Engineering of Fc Multimers as a Protein Therapy for Autoimmune Disease

Interactions of the anti-FcRn monoclonal antibody, rozanolixizumab, with Fcγ receptors and functional impact on immune cells in vitro

Rozanolixizumab is a humanized anti-neonatal Fc receptor (FcRn) monoclonal antibody (mAb) of the immunoglobulin G4 (IgG4) sub-class, currently in clinical development for the treatment of IgG autoantibody-driven diseases. This format is frequently used for therapeutic mAbs due to its intrinsic lower affinity for Fc gamma receptors (FcγR) and lack of C1q engagement. However, with growing evidence suggesting that no Fc-containing agent is truly "silent" in this respect, we explored the engagement of FcγRs and potential functional consequences with rozanolixizumab. In the study presented here, rozanolixizumab was shown to bind to FcγRs in both protein-protein and cell-based assays, and the kinetic data were broadly as expected based on published data for an IgG4 mAb. Rozanolixizumab was also able to mediate antibody bipolar bridging (ABB), a phenomenon that led to a reduction of labeled FcγRI from the surface of human macrophages in an FcRn-dependent manner. However, the presence of exogenous human IgG, even at low concentrations, was able to prevent both binding and ABB events. Furthermore, data from in vitro experiments using relevant human cell types that express both FcRn and FcγRI indicated no evidence for functional sequelae in relation to cellular activation events (e.g., intracellular signaling, cytokine production) upon either FcRn or FcγR binding of rozanolixizumab. These data raise important questions about whether therapeutic antagonistic mAbs like rozanolixizumab would necessarily engage FcγRs at doses typically administered to patients in the clinic, and hence challenge the relevance and interpretation of in vitro assays performed in the absence of competing IgG.

Complement component C1q is an immunological rheostat that regulates Fc:Fc[Formula: see text]R interactions

Though binding sites for the complement factor C1q and the canonical fragment crystallizable (Fc) gamma receptors (Fc[Formula: see text]Rs) on immunoglobulin G (IgG) molecules overlap, how C1q decoration of immune complexes (ICs) influences their ability to engage Fc[Formula: see text]Rs remains unknown. In this report, we use recombinant human Fc multimers as stable IC mimics to show that C1q engagement of ICs directly and transiently inhibits their interactions with Fc[Formula: see text]RIII (CD16) on human natural killer (NK) cells. This inhibition occurs by C1q engagement alone as well as in concert with other serum factors. Furthermore, the inhibition of Fc[Formula: see text]RIII engagement mediated by avid binding of C1q to ICs is directly associated with IC size and dependent on the concentrations of both C1q and Fc multimers present. Functionally, C1q-mediated Fc blockade limits the ability of NK cells to induce the upregulation of the cosignaling molecule, 4-1BB (CD137), and to mediate antibody-dependent cell-mediated cytotoxicity (ADCC). Although C1q is traditionally viewed as a soluble effector molecule, we demonstrate that C1q may also take on the role of an "immunologic rheostat," buffering Fc[Formula: see text]R-mediated activation of immune cells by circulating ICs. These data define a novel role for C1q as a regulator of immune homeostasis and add to our growing understanding that complement factors mediate pleiotropic effects.

Modulating Lysosomal pH through Innovative Multimerized Succinic Acid-Based Nucleolipid Derivatives

The multimerization of active compounds has emerged as a successful approach, mainly to address the multivalency of numerous biological targets. Regarding the pharmaceutical prospect, carrying several active ingredient units on the same synthetic scaffold was a practical approach to enhance drug delivery or biological activity with a lower global concentration. Various examples have highlighted better in vivo stability and therapeutic efficiency through sustained action over monomeric molecules. The synthesis strategy aims to covalently connect biologically active monomers to a central core using simple and efficient reaction steps. Despite extensive studies reporting carbohydrate or even peptide multimerization developed for therapeutic activities, very few are concerned with nucleic acid derivatives. In the context of our efforts to build non-viral nucleolipid (NL)-based nanocarriers to restore lysosomal acidification defects, we report here a straightforward synthesis of tetrameric NLs, designed as prodrugs that are able to release no more than one but four biocompatible succinic acid units. The use of oil-in-water nanoemulsion-type vehicles allowed the development of lipid nanosystems crossing the membranes of human neuroblastoma cells. Biological evaluations have proved the effective release of the acid within the lysosome of a genetic and cellular model of Parkinson's disease through the recovery of an optimal lysosomal pH associated with a remarkably fourfold lower concentration of active ingredients than with the corresponding monomers. Overall, these results suggest the feasibility, the therapeutic opportunity, and the better tolerance of multimeric compounds compared to only monomer molecules.

Multivalent ACE2 engineering-A promising pathway for advanced coronavirus nanomedicine development

The spread of coronavirus diseases has resulted in a clarion call to develop potent drugs and vaccines even as different strains appear beyond human prediction. An initial step that is integral to the viral entry into host cells results from an active-targeted interaction of the viral spike (S) proteins and the cell surface receptor, called angiotensin-converting enzyme 2 (ACE2). Thus, engineered ACE2 has been an interesting decoy inhibitor against emerging coronavirus infestation. This article discusses promising innovative ACE2 engineering pathways for current and emerging coronavirus therapeutic development. First, we provide a brief discussion of some ACE2-associated human coronaviruses and their cell invasion mechanism. Then, we describe and contrast the individual spike proteins and ACE2 receptor interactions, highlighting crucial hotspots across the ACE2-associated coronaviruses. Lastly, we address the importance of multivalency in ACE2 nanomedicine engineering and discuss novel approaches to develop and achieve multivalent therapeutic outcomes. Beyond coronaviruses, these approaches will serve as a paradigm to develop new and improved treatment technologies against pathogens that use ACE2 receptor for invasion.

Systems biology and artificial intelligence analysis highlights the pleiotropic effect of IVIg therapy in autoimmune diseases with a predominant role on B cells and complement system

Intravenous immunoglobulin (IVIg) is used as treatment for several autoimmune and inflammatory conditions, but its specific mechanisms are not fully understood. Herein, we aimed to evaluate, using systems biology and artificial intelligence techniques, the differences in the pathophysiological pathways of autoimmune and inflammatory conditions that show diverse responses to IVIg treatment. We also intended to determine the targets of IVIg involved in the best treatment response of the evaluated diseases. Our selection and classification of diseases was based on a previously published systematic review, and we performed the disease characterization through manual curation of the literature. Furthermore, we undertook the mechanistic evaluation with artificial neural networks and pathway enrichment analyses. A set of 26 diseases was selected, classified, and compared. Our results indicated that diseases clearly benefiting from IVIg treatment were mainly characterized by deregulated processes in B cells and the complement system. Indeed, our results show that proteins related to B-cell and complement system pathways, which are targeted by IVIg, are involved in the clinical response. In addition, targets related to other immune processes may also play an important role in the IVIg response, supporting its wide range of actions through several mechanisms. Although B-cell responses and complement system have a key role in diseases benefiting from IVIg, protein targets involved in such processes are not necessarily the same in those diseases. Therefore, IVIg appeared to have a pleiotropic effect that may involve the collaborative participation of several proteins. This broad spectrum of targets and 'non-specificity' of IVIg could be key to its efficacy in very different diseases.

Current therapeutic strategies and perspectives in refractory ITP: What have we learned recently?

Immune thrombocytopenia (ITP) is an acquired autoimmune bleeding disorder featured by increased platelet destruction and deficient megakaryocyte maturation. First-line treatments include corticosteroids, intravenous immunoglobulin and intravenous anti-D immunoglobulin. Second-line treatments consist of rituximab, thrombopoietin receptor agonists and splenectomy. Although most patients benefit from these treatments, an individualized treatment approach is warranted due to the large heterogeneity among ITP patients. In addition, ITP patients may relapse and there remains a subset of patients who become refractory to treatments. The management of these refractory patients is still a challenge. This review aims to summarize emerging therapeutic approaches for refractory ITP in several categories according to their different targets, including macrophages, platelets/megakaryocytes, T cells, B cells, and endothelial cells. Moreover, current management strategies and combination regimens of refractory ITP are also discussed.

A physical wiring diagram for the human immune system

The human immune system is composed of a distributed network of cells circulating throughout the body, which must dynamically form physical associations and communicate using interactions between their cell-surface proteomes¹. Despite their therapeutic potential², our map of these surface interactions remains incomplete^3,4. Here, using a high-throughput surface receptor screening method, we systematically mapped the direct protein interactions across a recombinant library that encompasses most of the surface proteins that are detectable on human leukocytes. We independently validated and determined the biophysical parameters of each novel interaction, resulting in a high-confidence and quantitative view of the receptor wiring that connects human immune cells. By integrating our interactome with expression data, we identified trends in the dynamics of immune interactions and constructed a reductionist mathematical model that predicts cellular connectivity from basic principles. We also developed an interactive multi-tissue single-cell atlas that infers immune interactions throughout the body, revealing potential functional contexts for new interactions and hubs in multicellular networks. Finally, we combined targeted protein stimulation of human leukocytes with multiplex high-content microscopy to link our receptor interactions to functional roles, in terms of both modulating immune responses and maintaining normal patterns of intercellular associations. Together, our work provides a systematic perspective on the intercellular wiring of the human immune system that extends from systems-level principles of immune cell connectivity down to mechanistic characterization of individual receptors, which could offer opportunities for therapeutic intervention.

Systematic measurements of the interactions between proteins found on the surfaces of human leukocytes provides a global view of the way that immune cells are dynamically connected by receptors.

FcγR-Mediated Trogocytosis 2.0: Revisiting History Gives Rise to a Unifying Hypothesis

There is increasing interest in the clinical implications and immunology of trogocytosis, a process in which the receptors on acceptor cells remove and internalize cognate ligands from donor cells. We have reported that this phenomenon occurs in cancer immunotherapy, in which cells that express FcγR remove and internalize CD20 and bound mAbs from malignant B cells. This process can be generalized to include other reactions including the immune adherence phenomenon and antibody-induced immunosuppression. We discuss in detail FcγR-mediated trogocytosis and the evidence supporting a proposed predominant role for liver sinusoidal endothelial cells via the action of the inhibitory receptor FcγRIIb2. We describe experiments to test the validity of this hypothesis. The elucidation of the details of FcγR-mediated trogocytosis has the potential to allow for the development of novel therapies that can potentially block or enhance this reaction, depending upon whether the process leads to unfavorable or positive biological effects.

Transient Complete Recovery of Chronic Refractory Idiopathic Thrombocytopenic Purpura after Treatment with Monoclonal Antibody Targeting SARS-CoV-2 Spike Protein

Idiopathic thrombocytopenic purpura (ITP), also known as immune thrombocytopenic purpura, is an immune-mediated acquired disease characterized by transient or persistent decrease of the platelet count due to autoimmune-related destruction of platelets. Therapy for ITP relies on competing and inhibiting the autoantibody binding and destruction (intravenous immunoglobulin and anti-D immunoglobulin and spleen tyrosine kinase (Syk) inhibitor fostamatinib), augmenting platelet production (thrombopoietin receptor agonists), immunosuppression to reduce the autoantibody production, as well as splenectomy. Studies on autoantigens on the platelets suggested epitopes to be located predominantly on the GP IIb/IIIa receptor or integrin αIIbβ3, though the trigger for the development of ITP is unclear. We report a case here of a 37-year-old gentleman who has chronic ITP managed on eltrombopag, who after receiving monoclonal antibody against SARS-CoV-2 (mAb) i.e. casirivimab and imdevimab for his COVID-19 infection, demonstrated complete recovery of his platelet count for a short period of time. We discuss a few potential mechanisms of action and propose further studies to elucidate the therapeutic effect of COVID-19 mAb in ITP.

Enhanced Immunomodulatory Effect of Intravenous Immunoglobulin by Fc Galactosylation and Nonfucosylation

Intravenous immunoglobulin (IVIG) is used as an immunomodulatory agent in the treatment of various autoimmune/inflammatory diseases although its mechanism of action remains elusive. Recently, nonfucosylated IgG has been shown to be preferentially bound to Fcγ receptor IIIa (FcγRIIIa) on circulating natural killer cells; therefore, we hypothesized that nonfucosylated IVIG may modulate immune responses through FcγRIIIa blockade. Here, homogeneous fucosylated or nonfucosylated glycoforms of normal polyclonal IgG bearing sialylated, galactosylated or nongalactosylated Fc oligosaccharides were generated by chemoenzymatic glycoengineering to investigate whether the IgG glycoforms can inhibit antibody-dependent cellular cytotoxicity (ADCC). Among the six IgG glycoforms, galactosylated, nonfucosylated IgG [(G2)₂] had the highest affinity to FcγRIIIa and 20 times higher potency to inhibit ADCC than native IgG. A pilot study of IVIG treatment in mice with collagen antibody-induced arthritis highlighted the low-dose (G2)₂ glycoform of IVIG (0.1 g/kg) as an effective immunomodulatory agent as the 10-fold higher dose of native IVIG. These preliminary results suggest that the anti-inflammatory activity of IVIG is in part mediated via activating FcγR blockade by galactosylated, nonfucosylated IgG and that such nonfucosylated IgG glycoforms bound to FcγRs on immune cells play immunomodulatory roles in health and disease. This study provides insights into improved therapeutic strategies for autoimmune/inflammatory diseases using glycoengineered IVIG and recombinant Fc.

Next generation antibody-based therapies in neurology

Antibody (Ab)-based therapeutics are now standard in the treatment of neuroinflammatory diseases, and the spectrum of neurological diseases targeted by those approaches continues to grow. The efficacy of Ab-based drug-platforms is largely determined by the specificity-conferring antigen-binding fragment (Fab) and the crystallizable fragment (Fc) driving antibody function. The latter provides specific instructions to the immune system by interacting with cellular Fc receptors and complement components. Extensive engineering efforts enabled tuning of Fc functions to modulate effector functions and to prolong or reduce Ab serum half-lives. Technologies that improve bioavailability of Ab-based treatment platforms within the central nervous system parenchyma are being developed and could invigorate drug discovery for a number of brain diseases for which current therapeutic options are limited. These powerful approaches are currently being tested in clinical trials or have been successfully translated into the clinic. Here, we review recent developments in the design and implementation of Ab-based treatment modalities in neurological diseases.

In Translation: FcRn across the Therapeutic Spectrum

As an essential modulator of IgG disposition, the neonatal Fc receptor (FcRn) governs the pharmacokinetics and functions many therapeutic modalities. In this review, we thoroughly reexamine the hitherto elucidated biological and thermodynamic properties of FcRn to provide context for our assessment of more recent advances, which covers antigen-binding fragment (Fab) determinants of FcRn affinity, transgenic preclinical models, and FcRn targeting as an immune-complex (IC)-clearing strategy. We further comment on therapeutic antibodies authorized for treating SARS-CoV-2 (bamlanivimab, casirivimab, and imdevimab) and evaluate their potential to saturate FcRn-mediated recycling. Finally, we discuss modeling and simulation studies that probe the quantitative relationship between in vivo IgG persistence and in vitro FcRn binding, emphasizing the importance of endosomal transit parameters.

Characterization of Aggregated Antibody-Silicone Oil Complexes: From Perspectives of Morphology, 3D Image, and Fcγ Receptor Activation

Pre-filled syringes (PFS) have been in widespread use as an administration device for therapeutic antibodies in recent decades. Generally, the inner barrel and syringe of PFS are coated with silicone oil (SO) for lubrication. Multiple studies have focused on the fact that the SO adsorbs denatured antibody molecules, and induces antibody aggregation. Aggregated antibodies are recognized as a potential risk for evoking immunogenic responses in patients. The characteristics of the aggregated antibody-SO complexes, including their concentration, population, shape, three-dimensional (3D) image, and Fcγ Receptors (FcγRs) activation have been obscurely acknowledged so far. In the present work, we prepared aggregated antibody-SO complexes by agitation and analyzed using multifaceted techniques such as flow imaging, confocal fluorescence microscopy, and cell-based assays for FcγRs activation. The results emphasized that the SO accelerates the increase in sub-visible particles and antibody aggregation. The confocal fluorescence microscopy analysis revealed the high-resolution 3D images of aggregated antibody-SO complexes. The FcγRs reporter cell assay clarified that the pre-mixed and agitated Ab + SO have higher FcγRs activation capability compared to the agitated Ab. Overall, this study advances the view that SO has an effect to increase the risk of agitation-induced aggregated antibody particles.