Serological fingerprints link antiviral activity of therapeutic antibodies to affinity and concentration.

The effectiveness of therapeutic monoclonal antibodies (mAbs) against variants of the SARS-CoV-2 virus is highly variable. As target recognition of mAbs relies on tight binding affinity, we assessed the affinities of five therapeutic mAbs to the receptor binding domain (RBD) of wild type (A), Delta (B.1.617.2), and Omicron BA.1 SARS-CoV-2 (B.1.1.529.1) spike using microfluidic diffusional sizing (MDS). Four therapeutic mAbs showed strongly reduced affinity to Omicron BA.1 RBD, whereas one (sotrovimab) was less impacted. These affinity reductions correlate with reduced antiviral activities suggesting that affinity could serve as a rapid indicator for activity before time-consuming virus neutralization assays are performed. We also compared the same mAbs to serological fingerprints (affinity and concentration) obtained by MDS of antibodies in sera of 65 convalescent individuals. The affinities of the therapeutic mAbs to wild type and Delta RBD were similar to the serum antibody response, indicating high antiviral activities. For Omicron BA.1 RBD, only sotrovimab retained affinities within the range of the serum antibody response, in agreement with high antiviral activity. These results suggest that serological fingerprints provide a route to evaluating affinity and antiviral activity of mAb drugs and could guide the development of new therapeutics.

Both COVID-19 infection and vaccination induce high-affinity cross-clade responses to SARS-CoV-2 variants.

The B.1.1.529 (omicron) variant has rapidly supplanted most other SARS-CoV-2 variants. Using microfluidics-based antibody affinity profiling (MAAP), we have characterized affinity and IgG concentration in the plasma of 39 individuals with multiple trajectories of SARS-CoV-2 infection and/or vaccination. Antibody affinity was similar against the wild-type, delta, and omicron variants (K A ranges: 122 ± 155, 159 ± 148, 211 ± 307 µM-1, respectively), indicating a surprisingly broad and mature cross-clade immune response. Postinfectious and vaccinated subjects showed different IgG profiles, with IgG3 (p-value = 0.002) against spike being more prominent in the former group. Lastly, we found that the ELISA titers correlated linearly with measured concentrations (R = 0.72) but not with affinity (R = 0.29). These findings suggest that the wild-type and delta spike induce a polyclonal immune response capable of binding the omicron spike with similar affinity. Changes in titers were primarily driven by antibody concentration, suggesting that B-cell expansion, rather than affinity maturation, dominated the response after infection or vaccination.

Evaluation of early-stage osteochondral defect repair using a biphasic scaffold based on a collagen-glycosaminoglycan biopolymer in a caprine model.

The aim of this study was to evaluate a new collagen-GAG-calcium phosphate biphasic scaffold for the repair of surgically created osteochondral defects in goats. Comparison of morphological, histological and mechanical performance of the repair tissue was made with defects repaired using a synthetic polymer scaffold. Defects were created in the medial femoral condyle (MFC) and lateral trochlear sulcus (LTS) of Boer Cross goats and evaluated at 12 and 26 weeks. It was found that the total histology score of the collagen-GAG based biomaterial (23.8; SD 1.7) provided a significant improvement (p<0.05) over the biphasic PLGA material (19;3) and the empty control defect (17.3;1.2) in the LTS. The overall trajectory of histological and morphological improvement between 12 and 26 weeks was found to be higher for the collagen-GAG scaffold compared to the PLGA material. The occurrence of sub-chondral bone cysts was lower for the collagen-GAG scaffold with an incidence of 17% of defects, compared to 67% for the PLGA material at 26 weeks. The cartilage repair tissue for both materials evaluated was superior after 26 weeks implantation than the empty control with 75% of the collagen-GAG-treated defects showing markedly more hyaline-like cartilage and 50% of the PLGA sites exhibiting hyaline-like appearances, compared to 17% for the empty control. These early stage data indicate biphasic scaffolds based on collagen-GAG and PLGA both provide indications of satisfactory development of a structural repair to surgically prepared osteochondral defects. Furthermore, the biomaterial composition of the collagen-GAG may provide a more favourable environment for osteochondral repair.

Design of a multiphase osteochondral scaffold III: Fabrication of layered scaffolds with continuous interfaces.

There is a need to improve current treatments for articular cartilage injuries. This article is the third in a series describing the design and development of an osteochondral scaffold based on collagen-glycosaminoglycan and calcium phosphate technologies for regenerative repair of articular cartilage defects. The previous articles in this series described methods for producing porous, three-dimensional mineralized collagen-GAG (CGCaP) scaffolds whose composition can be reproducibly varied to mimic the composition of subchondral bone, and pore microstructure and mineral phase can be modified. This article describes a method, "liquid-phase cosynthesis," that enables the production of porous, layered scaffolds that mimic the composition and structure of articular cartilage on one side, subchondral bone on the other side, and the continuous, gradual or "soft" interface between these tissues: the tidemark of articular joints. This design enables the layered scaffolds to be inserted into the subchondral bone at an osteochondral defect site without the need for sutures, glue, or screws, with a highly interconnected porous network throughout the entire osteochondral defect. Moreover, the differential moduli of the osseous and cartilaginous compartments enable these layered scaffolds to exhibit compressive deformation behavior that mimics the behavior observed in natural articular joints.

Design of a multiphase osteochondral scaffold. I. Control of chemical composition.

This is the first in a series of articles that describe the design and development of a family of osteochondral scaffolds based on collagen-glycosaminoglycan (collagen-GAG) and calcium phosphate technologies, engineered for the regenerative repair of defects in articular cartilage. The osteochondral scaffolds consist of two layers: a mineralized type I collagen-GAG scaffold designed to regenerate the underlying subchondral bone and a nonmineralized type II collagen-GAG scaffold designed to regenerate cartilage. The subsequent articles in this series describe the fabrication and properties of a mineralized scaffold as well as a two-layer (one mineralized, the other not) osteochondral scaffold for regeneration of the underlying bone and cartilage, respectively. This article describes a technology through which the chemical composition-particularly the calcium phosphate mass fraction-of triple coprecipitated nanocomposites of collagen, glycosaminoglycan, and calcium phosphate can be accurately and reproducibly varied without the need for titrants or other additives. Here, we describe how the mineral:organic ratio can be altered over a range that includes that for articular cartilage (0 wt % mineral) and for bone (75 wt % mineral). This technology achieves the objective of mimicking the composition of two main tissue types found in articular joints, with particular emphasis on the osseous compartment of an osteochondral scaffold. Exclusion of titrants avoids the formation of potentially harmful contaminant phases during freeze-drying steps crucial for scaffold fabrication, ensuring that the potential for binding growth factors and drugs is maintained.

Design of a multiphase osteochondral scaffold. II. Fabrication of a mineralized collagen-glycosaminoglycan scaffold.

This paper is the second in a series of papers describing the design and development of an osteochondral scaffold using collagen-glycosaminoglycan and calcium phosphate technologies engineered for the regenerative repair of articular cartilage defects. The previous paper described a technology (concurrent mapping) for systematic variation and control of the chemical composition of triple coprecipitated collagen, glycosaminoglycan, and calcium phosphate (CGCaP) nanocomposites without using titrants. This paper describes (1) fabricating porous, three-dimensional scaffolds from the CGCaP suspensions, (2) characterizing the microstructure and mechanical properties of such scaffolds, and (3) modifying the calcium phosphate mineral phase. The methods build on the previously demonstrated ability to vary the composition of a CGCaP suspension (calcium phosphate mass fraction between 0 and 80 wt %) and enable the production of scaffolds whose pore architecture (mean pore size: 50-1000 microm), CaP phase chemistry (brushite, octacalcium phosphate, apatite) and crosslinking density (therefore mechanical properties and degradation rate) can be independently controlled. The scaffolds described in this paper combine the desirable biochemical properties and pore architecture of porous collagen-glycosaminoglycan scaffolds with the strength and direct bone-bonding properties of calcium phosphate biomaterials in a manner that can be tailored to meet the demands of a range of applications in orthopedics and regenerative medicine.