Mouse strains with typical mammalian levels of complement activity

Impact of pre-existing anti-polyethylene glycol (PEG) IgM on biodistribution and humoral response of intramuscularly administered PEGylated mRNA loaded lipid nanoparticle

With the approval of mRNA vaccines for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), lipid nanoparticles (LNP) have emerged as a powerful tool for nucleic acid delivery. Modification of LNP with polyethylene glycol (PEG)-lipids contributes to their in vitro and in vivo stability by reducing aggregation of the particles. Despite the general acknowledgement of the low immunogenicity of PEG, there are numerous reports of the occurrence of anti-PEG antibodies in the blood of healthy individuals. Furthermore, there are reports that pre-existing anti-PEG IgM antibodies attenuated the efficacy of PEG-modified drugs administered systemically. Skeletal muscles, the administration site for mRNA vaccines, are highly vascularized by a network of blood vessels to provide them with nutrients and oxygen. Since skeletal muscles can contain circulating anti-PEG antibodies or the administered mRNA-LNP extravasate into bloodstream, the purpose of this study was to evaluate the effects of pre-existing anti-PEG IgM on the protein translation, biodistribution, and humoral responses to mRNA-loaded LNP (mRNA-LNP) administered intramuscularly (i.m.) in mice. We found that the presence of anti-PEG IgM in blood has only a minor effect on the translation and distribution of mRNA-LNP in the localized muscle area where the mRNA-LNP were administered. Circulating anti-PEG IgM did not increase the total accumulation of mRNA-LNP in the liver, but did markedly diminish its protein translation because the mRNA-LNP were delivered primarily to Kupffer cells rather than to hepatocytes. Binding of anti-PEG IgM to mRNA-LNP, and subsequent complement activation, suppressed mRNA translation loaded in LNP in the liver. Repeated intramuscular injections of SARS-CoV-2 Spike protein mRNA-LNP elicited a robust immune response. Our results indicate that the presence of circulating anti-PEG IgM does not interfere with the efficiency of mRNA vaccines administered i.m. in mice. We can speculate that non-specific translation of mRNA vaccines in somatic cells may be inhibited in vivo by circulating anti-PEG IgM, reducing adverse effects such as hepatitis and myocarditis that are caused by immune responses against translated antigen proteins.

Complement is primarily activated in the lung in a mouse model of severe COVID-19

In vitro studies and observational human disease data suggest the complement system contributes to SARS-CoV-2 pathogenesis, although how complement dysregulation develops in severe COVID-19 is unknown. Here, using a mouse-adapted SARS-CoV-2 virus (SARS2-N501YMA30) and a mouse model of COVID-19, we identify significant serologic and pulmonary complement activation post-infection. We observed C3 activation in airway and alveolar epithelia, and pulmonary vascular endothelia. Our evidence suggests the alternative pathway is the primary route of complement activation, however, components of both the alternative and classical pathways are produced locally by respiratory epithelial cells following infection, and increased in primary cultures of human airway epithelia following cytokine and SARS-CoV-2 exposure. This tissue-specific complement response appears to precede lung injury and inflammation. Our results suggest that complement activation is a defining feature of severe COVID-19 in mice, agreeing with previous publications, and provide the basis for further investigation into the role of complement in COVID-19.

Species differences in opsonization and phagocyte recognition of preclinical poly-2-alkyl-2-oxazoline-coated nanoparticles

Poly(ethylene glycol) (PEG) is widely used in nanomedicine design, but emerging PEG immunogenicity in the general population is of therapeutic concern. As alternative, polyoxazolines are gaining popularity, since "polyoxazolinated" nanoparticles show long-circulating properties comparable to PEGylated nanoparticles in mice. Here, we show species differences in opsonization and differential uptake by monocytes and macrophages of nanoparticles coated with either poly-2-methyl-2-oxazoline or poly-2-ethyl-2-oxazoline. These nanoparticles evade murine opsonization process and phagocytic uptake but porcine ficolin 2 (FCN2), through its S2 binding site, recognizes polyoxazolines, and mediates nanoparticle uptake exclusively by porcine monocytes. In human sera, FCN opsonization is isoform-dependent showing inter-individual variability but both FCN2 and complement opsonization promote nanoparticle uptake by human monocytes. However, nanoparticle uptake by human and porcine macrophages is complement-dependent. These findings advance mechanistic understanding of species differences in innate immune recognition of nanomaterials' molecular patterns, and applicable to the selection and chemical design of polymers for engineering of the next generation of stealth nanoparticles.

Enhancing complement activation by therapeutic anti-tumor antibodies: Mechanisms, strategies, and engineering approaches

The complement system plays an integral role in both innate and adaptive immune responses. Beyond its protective function against infections, complement is also known to influence tumor immunity, where its activation can either promote tumor progression or mediate tumor cell destruction, depending on the context. One such context can be provided by antibodies, with their inherent capacity to activate the classical complement pathway. In recent years, our understanding of the mechanisms governing complement activation by IgG and IgM antibodies has expanded significantly. At the same time, preclinical and clinical studies on antibodies such as rituximab, ofatumumab, and daratumumab have provided evidence for the role of complement in therapeutic success, encouraging strategies to further enhance its activity. In this review we examine the main determinants of antibody-mediated complement activation, highlighting the importance of antibody subclass, affinity, valency, and geometry of antigen engagement. We summarize the evidence for complement involvement in anti-tumor activity and challenges of accurately estimating the extent of its contribution to therapeutic efficacy. Furthermore, we explore several engineering approaches designed to enhance complement activation, including increased Fc oligomerization and C1q affinity, bispecific C1q-recruiting antibodies, IgG subclass chimeras, as well as antibody and paratope combinations. Strategies targeting membrane-bound complement regulatory proteins to overcome tumor-associated complement inhibition are also discussed as a method to boost therapeutic efficacy. Finally, we highlight the potential of complement-dependent cellular cytotoxicity (CDCC) and complement-dependent cellular phagocytosis (CDCP) as effector mechanisms that warrant deeper investigation. By integrating advances in antibody and complement biology with insights from efforts to enhance complement activation in therapeutic antibodies, this review aims to provide a comprehensive framework of antibody design and engineering strategies that optimize complement activity for improved anti-tumor efficacy.

Exemplifying interspecies variation of liposome in vivo fate by the effects of anti-PEG antibodies

The different fate of liposomes among species has been discovered and mentioned in many studies, but the underlying mechanisms have not been explored. In the present work, we concentrated on the in vivo fate of PEGylated liposomes (sLip) in three commonly used species (mice, rats, and dogs). It was exhibited that the accelerated blood clearance (ABC) phenomenon and hypersensitivity in large animals (beagle dogs) were much more significant than that in rodents. We demonstrated that anti-PEG IgM (partially) and complement (mostly) determined the elimination of sLip and linked the distinct interspecies performances with the diverse complement capacity among species. Based on the data from animals and clinical patients, it was revealed that the fate of sLip in large animals was closer to that in humans, for the sufficient complement capacity could expose the potential adverse reactions caused by anti-PEG antibodies. Our results suggested that the distinctive interspecies performances of sLip were highly related to the physiological variabilities among species, which should not be overlooked in the innovation and translation of nanomedicines.

Efficient generation of human immune system rats using human CD34+ cells

Human immune system (HIS) mice generated using human CD34+ hematopoietic stem cells serve as a pivotal model for the in vivo evaluation of immunotherapies for humans. Yet, HIS mice possess certain limitations. Rats, due to their size and comprehensive immune system, hold promise for translational experiments. Here, we describe an efficacious method for long-term immune humanization, through intrahepatic injection of hCD34+ cells in newborn immunodeficient rats expressing human SIRPα. In contrast to HIS mice and similar to humans, HIS rats showed in blood a predominance of T cells, followed by B cells. Immune humanization was also high in central and secondary lymphoid organs. HIS rats treated with the anti-human CD3 antibody were depleted of human T cells, and human cytokines were detected in sera. We describe for the first time a method to efficiently generate HIS rats. HIS rats have the potential to be a useful model for translational immunology.

Polyester nanoparticles delivering chemotherapeutics: Learning from the past and looking to the future to enhance their clinical impact in tumor therapy

Polymeric nanoparticles (NPs), specifically those comprised of biodegradable and biocompatible polyesters, have been heralded as a game-changing drug delivery platform. In fact, poly(α-hydroxy acids) such as polylactide (PLA), poly(lactide-co-glycolide) (PLGA), and poly(ε-caprolactone) (PCL) have been heavily researched in the past three decades as the material basis of polymeric NPs for drug delivery applications. As materials, these polymers have found success in resorbable sutures, biodegradable implants, and even monolithic, biodegradable platforms for sustained release of therapeutics (e.g., proteins and small molecules) and diagnostics. Few fields have gained more attention in drug delivery through polymeric NPs than cancer therapy. However, the clinical translational of polymeric nanomedicines for treating solid tumors has not been congruent with the fervor or funding in this particular field of research. Here, we attempt to provide a comprehensive snapshot of polyester NPs in the context of chemotherapeutic delivery. This includes a preliminary exploration of the polymeric nanomedicine in the cancer research space. We examine the various processes for producing polyester NPs, including methods for surface-functionalization, and related challenges. After a detailed overview of the multiple factors involved with the delivery of NPs to solid tumors, the crosstalk between particle design and interactions with biological systems is discussed. Finally, we report state-of-the-art approaches toward effective delivery of NPs to tumors, aiming at identifying new research areas and re-evaluating the reasons why some research avenues have underdelivered. We hope our effort will contribute to a better understanding of the gap to fill and delineate the future research work needed to bring polyester-based NPs closer to clinical application. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies.

A predominately pulmonary activation of complement in a mouse model of severe COVID-19

Evidence from in vitro studies and observational human disease data suggest the complement system plays a significant role in SARS-CoV-2 pathogenesis, although how complement dysregulation develops in patients with severe COVID-19 is unknown. Here, using a mouse-adapted SARS-CoV-2 virus (SARS2-N501YMA30) and a mouse model of severe COVID-19, we identify significant serologic and pulmonary complement activation following infection. We observed C3 activation in airway and alveolar epithelia, and in pulmonary vascular endothelia. Our evidence suggests that while the alternative pathway is the primary route of complement activation, components of both the alternative and classical pathways are produced locally by respiratory epithelial cells following infection, and increased in primary cultures of human airway epithelia in response to cytokine exposure. This locally generated complement response appears to precede and subsequently drive lung injury and inflammation. Results from this mouse model recapitulate findings in humans, which suggest sex-specific variance in complement activation, with predilection for increased C3 activity in males, a finding that may correlate with more severe disease. Our findings indicate that complement activation is a defining feature of severe COVID-19 in mice and lay the foundation for further investigation into the role of complement in COVID-19.

Therapeutic Intervention of Neuroinflammatory Alzheimer Disease Model by Inhibition of Classical Complement Pathway with the Use of Anti-C1r Loaded Exosomes

Alzheimer's disease (AD) is a complex neurodegenerative disease associated with memory decline, cognitive impairment, amyloid plaque formation and tau tangles. Neuroinflammation has been shown to be a precursor to apparent amyloid plaque accumulation and subsequent synaptic loss and cognitive decline. In this study, the ability of a novel, small molecule, T-ALZ01, to inhibit neuroinflammatory processes was analyzed. T-ALZ01, an inhibitor of complement component C1r, demonstrated a significant reduction in the levels of the inflammatory cytokines, IL-6 and TNF-α in vitro. An LPS-induced animal model, whereby animals were injected intraperitoneally with 0.5 mg/kg LPS, was used to analyze the effect of T-ALZ01 on neuroinflammation in vivo. Moreover, exosomes (nanosized, endogenous extracellular vehicles) were used as drug delivery vehicles to facilitate intranasal administration of T-ALZ01 across the blood-brain barrier. T-ALZ01 demonstrated significant reduction in degenerating neurons and the activation of resident microglia and astrocytes, as well as inflammatory markers in vivo. This study demonstrates a significant use of small molecule complement inhibitors via exosome drug delivery as a possible therapeutic in disorders characterized by neuroinflammation, such AD.

Macrophage-mediated trogocytosis contributes to destroying human schistosomes in a non-susceptible rodent host, Microtus fortis

Schistosoma parasites, causing schistosomiasis, exhibit typical host specificity in host preference. Many mammals, including humans, are susceptible to infection, while the widely distributed rodent, Microtus fortis, exhibits natural anti-schistosome characteristics. The mechanisms of host susceptibility remain poorly understood. Comparison of schistosome infection in M. fortis with the infection in laboratory mice (highly sensitive to infection) offers a good model system to investigate these mechanisms and to gain an insight into host specificity. In this study, we showed that large numbers of leukocytes attach to the surface of human schistosomes in M. fortis but not in mice. Single-cell RNA-sequencing analyses revealed that macrophages might be involved in the cell adhesion, and we further demonstrated that M. fortis macrophages could be mediated to attach and kill schistosomula with dependence on Complement component 3 (C3) and Complement receptor 3 (CR3). Importantly, we provided direct evidence that M. fortis macrophages could destroy schistosomula by trogocytosis, a previously undescribed mode for killing helminths. This process was regulated by Ca2+/NFAT signaling. These findings not only elucidate a novel anti-schistosome mechanism in M. fortis but also provide a better understanding of host parasite interactions, host specificity and the potential generation of novel strategies for schistosomiasis control.

Preclinical anti-tumour activity of HexaBody-CD38, a next-generation CD38 antibody with superior complement-dependent cytotoxic activity

BACKGROUND

HexaBody®-CD38 (GEN3014) is a hexamerization-enhanced human IgG1 that binds CD38 with high affinity. The E430G mutation in its Fc domain facilitates the natural process of antibody hexamer formation upon binding to the cell surface, resulting in increased binding of C1q and potentiated complement-dependent cytotoxicity (CDC).

METHODS

Co-crystallization studies were performed to identify the binding interface of HexaBody-CD38 and CD38. HexaBody-CD38-induced CDC, antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), trogocytosis, and apoptosis were assessed using flow cytometry assays using tumour cell lines, and MM patient samples (CDC). CD38 enzymatic activity was measured using fluorescence spectroscopy. Anti-tumour activity of HexaBody-CD38 was assessed in patient-derived xenograft mouse models in vivo.

FINDINGS

HexaBody-CD38 binds a unique epitope on CD38 and induced potent CDC in multiple myeloma (MM), acute myeloid leukaemia (AML), and B-cell non-Hodgkin lymphoma (B-NHL) cells. Anti-tumour activity was confirmed in patient-derived xenograft models in vivo. Sensitivity to HexaBody-CD38 correlated with CD38 expression level and was inversely correlated with expression of complement regulatory proteins. Compared to daratumumab, HexaBody-CD38 showed enhanced CDC in cell lines with lower levels of CD38 expression, without increasing lysis of healthy leukocytes. More effective CDC was also confirmed in primary MM cells. Furthermore, HexaBody-CD38 efficiently induced ADCC, ADCP, trogocytosis, and apoptosis after Fc-crosslinking. Moreover, HexaBody-CD38 strongly inhibited CD38 cyclase activity, which is hypothesized to relieve immune suppression in the tumour microenvironment.

INTERPRETATION

Based on these preclinical studies, a clinical trial was initiated to assess the clinical safety of HexaBody-CD38 in patients with MM.

FUNDING

Genmab.

Perspectives on complement and phagocytic cell responses to nanoparticles: From fundamentals to adverse reactions

The complement system, professional phagocytes and other cells such as Natural killer cells and mast cells are among the important components of the innate arm of the immune system. These constituents provide an orchestrated array of defences and responses against tissue injury and foreign particles, including nanopharmaceuticals. While interception of nanopharmaceuticals by the immune system is beneficial for immunomodulation and treatment of phagocytic cell disorders, it is imperative to understand the multifaceted mechanisms by which nanopharmaceuticals interacts with the immune system and evaluate the subsequent balance of beneficial versus adverse reactions. An example of the latter is adverse infusion reactions to regulatory-approved nanopharmaceuticals seen in human subjects. Here, we discuss collective opinions and findings from our laboratories in mapping nanoparticle-mediated complement and leucocyte/macrophage responses.

Antibodies against Poly(ethylene glycol) Activate Innate Immune Cells and Induce Hypersensitivity Reactions to PEGylated Nanomedicines

Nanomedicines and macromolecular drugs can induce hypersensitivity reactions (HSRs) with symptoms ranging from flushing and breathing difficulties to hypothermia, hypotension, and death in the most severe cases. Because many normal individuals have pre-existing antibodies that bind to poly(ethylene glycol) (PEG), which is often present on the surface of nanomedicines and macromolecular drugs, we examined if and how anti-PEG antibodies induce HSRs to PEGylated liposomal doxorubicin (PLD). Anti-PEG IgG but not anti-PEG IgM induced symptoms of HSRs including hypothermia, altered lung function, and hypotension after PLD administration in C57BL/6 and nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. Hypothermia was significantly reduced by blocking FcγRII/III, by depleting basophils, monocytes, neutrophils, or mast cells, and by inhibiting secretion of histamine and platelet-activating factor. Anti-PEG IgG also induced hypothermia in mice after administration of other PEGylated liposomes, nanoparticles, or proteins. Humanized anti-PEG IgG promoted binding of PEGylated nanoparticles to human immune cells and induced secretion of histamine from human basophils in the presence of PLD. Anti-PEG IgE could also induce hypersensitivity reactions in mice after administration of PLD. Our results demonstrate an important role for IgG antibodies in induction of HSRs to PEGylated nanomedicines through interaction with Fcγ receptors on innate immune cells and provide a deeper understanding of HSRs to PEGylated nanoparticles and macromolecular drugs that may facilitate development of safer nanomedicines.

An anti-HER2 biparatopic antibody that induces unique HER2 clustering and complement-dependent cytotoxicity

Human epidermal growth factor receptor 2 (HER2) is a receptor tyrosine kinase that plays an oncogenic role in breast, gastric and other solid tumors. However, anti-HER2 therapies are only currently approved for the treatment of breast and gastric/gastric esophageal junction cancers and treatment resistance remains a problem. Here, we engineer an anti-HER2 IgG1 bispecific, biparatopic antibody (Ab), zanidatamab, with unique and enhanced functionalities compared to both trastuzumab and the combination of trastuzumab plus pertuzumab (tras + pert). Zanidatamab binds adjacent HER2 molecules in trans and initiates distinct HER2 reorganization, as shown by polarized cell surface HER2 caps and large HER2 clusters, not observed with trastuzumab or tras + pert. Moreover, zanidatamab, but not trastuzumab nor tras + pert, elicit potent complement-dependent cytotoxicity (CDC) against high HER2-expressing tumor cells in vitro. Zanidatamab also mediates HER2 internalization and downregulation, inhibition of both cell signaling and tumor growth, antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP), and also shows superior in vivo antitumor activity compared to tras + pert in a HER2-expressing xenograft model. Collectively, we show that zanidatamab has multiple and distinct mechanisms of action derived from the structural effects of biparatopic HER2 engagement.

Phenotypical Differences between Leishmania (Leishmania) amazonensis PH8 and LV79 Strains May Impact Survival in Mammal Host and in Phlebotomine Sand Flies

We previously showed that L. (Leishmania) amazonensis promastigotes and amastigotes of the PH8 strain generated larger lesions in mice than LV79, and that lesion-derived amastigotes from the two strains differ in their proteomes. We recently reported that PH8 promastigotes are more phagocytized by macrophages. Promastigotes' membrane-enriched proteomes showed several differences, and samples of each strain clustered based on proteomes. In this paper, we show phenotypic differences between PH8 and LV79 promastigotes that may explain the higher virulence of PH8. We compared in vitro macrophage infections by day 4 (early) and day 6 (late stationary phase) cultures, resistance to complement, and LPG characteristics. PH8 promastigotes showed a higher infectivity and were more resistant to murine complement. LPG was different between the strains, which may influence the interaction with macrophages and survival to complement. We compared the infection of the permissive vector Lutzomyia longipalpis. PH8 was more abundant in the vector's gut 72 h after feeding, which is a moment where blood digestion is finished and the parasites are exposed to the gut environment. Our results indicate that PH8 promastigotes are more infective, more resistant to complement, and infect the permissive vector more efficiently. These data suggest that PH8 is probably better adapted to the sand fly and more prone to survive in the vertebrate host.

Development of Allogeneic Stem Cell-Based Platform for Delivery and Potentiation of Oncolytic Virotherapy

We describe the repurposing and optimization of the TK-positive (thymidine kinase) vaccinia virus strain ACAM1000/ACAM2000™ as an oncolytic virus. This virus strain has been widely used as a smallpox vaccine and was also used safely in our recent clinical trial in patients with advanced solid tumors and Acute Myeloid Leukemia (AML). The vaccinia virus was amplified in CV1 cells and named CAL1. CAL1 induced remarkable oncolysis in various human and mouse cancer cells and preferentially amplified in cancer cells, supporting the use of this strain as an oncolytic virus. However, the therapeutic potential of CAL1, as demonstrated with other oncolytic viruses, is severely restricted by the patients' immune system. Thus, to develop a clinically relevant oncolytic virotherapy agent, we generated a new off-the-shelf therapeutic called Supernova1 (SNV1) by loading CAL1 virus into allogeneic adipose-derived mesenchymal stem cells (AD-MSC). Culturing the CAL1-infected stem cells allows the expression of virally encoded proteins and viral amplification prior to cryopreservation. We found that the CAL1 virus loaded into AD-MSC was resistant to humoral inactivation. Importantly, the virus-loaded stem cells (SNV1) released larger number of infectious viral particles and virally encoded proteins, leading to augmented therapeutic efficacy in vitro and in animal tumor models.

Nanometer- and angstrom-scale characteristics that modulate complement responses to nanoparticles

The contribution of the complement system to non-specific host defence and maintenance of homeostasis is well appreciated. Many particulate systems trigger complement activation but the underlying mechanisms are still poorly understood. Activation of the complement cascade could lead to particle opsonisation by the cleavage products of the third complement protein and might promote inflammatory reactions. Antibody binding in a controlled manner and/or sensing of particles by the complement pattern-recognition molecules such as C1q and mannose-binding lectin can trigger complement activation. Particle curvature and spacing arrangement/periodicity of surface functional groups/ligands are two important parameters that modulate complement responses through multivalent engagement with and conformational regulation of surface-bound antibodies and complement pattern-recognition molecules. Thus, a better fundamental understanding of nanometer- and angstrom-scale parameters that modulate particle interaction with antibodies and complement proteins could portend new possibilities for engineering of particulate drug carriers and biomedical platforms with tuneable complement responses and is discussed here.

Protective Immunity Induced by Immunization with Baculovirus, Virus-like Particle, and Vaccinia Virus Expressing the AMA1 of Plasmodium berghei

Heterologous prime–boost immunization regimens using various vaccine platforms demonstrated promising results against infectious diseases. Here, mice were sequentially immunized with the recombinant baculovirus (rBV), virus-like particle (VLP), and recombinant vaccinia virus (rVV) vaccines expressing the Plasmodium berghei apical membrane antigen 1 (AMA1) for protective efficacy evaluation. The rBV_V_rVV heterologous immunization regimen elicited high levels of parasite-specific IgG, IgG2a, and IgG2b antibody responses in sera. Upon P. berghei challenge infection, proliferations of germinal center B cells in the inguinal lymph nodes, as well as blood CD4+ and CD8+ T cells were induced. More importantly, rBV_V_rVV immunization significantly diminished the parasitemia and prevented drastic bodyweight loss in mice post-challenge infection with P. berghei. Our findings revealed that immunization with rBV, VLP, and rVV expressing the AMA1 conferred protection against P. berghei infection, providing evidence for the potential implementation of this strategy.

Mechanisms of selective monocyte targeting by liposomes functionalized with a cationic, arginine-rich lipopeptide

Stimulation of monocytes with immunomodulating agents can harness the immune system to treat a long range of diseases, including cancers, infections and autoimmune diseases. To this end we aimed to develop a monocyte-targeting delivery platform based on cationic liposomes, which can be utilized to deliver immunomodulators and thus induce monocyte-mediated immune responses while avoiding off-target side-effects. The cationic liposome design is based on functionalizing the liposomal membrane with a cholesterol-anchored tri-arginine peptide (TriArg). We demonstrate that TriArg liposomes can target monocytes with high specificity in both human and murine blood and that this targeting is dependent on the content of TriArg in the liposomal membrane. In addition, we show that the mechanism of selective monocyte targeting involves the CD14 co-receptor, and selectivity is compromised when the TriArg content is increased, resulting in complement-mediated off-target uptake in granulocytes. The presented mechanistic findings of uptake by peripheral blood leukocytes may guide the design of future drug delivery systems utilized for immunotherapy. STATEMENT OF SIGNIFICANCE: Monocytes are attractive targets for immunotherapies of cancers, infections and autoimmune diseases. Specific delivery of immunostimulatory drugs to monocytes is typically achieved using ligand-targeted drug delivery systems, but a simpler approach is to target monocytes using cationic liposomes. To achieve this, however, a deep understanding of the mechanisms governing the interactions of cationic liposomes with monocytes and other leukocytes is required. We here investigate these interactions using liposomes incorporating a cationic arginine-rich lipopeptide. We demonstrate that monocyte targeting can be achieved by fine-tuning the lipopeptide content in the liposomes. Additionally, we reveal that the CD14 receptor is involved in the targeting process, whereas the complement system is not. These mechanistic findings are critical for future design of monocyte-targeting liposomal therapies.

PLGA's Plight and the Role of Stealth Surface Modification Strategies in Its Use for Intravenous Particulate Drug Delivery

Numerous human disorders can benefit from targeted, intravenous (IV) drug delivery. Polymeric nanoparticles have been designed to undergo systemic circulation and deliver their therapeutic cargo to target sites in a controlled manner. Poly(lactic-co-glycolic) acid (PLGA) is a particularly promising biomaterial for designing intravenous drug carriers due to its biocompatibility, biodegradability, and history of clinical success across other routes of administration. Despite these merits, PLGA remains markedly absent in clinically approved IV drug delivery formulations. A prominent factor in PLGA particles' inability to succeed intravenously may lie in the hydrophobic character of the polyester, leading to the adsorption of serum proteins (i.e., opsonization) and a cascade of events that end in their premature clearance from the bloodstream. PEGylation, or surface-attached polyethylene glycol chains, is a common strategy for shielding particles from opsonization. Polyethylene glycol (PEG) continues to be regarded as the ultimate "stealth" solution despite the lack of clinical progress of PEGylated PLGA carriers. This review reflects on some of the reasons for the clinical failure of PLGA, particularly the drawbacks of PEGylation, and highlights alternative surface coatings on PLGA particles. Ultimately, a new approach will be needed to harness the potential of PLGA nanoparticles and allow their widespread clinical adoption.

Revisiting the outstanding questions in cancer nanomedicine with a future outlook

The field of cancer nanomedicine has been fueled by the expectation of mitigating the inefficiencies and life-threatening side effects of conventional chemotherapy. Nanomedicine proposes to utilize the unique nanoscale properties of nanoparticles to address the most pressing questions in cancer treatment and diagnosis. The approval of nano-based products in the 1990s inspired scientific explorations in this direction. However, despite significant progress in the understanding of nanoscale properties, there are only very few success stories in terms of substantial increase in clinical efficacy and overall patient survival. All existing paradigms such as the concept of enhanced permeability and retention (EPR), the stealth effect and immunocompatibility of nanomedicine have been questioned in recent times. In this review we critically examine impediments posed by biological factors to the clinical success of nanomedicine. We put forth current observations on critical outstanding questions in nanomedicine. We also provide the promising side of cancer nanomedicine as we move forward in nanomedicine research. This would provide a future direction for research in nanomedicine and inspire ongoing investigations.

Next-generation strategies for gene-targeted therapies of central nervous system disorders: A workshop summary

The National Institute of Neurological Disorders and Stroke (NINDS) held a workshop titled "Next generation strategies for gene-targeted therapies of central nervous system (CNS) disorders" in September 2019 in Bethesda, MD, USA. The meeting brought together a multi-disciplinary group of experts in the field of CNS-directed gene-targeted therapy delivery from academia, industry, advocacy, and the government. The group was charged with identifying the key challenges and gaps in this evolving field, as well as suggesting potential solutions. The workshop was divided into four sessions: (1) control of level and location, (2) improving delivery and distribution, (3) enhancing models and manufacturing, and (4) impacting patients. Prior to the workshop, NINDS established working groups of key opinion leaders (KOLs) for each session. In pre-meeting teleconferences, KOLs were tasked with identifying the research gaps and key obstacles that delay and/or prevent gene-targeted therapies to move into the clinic. This approach allowed for the workshop to begin with problem-solving discussions and strategy development, as the key issues had been established. The overall purpose of the workshop was to consider knowledge gaps and potential strategies to inform the community around CNS gene-targeted therapies, including but not limited to researchers and funders.

The lectin pathway does not contribute to glomerular injury in the nephrotoxic nephritis model

AIMS

Rapidly progressive crescentic glomerulonephritis occurs in number systemic and primary glomerular diseases, including anti-glomerular basement membrane disease, anti-neutrophil cytoplasmic antibody vasculitis and lupus nephritis. Our understanding of pathogenic mechanisms comes from animal models of disease such as the nephrotoxic nephritis model. The lectin pathway of complement activation has been shown to play a key role in several models of inflammation including renal ischaemia reperfusion. However, the lectin pathway is not required for crescentic glomerulonephritis in the anti-myeloperoxidase model of anti-neutrophil cytoplasmic antibody vasculitis. The aim of the current study was to explore the role of the lectin pathway in the nephrotoxic nephritis model, which is another model of crescentic glomerulonephritis.

METHODS

Nephrotoxic nephritis was induced in wild type and mannan-binding lectin-associated serine protease-2 deficient mice. Diseases were assessed by quantifying glomerular crescents and macrophages, in addition to albuminuria and serum creatinine.

RESULTS

There was no difference between wild type and MASP-2 deficient mice in any of the histological or biochemical parameters of disease assessed. In addition, there was no difference in the humoral immune response to sheep IgG.

CONCLUSION

These data show that the lectin pathway of complement activation is not required for the development of crescentic glomerulonephritis in the nephrotoxic nephritis model, reinforcing previous findings in the anti-myeloperoxidase model.

Spotlight on the protein corona of liposomes

Although an established drug delivery platform, liposomes have not fulfilled their true potential. In the body, interactions of liposomes are mediated by the layer of plasma proteins adsorbed on the surface, the protein corona. The review aims to collect the data of the last decade on liposome protein corona, tracing the path from interactions of individual proteins to the effects mediated by the protein corona in vivo. It offers a classification of the approaches to exploitation of the protein corona-rather than elimination thereof-based on the bilayer composition-corona composition-molecular interactions-biological performance framework. The multitude of factors that affect each level of this relationship urge to the widest implementation of bioinformatics tools to predict the most effective liposome compositions relying on the data on protein corona. Supplementing the picture with new pieces of accurately reported experimental data will contribute to the accuracy and efficiency of the predictions. STATEMENT OF SIGNIFICANCE: The review focuses on liposomes as an established nanomedicine platform and analyzes the available data on how the protein corona formed on liposome surface in biological fluids affects performance of the liposomes. The review offers a rigorous account of existing literature and critical analysis of methodology currently applied to the assessment of liposome-plasma protein interactions. It introduces a classification of the approaches to exploitation of the protein corona and tailoring liposome carriers to advance the field of nanoparticulate drug delivery systems for the benefit of patients.

Multi-functional antibody profiling for malaria vaccine development and evaluation

INTRODUCTION

A vaccine would greatly accelerate current global efforts toward malaria elimination. While a partially efficacious vaccine has been achieved for Plasmodium falciparum, a major bottleneck in developing highly efficacious vaccines is a lack of reliable correlates of protection, and the limited application of assays that quantify functional immune responses to evaluate and down-select vaccine candidates in pre-clinical studies and clinical trials.

AREAS COVERED

In this review, we describe the important role of antibodies in immunity against malaria and detail the nature and functional activities of antibodies against the malaria-causing parasite. We highlight the growing understanding of antibody effector functions against malaria and in vitro assays to measure these functional antibody responses. We discuss the application of these assays to quantify antibody functions in vaccine development and evaluation.

EXPERT OPINION

It is becoming increasingly clear that multiple antibody effector functions are involved in immunity to malaria. Therefore, we propose that evaluating vaccine candidates needs to move beyond individual assays or measuring IgG magnitude alone. Instead, vaccine evaluation should incorporate the full breadth of antibody response types and harness a wider range of assays measuring functional antibody responses. We propose a 3-tier approach to implementing assays to inform vaccine evaluation.

Interplay between nanomedicine and protein corona

Nanomedicine is recognized as a promising agent for diverse biomedical applications; however, its safety and efficiency in clinical practice remains to be enhanced. A priority issue is the protein corona (PC), which imparts unique biological identities to prototype and determines the actual biological functions in biological fluids. Decades of work has already illuminated abundant considerations that influence the composition of the protein corona. Thereinto, the physical assets of nanomedicines (e.g., size and shape, surface properties, nanomaterials) and the biological environment collectively play fundamental roles in shaping the PC, including the types and quantities of plasma proteins. The properties of nanomedicines are dependent on certain factors. This review aims to explore the applications of nanomedicines by regulating their interplay with PC.

Interrogating preclinical study of liposomes: The effect of mouse strain reexamined

Mice are arguably the most important tool in the preclinical evaluation of liposomes; however, the effects of inter-strain physiological variabilities on in vivo performance of liposomes have been seriously overlooked. The present study validated that plasma proteins (PPs) and the capability of mononuclear phagocyte system (MPS) (typically expressed by phagocytosis rate, K) were mice strain-dependent. Physiological variabilities in PPs and the phagocytosis rate jointly contributed to the inter-strain inconsistency of pharmacokinetic (PK) profiles of liposomes. For the PPs sensitive liposomes (such as plain PEGylated liposomes and folic acid functionalized PEGylated liposomes), inter-strain variabilities in PK profiles could be calibrated using the corrected phagocytic rate (K_C = K×(c × Ig)/(alb×apo)), where c, Ig, alb and apo were respective the total content of complement proteins, immunoglobulins, albumin and apolipoproteins. While for the PPs insensitive liposomes (e.g., cRGD functionalized liposomes), phagocytic rate could be directly used to calibrate inter-strain difference of liposome PK profiles. Our data also warn that the reciprocal interaction between payloads and organisms would be much more complicated than that between liposomes and organisms, thus independent investigation should be conducted for each individual therapeutic agent.

Advances in Genome Editing and Application to the Generation of Genetically Modified Rat Models

The rat has been extensively used as a small animal model. Many genetically engineered rat models have emerged in the last two decades, and the advent of gene-specific nucleases has accelerated their generation in recent years. This review covers the techniques and advances used to generate genetically engineered rat lines and their application to the development of rat models more broadly, such as conditional knockouts and reporter gene strains. In addition, genome-editing techniques that remain to be explored in the rat are discussed. The review also focuses more particularly on two areas in which extensive work has been done: human genetic diseases and immune system analysis. Models are thoroughly described in these two areas and highlight the competitive advantages of rat models over available corresponding mouse versions. The objective of this review is to provide a comprehensive description of the advantages and potential of rat models for addressing specific scientific questions and to characterize the best genome-engineering tools for developing new projects.

Humanization of Immunodeficient Animals for the Modeling of Transplantation, Graft Versus Host Disease, and Regenerative Medicine

The humanization of animals is a powerful tool for the exploration of human disease pathogenesis in biomedical research, as well as for the development of therapeutic interventions with enhanced translational potential. Humanized models enable us to overcome biologic differences that exist between humans and other species, while giving us a platform to study human processes in vivo. To become humanized, an immune-deficient recipient is engrafted with cells, tissues, or organoids. The mouse is the most well studied of these hosts, with a variety of immunodeficient strains available for various specific uses. More recently, efforts have turned to the humanization of other animal species such as the rat, which offers some technical and immunologic advantages over mice. These advances, together with ongoing developments in the incorporation of human transgenes and additional mutations in humanized mouse models, have expanded our opportunities to replicate aspects of human allotransplantation and to assist in the development of immunotherapies. In this review, the immune and tissue humanization of various species is presented with an emphasis on their potential for use as models for allotransplantation, graft versus host disease, and regenerative medicine.

A chemokine-fusion vaccine targeting immature dendritic cells elicits elevated antibody responses to malaria sporozoites in infant macaques

Infants and young children are the groups at greatest risk for severe disease resulting from Plasmodium falciparum infection. We previously demonstrated in mice that a protein vaccine composed of the chemokine macrophage inflammatory protein 3α genetically fused to the minimally truncated circumsporozoite protein of P. falciparum (MCSP) elicits high concentrations of specific antibody and significant reduction of liver sporozoite load in a mouse model system. In the current study, a squalene based adjuvant (AddaVax, InvivoGen, San Diego, Ca) equivalent to the clinically approved MF59 (Seqiris, Maidenhead, UK) elicited greater antibody responses in mice than the previously employed adjuvant polyinosinic:polycytidylic acid, ((poly(I:C), InvivoGen, San Diego, Ca) and the clinically approved Aluminum hydroxide gel (Alum, Invivogen, San Diego, Ca) adjuvant. Use of the AddaVax adjuvant also expanded the range of IgG subtypes elicited by mouse vaccination. Sera passively transferred into mice from MCSP/AddaVax immunized 1 and 6 month old macaques significantly reduced liver sporozoite load upon sporozoite challenge. Protective antibody concentrations attained by passive transfer in the mice were equivalent to those observed in infant macaques 18 weeks after the final immunization. The efficacy of this vaccine in a relevant non-human primate model indicates its potential usefulness for the analogous high risk human population.

Monitoring of the Complement System Status in Patients With B-Cell Malignancies Treated With Rituximab

Rituximab is a pioneering anti-CD20 monoclonal antibody that became the first-line drug used in immunotherapy of B-cell malignancies over the last twenty years. Rituximab activates the complement system in vitro, but there is an ongoing debate on the exact role of this effector mechanism in therapeutic effect. Results of both in vitro and in vivo studies are model-dependent and preclude clear clinical conclusions. Additional confounding factors like complement inhibition by tumor cells, loss of target antigen and complement depletion due to excessively applied immunotherapeutics, intrapersonal variability in the concentration of main complement components and differences in tumor burden all suggest that a personalized approach is the best strategy for optimization of rituximab dosage and therapeutic schedule. Herein we critically review the existing knowledge in support of such concept and present original data on markers of complement activation, complement consumption, and rituximab accumulation in plasma of patients with chronic lymphocytic leukemia (CLL) and non-Hodgkin’s lymphomas (NHL). The increase of markers such as C4d and terminal complement complex (TCC) suggest the strongest complement activation after the first administration of rituximab, but not indicative of clinical outcome in patients receiving rituximab in combination with chemotherapy. Both ELISA and complement-dependent cytotoxicity (CDC) functional assay showed that a substantial number of patients accumulate rituximab to the extent that consecutive infusions do not improve the cytotoxic capacity of their sera. Our data suggest that individual assessment of CDC activity and rituximab concentration in plasma may support clinicians’ decisions on further drug infusions, or instead prescribing a therapy with anti-CD20 antibodies like obinutuzumab that more efficiently activate effector mechanisms other than complement.

Preclinical Rationale for Targeting the PD-1/PD-L1 Axis in Combination with a CD38 Antibody in Multiple Myeloma and Other CD38-Positive Malignancies

Simple Summary

The CD38-targeting antibody daratumumab mediates its anti-myeloma activities not only through direct effects on tumor cells, but also by its effects on T-cell immunity through depletion of CD38⁺ immune suppressor cells. We hypothesized that combining daratumumab with modulators of other potent immune inhibitory pathways, such as the PD-1/PD-L1 axis, may further improve its efficacy. We show that during MM progression there is increased expression of the PD-1/PD-L1 pathway components in the bone marrow microenvironment. Although nivolumab (a PD-1 checkpoint inhibitor) moderately increased T-cell frequencies in ex vivo experiments with bone marrow samples from MM patients, no single agent activity was observed, and addition of nivolumab did not enhance the activity of daratumumab in these short-term assays. However, with a longer treatment duration, in mouse experiments, we demonstrate that anti-CD38 and anti-PD-1 antibodies synergize to eradicate MM cells. In addition, our results suggest that this combined immunotherapeutic approach may also be beneficial in other CD38-positive malignancies.

Abstract

The CD38-targeting antibody daratumumab mediates its anti-myeloma activities not only through Fc-receptor-dependent effector mechanisms, but also by its effects on T-cell immunity through depletion of CD38⁺ regulatory T-cells, regulatory B-cells, and myeloid-derived suppressor cells. Therefore, combining daratumumab with modulators of other potent immune inhibitory pathways, such as the PD-1/PD-L1 axis, may further improve its efficacy. We show that multiple myeloma (MM) cells from relapsed/refractory patients have increased expression of PD-L1, compared to newly diagnosed patients. Furthermore, PD-1 is upregulated on T-cells from both newly diagnosed and relapsed/refractory MM patients, compared to healthy controls. In short-term experiments with bone marrow samples from MM patients, daratumumab-mediated lysis was mainly associated with the MM cells’ CD38 expression levels and the effector (NK-cells/monocytes/T-cells)-to-target ratio, but not with the PD-L1 expression levels or PD-1⁺ T-cell frequencies. Although PD-1 blockade with nivolumab did not affect MM cell viability or enhanced daratumumab-mediated lysis in short-term ex vivo experiments, nivolumab resulted in a mild but clear increase in T-cell numbers. Moreover, with a longer treatment duration, PD-1 blockade markedly improved anti-CD38 antibody-mediated cytotoxicity in vivo in murine CD38⁺ tumor models. In conclusion, dual targeting of CD38 and PD-1 may represent a promising strategy for treating MM and other CD38-positive malignancies.

Analysis of complement deposition and processing on Chlamydia trachomatis

Chlamydia trachomatis (C. trachomatis) is the leading cause of sexually transmitted bacterial infections worldwide, with over 120 million annual cases. C. trachomatis infections are associated with severe reproductive complications in women such as extrauterine pregnancy and tubal infertility. The infections are often long lasting, associated with immunopathology, and fail to elicit protective immunity which makes recurrent infections common. The immunological mechanisms involved in C. trachomatis infections are only partially understood. Murine infection models suggest that the complement system plays a significant role in both protective immunity and immunopathology during primary Chlamydia infections. However, only limited structural and mechanistic evidence exists on complement-mediated immunity against C. trachomatis. To expand our current knowledge on this topic, we analyzed global complement deposition on C. trachomatis using comprehensive in-depth mass spectrometry-based proteomics. We show that factor B, properdin, and C4b bind to C. trachomatis demonstrating that C. trachomatis-induced complement activation proceeds through at least two activation pathways. Complement activation leads to cleavage and deposition of C3 and C5 activation products, causing initiation of the terminal complement pathway and deposition of C5b, C6, C7, C8, C9 on C. trachomatis. Interestingly, using immunoelectron microscopy, we show that C5b-9 deposition occurred sporadically and only in rare cases formed complete lytic terminal complexes, possibly caused by the presence of the negative regulators vitronectin and clusterin. Finally, cleavage analysis of C3 demonstrated that deposited C3b is degraded to the opsonins iC3b and C3dg and that this complement opsonization facilitates C. trachomatis binding to human B-cells.

Complement C6 deficiency exacerbates pathophysiology after spinal cord injury

Historically, the membrane attack complex, composed of complement components C5b-9, has been connected to lytic cell death and implicated in secondary injury after a CNS insult. However, studies to date have utilized either non-littermate control rat models, or mouse models that lack significant C5b-9 activity. To investigate what role C5b-9 plays in spinal cord injury and recovery, we generated littermate PVG C6 wildtype and deficient rats and tested functional and histological recovery after moderate contusion injury using the Infinite Horizon Impactor. We compare the effect of C6 deficiency on recovery of locomotor function and histological injury parameters in PVG rats under two conditions: (1) animals maintained as separate C6 WT and C6-D homozygous colonies; and (2) establishment of a heterozygous colony to generate C6 WT and C6-D littermate controls. The results suggest that maintenance of separate homozygous colonies is inadequate for testing the effect of C6 deficiency on locomotor and histological recovery after SCI, and highlight the importance of using littermate controls in studies involving genetic manipulation of the complement cascade.

In Vivo Analysis of Human Immune Responses in Immunodeficient Rats

Supplemental Digital Content is available in the text.

Background.

Humanized immune system immunodeficient mice have been extremely useful for the in vivo analyses of immune responses in a variety of models, including organ transplantation and graft versus host disease (GVHD) but they have limitations. Rat models are interesting complementary alternatives presenting advantages over mice, such as their size and their active complement compartment. Immunodeficient rats have been generated but human immune responses have not yet been described.

Methods.

We generated immunodeficient Rat Rag−/− Gamma chain−/− human signal regulatory protein alpha-positive (RRGS) rats combining Rag1 and Il2rg deficiency with the expression of human signal regulatory protein alpha, a negative regulator of macrophage phagocytosis allowing repression of rat macrophages by human CD47-positive cells. We then immune humanized RRGS animals with human peripheral blood mononuclear cells (hPBMCs) to set up a human acute GVHD model. Treatment of GVHD was done with a new porcine antihuman lymphocyte serum active through complement-dependent cytotoxicity. We also established a tumor xenograft rejection model in these hPBMCs immune system RRGS animals by subcutaneous implantation of a human tumor cell line.

Results.

RRGS animals receiving hPBMCs showed robust and reproducible reconstitution, mainly by T and B cells. A dose-dependent acute GVHD process was observed with progressive weight loss, tissue damage, and death censoring. Antihuman lymphocyte serum (L1S1) antibody completely prevented acute GVHD. In the human tumor xenograft model, detectable tumors were rejected upon hPBMCs injection.

Conclusions.

hPBMC can be implanted in RRGS animals and elicit acute GVHD or rejection of human tumor cells and these are useful models to test new immunotherapies.

Factors Influencing the Immunogenicity and Immunotoxicity of Cyclic RGD Peptide-Modified Nanodrug Delivery Systems

c(RGDyK)-modified liposomes have been shown to be immunogenic and potentially trigger acute systemic anaphylaxis upon repeated intravenous injection in both BALB/c nude mice and ICR mice. However, questions concerning the potential influence of mouse strains, immunization routes, drug carrier properties, and changes in c(RGDyK) itself on the immunogenicity and resultant immunotoxicity (anaphylaxis) of cyclic RGD peptide-modified nanodrug delivery systems remain unanswered. Here, these potential impact factors were investigated, aiming to better understand the immunological properties of cyclic RGD peptide-based nanodrug delivery systems and seek for solutions for this immunogenicity-associated issue. It was revealed that anaphylaxis caused by intravenous c(RGDyK)-modified drug delivery systems might be avoided by altering the preimmunization route (i.e., subcutaneous injection), introducing positively charged lipids into the liposomes and by using micelles or red blood cell membrane (RBC)-based drug delivery systems as the carrier. Different murine models showed different incidences of anaphylaxis following intravenous c(RGDyK)-liposome stimulation: anaphylaxis was not observed in both SD rats and BALB/c mice and was less frequent in C57BL/6 mice than that in ICR mice. In addition, enlarging the peptide ring of c(RGDyK) by introducing amino sequence serine-glycine-serine reduced the incidence of anaphylaxis post the repeated intravenous c(RGDyKSGS)-liposome stimulation. However, immunogenicity of cyclic RGD-modified drug carriers could not be reversed, although some reduction in IgG antibody production was observed when ICR mice were intravenously stimulated with c(RGDyK)-modified micelles, RBC membrane-based drug delivery systems and c(RGDyKSGS)-liposomes instead of c(RGDyK)-liposomes. This study provides a valuable reference for future application of cyclic RGD peptide-modified drug delivery systems.

Premature Drug Release from Polyethylene Glycol (PEG)-Coated Liposomal Doxorubicin via Formation of the Membrane Attack Complex

Anti-polyethylene glycol (PEG) antibodies are present in many healthy individuals as well as in patients receiving polyethylene glycol-functionalized drugs. Antibodies against PEG-coated nanocarriers can accelerate their clearance, but their impact on nanodrug properties including nanocarrier integrity is unclear. Here, we show that anti-PEG IgG and IgM antibodies bind to PEG molecules on the surface of PEG-coated liposomal doxorubicin (Doxil, Doxisome, LC-101, and Lipo-Dox), resulting in complement activation, formation of the membrane attack complex (C5b-9) in the liposomal membrane, and rapid release of encapsulated doxorubicin from the liposomes. Drug release depended on both classical and alternative pathways of complement activation. Doxorubicin release of up to 40% was also observed in rats treated with anti-PEG IgG and PEG-coated liposomal doxorubicin. Our results demonstrate that anti-PEG antibodies can disrupt the membrane integrity of PEG-coated liposomal doxorubicin through activation of complement, which may alter therapeutic efficacy and safety in patients with high levels of pre-existing antibodies against PEG.

Complement-dependent synapse loss and microgliosis in a mouse model of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory, neurodegenerative disease of the CNS characterized by both grey and white matter injury. Microglial activation and a reduction in synaptic density are key features of grey matter pathology that can be modeled with MOG_35-55 experimental autoimmune encephalomyelitis (EAE). Complement deposition combined with microglial engulfment has been shown during normal development and in disease as a mechanism for pruning synapses. We tested whether there is excess complement production in the EAE hippocampus and whether complement-dependent synapse loss is a source of degeneration in EAE using C1qa and C3 knockout mice. We found that C1q and C3 protein and mRNA levels were elevated in EAE mice. Genetic loss of C3 protected mice from EAE-induced synapse loss, reduced microglial activation, decreased the severity of the EAE clinical score, and protected memory/freezing behavior after contextual fear conditioning. C1qa KO mice with EAE showed little to no change on these measurements compared to WT EAE mice. Thus, pathologic expression and activation of the early complement pathway, specifically at the level of C3, contributes to hippocampal grey matter pathology in the EAE.

Absence of complement component 3 does not prevent classical pathway-mediated hemolysis

Complement component 3 (C3) is emerging as a potential therapeutic target. We studied complement-mediated hemolysis using normal and C3-depleted human sera, wild-type (WT) and C3-deficient rat sera, and WT and C3 knockout rat models. In all of the in vitro and in vivo experiments, we found that the loss of C3 did not prevent classical pathway-mediated hemolysis, but it did almost abolish alternative pathway-mediated hemolysis. Experiments using preassembled classical pathway C3 convertases confirmed that C4b2a directly activated complement component 5 (C5), leading to membrane attack complex formation and hemolysis. Our results suggest that targeting C3 should effectively inhibit hemolysis and tissue damage mediated by the alternative pathway of complement activation, but this approach might have limited efficacy in treating classical pathway-mediated pathological conditions.

Compensatory role of C3 convertase on the strain difference for C3 protein expression in FVB/N, C3H/HeN and C57BL/6N mice

To investigate the role of complement C3 (C3) convertase on the strain difference for C3 protein expression in three inbred mice strains, we compared the levels of C2, C3 and C4 mRNA, as well as C3 protein and C3 convertase activity in the serum and liver tissue of FVB/N, C3H/HeN and C57BL/6N mice. The level of mRNA, inactive form (InACF) and active form (ACF) for C3 showed a regular pattern, which they were higher in the FVB/N and C57BL/6N mice than C3H/HeN mice. However, the level of C3b fragments (C3bα and β) derived from C3 protein were constantly maintained in the liver of FVB/N, C3H/HeN and C57BL/6N mice in spite of the strain difference on the transcriptional and translation level of C3. Especially, a reverse pattern of the level of mRNA, InACF and ACF for C3 was observed on the activity level of C3 convertase activity. The highest level of C3 convertase activity was measured in C3H/HeN mice, followed by C57BL/6N and FVB/N mice. In case of C3 convertase components, the level of C2 mRNA was higher in C3H/HeN mice than FVB/N and C57BL/6 N mice, while levels of C4 mRNA were higher in FVB/N and C57BL/6N mice than C3H/HeN mice. The current study results provide the first scientific evidence that C3 convertase may play complementary role to overcome the strain difference on the C3 protein expression in FVB/N, C3H/HeN and C57BL/6N mice.

Complement in malaria immunity and vaccines

Developing efficacious vaccines for human malaria caused by Plasmodium falciparum is a major global health priority, although this has proven to be immensely challenging over the decades. One major hindrance is the incomplete understanding of specific immune responses that confer protection against disease and/or infection. While antibodies to play a crucial role in malaria immunity, the functional mechanisms of these antibodies remain unclear as most research has primarily focused on the direct inhibitory or neutralizing activity of antibodies. Recently, there is a growing body of evidence that antibodies can also mediate effector functions through activating the complement system against multiple developmental stages of the parasite life cycle. These antibody‐complement interactions can have detrimental consequences to parasite function and viability, and have been significantly associated with protection against clinical malaria in naturally acquired immunity, and emerging findings suggest these mechanisms could contribute to vaccine‐induced immunity. In order to develop highly efficacious vaccines, strategies are needed that prioritize the induction of antibodies with enhanced functional activity, including the ability to activate complement. Here we review the role of complement in acquired immunity to malaria, and provide insights into how this knowledge could be used to harness complement in malaria vaccine development.

Xenoantigen-Dependent Complement-Mediated Neutralization of Lymphocytic Choriomeningitis Virus Glycoprotein-Pseudotyped Vesicular Stomatitis Virus in Human Serum

Neutralization by antibodies and complement limits the effective dose and thus the therapeutic efficacy of oncolytic viruses after systemic application. We and others previously showed that pseudotyping of oncolytic rhabdoviruses such as maraba virus and vesicular stomatitis virus (VSV) with the lymphocytic choriomeningitis virus glycoprotein (LCMV-GP) results in only a weak induction of neutralizing antibodies. Moreover, LCMV-GP-pseudotyped VSV (VSV-GP) was significantly more stable in normal human serum (NHS) than VSV. Here, we demonstrate that depending on the cell line used for virus production, VSV-GP showed different complement sensitivities in nonimmune NHS. The NHS-mediated titer reduction of VSV-GP was dependent on activation of the classical complement pathway, mainly by natural IgM antibodies against xenoantigens such as galactose-α-(1,3)-galactose (α-Gal) or N-glycolylneuraminic acid (Neu5Gc) expressed on nonhuman production cell lines. VSV-GP produced on human cell lines was stable in NHS. However, VSV-GP generated in transduced human cells expressing α-Gal became sensitive to NHS. Furthermore, GP-specific antibodies induced complement-mediated neutralization of VSV-GP independently of the producer cell line, suggesting that complement regulatory proteins potentially acquired by the virus during the budding process are not sufficient to rescue the virus from antibody-dependent complement-mediated lysis. Thus, our study points to the importance of a careful selection of cell lines for viral vector production for clinical use.IMPORTANCE Systemic application aims to deliver oncolytic viruses to tumors as well as to metastatic lesions. However, we found that xenoantigens incorporated onto the viral surface from nonhuman production cell lines are recognized by natural antibodies in human serum and that the virus is thereby inactivated by complement lysis. Hence, to maximize the effective dose, careful selection of cell lines for virus production is crucial.

Immunization of Malaria-Preexposed Volunteers With PfSPZ Vaccine Elicits Long-Lived IgM Invasion-Inhibitory and Complement-Fixing Antibodies

Background

The assessment of antibody responses after immunization with radiation-attenuated, aseptic, purified, cryopreserved Plasmodium falciparum sporozoites (Sanaria PfSPZ Vaccine) has focused on IgG isotype antibodies. Here, we aimed to investigate if P. falciparum sporozoite binding and invasion-inhibitory IgM antibodies are induced following immunization of malaria-preexposed volunteers with PfSPZ Vaccine.

Methods

Using serum from volunteers immunized with PfSPZ, we measured vaccine-induced IgG and IgM antibodies to P. falciparum circumsporozoite protein (PfCSP) via ELISA. Function of this serum as well as IgM antibody fractions was measured via in vitro in an inhibition of sporozoite invasion assay. These IgM antibody fractions were also measured for binding to sporozoites by immunofluorescence assay and complement fixation on whole sporozoites.

Results

We found that in addition to anti-PfCSP IgG, malaria-preexposed volunteers developed anti-PfCSP IgM antibodies after immunization with PfSPZ Vaccine and that these IgM antibodies inhibited P. falciparum sporozoite invasion of hepatocytes in vitro. These IgM plasma fractions also fixed complement to whole P. falciparum sporozoites.

Conclusions

This is the first finding that PfCSP and P. falciparum sporozoite-binding IgM antibodies are induced following immunization of PfSPZ Vaccine in malaria-preexposed individuals and that IgM antibodies can inhibit P. falciparum sporozoite invasion into hepatocytes in vitro and fix complement on sporozoites. These findings indicate that the immunological assessment of PfSPZ Vaccine-induced antibody responses could be more sensitive if they include parasite-specific IgM in addition to IgG antibodies.

Clinical Trials Registration

NCT02132299.

IgM in human immunity to Plasmodium falciparum malaria

Most studies on human immunity to malaria have focused on the roles of immunoglobulin G (IgG), whereas the roles of IgM remain undefined. Analyzing multiple human cohorts to assess the dynamics of malaria-specific IgM during experimentally induced and naturally acquired malaria, we identified IgM activity against blood-stage parasites. We found that merozoite-specific IgM appears rapidly in Plasmodium falciparum infection and is prominent during malaria in children and adults with lifetime exposure, together with IgG. Unexpectedly, IgM persisted for extended periods of time; we found no difference in decay of merozoite-specific IgM over time compared to that of IgG. IgM blocked merozoite invasion of red blood cells in a complement-dependent manner. IgM was also associated with significantly reduced risk of clinical malaria in a longitudinal cohort of children. These findings suggest that merozoite-specific IgM is an important functional and long-lived antibody response targeting blood-stage malaria parasites that contributes to malaria immunity.

A stealth adhesion factor contributes to Vibrio vulnificus pathogenicity: Flp pili play roles in host invasion, survival in the blood stream and resistance to complement activation

The tad operons encode the machinery required for adhesive Flp (fimbrial low-molecular-weight protein) pili biogenesis. Vibrio vulnificus, an opportunistic pathogen, harbors three distinct tad loci. Among them, only tad1 locus was highly upregulated in in vivo growing bacteria compared to in vitro culture condition. To understand the pathogenic roles of the three tad loci during infection, we constructed single, double and triple tad loci deletion mutants. Interestingly, only the Δtad123 triple mutant cells exhibited significantly decreased lethality in mice. Ultrastructural observations revealed short, thin filamentous projections disappeared on the Δtad123 mutant cells. Since the pilin was paradoxically non-immunogenic, a V5 tag was fused to Flp to visualize the pilin protein by using immunogold EM and immunofluorescence microscopy. The Δtad123 mutant cells showed attenuated host cell adhesion, decreased biofilm formation, delayed RtxA1 exotoxin secretion and subsequently impaired translocation across the intestinal epithelium compared to wild type, which could be partially complemented with each wild type operon. The Δtad123 mutant was susceptible to complement-mediated bacteriolysis, predominantly via the alternative pathway, suggesting stealth hiding role of the Tad pili. Complement depletion by treating with anti-C5 antibody rescued the viable count of Δtad123 in infected mouse bloodstream to the level comparable to wild type strain. Taken together, all three tad loci cooperate to confer successful invasion of V. vulnificus into deeper tissue and evasion from host defense mechanisms, ultimately resulting in septicemia.

Plasmodium-specific antibodies block in vivo parasite growth without clearing infected red blood cells

Plasmodium parasites invade and multiply inside red blood cells (RBC). Through a cycle of maturation, asexual replication, rupture and release of multiple infective merozoites, parasitised RBC (pRBC) can reach very high numbers in vivo, a process that correlates with disease severity in humans and experimental animals. Thus, controlling pRBC numbers can prevent or ameliorate malaria. In endemic regions, circulating parasite-specific antibodies associate with immunity to high parasitemia. Although in vitro assays reveal that protective antibodies could control pRBC via multiple mechanisms, in vivo assessment of antibody function remains challenging. Here, we employed two mouse models of antibody-mediated immunity to malaria, P. yoelii 17XNL and P. chabaudi chabaudi AS infection, to study infection-induced, parasite-specific antibody function in vivo. By tracking a single generation of pRBC, we tested the hypothesis that parasite-specific antibodies accelerate pRBC clearance. Though strongly protective against homologous re-challenge, parasite-specific IgG did not alter the rate of pRBC clearance, even in the presence of ongoing, systemic inflammation. Instead, antibodies prevented parasites progressing from one generation of RBC to the next. In vivo depletion studies using clodronate liposomes or cobra venom factor, suggested that optimal antibody function required splenic macrophages and dendritic cells, but not complement C3/C5-mediated killing. Finally, parasite-specific IgG bound poorly to the surface of pRBC, yet strongly to structures likely exposed by the rupture of mature schizonts. Thus, in our models of humoral immunity to malaria, infection-induced antibodies did not accelerate pRBC clearance, and instead co-operated with splenic phagocytes to block subsequent generations of pRBC.

Malaria occurs when Plasmodium parasites replicate inside red blood cells, with the number of parasitised cells (pRBC) correlating with disease severity. Antibodies are highly effective at controlling pRBC numbers in the bloodstream, and yet we know very little about how they function in vivo. Human in vitro studies predict that antibodies may function in a number of ways, including via phagocytes or different complement mechanisms. However, to date it has been challenging to explore how antibodies might control parasite numbers in vivo. Here, we have used a unique method in mice, where clearance and replication of a single cohort of pRBC was closely tracked in the presence of protective antibodies. Surprisingly, antibodies played no role whatsoever in accelerating the removal of pRBC. Instead, antibodies were highly effective at preventing parasites from progressing from one generation of pRBC to the next. This process partly depended on host phagocytes. However, we found no role for complement-mediated direct killing. Together, our in vivo data suggest in mouse models that naturally-acquired antibodies do not clear pRBC, and instead prevent transition from one red blood cell to the next.

Targets of complement-fixing antibodies in protective immunity against malaria in children

Antibodies against P. falciparum merozoites fix complement to inhibit blood-stage replication in naturally-acquired and vaccine-induced immunity; however, specific targets of these functional antibodies and their importance in protective immunity are unknown. Among malaria-exposed individuals, we show that complement-fixing antibodies to merozoites are more strongly correlated with protective immunity than antibodies that inhibit growth quantified using the current reference assay for merozoite vaccine evaluation. We identify merozoite targets of complement-fixing antibodies and identify antigen-specific complement-fixing antibodies that are strongly associated with protection from malaria in a longitudinal study of children. Using statistical modelling, combining three different antigens targeted by complement-fixing antibodies could increase the potential protective effect to over 95%, and we identify antigens that were common in the most protective combinations. Our findings support antibody-complement interactions against merozoite antigens as important anti-malaria immune mechanisms, and identify specific merozoite antigens for further evaluation as vaccine candidates.

Antibodies against Plasmodium falciparum merozoites that fix complement can inhibit blood-stage replication. Here, Reiling et al. show that complement-fixing antibodies strongly correlate with protective immunity in children, identify the merozoite targets, and predict antigen combinations that should result in strong protection.

In vivo pathogenicity of IgG from patients with anti-SRP or anti-HMGCR autoantibodies in immune-mediated necrotising myopathy

OBJECTIVES

In autoimmunity, autoantibodies (aAb) may be simple biomarkers of disease or true pathogenic effectors. A form of idiopathic inflammatory myopathy associated with anti-signal recognition particle (SRP) or anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) aAb has been individualised and is referred to as immune-mediated necrotising myopathy (IMNM). The level of aAb correlates with IMNM activity and disease may respond to immunosuppression, suggesting that they are pathogenic. We aimed to evaluate the pathogenicity of IgG from patients with anti-SRP or anti-HMGCR aAb in vivo by developing the first mouse model of IMNM.

METHODS

IgG from patients suffering from anti-SRP or anti-HMGCR associated IMNM were passively transferred to wild-type, Rag2-/- or complement C3-/- mice. Muscle deficiency was evaluated by muscle strength on electrostimulation and grip test. Histological analyses were performed after haematoxylin/eosin staining or by immunofluorescence or immunohistochemistry analysis. Antibody levels were quantified by addressable laser bead assay (ALBIA).

RESULTS

Passive transfer of IgG from patients suffering from IMNM to C57BL/6 or Rag2-/- mice provoked muscle deficiency. Pathogenicity of aAb was reduced in C3-/- mice while increased by supplementation with human complement. Breakage of tolerance by active immunisation with SRP or HMGCR provoked disease.

CONCLUSION

This study demonstrates that patient-derived anti-SRP+ and anti-HMGCR+ IgG are pathogenic towards muscle in vivo through a complement-mediated mechanism, definitively establishing the autoimmune character of IMNM. These data support the use of plasma exchanges and argue for evaluating complement-targeting therapies in IMNM.