy conditioning and HSC transplantation.

Ex Vivo and In Vivo CD46 Receptor Utilization by Species D Human Adenovirus Serotype 26 (HAdV26)

Human adenovirus serotype 26 (Ad26) is used as a gene-based vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and HIV-1. However, its primary receptor portfolio remains controversial, potentially including sialic acid, coxsackie and adenovirus receptor (CAR), integrins, and CD46. We and others have shown that Ad26 can use CD46, but these observations were questioned on the basis of the inability to cocrystallize Ad26 fiber with CD46. Recent work demonstrated that Ad26 binds CD46 with its hexon protein rather than its fiber. We examined the functional consequences of Ad26 for infection in vitro and in vivo. Ectopic expression of human CD46 on Chinese hamster ovary cells increased Ad26 infection significantly. Deletion of the complement control protein domain CCP1 or CCP2 or the serine-threonine-proline (STP) region of CD46 reduced infection. Comparing wild-type and sialic acid-deficient CHO cells, we show that the usage of CD46 is independent of its sialylation status. Ad26 transduction was increased in CD46 transgenic mice after intramuscular (i.m.) injection but not after intranasal (i.n.) administration. Ad26 transduction was 10-fold lower than Ad5 transduction after intratumoral (i.t.) injection of CD46-expressing tumors. Ad26 transduction of liver was 1,000-fold lower than that ofAd5 after intravenous (i.v.) injection. These data demonstrate the use of CD46 by Ad26 in certain situations but also show that the receptor has little consequence by other routes of administration. Finally, i.v. injection of high doses of Ad26 into CD46 mice induced release of liver enzymes into the bloodstream and reduced white blood cell counts but did not induce thrombocytopenia. This suggests that Ad26 virions do not induce direct clotting side effects seen during coronavirus disease 2019 (COVID-19) vaccination with this serotype of adenovirus. IMPORTANCE The human species D Ad26 is being investigated as a low-seroprevalence vector for oncolytic virotherapy and gene-based vaccination against HIV-1 and SARS-CoV-2. However, there is debate in the literature about its tropism and receptor utilization, which directly influence its efficiency for certain applications. This work was aimed at determining which receptor(s) this virus uses for infection and its role in virus biology, vaccine efficacy, and, importantly, vaccine safety.

In vivo HSC gene therapy for SARS-CoV2 infection using a decoy receptor

While SARS-CoV2 vaccines have shown an unprecedented success, the ongoing emergence of new variants and necessity to adjust vaccines justify the development of alternative prophylaxis and therapy approaches. Hematopoietic stem cell (HSC) gene therapy using a secreted CoV2 decoy receptor protein (sACE2-Ig) would involve a one-time intervention resulting in long-term protection against airway infection, viremia, and extrapulmonary symptoms. We recently developed a technically simple and portable in vivo hematopoietic HSC transduction approach that involves HSC mobilization from the bone marrow into the peripheral blood stream and the intravenous injection of an integrating, helper-dependent adenovirus (HDAd5/35⁺⁺) vector system. Considering the abundance of erythrocytes, in this study, we directed sACE2-Ig expression to erythroid cells using strong β-globin transcriptional regulatory elements. We performed in vivo HSC transduction of CD46-transgenic mice with an HDAd-sACE2-Ig vector. Serum sACE2-Ig levels reached 500–1,300 ng/mL after in vivo selection. At 22 weeks, we used genetically modified HSCs from these mice to substitute the hematopoietic system in human ACE2-transgenic mice, thus creating a model that is susceptible to SARS-CoV2 infection. Upon challenge with a lethal dose of CoV2 (WA-1), sACE2-Ig expressed from erythroid cells of test mice diminishes infection sequelae. Treated mice lost significantly less weight, had less viremia, and displayed reduced cytokine production and lung pathology. The second objective of this study was to assess the safety of in vivo HSC transduction and long-term sACE2-Ig expression in a rhesus macaque. With appropriate cytokine prophylaxis, intravenous injection of HDAd-sACE2-Ig into the mobilized animal was well tolerated. In vivo transduced HSCs preferentially localized to and survived in the spleen. sACE2-Ig expressed from erythroid cells did not affect erythropoiesis and the function of erythrocytes. While these pilot studies are promising, the antiviral efficacy of the approach has to be improved, for example, by using of decoy receptors with enhanced neutralizing capacity and/or expression of multiple antiviral effector proteins.

In vivo HSPC gene therapy with base editors allows for efficient reactivation of fetal γ-globin in β-YAC mice

Base editors are capable of installing precise genomic alterations without creating double-strand DNA breaks. In this study, we targeted critical motifs regulating γ-globin reactivation with base editors delivered via HDAd5/35++ vectors. Through optimized design, we successfully produced a panel of cytidine and adenine base editor (ABE) vectors targeting the erythroid BCL11A enhancer or recreating naturally occurring hereditary persistence of fetal hemoglobin (HPFH) mutations in the HBG1/2 promoter. All 5 tested vectors efficiently installed target base conversion and led to γ-globin reactivation in human erythroid progenitor cells. We observed ~23% γ-globin protein production over β-globin, when using an ABE vector (HDAd-ABE-sgHBG-2) specific to the -113A>G HPFH mutation. In a β-YAC mouse model, in vivo hematopoietic progenitor/stem cell (HSPC) transduction with HDAd-ABE-sgHBG-2 followed by in vivo selection resulted in >40% γ-globin+ erythrocytes in the peripheral blood. This result corresponded to 21% γ-globin production over human β-globin. The average -113A>G conversion in total bone marrow cells was 20%. No alterations in hematological parameters, erythropoiesis, and bone marrow cellular composition were observed after treatment. No detectable editing was found at top-scoring, off-target genomic sites. Bone marrow lineage-negative cells from primary mice were capable of reconstituting secondary transplant-recipient mice with stable γ-globin expression. Importantly, the advantage of base editing over CRISPR/Cas9 was reflected by the markedly lower rates of intergenic HBG1/2 deletion and the absence of detectable toxicity in human CD34+ cells. Our observations suggest that HDAd-vectorized base editors represent a promising strategy for precise in vivo genome engineering for the treatment of β-hemoglobinopathies.

Single-dose MGTA-145/plerixafor leads to efficient mobilization and in vivo transduction of HSCs with thalassemia correction in mice

We have developed an in vivo hemopoietic stem cell (HSC) gene therapy approach without the need for myelosuppressive conditioning and autologous HSC transplantation. It involves HSC mobilization and IV injection of a helper-dependent adenovirus HDAd5/35++ vector system. The current mobilization regimen consists of granulocyte colony-stimulating factor (G-CSF) injections over a 4-day period, followed by the administration of plerixafor/AMD3100. We tested a simpler, 2-hour, G-CSF-free mobilization regimen using truncated GRO-β (MGTA-145; a CXCR2 agonist) and plerixafor in the context of in vivo HSC transduction in mice. The MGTA-145+plerixafor combination resulted in robust mobilization of HSCs. Importantly, compared with G-CSF+plerixafor, MGTA-145+plerixafor led to significantly less leukocytosis and no elevation of serum interleukin-6 levels and was thus likely to be less toxic. With both mobilization regimens, after in vivo selection with O6-benzylguanine (O6BG)/BCNU, stable GFP marking was achieved in >90% of peripheral blood mononuclear cells. Genome-wide analysis showed random, multiclonal vector integration. In vivo HSC transduction after mobilization with MGTA-145+plerixafor in a mouse model for thalassemia resulted in >95% human γ-globin+ erythrocytes at a level of 36% of mouse β-globin. Phenotypic analyses showed a complete correction of thalassemia. The γ-globin marking percentage and level were maintained in secondary recipients, further demonstrating that MGTA145+plerixafor mobilizes long-term repopulating HSCs. Our study indicates that brief exposure to MGTA-145+plerixafor may be advantageous as a mobilization regimen for in vivo HSC gene therapy applications across diseases, including thalassemia and sickle cell disease.

In Vivo HSC Gene Therapy Using a Bi-modular HDAd5/35++ Vector Cures Sickle Cell Disease in a Mouse Model

We have recently reported that, after in vivo hematopoietic stem cell/progenitor (HSPC) transduction with HDAd5/35++ vectors, SB100x transposase-mediated γ-globin gene addition achieved 10%-15% γ-globin of adult mouse globin, resulting in significant but incomplete phenotypic correction in a thalassemia intermedia mouse model. Furthermore, genome editing of a γ-globin repressor binding site within the γ-globin promoter by CRISPR-Cas9 results in efficient reactivation of endogenous γ-globin. Here, we aimed to combine these two mechanisms to obtain curative levels of γ-globin after in vivo HSPC transduction. We generated a HDAd5/35++ adenovirus vector (HDAd-combo) containing both modules and tested it in vitro and after in vivo HSPC transduction in healthy CD46/β-YAC mice and in a sickle cell disease mouse model (CD46/Townes). Compared to HDAd vectors containing either the γ-globin addition or the CRISPR-Cas9 reactivation units alone, in vivo HSC transduction of CD46/Townes mice with the HDAd-combo resulted in significantly higher γ-globin in red blood cells, reaching 30% of that of adult human α and βS chains and a complete phenotypic correction of sickle cell disease.

Advances in Transgenic Mouse Models to Study Infections by Human Pathogenic Viruses

Medical research is changing into direction of precision therapy, thus, sophisticated preclinical models are urgently needed. In human pathogenic virus research, the major technical hurdle is not only to translate discoveries from animals to treatments of humans, but also to overcome the problem of interspecies differences with regard to productive infections and comparable disease development. Transgenic mice provide a basis for research of disease pathogenesis after infection with human-specific viruses. Today, humanized mice can be found at the very heart of this forefront of medical research allowing for recapitulation of disease pathogenesis and drug mechanisms in humans. This review discusses progress in the development and use of transgenic mice for the study of virus-induced human diseases towards identification of new drug innovations to treat and control human pathogenic infectious diseases.

Curative in vivo hematopoietic stem cell gene therapy of murine thalassemia using large regulatory elements

Recently, we demonstrated that hematopoietic stem/progenitor cell (HSPC) mobilization followed by intravenous injection of integrating, helper-dependent adenovirus HDAd5/35++ vectors resulted in efficient transduction of long-term repopulating cells and disease amelioration in mouse models after in vivo selection of transduced HSPCs. Acute innate toxicity associated with HDAd5/35++ injection was controlled by appropriate prophylaxis, making this approach feasible for clinical translation. Our ultimate goal is to use this technically simple in vivo HSPC transduction approach for gene therapy of thalassemia major or sickle cell disease. A cure of these diseases requires high expression levels of the therapeutic protein (γ- or β-globin), which is difficult to achieve with lentivirus vectors because of their genome size limitation not allowing larger regulatory elements to be accommodated. Here, we capitalized on the 35 kb insert capacity of HDAd5/35++ vectors to demonstrate that transcriptional regulatory regions of the β-globin locus with a total length of 29 kb can efficiently be transferred into HSPCs. The in vivo HSPC transduction resulted in stable γ-globin levels in erythroid cells that conferred a complete cure of murine thalassemia intermedia. Notably, this was achieved with a minimal in vivo HSPC selection regimen.

Employing large regulatory elements in the context of HDAd5/35++ vectors for in vivo transduction of HSPCs achieved gamma-globin levels in erythroid cells that cured murine thalassemia intermedia.

Human Desmoglein-2 and Human CD46 Mediate Human Adenovirus Type 55 Infection, but Human Desmoglein-2 Plays the Major Roles

Human adenovirus type 55 (HAdV55) represents an emerging respiratory pathogen and causes severe pneumonia with high fatality in humans. The cellular receptors, which are essential for understanding the infection and pathogenesis of HAdV55, remain unclear. In this study, we found that HAdV55 binding and infection were sharply reduced by disrupting the interaction of viral fiber protein with human desmoglein-2 (hDSG2) but only slightly reduced by disrupting the interaction of viral fiber protein with human CD46 (hCD46). Loss-of-function studies using soluble receptors, blocking antibodies, RNA interference, and gene knockout demonstrated that hDSG2 predominantly mediated HAdV55 infection. Nonpermissive rodent cells became susceptible to HAdV55 infection when hDSG2 or hCD46 was expressed, but hDSG2 mediated more efficient HAd55 infection than hCD46. We generated two transgenic mouse lines that constitutively express either hDSG2 or hCD46. Although nontransgenic mice were resistant to HAdV55 infection, infection with HAdV55 was significantly increased in hDSG2^+/+ mice but was much less increased in hCD46^+/+ mice. Our findings demonstrate that both hDSG2 and hCD46 are able to mediate HAdV55 infection but hDSG2 plays the major roles. The hDSG2 transgenic mouse can be used as a rodent model for evaluation of HAdV55 vaccine and therapeutics.IMPORTANCE Human adenovirus type 55 (HAdV55) has recently emerged as a highly virulent respiratory pathogen and has been linked to severe and even fatal pneumonia in immunocompetent adults. However, the cellular receptors mediating the entry of HAdV55 into host cells remain unclear, which hinders the establishment of HAdV55-infected animal models and the development of antiviral approaches. In this study, we demonstrated that human desmoglein-2 (hDSG2) plays the major roles during HAdV55 infection. Human CD46 (hCD46) could also mediate the infection of HAdV55, but the efficiency was much lower than for hDSG2. We generated two transgenic mouse lines that express either hDSG2 or hCD46, both of which enabled HAd55 infection in otherwise nontransgenic mice. hDSG2 transgenic mice enabled more efficient HAdV55 infection than hCD46 transgenic mice. Our study adds to our understanding of HAdV55 infection and provides an animal model for evaluating HAdV55 vaccines and therapeutics.

Complement and human T cell metabolism: Location, location, location

The complement system represents one of the evolutionary oldest arms of our immune system and is commonly recognized as a liver-derived and serum-active system critical for providing protection against invading pathogens. Recent unexpected findings, however, have defined novel and rather "uncommon" locations and activities of complement. Specifically, the discovery of an intracellularly active complement system-the complosome-and its key role in the regulation of cell metabolic pathways that underly normal human T cell responses have taught us that there is still much to be discovered about this system. Here, we summarize the current knowledge about the emerging functions of the complosome in T cell metabolism. We further place complosome activities among the non-canonical roles of other intracellular innate danger sensing systems and argue that a "location-centric" view of complement evolution could logically justify its close connection with the regulation of basic cell physiology.

Prophylactic In Vivo Hematopoietic Stem Cell Gene Therapy with an Immune Checkpoint Inhibitor Reverses Tumor Growth in Syngeneic Mouse Tumor Models

Population-wide testing for cancer-associated mutations has established that more than one-fifth of ovarian and breast carcinomas are associated with inherited risk. Salpingo-oophorectomy and/or mastectomy are currently the only effective options offered to women with high-risk germline mutations. Our goal here is to develop a long-lasting approach that provides immunoprophylaxis for mutation carriers. Our approach leverages the fact that at early stages, tumors recruit hematopoietic stem/progenitor cells (HSPC) from the bone marrow and differentiate them into tumor-supporting cells. We developed a technically simple technology to genetically modify HSPCs in vivo. The technology involves HSPC mobilization and intravenous injection of an integrating HDAd5/35++ vector. In vivo HSPC transduction with a GFP-expressing vector and subsequent implantation of syngeneic tumor cells showed >80% GFP marking in tumor-infiltrating leukocytes. To control expression of transgenes, we developed a miRNA regulation system that is activated only when HSPCs are recruited to and differentiated by the tumor. We tested our approach using the immune checkpoint inhibitor anti-PD-L1-γ1 as an effector gene. In in vivo HSPC-transduced mice with implanted mouse mammary carcinoma (MMC) tumors, after initial tumor growth, tumors regressed and did not recur. Conventional treatment with an anti-PD-L1 mAb had no significant antitumor effect, indicating that early, self-activating expression of anti-PD-L1-γ1 can overcome the immunosuppressive environment in MMC tumors. The efficacy and safety of this approach was further validated in an ovarian cancer model with typical germline mutations (ID8 p53-/- brca2-/-), both in a prophylactic and therapeutic setting. This HSPC gene therapy approach has potential for clinical translation. SIGNIFICANCE: Considering the limited prophylactic options that are currently offered to women with high-risk germ-line mutations, the in vivo HSPC gene therapy approach is a promising strategy that addresses a major medical problem.

Adenovirus vectors in hematopoietic stem cell genome editing

Genome editing of hematopoietic stem cells (HSCs) represents a therapeutic option for a number of hematological genetic diseases, as HSCs have the potential for self-renewal and differentiation into all blood cell lineages. This review presents advances of genome editing in HSCs utilizing adenovirus vectors as delivery vehicles. We focus on capsid-modified, helper-dependent adenovirus vectors that are devoid of all viral genes and therefore exhibit an improved safety profile. We discuss HSC genome engineering for several inherited disorders and infectious diseases including hemoglobinopathies, Fanconi anemia, hemophilia, and HIV-1 infection by ex vivo and in vivo editing in transgenic mice, nonhuman primates, as well as in human CD34+ cells. Mechanisms of therapeutic gene transfer including episomal expression of designer nucleases and base editors, transposase-mediated random integration, and targeted homology-directed repair triggered integration into selected genomic safe harbor loci are also reviewed.

Targeted Integration and High-Level Transgene Expression in AAVS1 Transgenic Mice after In Vivo HSC Transduction with HDAd5/35++ Vectors

Our goal is the development of in vivo hematopoietic stem cell (HSC) transduction technology with targeted integration. To achieve this, we modified helper-dependent HDAd5/35++ vectors to express a CRISPR/Cas9 specific to the "safe harbor" adeno-associated virus integration site 1 (AAVS1) locus and to provide a donor template for targeted integration through homology-dependent repair. We tested the HDAd-CRISPR + HDAd-donor vector system in AAVS1 transgenic mice using a standard ex vivo HSC gene therapy approach as well as a new in vivo HSC transduction approach that involves HSC mobilization and intravenous HDAd5/35++ injections. In both settings, the majority of treated mice had transgenes (GFP or human γ-globin) integrated into the AAVS1 locus. On average, >60% of peripheral blood cells expressed the transgene after in vivo selection with low-dose O⁶BG/bis-chloroethylnitrosourea (BCNU). Ex vivo and in vivo HSC transduction and selection studies with HDAd-CRISPR + HDAd-globin-donor resulted in stable γ-globin expression at levels that were significantly higher (>20% γ-globin of adult mouse globin) than those achieved in previous studies with a SB100x-transposase-based HDAd5/35++ system that mediates random integration. The ability to achieve therapeutically relevant transgene expression levels after in vivo HSC transduction and selection and targeted integration make our HDAd5/35++-based vector system a new tool in HSC gene therapy.

Clinical Trials with Oncolytic Measles Virus: Current Status and Future Prospects

Attenuated Edmonston lineage measles virus (MV-Edm) vaccine strains can preferentially infect and lyse a wide variety of cancer cells. Oncolytic MV-Edm derivatives are genetically engineered to express the human carcinoembryonic antigen (MV-CEA virus) or the human sodium iodide symporter (MV-NIS virus) and are currently being tested in clinical trials against ovarian cancer, glioblastoma multiforme, multiple myeloma, mesothelioma, head and neck cancer, breast cancer and malignant peripheral nerve sheath tumors. This review describes the basic and preclinical data that facilitated the clinical translation of MV-Edm strains, and summarizes the clinical results of this oncolytic platform to date. Furthermore, we discuss the latest clinically relevant MV-Edm vector developments and creative strategies for future translational steps.

Polyvalent Diazonium Polymers Provide Efficient Protection of Oncolytic Adenovirus Enadenotucirev from Neutralizing Antibodies while Maintaining Biological Activity In Vitro and In Vivo

Oncolytic viruses offer many advantages for cancer therapy when administered directly to confined solid tumors. However, the systemic delivery of these viruses is problematic because of the host immune response, undesired interactions with blood components, and inherent targeting to the liver. Efficacy of systemically administered viruses has been improved by masking viral surface proteins with polymeric materials resulting in modulation of viral pharmacokinetic profile and accumulation in tumors in vivo. Here we describe a new class of polyvalent reactive polymer based on poly( N-(2-hydroxypropyl)methacrylamide) (polyHPMA) with diazonium reactive groups and their application in the modification of the chimeric group B oncolytic virus enadenotucirev (EnAd). A series of six copolymers with different chain lengths and density of reactive groups was synthesized and used to coat EnAd. Polymer coating was found to be extremely efficient with concentrations as low as 1 mg/mL resulting in complete (>99%) ablation of neutralizing antibody binding. Coating efficiency was found to be dependent on both chain length and reactive group density. Coated viruses were found to have reduced transfection activity both in vitro and in vivo, with greater protection against neutralizing antibodies resulting in lower transgene production. However, in the presence of neutralizing antibodies, some in vivo transgene expression was maintained for coated virus compared to the uncoated control. The decrease in transgene expression was found not to be solely due to lower cellular uptake but due to reduced unpackaging of the virus within the cells and reduced replication, indicating that the polymer coating does not cause permanent inactivation of the virus. These data suggest that virus activity may be modulated by the appropriate design of coating polymers while retaining protection against neutralizing antibodies.

CD46 knock-out using CRISPR/Cas9 editing of hTERT immortalized human cells modulates complement activation

The kidney is especially sensitive to diseases associated with overactivation of the complement system. While most of these diseases affect kidney glomeruli and the microvasculature, there is also evidence for tubulointerstitial deposition of complement factors. Complement inactivating factors on cell membranes comprise CD55, CD59 and CD46, which is also termed membrane cofactor protein (MCP). CD46 has been described as localized to glomeruli, but especially also to proximal tubular epithelial cells (RPTECs). However, human cell culture models to assess CD46 function on RPTECs are still missing. Therefore, we here performed gene editing of RPTEC/TERT1 cells generating a monoclonal CD46^-/- cell line that did not show changes of the primary cell like characteristics. In addition, factor I and CD46-mediated cleavage of C4b into soluble C4c and membrane deposited C4d was clearly reduced in the knock-out cell line as compared to the maternal cells. Thus, human CD46^-/- proximal tubular epithelial cells will be of interest to dissect the roles of the epithelium and the kidney in various complement activation mediated tubulointerstitial pathologies or in studying CD46 mediated uropathogenic internalization of bacteria. In addition, this gives proof-of-principle, that telomerized cells can be used in the generation of knock-out, knock-in or any kind of reporter cell lines without losing the primary cell characteristics of the maternal cells.

In vivo hematopoietic stem cell gene therapy ameliorates murine thalassemia intermedia

Current thalassemia gene therapy protocols require the collection of hematopoietic stem/progenitor cells (HSPCs), in vitro culture, lentivirus vector transduction, and retransplantation into myeloablated patients. Because of cost and technical complexity, it is unlikely that such protocols will be applicable in developing countries, where the greatest demand for a β-thalassemia therapy lies. We have developed a simple in vivo HSPC gene therapy approach that involves HSPC mobilization and an intravenous injection of integrating HDAd5/35++ vectors. Transduced HSPCs homed back to the bone marrow, where they persisted long-term. HDAd5/35++ vectors for in vivo gene therapy of thalassemia had a unique capsid that targeted primitive HSPCs through human CD46, a relatively safe SB100X transposase-based integration machinery, a micro-LCR-driven γ-globin gene, and an MGMT(P140K) system that allowed for increasing the therapeutic effect by short-term treatment with low-dose O6-benzylguanine plus bis-chloroethylnitrosourea. We showed in "healthy" human CD46-transgenic mice and in a mouse model of thalassemia intermedia that our in vivo approach resulted in stable γ-globin expression in the majority of circulating red blood cells. The high marking frequency was maintained in secondary recipients. In the thalassemia model, a near-complete phenotypic correction was achieved. The treatment was well tolerated. This cost-efficient and "portable" approach could permit a broader clinical application of thalassemia gene therapy.

Asparaginyl Endopeptidase (Legumain) Supports Human Th1 Induction via Cathepsin L-Mediated Intracellular C3 Activation

Autocrine activation of the complement receptors C3aR and CD46 by complement activation components C3a and C3b produced through C3 cleavage by the protease cathepsin L (CTSL) during T cell stimulation is a requirement for IFN-γ production and Th1 induction in human CD4⁺ T cells. Thus, lack of autocrine CD46 activation, such as in CD46-deficient patients, is associated with defective Th1 responses and recurrent infections. We have identified LGMN [the gene coding for legumain, also known as asparaginyl endopeptidase (AEP)] as one of the key genes induced by CD46 co-stimulation during human CD4⁺ T cell activation. AEP processes and activates a range of proteins, among those α1-thymosin and CTSL, which both drive intrinsically Th1 activity-but has so far not been described to be functionally active in human T cells. Here we found that pharmacological inhibition of AEP during activation of human CD4⁺ T cells reduced CTSL activation and the CTSL-mediated generation of intracellular C3a. This translated into a specific reduction of IFN-γ production without affecting cell proliferation or survival. In line with these findings, CD4⁺ T cells isolated from Lgmn ^-/- mice also displayed a specific defect in IFN-γ secretion and Th1 induction. Furthermore, we did not observe a role for AEP-driven autocrine α1-thymosin activation in T cell-derived IFN-γ production. These data suggest that AEP is an "upstream" activator of the CTSL-C3-IFN-γ axis in human CD4⁺ T cells and hence an important supporter of human Th1 induction.

Integrating HDAd5/35++ Vectors as a New Platform for HSC Gene Therapy of Hemoglobinopathies

We generated an integrating, CD46-targeted, helper-dependent adenovirus HDAd5/35++ vector system for hematopoietic stem cell (HSC) gene therapy. The ∼12-kb transgene cassette included a β-globin locus control region (LCR)/promoter driven human γ-globin gene and an elongation factor alpha-1 (EF1α)-mgmtP140K expression cassette, which allows for drug-controlled increase of γ-globin-expressing erythrocytes. We transduced bone marrow lineage-depleted cells from human CD46-transgenic mice and transplanted them into lethally irradiated recipients. The percentage of γ-globin-positive cells in peripheral blood erythrocytes in primary and secondary transplant recipients was stable and greater than 90%. The γ-globin level was 10%-20% of adult mouse globin. Transgene integration, mediated by a hyperactive Sleeping Beauty SB100x transposase, was random, without a preference for genes. A second set of studies was performed with peripheral blood CD34+ cells from mobilized donors. 10 weeks after transplantation of transduced cells, human cells were harvested from the bone marrow and differentiated ex vivo into erythroid cells. Erythroid cells expressed γ-globin at a level of 20% of adult α-globin. Our studies suggest that HDAd35++ vectors allow for efficient transduction of long-term repopulating HSCs and high-level, almost pancellular γ-globin expression in erythrocytes. Furthermore, our HDAd5/35++ vectors have a larger insert capacity and a safer integration pattern than currently used lentivirus vectors.

Reactivation of γ-globin in adult β-YAC mice after ex vivo and in vivo hematopoietic stem cell genome editing

Disorders involving β-globin gene mutations, primarily β-thalassemia and sickle cell disease, represent a major target for hematopoietic stem/progenitor cell (HSPC) gene therapy. This includes CRISPR/Cas9-mediated genome editing approaches in adult CD34⁺ cells aimed toward the reactivation of fetal γ-globin expression in red blood cells. Because models involving erythroid differentiation of CD34⁺ cells have limitations in assessing γ-globin reactivation, we focused on human β-globin locus-transgenic (β-YAC) mice. We used a helper-dependent human CD46-targeting adenovirus vector expressing CRISPR/Cas9 (HDAd-HBG-CRISPR) to disrupt a repressor binding region within the γ-globin promoter. We transduced HSPCs from β-YAC/human CD46-transgenic mice ex vivo and subsequently transplanted them into irradiated recipients. Furthermore, we used an in vivo HSPC transduction approach that involves HSPC mobilization and the intravenous injection of HDAd-HBG-CRISPR into β-YAC/CD46-transgenic mice. In both models, we demonstrated efficient target site disruption, resulting in a pronounced switch from human β- to γ-globin expression in red blood cells of adult mice that was maintained after secondary transplantation of HSPCs. In long-term follow-up studies, we did not detect hematological abnormalities, indicating that HBG promoter editing does not negatively affect hematopoiesis. This is the first study that shows successful in vivo HSPC genome editing by CRISPR/Cas9.

Streptococcal M protein promotes IL-10 production by cGAS-independent activation of the STING signaling pathway

From an evolutionary point of view a pathogen might benefit from regulating the inflammatory response, both in order to facilitate establishment of colonization and to avoid life-threatening host manifestations, such as septic shock. In agreement with this notion Streptococcus pyogenes exploits type I IFN-signaling to limit detrimental inflammation in infected mice, but the host-pathogen interactions and mechanisms responsible for induction of the type I IFN response have remained unknown. Here we used a macrophage infection model and report that S. pyogenes induces anti-inflammatory IL-10 in an M protein-dependent manner, a function that was mapped to the B- and C-repeat regions of the M5 protein. Intriguingly, IL-10 was produced downstream of type I IFN-signaling, and production of type I IFN occurred via M protein-dependent activation of the STING signaling pathway. Activation of STING was independent of the cytosolic double stranded DNA sensor cGAS, and infection did not induce detectable release into the cytosol of either mitochondrial, nuclear or bacterial DNA-indicating DNA-independent activation of the STING pathway in S. pyogenes infected macrophages. These findings provide mechanistic insight concerning how S. pyogenes induces the type I IFN response and identify a previously unrecognized macrophage-modulating role for the streptococcal M protein that may contribute to curb the inflammatory response to infection.

A Combined In Vivo HSC Transduction/Selection Approach Results in Efficient and Stable Gene Expression in Peripheral Blood Cells in Mice

We recently reported on an in vivo hematopoietic stem cell (HSC) gene therapy approach. It involves the subcutaneous injections of G-CSF/AMD3100 to mobilize HSCs from the bone marrow into the peripheral blood stream and the intravenous injection of an integrating helper-dependent adenovirus vector system. HSCs transduced in the periphery homed back to the bone marrow, where they persisted long-term. However, high transgene marking rates found in primitive bone marrow HSCs were not reflected in peripheral blood cells. Here, we tested small-molecule drugs to achieve selective mobilization and transduction of HSCs. We found more efficient GFP marking in bone marrow HSCs but no increased marking in the peripheral blood cells. We then used an in vivo HSC chemo-selection based on a mutant of the O⁶-methylguanine-DNA methyltransferase (mgmt^P140K) gene that confers resistance to O⁶-BG/BCNU and should give stably transduced HSCs a proliferation stimulus and allow for the selective survival and expansion of progeny cells. Short-term exposure of G-CSF/AMD3100-mobilized, in vivo-transduced mice to relatively low selection drug doses resulted in stable GFP expression in up to 80% of peripheral blood cells. Overall, the further improvement of our in vivo HSC transduction approach creates the basis for a simpler HSC gene therapy.

Potential and clinical translation of oncolytic measles viruses

INTRODUCTION

Oncolytic viruses represent a novel treatment modality that is unencumbered by the standard resistance mechanisms limiting the therapeutic efficacy of conventional antineoplastic agents. Attenuated engineered measles virus strains derived from the Edmonston vaccine lineage have undergone extensive preclinical evaluation with significant antitumor activity observed in a broad range of preclinical tumoral models. These have laid the foundation for several clinical trials in both solid and hematologic malignancies, which have demonstrated safety, biologic activity and the ability to elicit antitumor immune responses. Areas covered: This review examines the published preclinical data which supported the clinical translation of this therapeutic platform, reviews the available clinical trial data and expands on ongoing phase II testing. It also looks at approaches to optimize clinical applicability and offers future perspectives. Expert opinion: Reverse genetic engineering has allowed the generation of oncolytic MV strains retargeted to increase viral tumor specificity, or armed with therapeutic and immunomodulatory genes in order to enhance anti-tumor efficacy. Continuous efforts focusing on exploring methods to overcome resistance pathways and determining optimal combinatorial strategies will facilitate further development of this encouraging antitumor strategy.

Preclinical Safety Studies of Enadenotucirev, a Chimeric Group B Human-Specific Oncolytic Adenovirus

Enadenotucirev is an oncolytic group B adenovirus identified by a process of bio-selection for the ability to selectively propagate in and rapidly kill carcinoma cells. It is resistant to inactivation by human blood components, potentially enabling intravenous dosing in patients with metastatic cancer. However, there are no known permissive animal models described for group B adenoviruses that could facilitate a conventional approach to preclinical safety studies. In this manuscript, we describe our tailored preclinical strategy designed to evaluate the key biological properties of enadenotucirev. As enadenotucirev does not replicate in animal cells, a panel of primary human cells was used to evaluate enadenotucirev replication selectivity in vitro, demonstrating that virus genome levels were >100-fold lower in normal cells relative to tumor cells. Acute intravenous tolerability in mice was used to assess virus particle-mediated toxicology and effects on innate immunity. These studies showed that particle toxicity could be ameliorated by dose fractionation, using an initial dose of virus to condition the host such that cytokine responses to subsequent doses were significantly attenuated. This, in turn, supported the initiation of a phase I intravenous clinical trial with a starting dose of 1 × 1010 virus particles given on days 1, 3, and 5.

Intracellular complement - the complosome - in immune cell regulation

The complement system was defined over a century ago based on its ability to "complement" the antibody-mediated and cell-mediated immune responses against pathogens. Today our understanding of this ancient part of innate immunity has changed substantially and we know now that complement plays an undisputed pivotal role in the regulation of both innate and adaptive immunity. The complement system consists of over 50 blood-circulating, cell-surface expressed and intracellular proteins. It is key in the recognition and elimination of invading pathogens, also in the removal of self-derived danger such as apoptotic cells, and it supports innate immune responses and the initiation of the general inflammatory reactions. The long prevailing classic view of complement was that of a serum-operative danger sensor and first line of defence system, however, recent experimental and clinical evidences have demonstrated that "local" tissue and surprisingly intracellular complement (the complosome) activation impacts on normal cell physiology. This review will focus on novel aspects of intracellular complement activation and its unexpected roles in basic cell processes such as metabolism. We also discuss what the existence of the complosome potentially means for how the host handles intracellular pathogens such as viruses.

VEGF regulates local inhibitory complement proteins in the eye and kidney

Outer retinal and renal glomerular functions rely on specialized vasculature maintained by VEGF that is produced by neighboring epithelial cells, the retinal pigment epithelium (RPE) and podocytes, respectively. Dysregulation of RPE- and podocyte-derived VEGF is associated with neovascularization in wet age-related macular degeneration (ARMD), choriocapillaris degeneration, and glomerular thrombotic microangiopathy (TMA). Since complement activation and genetic variants in inhibitory complement factor H (CFH) are also features of both ARMD and TMA, we hypothesized that VEGF and CFH interact. Here, we demonstrated that VEGF inhibition decreases local CFH and other complement regulators in the eye and kidney through reduced VEGFR2/PKC-α/CREB signaling. Patient podocytes and RPE cells carrying disease-associated CFH genetic variants had more alternative complement pathway deposits than controls. These deposits were increased by VEGF antagonism, a common wet ARMD treatment, suggesting that VEGF inhibition could reduce cellular complement regulatory capacity. VEGF antagonism also increased markers of endothelial cell activation, which was partially reduced by genetic complement inhibition. Together, these results suggest that VEGF protects the retinal and glomerular microvasculature, not only through VEGFR2-mediated vasculotrophism, but also through modulation of local complement proteins that could protect against complement-mediated damage. Though further study is warranted, these findings could be relevant for patients receiving VEGF antagonists.

Antibody-drug conjugate targeting CD46 eliminates multiple myeloma cells

Multiple myeloma is incurable by standard approaches because of inevitable relapse and development of treatment resistance in all patients. In our prior work, we identified a panel of macropinocytosing human monoclonal antibodies against CD46, a negative regulator of the innate immune system, and constructed antibody-drug conjugates (ADCs). In this report, we show that an anti-CD46 ADC (CD46-ADC) potently inhibited proliferation in myeloma cell lines with little effect on normal cells. CD46-ADC also potently eliminated myeloma growth in orthometastatic xenograft models. In primary myeloma cells derived from bone marrow aspirates, CD46-ADC induced apoptosis and cell death, but did not affect the viability of nontumor mononuclear cells. It is of clinical interest that the CD46 gene resides on chromosome 1q, which undergoes genomic amplification in the majority of relapsed myeloma patients. We found that the cell surface expression level of CD46 was markedly higher in patient myeloma cells with 1q gain than in those with normal 1q copy number. Thus, genomic amplification of CD46 may serve as a surrogate for target amplification that could allow patient stratification for tailored CD46-targeted therapy. Overall, these findings indicate that CD46 is a promising target for antibody-based treatment of multiple myeloma, especially in patients with gain of chromosome 1q.

Development of replication-deficient adenovirus malaria vaccines

INTRODUCTION

Malaria remains a major threat to endemic populations and travelers, including military personnel to these areas. A malaria vaccine is feasible, as radiation attenuated sporozoites induce nearly 100% efficacy. Areas covered: This review covers current malaria clinical trials using adenoviruses and pre-clinical research. Heterologous prime-boost regimens, including replication-deficient human adenovirus 5 (HuAd5) carrying malaria antigens, are efficacious. However, efficacy appears to be adversely affected by pre-existing anti-HuAd5 antibodies. Current strategies focus on replacing HuAd5 with rarer human adenoviruses or adenoviruses isolated from non-human primates (NHPs). The chimpanzee adenovirus ChAd63 is undergoing evaluation in clinical trials including infants in malaria-endemic areas. Key antigens have been identified and are being used alone, in combination, or with protein subunit vaccines. Gorilla adenoviruses carrying malaria antigens are also currently being evaluated in preclinical models. These replacement adenovirus vectors will be successfully used to develop vaccines against malaria, as well as other infectious diseases. Expert commentary: Simplified prime-boost single shot regimens, dry-coated live vector vaccines or silicon microneedle arrays could be developed for malaria or other vaccines. Replacement vectors with similar or superior immunogenicity have rapidly advanced, and several are now in extensive Phase 2 and beyond in malaria as well as other diseases, notably Ebola.

Soluble forms of CD46 are detected in Bos taurus plasma and neutralize BVDV, the bovine pestivirus

The pestivirus bovine viral diarrhea virus (BVDV) is known to bind to the CD46 molecule, which subsequently promotes entry of the virus. Mapping of the BVD-virion-binding site has shown that two peptides, 66EQIV69 and 82GQVLAL87, located on antiparallel beta sheets in the most distal complement control protein module (CCP1), provide the attachment platform. In the present study, we reveal new CD46-encoding transcripts that are predicted to encode CCP1-containing soluble forms. Further, we show that the serum of most adult cattle contains soluble CD46 (sCD46) and that a recombinant soluble isoform neutralizes BVDV infectivity in an in vitro assay. We have then established an ELISA for determination of plasma sCD46 in a large cohort of animals. Overall, serum sCD46 amounts to 8±18ng/mL (mean±SD, n=440), with a IC [95-105] ranging from 6,4 to 9,8ng/mL and extreme values ​​between 0 and 178ng/mL. We found that sCD46 is not detectable in fetal and neonatal sera and that its plasma concentration increases progressively up to adulthood. We also detected high- and low-sCD46 performers and show that this phenotype does not depend of environment. As modern rearing techniques make it possible to disseminate genetically-determined phenotypes very quickly in a population, a large-scale study examining whether high-sCD46 animals provide epidemiological protection against BVDV infection and transmission should be undertaken.

In vivo transduction of primitive mobilized hematopoietic stem cells after intravenous injection of integrating adenovirus vectors

Current protocols for hematopoietic stem/progenitor cell (HSPC) gene therapy, involving the transplantation of ex vivo genetically modified HSPCs are complex and not without risk for the patient. We developed a new approach for in vivo HSPC transduction that does not require myeloablation and transplantation. It involves subcutaneous injections of granulocyte-colony-stimulating factor/AMD3100 to mobilize HSPCs from the bone marrow (BM) into the peripheral blood stream and the IV injection of an integrating, helper-dependent adenovirus (HD-Ad5/35⁺⁺) vector system. These vectors target CD46, a receptor that is uniformly expressed on HSPCs. We demonstrated in human CD46 transgenic mice and immunodeficient mice with engrafted human CD34⁺ cells that HSPCs transduced in the periphery home back to the BM where they stably express the transgene. In hCD46 transgenic mice, we showed that our in vivo HSPC transduction approach allows for the stable transduction of primitive HSPCs. Twenty weeks after in vivo transduction, green fluorescent protein (GFP) marking in BM HSPCs (Lin^-Sca1⁺Kit^- cells) in most of the mice was in the range of 5% to 10%. The percentage of GFP-expressing primitive HSPCs capable of forming multilineage progenitor colonies (colony-forming units [CFUs]) increased from 4% of all CFUs at week 4 to 16% at week 12, indicating transduction and expansion of long-term surviving HSPCs. Our approach was well tolerated, did not result in significant transduction of nonhematopoietic tissues, and was not associated with genotoxicty. The ability to stably genetically modify HSPCs without the need of myeloablative conditioning is relevant for a broader clinical application of gene therapy.

Inhibition of the alternative complement pathway preserves photoreceptors after retinal injury

Degeneration of photoreceptors is a primary cause of vision loss worldwide, making the underlying mechanisms surrounding photoreceptor cell death critical to developing new treatment strategies. Retinal detachment, characterized by the separation of photoreceptors from the underlying retinal pigment epithelium, is a sight-threatening event that can happen in a number of retinal diseases. The detached photoreceptors undergo apoptosis and programmed necrosis. Given that photoreceptors are nondividing cells, their loss leads to irreversible visual impairment even after successful retinal reattachment surgery. To better understand the underlying disease mechanisms, we analyzed innate immune system regulators in the vitreous of human patients with retinal detachment and correlated the results with findings in a mouse model of retinal detachment. We identified the alternative complement pathway as promoting early photoreceptor cell death during retinal detachment. Photoreceptors down-regulate membrane-bound inhibitors of complement, allowing for selective targeting by the alternative complement pathway. When photoreceptors in the detached retina were removed from the primary source of oxygen and nutrients (choroidal vascular bed), the retina became hypoxic, leading to an up-regulation of complement factor B, a key mediator of the alternative pathway. Inhibition of the alternative complement pathway in knockout mice or through pharmacological means ameliorated photoreceptor cell death during retinal detachment. Our current study begins to outline the mechanism by which the alternative complement pathway facilitates photoreceptor cell death in the damaged retina.

Preclinical safety, pharmacokinetics, pharmacodynamics, and biodistribution studies with Ad35K++ protein: a novel rituximab cotherapeutic

Rituximab is a mouse/human chimeric monoclonal antibody targeted toward CD20. It is efficient as first-line therapy of CD20-positive B-cell malignancies. However, a large fraction of treated patients relapse with rituximab-resistant disease. So far, only modest progress has been made in treatment options for rituximab refractory patients. One of the mechanisms for rituximab resistance involves the upregulation of CD46, which is a key cell surface protein that blocks the activation of complement. We have recently developed a technology that depletes CD46 from the cell surface and thereby sensitizes tumor cells to complement-dependent cytotoxicity. This technology is based on a small recombinant protein, Ad35K++ that binds with high affinity to CD46. In preliminary studies using a 6 × histidinyl tagged protein, we had demonstrated that intravenous Ad35K++ injection in combination with rituximab was safe and increased rituximab-mediated killing of CD20-positive target cells in mice and nonhuman primates (NHPs). The presence of the tag, while allowing for easy purification by Ni-NTA chromatography, has the potential to increase the immunogenicity of the recombinant protein. For clinical application, we therefore developed an Ad35K++ protein without His-tag. In the present study, we performed preclinical studies in two animal species (mice and NHPs) with this protein demonstrating its safety and efficacy. These studies estimated the Ad35K++ dose range and treatment regimen to be used in patients. Furthermore, we showed that intravenous Ad35K++ injection triggers the shedding of the CD46 extracellular domain in xenograft mouse tumor models and in macaques. Shed serum CD46 can be measured in the serum and can potentially be used as a pharmacodynamic marker for monitoring Ad35K++ activity in patient undergoing treatment with this agent. These studies create the basis for an investigational new drug application for the use of Ad35K++ in combination with rituximab in the treatment of patients with B-cell malignancies.

A highly susceptible CD46 transgenic mouse model of subcutaneous infection with Streptococcus dysgalactiae subspecies equisimilis

The Streptococcus dysgalactiae subspecies equisimilis (SDSE) possesses clinical similarities to group A streptococcus (GAS) and has recently been recognized as a causative pathogen of life-threatening streptococcal infections. Human membrane cofactor protein (CD46), a complement regulatory protein ubiquitously expressed on every cell type except for erythrocytes, has been implicated as a receptor for human-specific pathogens including GAS. In the present report, SDSE strain GGS_124 was isolated from a patient suffering from streptococcal toxic shock syndrome. When CD46-expressing transgenic (Tg) and non-Tg mice were infected subcutaneously into a hind footpad with 1 × 10(7) colony-forming units of GGS_124, both CD46 Tg and non-Tg mice showed similar levels of colonization in the popliteal lymph nodes at day 3 after infection. However, the following differences were found between CD46 Tg and non-Tg mice after infection. First, there was a statistically significant difference in mortality rates between CD46 Tg (33%) and non-Tg (0%) mice within 35 days after infection. Second, all surviving CD46 Tg mice developed ankle arthritis at day 35 after infection, whereas non-Tg mice did not develop ankle arthritis on the infected hind paws. Finally, CD46 Tg mice developed a pus-filled abscess accompanied by renal failure at day 6 or later after infection. These observations suggest that CD46, the host cell-surface pathogen receptor, functioned to attract GGS_124 into deep tissues, so that the subcutaneous infection with GGS_124 induced invasive streptococcal diseases in CD46 Tg mice.

Complement Regulates Nutrient Influx and Metabolic Reprogramming during Th1 Cell Responses

Expansion and acquisition of Th1 cell effector function requires metabolic reprogramming; however, the signals instructing these adaptations remain poorly defined. Here we found that in activated human T cells, autocrine stimulation of the complement receptor CD46, and specifically its intracellular domain CYT-1, was required for induction of the amino acid (AA) transporter LAT1 and enhanced expression of the glucose transporter GLUT1. Furthermore, CD46 activation simultaneously drove expression of LAMTOR5, which mediated assembly of the AA-sensing Ragulator-Rag-mTORC1 complex and increased glycolysis and oxidative phosphorylation (OXPHOS), required for cytokine production. T cells from CD46-deficient patients, characterized by defective Th1 cell induction, failed to upregulate the molecular components of this metabolic program as well as glycolysis and OXPHOS, but IFN-γ production could be reinstated by retrovirus-mediated CD46-CYT-1 expression. These data establish a critical link between the complement system and immunometabolic adaptations driving human CD4⁺ T cell effector function.

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CD46 regulates GLUT1 and LAT1 and enhances glucose and AA uptake in T cells

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LAMTOR5 mediates Ragulator-Rag-mTORC1 assembly in activated T cells

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Complement drives glycolysis and oxidative phosphorylation critical to Th1 cell induction

An immune competent mouse model for the characterization of recombinant measles vaccines

Today, immune compromised interferon-α-receptor deficient mice expressing hCD46 (IFNARCD46tg) are usually used for measles virus (MV) based vaccine characterization. However, for the development of MV-based recombinant vaccine candidates (rMV), an immune competent mouse model is desirable in order to induce and evaluate meaningful immune response. In this study, humoral and cellular immune response induced by rMV in immune competent mice expressing human MV receptor CD46 (hCD46tg) were compared with those induced in wild-type black/6, and IFNARCD46tg mice.   All three strains developed humoral and cellular response against MV, whereas only hCD46tg and IFNARCD46tg mice developed a humoral response against the transgene. Differences were observed in the magnitude of the response, where the IFNARCD46tg mice displayed the strongest immune responses, followed by the hCD46tg mice and the black/6 mice. Interestingly, hCD46tg and wt black/6 mice showed a predominant CD4(+) T-cell response against MV-N, whereas IFNARCD46tg mice developed both, CD4(+) and CD8(+) T-cell response against MV-N. Analysis of the cytokine profile of MV-N specific CD4(+) T-cells and transgene (SIVgag) specific CD8(+) T-cells revealed qualitative differences of the T-cell responses; noticeably a significant reduction of the frequency of CD4(+)IL-2(+) expressing cells in IFNARCD46tg mice as compared with hCD46tg or wt black/6 mice. We show in this study significant quantitative and qualitative differences in immune responses between immune competent and immune-compromised mice. Our results therefore highlight the importance of the animal model and support the use of hCD46tg mice as mouse model for the characterization of the immunological profile induced by recombinant measles virus vaccine candidates.

The alternative complement pathway regulates pathological angiogenesis in the retina

A defining feature in proliferative retinopathies is the formation of pathological neovessels. In these diseases, the balance between neovessel formation and regression determines blindness, making the modulation of neovessel growth highly desirable. The role of the immune system in these retinopathies is of increasing interest, but it is not completely understood. We investigated the role of the alternative complement pathway during the formation and resolution of aberrant neovascularization. We used alternative complement pathway-deficient (Fb(-/-)) mice and age- and strain-matched control mice to assess neovessel development and regression in an oxygen-induced retinopathy (OIR) mouse model. In the control mice, we found increased transcription of Fb after OIR treatment. In the Fb(-/-) mice, we prepared retinal flatmounts and identified an increased number of neovessels, peaking at postnatal day 17 (P17; P=0.001). Subjecting human umbilical vein endothelial cells (HUVECs) to low oxygen, mimicking a characteristic of neovessels, decreased the expression of the complement inhibitor Cd55. Finally, using laser capture microdissection (LCM) to isolate the neovessels after OIR, we found decreased expression of Cd55 (P=0.005). Together, our data implicate the alternative complement pathway in facilitating neovessel clearance by down-regulating the complement inhibitor Cd55 specifically on neovessels, allowing for their targeted removal while leaving the established vasculature intact.-Sweigard, J. H., Yanai, R., Gaissert, P., Saint-Geniez, M., Kataoka, K., Thanos, A., Stahl, G. L., Lambris, J. D., Connor, K. M. The alternative complement pathway regulates pathological angiogenesis in the retina.

Amalgamating oncolytic viruses to enhance their safety, consolidate their killing mechanisms, and accelerate their spread

Oncolytic viruses are structurally and biologically diverse, spreading through tumors and killing them by various mechanisms and with different kinetics. Here, we created a hybrid vesicular stomatitis/measles virus (VSV/MV) that harnesses the safety of oncolytic MV, the speed of VSV, and the tumor killing mechanisms of both viruses. Oncolytic MV targets CD46 and kills by forcing infected cells to fuse with uninfected neighbors, but propagates slowly. VSV spreads rapidly, directly lysing tumor cells, but is neurotoxic and loses oncolytic potency when neuroattenuated by conventional approaches. The hybrid VSV/MV lacks neurotoxicity, replicates rapidly with VSV kinetics, and selectively targets CD46 on tumor cells. Its in vivo performance in a myeloma xenograft model was substantially superior to either MV or widely used recombinant oncolytic VSV-M51.

Oncolytic measles virus strains as novel anticancer agents

INTRODUCTION

Replication-competent oncolytic measles virus (MV) strains preferentially infect and destroy a wide variety of cancer tissues. Clinical translation of engineered attenuated MV vaccine derivatives is demonstrating the therapeutic potential and negligible pathogenicity of these strains in humans.

AREAS COVERED

The present review summarizes the mechanisms of MV tumor selectivity and cytopathic activity as well as the current data on the oncolytic efficacy and preclinical testing of MV strains. Investigational strategies to reprogram MV selectivity, escape antiviral immunity and modulate the immune system to enhance viral delivery and tumor oncolysis are also discussed.

EXPERT OPINION

Clinical viral kinetic data derived from noninvasive monitoring of reporter transgene expression will guide future protocols to enhance oncolytic MV efficacy. Anti-measles immunity is a major challenge of measles-based therapeutics and various strategies are being investigated to modulate immunity. These include the combination of MV therapy with immunosuppressive drugs, such as cyclophosphamide, the use of cell carriers and the introduction of immunomodulatory transgenes and wild-type virulence genes. Available MV retargeting technologies can address safety considerations that may arise as more potent oncolytic MV vectors are being developed.