CDR3 Research Articles

Spontaneous high clonal expansion of Wilms’ tumor gene 1-specific cytotoxic T-lymphocytes in patients with Wilms’ tumor gene 1-expressing solid tumor

Wilms’ tumor protein 1 (WT1)-targeted immunotherapy has been used in patients with leukemia and solid tumors. However, the spontaneous WT1-specific immune response before WT1 peptide vaccination in patients with WT1-expressing tumors (PTs) remains unclear. Therefore, we investigated whether WT1-specific cytotoxic CD8+ T-lymphocytes (CTLs) are clonally expanded in the peripheral blood outside of tumor sites. Clonal expansion of WT1126 peptide (a.a.126–134)-specific CTLs (WT1126-CTLs) was compared between seven PTs and five healthy volunteers (HVs), and their T-cell receptors (TCRs) were analyzed at the single-cell level. Overall, 433 and 351 TCR β-chains of WT1126-CTLs were detected from PTs and HVs, respectively, and complementarity-determining region 3 was sequenced for clonality analysis. The frequencies of WT1126-CTLs were higher in human leukocyte antigen (HLA)-A*02:01+ PTs than in HLA-A*02:01+ HVs, although the difference was not statistically significant. WT1126-CTLs of differentiated types, including memory and effector, were higher in PTs than in HVs; whereas, those of the naïve type were higher in HVs than in PTs. WT1126-CTL clonality was significantly higher in PTs than in HVs. Furthermore, the frequency of effector WT1126-CTLs positively correlated with WT1126-CTL clonality in PTs; whereas, the frequency of naïve phenotype WT1126-CTLs tended to be negatively correlated with clonality. In conclusion, these results suggest that the WT1 protein in tumor cells is highly immunogenic, thereby stimulating endogenous naïve-type WT1126-CTLs and enabling them to clonally expand and differentiate into effector-type WT1126-CTLs.

Exploring the orphan immune receptor TREM2 and its non-protein ligands: In silico characterization

The triggering receptor expressed on myeloid cells 2 (TREM2) is an immunoreceptor that interacts with a wide range of non-protein ligands, and it has been implicated in infectious and non-infectious diseases. However, there is a limited understanding on how this receptor interacts with non-protein ligands and the potential of such information to develop new therapeutic drugs. Therefore, our study aimed to elucidate the interactions between TREM2 and its non-protein ligands. First, we searched PubChem and Protein Data Bank (PDB) for TREM2 structures and their corresponding non-protein ligands. Subsequently, these structures were employed in molecular docking and MM/GBSA simulations with the Maestro software and molecular dynamics in GROMACS software. TREM2 was subsequently subjected to druggable site prediction using CavityPlus and receptor-based drug repositioning via the DrugRep server. TREM2 interacts with high affinity with its 12 non-protein ligands, with affinity values ranging from −33.01 kcal/mol for phosphatidylserine to −80.87 kcal/mol for cardiolipin (CLP). In molecular dynamics simulations, homodimeric TREM2 bound more stably to its lipid ligands, such as CLP and PSF, whereas it was unstable when unbound. The interactions between the receptor and its non-protein ligands were driven by the complementarity determining regions (CDR) 1 and 2, that are present in the hydrophobic and positively charged regions, highlighting that the Y38–R98 region is fundamental for drugs targeting TREM2. Our data underscore the significance of TREM2's CDRs in recognizing its ligands, suggesting they as promising targets for prospective drug design studies.

Divergent modulation of activated protein C pleiotropic functions by antibodies that differ by a single amino acid

AbstractActivated protein C (APC) is a pleiotropic plasma protease with diverse functions derived from its anticoagulant, anti-inflammatory, and cytoprotective activities. The selective uncoupling and/or modulation of these APC activities by antibodies may have therapeutic benefit in diseases such as traumatic bleeding, hemophilia, sepsis, and ischemia. TPP-26870 is an antibody that targets a nonactive site of APC for the selective modulation of APC activities. To optimize the potency of TPP-26870, variants with single amino acid mutation in the complementarity-determining regions (CDRs) were screened, and 21 variants with improved KD were identified. Interestingly, the affinity maturation of TPP-26870 did not merely generate a panel of variants with higher potency in functional assays. Functional data demonstrated that the pleiotropic functions of APC were very sensitive to epitope-CDR interactions. Single amino acid mutations within the CDRs of TPP-26870 were sufficient to elicit divergent antagonistic and agonistic effects on the various APC functional activities. These include prolonged in vitro APC plasma half-life, increased inhibition of anticoagulant activity, and agonistic enhancement of histone H3 cleavage, while having less impact on protease-activated receptor 1 cleavage, compared with TPP-26870. This study illustrates that APC is highly sensitive to non–active site targeting that can lead to unpredictable changes in its activity profile of this pleiotropic enzyme. Furthermore, this study demonstrates the ability to modify APC functions to advance the potential development of APC-targeted antibodies as therapeutics for the treatment of diseases including trauma bleeding, hemophilia, ischemia, and sepsis.

Survival Distinctions for Cases Representing Immunologically Cold Tumors via Intrinsic Disorder Assessments for Blood-Sourced TRB Variable Regions.

T cell receptor beta (TRB) sequences were recovered from the Cancer Genome Atlas Uveal Melanoma blood exome files. Intrinsic disorder scores for amino acid (AA) sequences of the entire TRB variable region were obtained and evaluated as potentially representative of overall survival (OS) distinctions, i.e., for cases representing the upper and lower 50th percentiles for intrinsic disorder scores. Analyses using four intrinsic disorder assessment tools indicated that a lower intrinsic disorder of the blood-sourced TRB variable regions, including continuous AA sequences of the V-gene segment, the complementarity-determining region-3, and the J-gene segment, was associated with a better OS probability (with log-rank p-values ranging from 0.002 to 0.014). We further determined that intrinsic disorder assessments could be used for OS stratification for a second, immunologically cold cancer: MYCN amplified neuroblastoma. Thus, intrinsic disorder assessments of blood-sourced, full TRB variable regions may provide a novel patient stratification approach for patients with immunologically cold cancers.

Scifer: An R/Bioconductor package for large-scale integration of Sanger sequencing and flow cytometry data of index-sorted single cells

Sanger sequencing remains widely used in various experimental contexts, often in combination with flow cytometry for indexing specific cell populations. However, existing software lacks the capability to automate quality control (QC) of raw Sanger sequencing data and integrate it with flow cytometry information on a large scale. Here, we introduce scifer, an R package now available in the latest release of Bioconductor (3.20) showcasing its effectiveness in seamlessly integrating these types of data as demonstrated by analyses of B cell and T cell receptor sequences. Scifer preprocesses raw data from index sorts and immune receptor Sanger sequencing. It identifies high-quality sequences based on selected parameters, such as length, Phred scores, and heavy-chain complementarity-determining region 3 (HCDR3) quality. As a result, the quality of germline assignments is significantly increased and spurious variable gene mutations are reduced. Scifer is automated and can process thousands of sequences in less than an hour. Its output provides quality control reports, FASTA files, summarized tables, and electropherograms for manual inspection. In summary, scifer is a user-friendly software that speeds up the analysis of immune receptor repertoire sequences, offering wide applicability.

The characteristics of T-cell receptor repertoire in relation to systemic immune response of patients with ischemic stroke.

T lymphocytes play a vital role in the immune-inflammatory response following a stroke. However, the specific mechanisms behind the contrasting functions of T cells in the brain and peripheral tissues after a stroke remain unclear and require further investigation. T-cell receptors (TCRs) are essential in controlling how T lymphocytes develop and become active. This study aims to gain a deeper understanding of the biological function of T lymphocytes by analyzing the TCR repertoire in patients who have experienced an acute ischemic stroke (AIS). High-throughput TCR sequencing was conducted on peripheral blood samples from 25 AIS patients and 10 healthy controls. We compared the percentage of T cells and the characteristics of the TCR repertoire, specifically focusing on the recombination of V(D)J gene fragments and the diversity of the complementarity determining region 3 (CDR3) of the Vβ gene. Additionally, this study analyzed the potential biological significance of the skewed TCR repertoire in AIS patients. In patients with AIS, the proportion of circulating lymphocytes (LY%) decreased while the systemic immune-inflammatory index (SII) increased compared to healthy controls. The average number of TCR read pairs decreased, corresponding with the presence of lymphopenia. However, the recombination of V(D)J gene fragments, the number of CDR3 clonotypes, and the diversity of CDR3 was elevated in the peripheral blood of AIS patients. Furthermore, the increased number of CDR3 amino acid or nucleotide clonotypes was negatively correlated with neurologic deficits but positively correlated with AIS patients' systemic immune condition and functional outcomes. Our findings suggest that both immunosuppression and enhanced antigen-specific T-cell response may exist in the periphery of the AIS patients. Further investigation into the mechanisms underlying these opposing changes may lead to the discovery of novel targets to reverse immunosuppression or mitigate the detrimental effects of T cells in the lesioned brain of AIS patients.

Cryo-electron microscopy reveals a single domain antibody with a unique binding epitope on fibroblast activation protein alpha.

Fibroblast activation protein alpha (FAP) is a serine protease that is expressed at basal levels in benign tissues but is overexpressed in a variety of pathologies, including cancer. Despite this unique expression profile, designing effective diagnostic and therapeutic agents that effectively target this biomarker remain elusive. Here we report the structural characterization of the interaction between a novel single domain antibody (sdAbs), I3, and FAP using cryo-electron microscopy. The reconstructions were determined to a resolution of 2.7 Å and contained two distinct populations; one I3 bound and two I3 molecules bound to the FAP dimer. In both cases, the sdAbs bound a unique epitope that was distinct from the active site of the enzyme. Furthermore, this report describes the rational mutation of specific residues within the complementarity determining region 3 (CDR3) loop to enhance affinity and selectivity of the I3 molecule for FAP. This report represents the first sdAb-FAP structure to be described in the literature.

On the humanization of VHHs: Prospective case studies, experimental and computational characterization of structural determinants for functionality.

The humanization of camelid-derived variable domain heavy chain antibodies (VHHs) poses challenges including immunogenicity, stability, and potential reduction of affinity. Critical to this process are complementarity-determining regions (CDRs), Vernier and Hallmark residues, shaping the three-dimensional fold and influencing VHH structure and function. Additionally, the presence of non-canonical disulfide bonds further contributes to conformational stability and antigen binding. In this study, we systematically humanized two camelid-derived VHHs targeting the natural cytotoxicity receptor NKp30. Key structural positions in Vernier and Hallmark regions were exchanged with residues from the most similar human germline sequences. The resulting variants were characterized for binding affinities, yield, and purity. Structural binding modes were elucidated through crystal structure determination and AlphaFold2 predictions, providing insights into differences in binding affinity. Comparative structural and molecular dynamics characterizations of selected variants were performed to rationalize their functional properties and elucidate the role of specific sequence motifs in antigen binding. Furthermore, systematic analyses of next-generation sequencing (NGS) and Protein Data Bank (PDB) data was conducted, shedding light on the functional significance of Hallmark motifs and non-canonical disulfide bonds in VHHs in general. Overall, this study provides valuable insights into the structural determinants governing the functional properties of VHHs, offering a roadmap for their rational design, humanization, and optimization for therapeutic applications.

Direct recognition of an intact foreign protein by an αβ T cell receptor

αβ T cell receptors (αβTCRs) co-recognise antigens when bound to Major Histocompatibility Complex (MHC) or MHC class I-like molecules. Additionally, some αβTCRs can bind non-MHC molecules, but how much intact antigen reactivities are achieved remains unknown. Here, we identify an αβ T cell clone that directly recognises the intact foreign protein, R-phycoerythrin (PE), a multimeric (αβ)6γ protein complex. This direct αβTCR–PE interaction occurs in an MHC-independent manner, yet triggers T cell activation and bound PE with an affinity comparable to αβTCR–peptide–MHC interactions. The crystal structure reveals how six αβTCR molecules simultaneously engage the PE hexamer, mediated by the complementarity-determining regions (CDRs) of the αβTCR. Here, the αβTCR mainly binds to two α-helices of the globin fold in the PE α-subunit, which is analogous to the antigen-binding platform of the MHC molecule. Using retrogenic mice expressing this TCR, we show that it supports intrathymic T cell development, maturation, and exit into the periphery as mature CD4/CD8 double negative (DN) T cells with TCR-mediated functional capacity. Accordingly, we show how an αβTCR can recognise an intact foreign protein in an antibody-like manner.

Detection of anti-EBV TCR CDR3s associated with better outcomes for EBV-positive, Ugandan cases of Burkitt lymphoma.

Burkitt lymphoma (BL) has a tight association with Epstein-Barr virus (EBV), especially in sub-Saharan Africa. While the relationship between BL and EBV is well documented, the relationship between the anti-EBV adaptive immune response, particularly in sub-Saharan African cases, and disease course, has not been substantially investigated. An analysis of T-cell receptor (TCR) complementarity determining region-3 (CDR3) sequences, reported here, from EBV-positive, Ugandan BL tumor samples revealed a correlation between the presence of anti-EBV CDR3s and improved overall survival probabilities. Furthermore, chemical complementarity assessments demonstrated higher complementarity for TCR CDR3s and EBV epitopes in the cases where there had been a detection of the anti-EBV CDR3 AA sequence matches in the BL tumor samples. Overall, the results reported here raise the question of whether EBV targeted immunotherapy would lead to better BL outcomes?

Development, physico-chemical characterization, and in vivo stability of a novel aglycosylated monoclonal antibody targeting FAM19A5

AbstractIntroducing aglycosylation into therapeutic monoclonal antibodies (mAbs) can prevent side effects associated with fragment crystallizable (Fc)-mediated effector functions. This modification induces structural changes in the heavy chain constant domain 2-constant domain 3 within Fc regions, which decreases antibody stability at acidic pH and high temperature. In this study, NS101, a novel aglycosylated mAb targeting family with sequence similarity 19, A5 (FAM19A5) for neurological diseases was evaluated with respect to its developability and in vivo stability as therapeutics. When recombinant CHO cells producing NS101 were cultivated using a fed-batch mode in a 500 L bioreactor, cell growth and mAb production profiles were consistent across three consecutive runs. NS101, thus produced, features an additional intra-disulfide bond in the heavy chain complementarity-determining region 3, contributing strong and sophisticated binding to the cryptic epitope. The melting temperature (Tm) of NS101 was lower than that of commercial glycosylated therapeutic mAbs, but NS101 showed better stability at 4 °C for 36 months. The binding affinity of NS101 to FAM19A5 and neonatal Fc receptor were comparable to those of glycosylated NS101. In addition, in three human cohort groups receiving 6, 12, and 24 mg/kg of NS101, the mean half-life was 22 days, and NS101 exhibited in vivo stability, considering that the half-lives of commercialized therapeutic mAbs and endogenous IgGs are 2–4 weeks and 21 days, respectively. Taken together, the results obtained here demonstrate that NS101, a novel aglycosylated mAb, has potential as a therapeutic agent for neurological diseases.

Stratification of Wilms tumor patients using physicochemical properties of the adaptive immune receptor polypeptides, IGL and TRG

Wilms tumor (WT) is the most common pediatric renal malignancy. Current guidelines that stratify WT risk and determine treatment courses are inadequate, as over 60% of WT survivors develop treatment-related complications. Recently, numerous advances in establishing patient sub-groups with different clinical features have been realized by evaluating the adaptive immune receptor (IR) complementarity determining region-3 (CDR3) amino acid (AA) sequences, a reasonable series of successes, given the prominent role of the CDR3 in antigen binding, including tumor antigen binding. However, the possibility that adaptive IR chemical variability correlates with distinct survival outcomes for WT has not yet been explored. The goal of this study was to isolate the T-cell receptor and B-cell receptor recombination, sequencing reads from WT RNAseq files, representing the actual tumor tissue, translate the sequences to AAs, identify the adaptive IR CDR3 domains, and determine whether the physicochemical properties of those CDR3 AA sequences correlated with survival probability distinctions. WT RNA-seq files were mined to obtain the CDR3 AAs for various adaptive IRs. The physicochemical properties of these CDR3s were examined for trends in how those properties correlated with survival probabilities for WT patients, using a Kaplan-Meier analyses, verified via several approaches. The above processes indicated the association of the (a) IGL CDR3s' instability index and the (b) TRG CDR3s' fraction disorder promoting features with better outcomes. Additionally, the IGL CDR3 data were assessed using the Predictor of Natural Disordered Regions web tool, which strengthened the evidence for the association with the IGL CDR3 instability index with a better outcome. The approaches described here indicate that greater adaptive IR CDR3 instability and flexibility may serve as prognostic indicators; and may indicate the flexibility of CDR3 domains provides for greater opportunity to bind tumor antigens. Further exploration and development of these approaches and findings may lead to new guidelines for more precise treatment regimens, or even watchful waiting periods, that could thereby decrease the lifetime occurrence of adverse events.

CDR identification, epitope mapping and binding affinity determination of novel monoclonal antibodies generated against human apolipoprotein B-100

In-house generated mAbs to apolipoprotein B-100 (apoB-100) clones hLDL-E8, hLDL-2D8 and hLDL-F5 were extensively studied to determine their complementarity-determining regions (CDRs), binding epitopes and affinity. RT-PCR revealed that all mAbs consisted of kappa light chains and gamma heavy chains. DNA sequencing and bioinformatic analysis showed that the variable gene and protein sequences of their CDRs shared over 50 % identity with the existing databases. The 3D structures of the mAb variable fragments (Fv) with a QSQE score above 0.7 were constructed using the SWISS-MODEL platform. The structural accuracy was confirmed by Ramachandran plots, with 99 % of amino acid residues falling within acceptable regions. Thrombolytic cleavage of apoB-100 and Western blot analysis demonstrated that hLDL-E8 and hLDL-F5 specifically bind to the T3 fragment (aa 1297–3249), whereas hLDL-2D8 binds to the T4 fragment (aa 1–1297). These findings were supported with epitope-binding assays using inhibition ELISA, which indicated that hLDL-E8 binds at different epitopes from hLDL-2D8 and has some overlap with hLDL-F5. Lastly, the binding affinity of the mAbs was examined by indirect ELISA. The average affinity constants (Kaff) for mAbs hLDL-2D8, hLDL-E8 and hLDL-F5 are 1.51 ± 0.69 × 109 Mol−1, 7.25 ± 3.56 × 108 Mol−1 and 4.39 ± 2.63 × 106 Mol−1, respectively. Additionally, the behavior of the antibodies in the dose-response curve revealed that hLDL-F5 may recognize two epitopes of apoB-100 or have very low binding affinity. In contrast, hLDL-2D8 and hLDL-E8 each recognize a single epitope. These findings provide information that will be useful when selecting mAbs for both laboratory and clinical research purposes.

Computational Analysis of T-Cell Receptor Repertoire Workflow: From T-Cell Isolation to Bioinformatics Analysis.

The T-cell receptor (TCR) is the key molecule involved in the adaptive immune response. It is generated by the V(D)J recombination, responsible of the enormous diversity of the TCR repertoire, a crucial feature determining the individual capability to response to antigens and to build immunological memory. A pivotal role in the recognition of antigen is played by the hypervariable complementarity-determining region 3 (CDR3) of the V-beta chain of TCR. Investigating the CDR3 supports the understanding of the adaptive immune system dynamics in physiological processes, such as immune aging, and in disease, especially autoimmune disorders in which T cells are main actors. High-throughput sequencing (HTS) paved the way for a great progress in the investigation of TCR repertoire, enhancing the read depth in the process of library generation of sequencing and the number of samples that can be analyzed simultaneously. Therefore, the leverage of big datasets stressed the need to develop computational approach, by bioinformatics, to unravel the characteristics of the TCR repertoire.

Insights into lipid-modified recognition of Apolipoprotein E3 to extra-cellular domain of TREM2 associated with Alzheimer’s disease

E3 genotype of apolipoprotein E (ApoE) and triggering receptor expressed on myeloid cells 2 (TREM2) are critical genetic risk factors for late-onset Alzheimer’s diseases (AD) that influences the formation of plaques and neurofibrillary tangles associated with AD pathogenesis. In addition, variation in genetic association of ApoE and TREM2 in presence of lipids have been advocated to potentially regulate different aspects of AD pathology by facilitating the clearance of amyloid beta (Aβ) from brain. However, the proteinopathy and functional mechanism underlying their molecular interaction in presence of lipid remains poorly understood. Herein, to shed inherent insights into the mode of ApoE3-TREM2 interaction in both lipid and aqueous medium, we have used a combination of different state-of-the-art computational tools including knowledge-based protein–protein docking and molecular dynamics (MD) simulations. Remarkably, we find the direct involvement of regulatory complementarity-determining region-2 (CDR2) loop of TREM2 in interaction with the major hinge region and helix H4 of ApoE3. We further anticipate that ApoE3 attains distinct conformational states and forms an open and extended cavity-like structure in ApoE3-TREM2 complex in presence of lipids. Our data also exhibits reduced hydrophobicity in the ApoE3 binding interface of TREM2, which sets a baseline for reduced binding affinity towards ApoE3. Therefore, we hypothesize that this decline in hydrophobic index might have resulted due to structural variations in the H4 helix and major hinge region leading to altered TREM2 conformation in presence of lipids. Altogether, our findings demonstrate the effect of phospholipids on the structural dynamics and conformation of ApoE3, which contributes to our understanding of how APOE and TREM2 influences the development of AD. However, further experimental studies are necessary to validate and explore our findings which will open up new avenues towards development of novel therapeutic strategies for AD.

Insights into cytomegalovirus-associated T cell receptors in recipients following allogeneic hematopoietic stem cell transplantation

BackgroundCytomegalovirus (CMV) reactivation is a serious problem in recipients of allogeneic hematopoietic stem cell transplantation. Long-term latency depends on specific T cell immune reconstitution, which identifies various pathogens by T cell receptors (TCRs). However, the mechanisms underlying the selection of CMV-specific TCRs in recipients after transplantation remain unclear.MethodsUsing high-throughput sequencing and bioinformatics analysis, the T cell immune repertoire of seven CMV reactivated recipients (CRRs) were analyzed and compared to those of seven CMV non-activated recipients (CNRs) at an early stage after transplant.ResultsThe counts of unique complementarity-determining region 3 (CDR3) were significantly higher in CNRs than in CRRs. The CDR3 clones in the CNRs exhibit higher homogeneity compared to the CRRs. With regard to T cell receptor β-chain variable region (TRBV) and joint region (TRBJ) genotypes, significant differences were observed in the frequencies of TRBV6, BV23, and BV7–8 between the two groups. In addition to TRBV29–1/BJ1–2, TRBV2/BJ2–2, and TRBV12–4/BJ1–5, 11 V-J combinations had significantly different expression levels between CRRs and CNRs.ConclusionsThe differences in TCR diversity, TRBV segments, and TRBV-BJ combinations observed between CNRs and CRRs might be associated with post-transplant CMV reactivation and could serve as a foundation for further research.

AI-driven antibody design with generative diffusion models: current insights and future directions.

Therapeutic antibodies are at the forefront of biotherapeutics, valued for their high target specificity and binding affinity. Despite their potential, optimizing antibodies for superior efficacy presents significant challenges in both monetary and time costs. Recent strides in computational and artificial intelligence (AI), especially generative diffusion models, have begun to address these challenges, offering novel approaches for antibody design. This review delves into specific diffusion-based generative methodologies tailored for antibody design tasks, de novo antibody design, and optimization of complementarity-determining region (CDR) loops, along with their evaluation metrics. We aim to provide an exhaustive overview of this burgeoning field, making it an essential resource for leveraging diffusion-based generative models in antibody design endeavors.

Rapid affinity optimization of an anti-TREM2 clinical lead antibody by cross-lineage immune repertoire mining

We describe a process for rapid antibody affinity optimization by repertoire mining to identify clones across B cell clonal lineages based on convergent immune responses where antigen-specific clones with the same heavy (VH) and light chain germline segment pairs, or parallel lineages, bind a single epitope on the antigen. We use this convergence framework to mine unique and distinct VH lineages from rat anti-triggering receptor on myeloid cells 2 (TREM2) antibody repertoire datasets with high diversity in the third complementarity-determining loop region (CDR H3) to further affinity-optimize a high-affinity agonistic anti-TREM2 antibody while retaining critical functional properties. Structural analyses confirm a nearly identical binding mode of anti-TREM2 variants with subtle but significant structural differences in the binding interface. Parallel lineage repertoire mining is uniquely tailored to rationally explore the large CDR H3 sequence space in antibody repertoires and can be easily and generally applied to antibodies discovered in vivo.

Structure-guided mutations in CDRs for enhancing the affinity of neutralizing SARS-CoV-2 nanobody

The optimization of antibodies to attain the desired levels of affinity and specificity holds great promise for the development of next generation therapeutics. This study delves into the refinement and engineering of complementarity-determining regions (CDRs) through in silico affinity maturation followed by binding validation using isothermal titration calorimetry (ITC) and pseudovirus-based neutralization assays. Specifically, it focuses on engineering CDRs targeting the epitopes of receptor-binding domain (RBD) of the spike protein of SARS-CoV-2. A structure-guided virtual library of 112 single mutations in CDRs was generated and screened against RBD to select the potential affinity-enhancing mutations. Protein-protein docking analysis identified 32 single mutants of which nine mutants were selected for molecular dynamics (MD) simulations. Subsequently, biophysical ITC studies provided insights into binding affinity, and consistent with in silico findings, six mutations that demonstrated better binding affinity than native nanobody were further tested in vitro for neutralization activity against SARS-CoV-2 pseudovirus. Leu106Thr mutant was found to be most effective in virus-neutralization with IC50 values of ∼0.03 μM, as compared to the native nanobody (IC50 ∼0.77 μM). Thus, in this study, the developed computational pipeline guided by structure-aided interface profiles and thermodynamic analysis holds promise for the streamlined development of antibody-based therapeutic interventions against emerging variants of SARS-CoV-2 and other infectious pathogens.

An Integrated Strategy to Identify Tyrosine Sulfation from the Therapeutic Proteins.

Posttranslational modifications (PTMs) are potential critical quality attributes in biotherapeutic development, as they can affect drug efficacy and safety. Tyrosine sulfation plays a critical role in protein-protein interactions and has been found on many surface receptors as well as antibody complementarity-determining regions (CDR). However, the presence and function of tyrosine sulfation in therapeutic proteins have not been broadly investigated due to difficulties in detecting the modification. Here, we establish an integrated strategy to identify tyrosine sulfation in biotherapeutic proteins. In silico prediction was used to estimate possible modification sites, followed by the elucidation with intact LCMS and native SCX-MS. The combination of these three steps takes less than 1 h, which provides quick and confident preliminary detection of potential CQAs. Taking NB1 as an example, three +80 Da mass shifts were observed from intact mass analysis and three acidic peaks were monitored by SCX, allowing confirmation of modification as either phosphorylation or sulfation. Peptide mapping, Fe3+-IMAC enrichment, and dephosphorylation were further conducted to provide improved signal intensity and differentiation of modification such as sulfation or phosphorylation. With this integrated strategy, we were able to identify for the first time both tyrosine sulfation and serine phosphorylation in one therapeutic protein.