Characterization of a Novel ACE2-Based Therapeutic with Enhanced Rather than Reduced Activity against SARS-CoV-2 Variants.

The human angiotensin-converting enzyme 2 acts as the host cell receptor for SARS-CoV-2 and the other members of the Coronaviridae family SARS-CoV-1 and HCoV-NL63. Here, we report the biophysical properties of the SARS-CoV-2 spike variants D614G, B.1.1.7, B.1.351, and P.1 with affinities to the ACE2 receptor and infectivity capacity, revealing weaknesses in the developed neutralizing antibody approaches. Furthermore, we report a preclinical characterization package for a soluble receptor decoy engineered to be catalytically inactive and immunologically inert, with broad neutralization capacity, that represents an attractive therapeutic alternative in light of the mutational landscape of COVID-19. This construct efficiently neutralized four SARS-CoV-2 variants of concern. The decoy also displays antibody-like biophysical properties and manufacturability, strengthening its suitability as a first-line treatment option in prophylaxis or therapeutic regimens for COVID-19 and related viral infections. IMPORTANCE Mutational drift of SARS-CoV-2 risks rendering both therapeutics and vaccines less effective. Receptor decoy strategies utilizing soluble human ACE2 may overcome the risk of viral mutational escape since mutations disrupting viral interaction with the ACE2 decoy will by necessity decrease virulence, thereby preventing meaningful escape. The solution described here of a soluble ACE2 receptor decoy is significant for the following reasons: while previous ACE2-based therapeutics have been described, ours has novel features, including (i) mutations within ACE2 to remove catalytical activity and systemic interference with the renin/angiotensin system, (ii) abrogated FcγR engagement, reduced risk of antibody-dependent enhancement of infection, and reduced risk of hyperinflammation, and (iii) streamlined antibody-like purification process and scale-up manufacturability indicating that this receptor decoy could be produced quickly and easily at scale. Finally, we demonstrate that ACE2-based therapeutics confer a broad-spectrum neutralization potency for ACE2-tropic viruses, including SARS-CoV-2 variants of concern in contrast to therapeutic MAb.

Novel Bispecific Antibody for Synovial-Specific Target Delivery of Anti-TNF Therapy in Rheumatoid Arthritis.

Biologic drugs, especially anti-TNF, are considered as the gold standard therapy in rheumatoid arthritis. However, non-uniform efficacy, incidence of infections, and high costs are major concerns. Novel tissue-specific agents may overcome the current limitations of systemic administration, providing improved potency, and safety. We developed a bispecific antibody (BsAb), combining human arthritic joint targeting, via the synovial-specific single-chain variable fragment (scFv)-A7 antibody, and TNFα neutralization, via the scFv-anti-TNFα of adalimumab, with the binding/blocking capacity comparable to adalimumab -immunoglobulin G (IgG). Tissue-targeting capacity of the BsAb was confirmed on the human arthritic synovium in vitro and in a synovium xenograft Severe combined immune deficient (SCID) mouse model. Peak graft accumulation occurred at 48 h after injection with sustained levels over adalimumab-IgG for 7 days and increased therapeutic effect, efficiently decreasing tissue cellularity, and markers of inflammation with higher potency compared to the standard treatment. This study provides the first description of a BsAb capable of drug delivery, specifically to the disease tissue, and a strong evidence of improved therapeutic effect on the human arthritic synovium, with applications to other existing biologics.

Combining phage display with SMRTbell next-generation sequencing for the rapid discovery of functional scFv fragments.

Phage display technology in combination with next-generation sequencing (NGS) currently is a state-of-the-art method for the enrichment and isolation of monoclonal antibodies from diverse libraries. However, the current NGS methods employed for sequencing phage display libraries are limited by the short contiguous read lengths associated with second-generation sequencing platforms. Consequently, the identification of antibody sequences has conventionally been restricted to individual antibody domains or to the analysis of single domain binding moieties such as camelid VHH or cartilaginous fish IgNAR antibodies. In this study, we report the application of third-generation sequencing to address this limitation. We used single molecule real time (SMRT) sequencing coupled with hairpin adaptor loop ligation to facilitate the accurate interrogation of full-length single-chain Fv (scFv) libraries. Our method facilitated the rapid isolation and testing of scFv antibodies enriched from phage display libraries within days following panning. Two libraries against CD160 and CD123 were panned and monitored by NGS. Analysis of NGS antibody data sets led to the isolation of several functional scFv antibodies that were not identified by conventional panning and screening strategies. Our approach, which combines phage display selection of immune libraries with the full-length interrogation of scFv fragments, is an easy method to discover functional antibodies, with a range of affinities and biophysical characteristics.

Targeting the T cell receptor ß-chain constant region for immunotherapy of T cell malignancies.

Mature T cell cancers are typically aggressive, treatment resistant and associated with poor prognosis. Clinical application of immunotherapeutic approaches has been limited by a lack of target antigens that discriminate malignant from healthy (normal) T cells. Unlike B cell depletion, pan-T cell aplasia is prohibitively toxic. We report a new targeting strategy based on the mutually exclusive expression of T cell receptor ß-chain constant domains 1 and 2 (TRBC1 and TRBC2). We identify an antibody with unique TRBC1 specificity and use it to demonstrate that normal and virus-specific T cell populations contain both TRBC1+ and TRBC2+ compartments, whereas malignancies are restricted to only one. As proof of concept for anti-TRBC immunotherapy, we developed anti-TRBC1 chimeric antigen receptor (CAR) T cells, which recognized and killed normal and malignant TRBC1+, but not TRBC2+, T cells in vitro and in a disseminated mouse model of leukemia. Unlike nonselective approaches targeting the entire T cell population, TRBC-targeted immunotherapy could eradicate a T cell malignancy while preserving sufficient normal T cells to maintain cellular immunity.

AIRE-Deficient Patients Harbor Unique High-Affinity Disease-Ameliorating Autoantibodies.

APS1/APECED patients are defined by defects in the autoimmune regulator (AIRE) that mediates central T cell tolerance to many self-antigens. AIRE deficiency also affects B cell tolerance, but this is incompletely understood. Here we show that most APS1/APECED patients displayed B cell autoreactivity toward unique sets of approximately 100 self-proteins. Thereby, autoantibodies from 81 patients collectively detected many thousands of human proteins. The loss of B cell tolerance seemingly occurred during antibody affinity maturation, an obligatorily T cell-dependent step. Consistent with this, many APS1/APECED patients harbored extremely high-affinity, neutralizing autoantibodies, particularly against specific cytokines. Such antibodies were biologically active in vitro and in vivo, and those neutralizing type I interferons (IFNs) showed a striking inverse correlation with type I diabetes, not shown by other anti-cytokine antibodies. Thus, naturally occurring human autoantibodies may actively limit disease and be of therapeutic utility.

Going with the flow: harnessing the power of the vasculature for targeted therapy in rheumatoid arthritis.

Rheumatoid arthritis (RA) is a chronic, systemic, autoimmune disease that leads to excessive joint inflammation and is associated with significant morbidity and mortality. Although much is still to be learned about the aetiology RA, a growing body of evidence suggests that an altered vascular environment is an important aspect of its pathophysiology. In this context, RA shares many similarities with cancer, and it is expected that several angiogenic targets in cancer might be relevant to the treatment of RA. Here, we discuss how these targets can be combined with advances in drug development to generate the next generation of RA therapeutics.

Rational design of antirheumatic prodrugs specific for sites of inflammation.

OBJECTIVE: Biologic drugs, such as the anti-tumor necrosis factor (anti-TNF) antibody adalimumab, have represented a breakthrough in the treatment of rheumatoid arthritis. Yet, concerns remain over their lack of efficacy in a sizable proportion of patients and their potential for systemic side effects such as infection. Improved biologic prodrugs specifically targeted to the site of inflammation have the potential to alleviate current concerns surrounding biologic anticytokine therapies. The purpose of this study was to design, construct, and evaluate in vitro and ex vivo the targeting and antiinflammatory capacity of activatable bispecific antibodies. METHODS: Activatable dual variable domain (aDVD) antibodies were designed and constructed to target intercellular adhesion molecule 1 (ICAM-1), which is up-regulated at sites of inflammation, and anti-TNF antibodies (adalimumab and infliximab). These bispecific molecules included an external arm that targets ICAM-1 and an internal arm that comprises the therapeutic domain of an anti-TNF antibody. Both arms were linked to matrix metalloproteinase (MMP)-cleavable linkers. The constructs were tested for their ability to bind and neutralize both in vitro and ex vivo targets. RESULTS: Intact aDVD constructs demonstrated significantly reduced binding and anti-TNF activity in the prodrug formulation as compared to the parent antibodies. Human synovial fluid and physiologic concentrations of MMP enzyme were capable of cleaving the external domain of the antibody, revealing a fully active molecule. Activated antibodies retained the same binding and anti-TNF inhibitory capacities as the parent molecules. CONCLUSION: The design of a biologic prodrug with enhanced specificity for sites of inflammation (synovium) and reduced specificity for off-target TNF is described. This construct has the potential to form a platform technology that is capable of enhancing the therapeutic index of drugs for the treatment of RA and other inflammatory diseases.

Trojan horses and guided missiles: targeted therapies in the war on arthritis.

Despite major advances in the treatment of rheumatoid arthritis (RA) led by the success of biologic therapies, the lack of response to therapy in a proportion of patients, as well as therapy discontinuation owing to systemic toxicity, are still unsolved issues. Unchecked RA might develop into progressive structural joint damage, loss of function and long-term disability, disorders which are associated with a considerable health-economic burden. Therefore, new strategies are required to actively target and deliver therapeutic agents to disease sites in order to promote in situ activity and decrease systemic toxicity. Polymer-drug conjugates can improve the pharmacokinetics of therapeutic agents, conferring desirable properties such as increased solubility and tissue penetration at sites of active disease. Additionally, nanotechnology is an exciting modality in which drugs are encapsulated to protect them from degradation or early activation in the circulation, as well as to reduce systemic toxicity. Together with the targeting capacity of antibodies and site-specific peptides, these approaches will facilitate selective accumulation of therapeutic agents in the inflamed synovium, potentially improving drug efficacy at disease sites without affecting healthy tissues. This Review aims to summarize key developments in the past 5 years in polymer conjugation, nanoparticulate drug delivery and antibody or peptide-based targeting--strategies that might constitute the platform for the next generation of RA therapeutics.

Knotted fusion proteins reveal unexpected possibilities in protein folding.

Proteins that contain a distinct knot in their native structure are impressive examples of biological self-organization. Although this topological complexity does not appear to cause a folding problem, the mechanisms by which such knotted proteins form are unknown. We found that the fusion of an additional protein domain to either the amino terminus, the carboxy terminus, or to both termini of two small knotted proteins did not affect their ability to knot. The multidomain constructs remained able to fold to structures previously thought unfeasible, some representing the deepest protein knots known. By examining the folding kinetics of these fusion proteins, we found evidence to suggest that knotting is not rate limiting during folding, but instead occurs in a denatured-like state. These studies offer experimental insights into when knot formation occurs in natural proteins and demonstrate that early folding events can lead to diverse and sometimes unexpected protein topologies.