In vivo biodistribution and pharmacokinetics of sotrovimab, a SARS-CoV-2 monoclonal antibody, in healthy cynomolgus monkeys.

PURPOSE: Sotrovimab (VIR-7831), a human IgG1κ monoclonal antibody (mAb), binds to a conserved epitope on the SARS-CoV-2 spike protein receptor binding domain (RBD). The Fc region of VIR-7831 contains an LS modification to promote neonatal Fc receptor (FcRn)-mediated recycling and extend its serum half-life. Here, we aimed to evaluate the impact of the LS modification on tissue biodistribution, by comparing VIR-7831 to its non-LS-modified equivalent, VIR-7831-WT, in cynomolgus monkeys. METHODS: 89Zr-based PET/CT imaging of VIR-7831 and VIR-7831-WT was performed up to 14 days post injection. All major organs were analyzed for absolute concentration as well as tissue:blood ratios, with the focus on the respiratory tract, and a physiologically based pharmacokinetics (PBPK) model was used to evaluate the tissue biodistribution kinetics. Radiomics features were also extracted from the PET images and SUV values. RESULTS: SUVmean uptake in the pulmonary bronchi for 89Zr-VIR-7831 was statistically higher than for 89Zr-VIR-7831-WT at days 6 (3.43 ± 0.55 and 2.59 ± 0.38, respectively) and 10 (2.66 ± 0.32 and 2.15 ± 0.18, respectively), while the reverse was observed in the liver at days 6 (5.14 ± 0.80 and 8.63 ± 0.89, respectively), 10 (4.52 ± 0.59 and 7.73 ± 0.66, respectively), and 14 (4.95 ± 0.65 and 7.94 ± 0.54, respectively). Though the calculated terminal half-life was 21.3 ± 3.0 days for VIR-7831 and 16.5 ± 1.1 days for VIR-7831-WT, no consistent differences were observed in the tissue:blood ratios between the antibodies except in the liver. While the lung:blood SUVmean uptake ratio for both mAbs was 0.25 on day 3, the PBPK model predicted the total lung tissue and the interstitial space to serum ratio to be 0.31 and 0.55, respectively. Radiomics analysis showed VIR-7831 had mean-centralized PET SUV distribution in the lung and liver, indicating more uniform uptake than VIR-7831-WT. CONCLUSION: The half-life extended VIR-7831 remained in circulation longer than VIR-7831-WT, consistent with enhanced FcRn binding, while the tissue:blood concentration ratios in most tissues for both drugs remained statistically indistinguishable throughout the course of the experiment. In the bronchiolar region, a higher concentration of 89Zr-VIR-7831 was detected. The data also allow unparalleled insight into tissue distribution and elimination kinetics of mAbs that can guide future biologic drug discovery efforts, while the residualizing nature of the 89Zr label sheds light on the sites of antibody catabolism.

Strategy and validation of a nonclinical generic plug-and-play antidrug antibody method for human monoclonal antibody biotherapeutics.

The measurement of antidrug antibodies (ADA) in nonclinical studies provides limited value because the formation and incidence of nonclinical ADA does not translate to clinical experience. The formation and presence of ADA in nonclinical species can, however, correlate to reduced drug exposure and safety observations including vasculitis and immune complex disease. Generic ADA methods for humanized monoclonal antibody biotherapeutics mitigate the need to develop bespoke ADA methods during nonclinical drug development. A drug-tolerant, sensitive, generic ADA immunoassay has been developed and validated for measuring ADA in cynomolgus monkey serum samples, allowing for immediate qualification of future monoclonal antibody biotherapeutics. This approach allows us to differentiate complexed and free ADA in a rapidly deployable manner when needed.

The testing of antidrug antibodies (ADA) in animal studies offers low value because the presence of animal ADA does not translate to human studies. However, the impact of ADA can be seen with reduced drug levels and/or safety findings in animal studies. Generic ADA methods offer a way to measure ADA leading to time and cost savings. This article details the testing of a generic plug-and-play method to measure ADA in monkey serum and how to qualify future drugs. To date, 16 drugs have been qualified using this method, which has also been applied to mouse, rat and rabbit serum.

Unique challenges required reassessment and alterations to critical reagents to rescue a neutralizing antibody assay.

Aim: To redevelop a neutralizing antibody (NAb) assay to be much more drug tolerant, have a large dynamic range and have high inhibition when using high levels of positive control (PC). Materials & methods: Early assay data suggested that typical biotin labeling of the capture reagent (Drug 1, produced in a human cell line) was blocking it from binding with the PC or the detection target, and that the detection target was out competing the PC. Methodical biotin labeling experiments were performed at several challenge ratios and an Fc linker was added to the detection target. Results & conclusion: A larger dynamic range, high inhibition and higher drug tolerance were achieved by adding an acid dissociation step to the assay, performing atypical biotin labeling of Drug 1 and switching to a detection target that contained an Fc linker to increase steric hinderance and decrease its binding affinity to Drug 1.

Many of the drugs available today are produced by a living organism and these are called biologics. Biologics are larger than chemical drugs and the human body can detect them as foreign and create antibodies against them. This is called immunogenicity. When the antibodies created against the biologic blocks the drug's ability to work correctly, they are called neutralizing antibodies (NAbs). Testing for NAbs is one of the requirements of regulatory agencies for biologics. Here we describe challenges encountered developing an assay to test for NAbs against a biologic.

Concordance between alizarin red stained skeleton and micro-CT skeleton evaluation methods: A case study in New Zealand White rabbits.

OBJECTIVES: The objective of this study was to examine the fetal skeletons using both alizarin red stain and micro-computed tomography (CT) images; investigate differences, and to determine if the conclusions of the study were the same regardless of the examination method. METHODS: A candidate drug was given orally by gavage to pregnant New Zealand White rabbits on gestation day (GD) 7 to GD 19 (mating = GD 0) at doses of 0 (control), 0.02, 0.5, 5, and 15 mg/kg/day. Maternal toxicity was evident at ≥0.02 mg/kg/day. The 199 fetal skeletons (totaling 50,546 skeletal elements) obtained at cesarean delivery on GD29 were first stained with Alizarin Red S, then imaged by a Siemens Inveon micro-CT scanner. All fetal skeletons were examined by both methods, without knowledge of dose group, and the results were compared. RESULTS: In total, 33 types of skeletal abnormalities were identified. There was 99.8% concordance of results comparing stain to micro-CT. Ossification of the middle phalanx of the forepaw digit 5 showed the greatest difference between the two methods. CONCLUSION: Overall, micro-CT imaging is a realistic, and robust alternative to skeletal staining to examine fetal rabbit skeletons in developmental toxicity studies.

Immuno-PET Monitoring of CD8+ T Cell Infiltration Post ICOS Agonist Antibody Treatment Alone and in Combination with PD-1 Blocking Antibody Using a 89Zr Anti-CD8+ Mouse Minibody in EMT6 Syngeneic Tumor Mouse.

PURPOSE: The presence and functional competence of intratumoral CD8+ T cells is often a barometer for successful immunotherapeutic responses in cancer. Despite this understanding and the extensive number of clinical-stage immunotherapies focused on potentiation (co-stimulation) or rescue (checkpoint blockade) of CD8+ T cell antitumor activity, dynamic biomarker strategies are often lacking. To help fill this gap, immuno-PET nuclear imaging has emerged as a powerful tool for in vivo molecular imaging of antibody targeting. Here, we took advantage of immuno-PET imaging using 89Zr-IAB42M1-14, anti-mouse CD8 minibody, to characterize CD8+ T-cell tumor infiltration dynamics following ICOS (inducible T-cell co-stimulator) agonist antibody treatment alone and in combination with PD-1 blocking antibody in a model of mammary carcinoma. PROCEDURES: Female BALB/c mice with established EMT6 tumors received 10 µg, IP of either IgG control antibodies, ICOS agonist monotherapy, or ICOS/PD-1 combination therapy on days 0, 3, 5, 7, 9, 10, or 14. Imaging was performed at 24 and 48 h post IV dose of 89Zr IAB42M1-14. In addition to 89Zr-IAB42M1-14 uptake in tumor and tumor-draining lymph node (TDLN), 3D radiomic features were extracted from PET/CT images to identify treatment effects. Imaging mass cytometry (IMC) and immunohistochemistry (IHC) was performed at end of study. RESULTS: 89Zr-IAB42M1-14 uptake in the tumor was observed by day 11 and was preceded by an increase in the TDLN as early as day 4. The spatial distribution of 89Zr-IAB42M1-14 was more uniform in the drug treated vs. control tumors, which had spatially distinct tracer uptake in the periphery relative to the core of the tumor. IMC analysis showed an increased percentage of cytotoxic T cells in the ICOS monotherapy and ICOS/PD-1 combination group compared to IgG controls. Additionally, temporal radiomics analysis demonstrated early predictiveness of imaging features. CONCLUSION: To our knowledge, this is the first detailed description of the use of a novel immune-PET imaging technique to assess the kinetics of CD8+ T-cell infiltration into tumor and lymphoid tissues following ICOS agonist and PD-1 blocking antibody therapy. By demonstrating the capacity for increased spatial and temporal resolution of CD8+ T-cell infiltration across tumors and lymphoid tissues, these observations underscore the widespread potential clinical utility of non-invasive PET imaging for T-cell-based immunotherapy in cancer.

Characterization of the robust humoral immune response to GSK2618960, a humanized anti-IL-7 receptor monoclonal antibody, observed in healthy subjects in a Phase 1 study.

Interleukin-7 (IL-7) signaling modulates T cell activity and is implicated in numerous autoimmune diseases. An anti-IL-7 receptor monoclonal antibody (GSK2618960) biotherapeutic was evaluated in healthy subjects for safety, pharmacokinetics (PK), pharmacodynamics (PD) and immunogenicity in a single-dose escalation phase I study. We found that antibodies against GSK2618960 (i.e., anti-drug antibodies or ADA) developed in 83% and 100% of GSK2618960-treated subjects in the 0.6 and 2.0 mg/kg dose cohorts, respectively. Of the ADA positive subjects, 64% (7 of 11) had detectable neutralizing activity. Further investigation revealed the presence of GSK2618960-specific memory B cells, indicating the development of immunological memory for the ADAs. Ex vivo stimulation of peripheral blood mononuclear cell (PBMC) samples demonstrated a relatively strong CD4+ T cell proliferation response to GSK2618960 as compared to the control anti-RSV antibody (which is known to have only low immunogenic potential), confirming the high immunogenic potential of GSK2618960. Furthermore, GSK2618960 was found to bind in vitro monocyte-derived dendritic cells (DCs). GSK2618960 treatment of PBMCs increased the proportion of DC cells showing an increase in expression of CD83, CD86 and CD209, which indicated enhanced DC differentiation and activation relative to the isotype control anti-ß amyloid antibody. Collectively, the evidence supports that the high incidence of observed clinical immunogenicity was likely related to the receptor-mediated activity by GSK2618960.

Clinical accuracy of the AAPOS pediatric vision screening referral criteria.

BACKGROUND: The American Association for Pediatric Ophthalmology and Strabismus (AAPOS) referral criteria for amblyogenic risk factors are consensus criteria that were determined by the best-available data as well as survey results of pediatric ophthalmologists. In 2003 the AAPOS Vision Screening Committee published guidelines to standardize reporting the ability of vision screening devices to detect these factors. We attempted to assess the accuracy of the AAPOS referral criteria. METHODS: Billing records of one pediatric ophthalmologist were reviewed to identify all children who were seen in 2002. Records were excluded if photoscreening had not been performed at the initial visit or if photoscreening results were not available in the record. Of the remaining records, one-half were randomly selected for analysis. Cycloplegic refraction and binocular alignment were evaluated to determine whether the child would have been considered to be at risk for amblyopia on the basis of AAPOS referral critera. The sensitivity and specificity of these factors for detecting amblyopia was then determined. RESULTS: A total of 1,575 records were identified, of which 529 were randomly selected; 7 were excluded for incomplete data. AAPOS referral criteria would have referred 266 patients, of whom 255 had amblyopia and 11 did not; of the 256 patients who would not have been referred, 46 had amblyopia and 210 did not. In this population, the AAPOS referral criteria would have had an 85% sensitivity, 95% specificity, a 5% false-positive rate and a 15% false-negative rate for detecting amblyopia. CONCLUSIONS: Application of the AAPOS referral criteria resulted in underreporting of amblyopia in this study. We propose modifications that may result in increased sensitivity and a lower false-negative rate.