Antibody-binding Regions Research Articles

Establishment of human post-vaccination SARS-CoV-2 standard reference sera

There is a critical need to understand the effectiveness of serum elicited by different SARS-CoV-2 vaccines against SARS-CoV-2 variants. We describe the generation of reference reagents comprised of post-vaccination sera from recipients of different primary vaccines with or without different vaccine booster regimens in order to allow standardized characterization of SARS-CoV-2 neutralization in vitro. We prepared and pooled serum obtained from donors who received a either primary vaccine series alone, or a vaccination strategy that included primary and boosted immunization using available SARS-CoV-2 mRNA vaccines (BNT162b2, Pfizer and mRNA-1273, Moderna), replication-incompetent adenovirus type 26 vaccine (Ad26.COV2·S, Johnson and Johnson), or recombinant baculovirus-expressed spike protein in a nanoparticle vaccine plus Matrix-M adjuvant (NVX-CoV2373, Novavax). No subjects had a history of clinical SARS-CoV-2 infection, and sera were screened with confirmation that there were no nucleocapsid antibodies detected to suggest natural infection. Twice frozen sera were aliquoted, and serum antibodies were characterized for SARS-CoV-2 spike protein binding (estimated WHO antibody binding units/ml), spike protein competition for ACE-2 binding, and SARS-CoV-2 spike protein pseudotyped lentivirus transduction. These reagents are available for distribution to the research community (BEI Resources), and should allow the direct comparison of antibody neutralization results between different laboratories. Further, these sera are an important tool to evaluate the functional neutralization activity of vaccine-induced antibodies against emerging SARS-CoV-2 variants of concern. ImportanceThe explosion of COVID-19 demonstrated how novel coronaviruses can rapidly spread and evolve following introduction into human hosts. The extent of vaccine- and infection-induced protection against infection and disease severity is reduced over time due to the fall in concentration, and due to emerging variants that have altered antibody binding regions on the viral envelope spike protein. Here, we pooled sera obtained from individuals who were immunized with different SARS-CoV-2 vaccines and who did not have clinical or serologic evidence of prior infection. The sera pools were characterized for direct spike protein binding, blockade of virus-receptor binding, and neutralization of spike protein pseudotyped lentiviruses. These sera pools were aliquoted and are available to allow inter-laboratory comparison of results and to provide a tool to determine the effectiveness of prior vaccines in recognizing and neutralizing emerging variants of concern.

Oriented Antibody-Assembled Metal-Organic Frameworks for Persistent Wearable Sweat Cortisol Detection.

The level of cortisol can reflect people's psychological stress, help diagnose adrenal gland diseases, and is also related to several mental diseases. In this study, we developed a cortisol monoclonal antibody-oriented approach to modify an immunosensor for wearable label-free and persistent sweat cortisol detection. On such an antibody-oriented immunosensor, the fragment crystallizable (Fc) region is partially inserted within the metal-organic framework (MOF), and antibody-binding regions of the cortisol monoclonal antibody (Cmab) were exposed on the MOF surface via selective growth and self-assembly. Such ordered and oriented embedding of antibodies in the MOF resulted in excellent antibody activity and improved stability and antigen-binding capacity. We also engineered the full integrated system for on-body sweat cortisol biosensing performance in several volunteers, and the results indicated that this wearable sensor is suitable for practical cortisol detection with a good linear detection range from 1 pg/mL to 1 μg/mL with a lower limit of detection of 0.26 pg/mL. Moreover, the wearable sensor demonstrated good persistence in detecting cortisol, with only 4.1% decay after 9 days of storage. The present work represents a simple oriented antibody assembling approach to improve the stability of antibodies, providing an important step toward long-term continuous sweat biomarker detection.

Molecular insights into recognition of GUCY2C by T-cell engaging bispecific antibody anti-GUCY2CxCD3

The intestinal epithelial receptor Guanylyl Cyclase C (GUCY2C) is a tumor-associated cell surface antigen expressed across gastrointestinal malignancies that can serve as an efficacious target for colorectal cancer immunotherapy. Here, we describe a yeast surface-display approach combined with an orthogonal peptide-based mapping strategy to identify the GUCY2C binding epitope of a novel anti-GUCY2CxCD3 bispecific antibody (BsAb) that recently advanced into the clinic for the treatment of cancer. The target epitope was localized to the N-terminal helix H2 of human GUCY2C, which enabled the determination of the crystal structure of the minimal GUCY2C epitope in complex with the anti-GUCY2C antibody domain. To understand if this minimal epitope covers the entire antibody binding region and to investigate the impact of epitope position on the antibody’s activity, we further determined the structure of this interaction in the context of the full-length extracellular domain (ECD) of GUCY2C. We found that this epitope is positioned on the protruding membrane-distal helical region of GUCY2C and that its specific location on the surface of GUCY2C dictates the close spatial proximity of the two antigen arms in a diabody arrangement essential to the tumor killing activity of GUCY2CxCD3 BsAb.

Antibodies against platelet factor 4 and the risk of cerebral venous sinus thrombosis in patients with vaccine-induced immune thrombotic thrombocytopenia

BackgroundVaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare complication of adenoviral vector–based vaccines against SARS-CoV-2. This syndrome is caused by antibodies against platelet factor 4 (PF4; CXCL4) that lead to platelet activation and is characterized by thrombocytopenia and thrombosis in unusual locations, including cerebral venous sinus thrombosis (CVST). VITT can be classified based on anti-PF4 antibodies properties in vitro: those that require PF4 to activate platelets (PF4-dependent) and those that can activate platelets without additional PF4 (PF4-independent) in the serotonin release assay. ObjectivesWe aim to characterize the relationship of VITT platelet-activating profiles with CVST. MethodsWe conducted a retrospective cohort study involving patients with confirmed VITT who were tested between March and June 2021. Data were collected with an anonymized form and cases were identified as VITT with high clinical suspicion according to platelet activation assays. Anti-PF4 antibody binding regions on PF4 were further characterized with alanine scanning mutagenesis. ResultsOf the patients with confirmed VITT (n = 39), 17 (43.6%) had PF4-dependent antibodies and 22 (56.4%) had PF4-independent antibodies. CVST occurred almost exclusively in PF4-independent patients (11 of 22 vs 1 of 17; P < .05). Additionally, PF4-independent antibodies bound to 2 distinct epitopes on PF4, the heparin-binding region and a site typical for heparin-induced thrombocytopenia antibodies, whereas PF4-dependent antibodies bound to only the heparin-binding region. ConclusionThese findings suggest that VITT antibodies that cause PF4-independent platelet activation represent a unique subset of patients more likely to be associated with CVST, possibly due to the 2 different types of anti-PF4 antibodies.

Identification, binding, and structural characterization of single domain anti-PD-L1 antibodies inhibitory of immune regulatory proteins PD-1 and CD80

Programmed death-ligand 1 (PD-L1) is a key immune regulatory protein that interacts with programmed cell death protein 1 (PD-1), leading to T-cell suppression. Whilst this interaction is key in self-tolerance, cancer cells evade the immune system by overexpressing PD-L1. Inhibition of the PD-1/PD-L1 pathway with standard monoclonal antibodies has proven a highly effective cancer treatment, however, single domain antibodies (VHH) may offer numerous potential benefits. Here we report the identification and characterisation of a diverse panel of sixteen novel VHHs specific to PD-L1. The panel of VHHs demonstrate affinities of 0.7 nM to 5.1 μM and were able to completely inhibit PD-1 binding to PD-L1. The binding site for each VHH on PD-L1 was determined using NMR chemical shift perturbation mapping and revealed a common binding surface encompassing the PD-1 binding site. Additionally, we solved crystal structures of two representative VHHs in complex with PD-L1, which revealed unique binding modes. Similar NMR experiments were used to identify the binding site of CD80 on PD-L1, which is another immune response regulatory element and interacts with PD-L1 localized on the same cell surface. CD80 and PD-1 were revealed to share a highly overlapping binding site on PD-L1, with the panel of VHHs identified expected to inhibit CD80 binding. Comparison of the CD80 and PD-1 binding sites on PD-L1 enabled the identification of a potential antibody binding region able to confer specificity for the inhibition of PD-1 binding only, which may offer therapeutic benefits to counteract cancer cell evasion of the immune system.

Protective antigenic epitopes revealed by immunosignatures after three doses of inactivated SARS-CoV-2 vaccine.

BackgroundSARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) has infected millions of people around the world. Vaccination is a pillar in the strategy to control transmission of the SARS-CoV-2 spread. Immune responses to vaccination require elucidation.MethodsThe immune responses to vaccination with three doses of inactivated SARS-CoV-2 vaccine were followed in a cohort of 37 healthy adults (18–59 years old). Blood samples were collected at multiple time points and submitted to peptide array, machine learning modeling, and sequence alignment analyses, the results of which were used to generate vaccine-induced antibody-binding region (VIABR) immunosignatures (Registration number: ChiCTR2200058571).ResultsAntibody spectrum signals showed vaccination stimulated antibody production. Sequence alignment analyses revealed that a third vaccine dose generated a new highly represented VIABR near the A570D mutation, and the whole process of inoculation enhanced the VIABR near the N501Y mutation. In addition, the antigen conformational epitopes varied between short- and long-term samples. The amino acids with the highest scores in the short-term samples were distributed primarily in the receptor binding domain (RBD) and N-terminal domain regions of spike (S) protein, while in the long-term samples (12 weeks after the 2nd dose), some new conformational epitopes (CEs) were localized to crevices within the head of the S protein trimer.ConclusionProtective antigenic epitopes were revealed by immunosignatures after three doses of inactivated SARS-CoV-2 vaccine inoculation. A third dose results in a new top-10 VIABR near the A570D mutation site of S protein, and the whole process of inoculation enhanced the VIABR near the N501Y mutation, thus potentially providing protection from strains that have gained invasion and immune escape abilities through these mutation.

Omicron (B.1.1.529) - A new heavily mutated variant: Mapped location and probable properties of its mutations with an emphasis on S-glycoprotein

Omicron, another SARS-CoV-2 variant, has been recorded and reported as a VoC. It has already spread across >30 countries and is a highly mutated variant. We tried to understand the role of mutations in the investigated variants by comparison with previous characterized VoC. We have mapped the mutations in Omicron S-glycoprotein's secondary and tertiary structure landscape using bioinformatics tools and statistical software and developed different models. In addition, we analyzed the effect of diverse mutations in antibody binding regions of the S-glycoprotein on the binding affinity of the investigated antibodies. This study has chosen eight significant mutations in Omicron (D614G, E484A, N501Y, Q493K, K417N, S477N, Y505H G496S), and seven of them are located in the RBD region. We also performed a comparative analysis of the ΔΔG score of these mutations to understand the stabilizing or destabilizing properties of the investigated mutations. The analysis outcome shows that D614G, Q493K, and S477N mutations are stable mutations with ΔΔG scores of 0.351 kcal/mol, 0.470 kcal/mol, and 0.628 kcal/mol, respectively, according to DynaMut estimations. While other mutations (E484A, N501Y, K417N, Y505H, G496S) showed destabilizing results. The D614G, E484A, N501Y, K417N, Y505H, and G496S mutations increased the molecular flexibility of S-glycoprotein to interact with the ACE2 receptor, increasing the variant's infectivity. Our study will contribute to research on the SARS-CoV-2 variant, Omicron, by providing information on the mutational pattern and exciting properties of these eight significant mutations, such as antibody escape and infectivity quotient (stabilizing or destabilizing; increased or decreased molecular flexibility of S-glycoprotein to interact with the human ACE2 receptor).

Omicron variant (B.1.1.529) of SARS-CoV-2: understanding mutations in the genome, S-glycoprotein, and antibody-binding regions.

The Omicron variant has been detected in nearly 150 countries. We analyzed the mutational landscape of Omicron throughout the genome, focusing the S-glycoprotein. We also evaluated mutations in the antibody-binding regions and observed some important mutations overlapping those of previous variants including N501Y, D614G, H655Y, N679K, and P681H. Various new receptor-binding domain mutations were detected, including Q493K, G496S, Q498R, S477N, G466S, N440K, and Y505H. New mutations were found in the NTD (Δ143-145, A67V, T95I, L212I, and Δ211) including one new mutation in fusion peptide (D796Y). There are several mutations in the antibody-binding region including K417N, E484A, Q493K, Q498R, N501Y, and Y505H and several near the antibody-binding region (S477N, T478K, G496S, G446S, and N440K). The impact of mutations in regions important for the affinity between spike proteins and neutralizing antibodies was evaluated. Furthermore, we examined the effect of significant antibody-binding mutations (K417N, T478K, E484A, and N501Y) on antibody affinity, stability to ACE2 interaction, and possibility of amino acid substitution. All the four mutations destabilize the antibody-binding affinity. This study reveals future directions for developing neutralizing antibodies against the Omicron variant.Supplementary InformationThe online version contains supplementary material available at 10.1007/s11357-022-00532-4.

Self-Assembly of Oriented Antibody-Decorated Metal-Organic Framework Nanocrystals for Active-Targeting Applications.

Antibody (Ab)-targeted nanoparticles are becoming increasingly important for precision medicine. By controlling the Ab orientation, targeting properties can be enhanced; however, to afford such an ordered configuration, cumbersome chemical functionalization protocols are usually required. This aspect limits the progress of Abs-nanoparticles toward nanomedicine translation. Herein, a novel one-step synthesis of oriented monoclonal Ab-decorated metal-organic framework (MOF) nanocrystals is presented. The crystallization of a zinc-based MOF, Zn2 (mIM)2 (CO3 ), from a solution of Zn2+ and 2-methylimidazole (mIM), is triggered by the fragment crystallizable (Fc) region of the Ab. This selective growth yields biocomposites with oriented Abs on the MOF nanocrystals (MOF*Ab): the Fc regions are partially inserted within the MOF surface and the antibody-binding regions protrude from the MOF surface toward the target. This ordered configuration imparts antibody-antigen recognition properties to the biocomposite and shows preserved target binding when compared to the parental antibodies. Next, the biosensing performance of the system is tested by loading MOF*Ab with luminescent quantum dots (QD). The targeting efficiency of the QD-containing MOF*Ab is again, fully preserved. The present work represents a simple self-assembly approach for the fabrication of antibody-decorated MOF nanocrystals with broad potential for sensing, diagnostic imaging, and targeted drug delivery.

Evolution of the GII.3[P12] Norovirus from 2010 to 2019 in Jiangsu, China

ObjectivesNorovirus genotype GII.3[P12] strains have been an important pathogen for sporadic gastroenteritis infection. In previous studies of GII.3[P12], the number of specimens and time span are relatively small, which is difficult to truly reflect the infection and evolution of this type of norovirus. Here we report a molecular epidemiological study of the NoVs prevalent in Jiangsu between 2010 and 2019 to investigate the evolution of the GII.3[P12] strains in China.MethodsIn this study 60 GII.3[P12] norovirus strains were sequenced and analyzed for evolution, recombination, and selection pressure using bioanalysis software.ResultsThe GII.3[P12] strains were continuously detected during the study period, which showed a high constituent ratio in males, in winter and among children aged 0–11 months, respectively. A time-scaled evolutionary tree showed that both GII.P12 RdRp and GII.3 VP1 sequences were grouped into three major clusters (Cluster I–III). Most GII.3[P12] strains were mainly located in sub-cluster (SC) II of Cluster III. A SimPlot analysis identified GII.3[P12] strain to be as an ORF1-intragenic recombinant of GII.4[P12] and GII.3[P21]. The RdRp genes of the GII.3[P12] showed a higher mean substitution rate than those of all GII.P12, while the VP1 genes of the GII.3[P12] showed a lower mean substitution rate than those of all GII.3. Alignment of the GII.3 capsid sequences revealed that three HBGA binding sites of all known GII.3 strains remained conserved, while several amino acid mutations in the predicted antibody binding sites were detected. The mutation at 385 was within predicted antibody binding regions, close to host attachment factor binding sites. Positive and negative selection sites were estimated. Two common positively selected sites (sites 385 and 406) were located on the surface of the protruding domain. Moreover, an amino acid substitution (aa204) was estimated to be near the active site of the RdRp protein.ConclusionsWe conducted a comprehensive analysis on the epidemic and evolution of GII.3[P12] noroviruses and the results suggested that evolution was possibly driven by intergenic recombination and mutations in some key amino acid sites.

HDX-MS for Epitope Characterization of a Therapeutic ANTIBODY Candidate on the Calcium-Binding Protein Annexin-A1.

Annexin-A1 (ANXA1) belongs to a class of highly homologous Ca2+-dependent phospholipid-binding proteins. Its structure consists of a core region composed of four homologous repeats arranged in a compact, hydrolysis-resistant structure and an N-terminal region with a Ca2+-dependent conformation. ANXA1 is involved in several processes, including cell proliferation, apoptosis, metastasis, and the inflammatory response. Therefore, the development of antibodies blocking selected regions on ANXA1 holds great potential for the development of novel therapeutics treating inflammatory and cancer diseases. Here, we report the interaction site between an ANXA1-specific antibody known to inhibit T cell activation without adverse cytotoxic effects and ANXA1 using amide hydrogen–deuterium exchange mass spectrometry (HDX-MS). For the epitope determination, we applied two bottom-up HDX-MS approaches with pepsin digestion in solution and immobilized on beads. Both strategies revealed the interaction region within domain III of ANXA1 in Ca2+-bound conformation. The antibody-binding region correlates with the hydrophobic binding pocket of the N-terminal domain formed in the absence of calcium. This study demonstrates that even cryptic and flexible binding regions can be studied by HDX-MS, allowing a fast and efficient determination of the binding sites of antibodies which will help to define a mode of action profile for their use in therapy.

Structure-Function Analyses of New SARS-CoV-2 Variants B.1.1.7, B.1.351 and B.1.1.28.1: Clinical, Diagnostic, Therapeutic and Public Health Implications

SARS-CoV-2 (Severe Acute Respiratory Syndrome-Coronavirus 2) has accumulated multiple mutations during its global circulation. Recently, three SARS-CoV-2 lineages, B.1.1.7 (501Y.V1), B.1.351 (501Y.V2) and B.1.1.28.1 (P.1), have emerged in the United Kingdom, South Africa and Brazil, respectively. Here, we have presented global viewpoint on implications of emerging SARS-CoV-2 variants based on structural–function impact of crucial mutations occurring in its spike (S), ORF8 and nucleocapsid (N) proteins. While the N501Y mutation was observed in all three lineages, the 501Y.V1 and P.1 accumulated a different set of mutations in the S protein. The missense mutational effects were predicted through a COVID-19 dedicated resource followed by atomistic molecular dynamics simulations. Current findings indicate that some mutations in the S protein might lead to higher affinity with host receptors and resistance against antibodies, but not all are due to different antibody binding (epitope) regions. Mutations may, however, result in diagnostic tests failures and possible interference with binding of newly identified anti-viral candidates against SARS-CoV-2, likely necessitating roll out of recurring “flu-like shots” annually for tackling COVID-19. The functional relevance of these mutations has been described in terms of modulation of host tropism, antibody resistance, diagnostic sensitivity and therapeutic candidates. Besides global economic losses, post-vaccine reinfections with emerging variants can have significant clinical, therapeutic and public health impacts.

Bispecific Tau Antibodies with Additional Binding to C1q or Alpha-Synuclein.

Alzheimer's disease (AD) and other tauopathies are neurodegenerative disorders characterized by cellular accumulation of aggregated tau protein. Tau pathology within these disorders is accompanied by chronic neuroinflammation, such as activation of the classical complement pathway by complement initiation factor C1q. Additionally, about half of the AD cases present with inclusions composed of aggregated alpha-synuclein called Lewy bodies. Lewy bodies in disorders such as Parkinson's disease and Lewy body dementia also frequently occur together with tau pathology. Immunotherapy is currently the most promising treatment strategy for tauopathies. However, the presence of multiple pathological processes within tauopathies makes it desirable to simultaneously target more than one disease pathway. Herein, we have developed three bispecific antibodies based on published antibody binding region sequences. One bispecific antibody binds to tau plus alpha-synuclein and two bispecific antibodies bind to tau plus C1q. Affinity of the bispecific antibodies to their targets compared to their monospecific counterparts ranged from nearly identical to one order of magnitude lower. All bispecific antibodies retained binding to aggregated protein in patient-derived brain sections. The bispecific antibodies also retained their ability to inhibit aggregation of recombinant tau, regardless of whether the tau binding sites were in IgG or scFv format. Mono- and bispecific antibodies inhibited cellular seeding induced by AD-derived pathological tau with similar efficacy. Finally, both Tau-C1q bispecific antibodies completely inhibited the classical complement pathway. Bispecific antibodies that bind to multiple pathological targets may therefore present a promising approach to treat tauopathies and other neurodegenerative disorders.

Mapping the Epitope Interactions of Trastuzumab Via Plasma Induced Modification of Biomolecules (PLIMB)

Epitope mapping is the process of identifying the site(s) of an antigen where an antibody binds. Knowledge of epitopes facilitates drug design and patent applications; hence it is a key element of vaccine and drug development. Hydroxyl radical protein footprinting coupled with mass spectrometry offers opportunities to map antibody-binding regions of antigens with greater simplicity and increased throughput over x-ray crystallography. We report here the use of hydroxyl radical protein footprinting via Plasma Induced Modification of Biomolecules (PLIMB) to characterize the epitopes of trastuzumab (Herceptin) bound to receptor tyrosine-protein kinase erbB-2 (HER2). The protein samples were exposed to plasma for hydroxyl radical labeling, the labeled sites were identified using mass spectrometry, and the data was analyzed using Byos (Protein Metrics). The PLIMB data is compared to previously published results that determined the epitope of trastuzumab using x-ray crystallography.

IgE and IgG4 epitopes revealed on the major fish allergen Lat c 1

BackgroundThe IgE- and IgG4-binding patterns of the major fish allergen parvalbumins are not clearly understood. IgE antibody-binding to parvalbumin from Asian seabass, Lat c 1.01, is implicated in up to 90 % of allergic reactions, although the region of IgE or IgG4 epitopes are unknown. In the present study, we characterized the specific IgE- and IgG4-binding regions of Lat c 1.01 using serum from pediatric and adult patients with clinically-confirmed fish allergy. MethodsA comparative investigation of patient IgE- and IgG4-binding to recombinant Lat c 1.01 was performed by immunoblotting and indirect ELISA using serum from 15 children and eight adults with clinically confirmed IgE-mediated reactions to fish. The IgE- and IgG4-binding regions of Lat c 1.01 were determined by inhibition ELISA using seven overlapping peptides spanning the entire 102 amino acid sequence. Elucidated IgE-binding regions were modelled and compared to known antibody-binding regions of parvalbumins from five other fish species. ResultsNinety five percent (22/23) patients demonstrated IgE-binding to rLat c 1.01, while fewer patients (10/15 children and 7/8 adults) demonstrated robust IgG4 binding when determined by immunoblots. IgE-binding for both cohorts was significantly higher compared to IgG4-binding by ELISA. All patients in this study presented individual IgE and IgG4 epitope-recognition profiles. In addition to these patient-specific antibody binding sites, general IgE epitopes were also identified at the C- and N-terminal regions of this major fish allergen. Conclusions and Clinical relevanceOur findings demonstrate two specific IgE epitopes on parvalbumin from Asian seabass, while IgG4 binding is much lower and patient specific. This study highlights the importance of advancement in epitope analysis regardless of the age group for diagnostics and immunotherapies for fish allergy.

Targeting TGF-β-Mediated SMAD Signaling Pathway via Novel Recombinant Cytotoxin II: A Potent Protein from Naja naja oxiana Venom in Melanoma.

Since the current treatments have not resulted in the desired outcomes for melanoma patients, there is a need to identify more effective medications. Together with other snake venom proteins, cytotoxin-II has shown promising results in tumoral cells. In this study, recombinant cytotoxin-II (rCTII) was expressed in SHuffle® T7 Express cells, while the epitope mapping of rCTII was performed to reveal the antibody-binding regions of rCTII. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was used to assess the viability of SK-MEL-3 and HFF-2 cells after treating these cells with rCTII. The qRT-PCR was performed to evaluate the expression levels of matrix metallopeptidase 3 (MMP-3), SMAD2, SMAD3, caspase-8, caspase-9, and miR-214 in order to reveal the rCTII-induced signaling pathways in melanoma. Our results have shown that two regions of amino acids, 6–16 and 19–44, as predicted epitopes of this toxin, are essential for understanding the toxicity of rCTII. Treating the melanoma cells with rCTII substantially inhibited the transforming growth factor-beta (TGF-β)–SMAD signaling pathway and down-regulated the expression of MMP-3 and miR-214 as well. This cytotoxin also restored apoptosis mainly via the intrinsic pathway. The down-regulation of MMP-3 and miR-214 might be associated with the anti-metastatic property of rCTII in melanoma. The inhibitory effect of rCTII on the TGF-β signaling pathway might be associated with increased apoptosis and decreased cancer cell proliferation. It is interesting to see that the IC50 value of rCTII has been lower in the melanoma cells than non-tumoral cells, which may indicate its potential effects as a drug. In conclusion, rCTII, as a novel medication, might serve as a potent and efficient anticancer drug in melanoma.

Plasma Induced Modification of Biomolecules (PLIMB) for Epitope Mapping

Epitope mapping is the process of identifying the site(s) of an antigen where an antibody binds. Knowledge of epitopes facilitates drug design and patent applications; hence it is a key element of vaccine and drug development. Hydroxyl radical protein footprinting coupled with mass spectrometry offers opportunities to map antibody-binding regions of antigens. We report here the use of hydroxyl radical protein footprinting via Plasma Induced Modification of Biomolecules (PLIMB) to characterize the epitopes of antithrombin bound to the serine-protease thrombin, and monoclonal antibody (mAb) IIB8 to human transcription factor II B (TFIIB). The protein samples were exposed to plasma for hydroxyl radical labeling and the labeled sites were identified using mass spectrometry. The data was analyzed using Byos (Protein Metrics). The PLIMB data is compared to previously published results that determined the epitope of thrombin and TFIIB using other techniques.

Suicide Gene Therapy with a CD33 Targeted AAV6 Vector Expressing an Inducible Caspase-9 Suicide Gene Is Therapeutic in a Xenotransplantation Model of Acute Myeloid Leukemia

Suicide gene therapy for Acute myeloid leukemia (AML) can offer a high therapeutic index if the pro-apoptotic genes can be selectively introduced into cancer cells with high efficiency with no apparent vector-related toxicities in the recipient. Since hematopoietic cells or myeloid cells are particularly intransigent to transduction with gene delivery vectors such as Adeno-associated virus (AAV), we reasoned that a cell-receptor specific AAV that can target the CD33 antigen, over-expressed in leukemic cells may be beneficial.For designing a targeting peptide, we used bioinformatic tools to identify antibody binding region (ABR) from a monoclonal antibody (M195) available against CD33. After further validation, a consensus antigen-binding region comprising a heptamer sequence was selected and inserted into the loop IV region of the best infecting AAV serotype (AAV1-rh10) in leukemic cells, the AAV6 by standard cloning techniques. The AAV6-CD33 vectors thus developed was packaged with a inducible caspase 9 based suicide gene (iCasp9) and further verified for its capsid integrity and functionality. In the next set of studies, we wished to determine if the AAV6-CD33 vectors can enhance suicide gene transfer in AML cells. We evaluated their cytotoxic effect by a luminescence based ATP assay, in a panel of cell lines which were of hematopoietic origin, that either over-express the CD33 antigen (U937) or that do not express CD33 antigen (CEM) or a control hepatic cell line, Huh7. Interestingly, the targeted AAV6 vectors were highly cytotoxic (1.6 fold, 41 vs 67 % viability, p&lt; 0.0004) when compared to AAV6- wild type (WT) vectors in the CD33 positive U937 cells. However, in cells that do not express CD33 antigen, such as CEM or Huh7, AAV6-CD33 vectors showed no advantage over WT-AAV6 vectors in terms of their cytotoxicity. These data demonstrated the specificity of CD33 receptor targeted AAV6 vectors in AML cells in vitro.To further validate the novel AAV6 vector, we developed a Zebrafish xenograft model of AML. Briefly, ~1×105 fluorescently labelled U937 cells per recipient were transplanted into busulfan (20mg/kg bodyweight) conditioned Zebrafish. Four days after engraftment of leukemic cells, fish were randomised to: mock-treated, AAV6-WT iCasp9 vector administered either systemically (retro-orbital,RO) or locally (intra-tumoral,IT) and the receptor targeted AAV vector (AAV6-CD33) administered systemically through the retro-orbital plexus. Ten days later, the rate of tumor growth in vector treated fish was significantly lower in vector treated fishes when compared to mock-treated Zebrafish. The survival was significantly higher in the treatment group that received AAV6-iCasp9 vectors as compared to mock-treated control fishes (~80% vs 15%, p&lt;0.0001). Moreover, Zebrafish in the AAV6-CD33 treatment arm showed better survival as compared to untreated fishes (~100% vs 15%, p&lt;0.0001) or to those treated with wild type AAV6 vectors administered either by RO or IT route (100% vs 77% or 80%). A morphological characterisation and a TUNEL based apoptosis assay further revealed that fishes treated with CD33 targeted AAV6-iCasp9 vectors by systemic administration, had a significantly higher (~39 fold) increase in TUNEL positive cells in comparison to the control group. Interestingly, the receptor targeted AAV6 vectors augmented the in vivocytotoxicity of U937 tumors by at least 3-fold (p&lt;0.0001) when administered retro-orbitally in comparison to AAV6-WT vector administered group. Taken together, our work demonstrates the efficacy and translational potential of CD33-targeted AAV6 vectors for cytotoxic gene therapy in AML. Disclosures No relevant conflicts of interest to declare.

Disruption of ADAMTS13-Autoantibody Complexes with an ADAMTS13 Spacer Domain As a Potential Therapeutic Strategy for Immune Thrombotic Thrombocytopenic Purpura

Background: Immune thrombotic thrombocytopenic purpura (iTTP) is primarily caused by acquired immunoglobulin (Ig) G against ADAMTS13, a member of the A Disintegrin and Metalloprotease with Thrombospondin Type 1 repeats family, which specifically cleaves von Willebrand factor (VWF). Such proteolytic cleavage is essential for normal hemostasis. An inability to cleave VWF due to IgG autoantibody-mediated inhibition of plasma ADAMTS13 activity results in an accumulation of ultra large VWF multimers and disseminated microvascular thromboses, a pathognomonic feature of TTP. Previous studies have demonstrated that the spacer domain of ADAMTS13 is the primary target of IgG autoantibody; also, spacer domain is important for recognition of VWF under various conditions. Objective: In the present study, we explored if an isolated spacer domain can compete or reverse IgG autoantibody-mediated inhibition of ADAMTS13 activity, an important question to be addressed for developing a new strategy to treat iTTP. Methods:A recombinant ADAMTS13-spacer domain was expressed and purified to homogeneity; additionally, a single-chain fragment of the variable region of anti-ADAMTS13 IgG (i.e. scFv4-20) was isolated via phage display from a patient with iTTP, which was shown to specifically target the spacer domain and potently inhibit plasma ADAMTS13 activity with sub-nanomolar affinity. A functional assay with a fluorescein-labeled VWF73 substrate was used to determine the ADAMTS13 activity. Results: First, when a purified recombinant spacer domain (0-1.0 µM) was pre-incubated with scFv4-20 at various concentrations, followed by an addition of normal human plasma (NHP) that provides wild-type ADAMTS13 and a fluorescein-labeled recombinant VWF73 (F-rVWF73) substrate, we demonstrated that the inhibitory activity of scFv4-20 towards plasma ADAMTS13 decreased in a concentration-dependent manner. As a control, recombinant Cys-rich domain had no effect on blocking the scFv4-20-mediated inhibition of plasma ADAMTS13 activity under the same conditions. When scFv4-20 was pre-incubated with plasma ADAMTS13, recombinant spacer domain could also reverse the scFv4-20-mediated inhibition of ADAMTS13 activity but to a lesser degree. At the final concentration of 1.0 µM, recombinant spacer domain was able to increase ADAMTS13 activity by 2.1-fold when the recombinant spacer domain was added prior to the formation of ADAMTS13-antibody complexes but only by 1.5-fold if the recombinant spacer domain was added after the ADAMTS13 and antibody complexes were formed. Conclusion: Our results demonstrate that autoantibody-mediated inhibition of plasma ADAMTS13 is reversible and can be blocked by a molecular mimic that is the primary antibody-binding region of the full-length ADAMTS13 protein. The data suggest that it may be feasible to explore the development of agents capable of displacing inhibitory antibodies against ADAMTS13 in patients with iTTP. Disclosures Zheng: Alexion: Speakers Bureau; Ablynx/Sanofi: Consultancy, Speakers Bureau; Shire/Takeda: Research Funding; Clotsolution: Other: Co-Founder.

Structure and Functional Binding Epitope of V-domain Ig Suppressor of T Cell Activation

V-domain immunoglobulin (Ig) suppressor of Tcell activation (VISTA) is an immune checkpoint protein that inhibits the Tcell response against cancer. Similar to PD-1 and CTLA-4, a blockade of VISTA promotes tumor clearance by the immune system. Here, we report a 1.85Å crystal structure of the elusive human VISTA extracellular domain, whose lack of homology necessitated a combinatorial MR-Rosetta approach for structure determination. We highlight features that make the VISTA immunoglobulin variable (IgV)-like fold unique among B7 family members, including two additional disulfide bonds and an extended loop region with an attached helix that we show forms a contiguous binding epitope for a clinically relevant anti-VISTA antibody. We propose an overlap of this antibody-binding region with the binding epitope for V-set and Ig domain containing 3 (VSIG3), a purported functional binding partner of VISTA. The structure and functional epitope presented here will help guide future drug development efforts against this important checkpoint target.