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.

An APRIL-based chimeric antigen receptor for dual targeting of BCMA and TACI in multiple myeloma.

B-cell maturation antigen (BCMA) is a promising therapeutic target for multiple myeloma (MM), but expression is variable, and early reports of BCMA targeting chimeric antigen receptors (CARs) suggest antigen downregulation at relapse. Dual-antigen targeting increases targetable tumor antigens and reduces the risk of antigen-negative disease escape. "A proliferation-inducing ligand" (APRIL) is a natural high-affinity ligand for BCMA and transmembrane activator and calcium-modulator and cyclophilin ligand (TACI). We quantified surface tumor expression of BCMA and TACI on primary MM cells (n = 50). All cases tested expressed BCMA, and 39 (78%) of them also expressed TACI. We engineered a third-generation APRIL-based CAR (ACAR), which killed targets expressing either BCMA or TACI (P < .01 and P < .05, respectively, cf. control, effector-to-target [E:T] ratio 16:1). We confirmed cytolysis at antigen levels similar to those on primary MM, at low E:T ratios (56.2% ± 3.9% killing of MM.1s at 48 h, E:T ratio 1:32; P < .01) and of primary MM cells (72.9% ± 12.2% killing at 3 days, E:T ratio 1:1; P < .05, n = 5). Demonstrating tumor control in the absence of BCMA, we maintained cytolysis of primary tumor expressing both BCMA and TACI in the presence of a BCMA-targeting antibody. Furthermore, using an intramedullary myeloma model, ACAR T cells caused regression of an established tumor within 2 days. Finally, in an in vivo model of tumor escape, there was complete ACAR-mediated tumor clearance of BCMA+TACI- and BCMA-TACI+ cells, and a single-chain variable fragment CAR targeting BCMA alone resulted in outgrowth of a BCMA-negative tumor. These results support the clinical potential of this approach.

Designer Small-Molecule Control System Based on Minocycline-Induced Disruption of Protein-Protein Interaction.

A versatile, safe, and effective small-molecule control system is highly desirable for clinical cell therapy applications. Therefore, we developed a two-component small-molecule control system based on the disruption of protein-protein interactions using minocycline, an FDA-approved antibiotic with wide availability, excellent biodistribution, and low toxicity. The system comprises an anti-minocycline single-domain antibody (sdAb) and a minocycline-displaceable cyclic peptide. Here, we show how this versatile system can be applied to OFF-switch split CAR systems (MinoCAR) and universal CAR adaptors (MinoUniCAR) with reversible, transient, and dose-dependent suppression; to a tunable T cell activation module based on MyD88/CD40 signaling; to a controllable cellular payload secretion system based on IL12 KDEL retention; and as a cell/cell inducible junction. This work represents an important step forward in the development of a remote-controlled system to precisely control the timing, intensity, and safety of therapeutic interventions.

Structure-guided engineering of immunotherapies targeting TRBC1 and TRBC2 in T cell malignancies.

Peripheral T cell lymphomas are typically aggressive with a poor prognosis. Unlike other hematologic malignancies, the lack of target antigens to discriminate healthy from malignant cells limits the efficacy of immunotherapeutic approaches. The T cell receptor expresses one of two highly homologous chains [T cell receptor ß-chain constant (TRBC) domains 1 and 2] in a mutually exclusive manner, making it a promising target. Here we demonstrate specificity redirection by rational design using structure-guided computational biology to generate a TRBC2-specific antibody (KFN), complementing the antibody previously described by our laboratory with unique TRBC1 specificity (Jovi-1) in targeting broader spectrum of T cell malignancies clonally expressing either of the two chains. This permits generation of paired reagents (chimeric antigen receptor-T cells) specific for TRBC1 and TRBC2, with preclinical evidence to support their efficacy in T cell malignancies.

Fibroblast Activation Protein (FAP)-Targeted CAR-T Cells: Launching an Attack on Tumor Stroma.

Fibroblast activation protein (FAP) is a membrane protease that is highly expressed by cancer-associated fibroblasts (CAFs). FAP can modulate the tumor microenvironment (TME) by remodeling the extracellular matrix (ECM), and its overexpression on CAFs is associated with poor prognosis in various cancers. The TME is in part accountable for the limited efficacy of chimeric antigen receptor (CAR)-T cell therapy in treatment of solid tumors. Targeting FAP with CAR-T cells is one of the strategies being researched to overcome the challenges in the TME. This review describes the role of FAP in the TME and its potential as a target in CAR-T cell immunotherapy, summarizes the preclinical studies and clinical trials of anti-FAP-CAR-T cells to date, and reviews possible optimizations to augment their cytotoxic efficiency in solid tumors.

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.

Optimised Method for the Production and Titration of Lentiviral Vectors Pseudotyped with the SARS-CoV-2 Spike.

The use of recombinant lentivirus pseudotyped with the coronavirus Spike protein of SARS-CoV-2 would circumvent the requirement of biosafety-level 3 (BSL-3) containment facilities for the handling of SARS-CoV-2 viruses. Herein, we describe a fast and reliable protocol for the transient production of lentiviruses pseudotyped with SARS-CoV-2 Spike (CoV-2 S) proteins and green fluorescent protein (GFP) reporters. The virus titer is determined by the GFP reporter (fluorescent) expression with a flow cytometer. High titers (>1.00 E+06 infectious units/ml) are produced using codon-optimized CoV-2 S, harbouring the prevalent D614G mutation and lacking its ER retention signal. Enhanced and consistent cell entry is achieved by using permissive HEK293T/17 cells that were genetically engineered to stably express the SARS-CoV-2 human receptor ACE2 along with the cell surface protease TMPRSS2 required for efficient fusion. For the widespread use of this protocol, its reagents have been made publicly available. Graphic abstract: Production and quantification of lentiviral vectors pseudotyped with the SARS-CoV-2 Spike glycoprotein.