The TITAN trial--assessing the efficacy and safety of an anti-von Willebrand factor Nanobody in patients with acquired thrombotic thrombocytopenic purpura

Nanobodies: Robust miniprotein binders in biomedicine

Variable domains of heavy chain-only antibodies (VHH), also known as nanobodies (Nbs), are monomeric antigen-binding domains derived from the camelid heavy chain-only antibodies. Nbs are characterized by small size, high target selectivity, and marked solubility and stability, which collectively facilitate high-quality drug development. In addition, Nbs are readily expressed from various expression systems, including E. coli and yeast cells. For these reasons, Nbs have emerged as preferred antibody fragments for protein engineering, disease diagnosis, and treatment. To date, two Nb-based therapies have been approved by the U.S. Food and Drug Administration (FDA). Numerous candidates spanning a wide spectrum of diseases such as cancer, immune disorders, infectious diseases, and neurodegenerative disorders are under preclinical and clinical investigation. Here, we discuss the structural features of Nbs that allow for specific, versatile, and strong target binding. We also summarize emerging technologies for identification, structural analysis, and humanization of Nbs. Our main focus is to review recent advances in using Nbs as a modular scaffold to facilitate the engineering of multivalent polymers for cutting-edge applications. Finally, we discuss remaining challenges for Nb development and envision new opportunities in Nb-based research.

Study review of camelid and shark antibodies for biomedical and biotechnological applications

The antibodies of camelids and sharks are about one–half of the conventional ones while regular antibodies have four protein chains: two light and two heavy, these small antibodies studied have just two heavy chains; they lack a light chain. In recent years, nanobodies have been the focus of attention because they can recognize epitopes that are usually not antigenic (hidden) for conventional antibodies. On the clinical side, researchers are testing nanobodies (Nbs) in the fight against diseases and disease diagnosis. Nanobodies also are attractive because they can prevent protein aggregation and clear the already existing aggregates. Furthermore, new treatments using these Nbs can neutralize the severe acute respiratory syndrome coronavirus (SARS-CoV-2) for preventing COVID-19. In this review, we sum up recent findings of the proposed nanobodies for their potential application.

Thrombotische Mikroangiopathie

Die thrombotische Mikroangiopathie (TMA) zeichnet sich durch eine endothelschadenassoziierte Bildung von Plättchenthromben in arteriellen und venösen Mikrogefäßen aus. Die damit einhergehende Ischämie führt zu schwerwiegenden Organdysfunktionen und kann akut lebensbedrohlich sein. Ätiologisch verbirgt sich hinter der TMA ein sehr heterogenes Erkrankungsspektrum. Neben der thrombotisch-thrombozytopenischen Purpura, die durch eine stark reduzierte ADAMTS13(„a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13“)-Aktivität gekennzeichnet ist, dem infektassoziierten klassischen hämolytisch-urämischen Syndrom (HUS) sowie dem komplementvermittelten atypischen HUS (aHUS) können weitere sehr seltene Erkrankungen oder sekundäre Formen vorliegen. Die differenzialdiagnostische Einteilung ist aufgrund unterschiedlicher therapeutischer Ansätze erforderlich. Der Einsatz neuer spezifischer medikamentöser Behandlungsmethoden hat die Prognose der TMA deutlich verbessert.

Transfusion of Platelets Loaded With Recombinant ADAMTS13 (A Disintegrin and Metalloprotease With Thrombospondin Type 1 Repeats-13) Is Efficacious for Inhibiting Arterial Thrombosis Associated With Thrombotic Thrombocytopenic Purpura

Objective- ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats-13) cleaves VWF (von Willebrand factor). This process is essential for hemostasis. Severe deficiency of plasma ADAMTS13 activity, most commonly resulting from autoantibodies against ADAMTS13, causes thrombotic thrombocytopenic purpura. Therapeutic plasma exchange is the standard of care to date, which removes autoantibodies and replenishes ADAMTS13. However, such a therapy is often ineffective to raise plasma ADAMTS13 activity, and in-hospital mortality rate remains as high as 20%. Approach and Results- To overcome the inhibition by autoantibodies, we developed a novel approach by delivering rADAMTS13 (recombinant ADAMTS13 ) using platelets as vehicles. We show that both human and murine platelets can uptake rADAMTS13 ex vivo. The endocytosed rADAMTS13 within platelets remains intact, active, and is stored in α-granules. Under arterial shear (100 dyne/cm²), the rADAMTS13 in platelets is released and effectively inhibits platelet adhesion and aggregation on a collagen-coated surface in a concentration-dependent manner. Transfusion of rADAMTS13-loaded platelets into Adamts13^-/- mice dramatically reduces the rate of thrombus formation in the mesenteric arterioles after FeCl₃ injury. An ex vivo transfusion of rADAMTS13-loaded platelets to a reconstituted whole blood containing plasma from a patient with immune-mediated thrombotic thrombocytopenic purpura and the cellular components (eg, erythrocytes and leukocytes) from a healthy individual, as well as a fresh whole blood obtained from a patient with congenital or immune-mediated thrombotic thrombocytopenic purpura also dramatically reduces the rate of thrombus formation under arterial flow. Conclusions- Our results demonstrate that transfusion of rADAMTS13-loaded platelets may be a novel and potentially effective therapeutic approach for arterial thrombosis, associated with congenital and immune-mediated thrombotic thrombocytopenic purpura.

Clinical pharmacology of caplacizumab for the treatment of patients with acquired thrombotic thrombocytopenic purpura

Introduction: Caplacizumab is a humanized anti-von Willebrand Factor (vWF) Nanobody® for the treatment of acquired Thrombotic Thrombocytopenic Purpura (aTTP). Caplacizumab targets the A1-domain of vWF, inhibiting the interaction between vWF and platelets. Clinical studies conducted in aTTP patients confirmed the rapid and sustained complete suppression of the vWF activity using an initial intravenous dose of 10 mg, and a maintenance subcutaneous 10 mg daily dosing regimen, with corresponding favorable efficacy and safety profiles. Areas covered: The pharmacokinetics of caplacizumab are non-linear, characterized by a target-mediated disposition and the exposure is dependent upon drug and target concentration over time. The pharmacokinetics of caplacizumab are predictable when considering the turn-over of the circulating vWF and its modulation by the drug over time. Renal and hepatic impairment are not expected to influence the exposure to the drug, and no direct or indirect drug-drug pharmacokinetic interactions are anticipated based on the mechanism of action and the specificity of the pharmacodynamic effect of caplacizumab. Expert opinion: Caplacizumab prevents the interaction between vWF and platelets, offering a direct and rapid therapeutic intervention to stop microthrombosis. The combination of caplacizumab with plasma exchange and immunosuppression represents an important, potentially life-saving advance in the treatment of aTTP patients.

A Novel Nanobody Targeting Middle East Respiratory Syndrome Coronavirus (MERS-CoV) Receptor-Binding Domain Has Potent Cross-Neutralizing Activity and Protective Efficacy against MERS-CoV

Therapeutic development is critical for preventing and treating continual MERS-CoV infections in humans and camels. Because of their small size, nanobodies (Nbs) have advantages as antiviral therapeutics (e.g., high expression yield and robustness for storage and transportation) and also potential limitations (e.g., low antigen-binding affinity and fast renal clearance). Here, we have developed novel Nbs that specifically target the receptor-binding domain (RBD) of MERS-CoV spike protein. They bind to a conserved site on MERS-CoV RBD with high affinity, blocking RBD's binding to MERS-CoV receptor. Through engineering a C-terminal human Fc tag, the in vivo half-life of the Nbs is significantly extended. Moreover, the Nbs can potently cross-neutralize the infections of diverse MERS-CoV strains isolated from humans and camels. The Fc-tagged Nb also completely protects humanized mice from lethal MERS-CoV challenge. Taken together, our study has discovered novel Nbs that hold promise as potent, cost-effective, and broad-spectrum anti-MERS-CoV therapeutic agents.

The newly emerged Middle East respiratory syndrome coronavirus (MERS-CoV) continues to infect humans and camels, calling for efficient, cost-effective, and broad-spectrum strategies to control its spread. Nanobodies (Nbs) are single-domain antibodies derived from camelids and sharks and are potentially cost-effective antivirals with small size and great expression yield. In this study, we developed a novel neutralizing Nb (NbMS10) and its human-Fc-fused version (NbMS10-Fc), both of which target the MERS-CoV spike protein receptor-binding domain (RBD). We further tested their receptor-binding affinity, recognizing epitopes, cross-neutralizing activity, half-life, and efficacy against MERS-CoV infection. Both Nbs can be expressed in yeasts with high yield, bind to MERS-CoV RBD with high affinity, and block the binding of MERS-CoV RBD to the MERS-CoV receptor. The binding site of the Nbs on the RBD was mapped to be around residue Asp539, which is part of a conserved conformational epitope at the receptor-binding interface. NbMS10 and NbMS10-Fc maintained strong cross-neutralizing activity against divergent MERS-CoV strains isolated from humans and camels. Particularly, NbMS10-Fc had significantly extended half-life in vivo; a single-dose treatment of NbMS10-Fc exhibited high prophylactic and therapeutic efficacy by completely protecting humanized mice from lethal MERS-CoV challenge. Overall, this study proves the feasibility of producing cost-effective, potent, and broad-spectrum Nbs against MERS-CoV and has produced Nbs with great potentials as anti-MERS-CoV therapeutics.

IMPORTANCE Therapeutic development is critical for preventing and treating continual MERS-CoV infections in humans and camels. Because of their small size, nanobodies (Nbs) have advantages as antiviral therapeutics (e.g., high expression yield and robustness for storage and transportation) and also potential limitations (e.g., low antigen-binding affinity and fast renal clearance). Here, we have developed novel Nbs that specifically target the receptor-binding domain (RBD) of MERS-CoV spike protein. They bind to a conserved site on MERS-CoV RBD with high affinity, blocking RBD's binding to MERS-CoV receptor. Through engineering a C-terminal human Fc tag, the in vivo half-life of the Nbs is significantly extended. Moreover, the Nbs can potently cross-neutralize the infections of diverse MERS-CoV strains isolated from humans and camels. The Fc-tagged Nb also completely protects humanized mice from lethal MERS-CoV challenge. Taken together, our study has discovered novel Nbs that hold promise as potent, cost-effective, and broad-spectrum anti-MERS-CoV therapeutic agents.

Evolution of Therapeutic Antibodies, Influenza Virus Biology, Influenza, and Influenza Immunotherapy

This narrative review article summarizes past and current technologies for generating antibodies for passive immunization/immunotherapy. Contemporary DNA and protein technologies have facilitated the development of engineered therapeutic monoclonal antibodies in a variety of formats according to the required effector functions. Chimeric, humanized, and human monoclonal antibodies to antigenic/epitopic myriads with less immunogenicity than animal-derived antibodies in human recipients can be produced in vitro. Immunotherapy with ready-to-use antibodies has gained wide acceptance as a powerful treatment against both infectious and noninfectious diseases. Influenza, a highly contagious disease, precipitates annual epidemics and occasional pandemics, resulting in high health and economic burden worldwide. Currently available drugs are becoming less and less effective against this rapidly mutating virus. Alternative treatment strategies are needed, particularly for individuals at high risk for severe morbidity. In a setting where vaccines are not yet protective or available, human antibodies that are broadly effective against various influenza subtypes could be highly efficacious in lowering morbidity and mortality and controlling unprecedented epidemic/pandemic. Prototypes of human single-chain antibodies to several conserved proteins of influenza virus with no Fc portion (hence, no ADE effect in recipients) are available. These antibodies have high potential as a novel, safe, and effective anti-influenza agent.

Suppression of Breast Cancer Cell Proliferation by Selective Single-Domain Antibody for Intracellular STAT3

Background:

The serendipitous discovery of heavy-chain antibodies devoid of light chains in camelids and the subsequent development of VHHs (variable region of camelid heavy chain) have provided a very important tool for research and possibly for therapeutics. In this study, we synthesized single-domain 15-kDa antibody SBT-100 (anti-STAT3 B VHH13) against human STAT3 (signal transducer and activator of transcription) that binds selectively to STAT3 and suppresses the function of phosphorylated STAT3 (p-STAT3).

Methods:

Single-chain VHH nanobodies were generated by immunizing camelid with humanized STAT3. Commercially available breast cancer cell lines including MDA-MB-231, MDA-MB-468, MDA-MB-453, MCF-7, and BT474 were used. Cell proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The association of anti-STAT3 B VHH13 with STAT3 and p-STAT3 was determined by immunoprecipitation and Western blot analyses. The efficacy of SBT-100 on the growth of MDA-MB-231 xenografts in vivo was determined using athymic mice. Statistical significance for cell proliferation was determined using analysis of variance. If a significant difference (P < .05) was observed, then Tukey-Kramer multiple comparison test was conducted.

Results:

SBT-100 suppressed cell proliferation of triple-negative breast cancer cells (P < .01) as well as provided significant inhibition of tumor growth (P < .05) in a xenograft model without any toxicity. Results are presented to show that anti-STAT3 B VHH13 selectively binds to STAT3 suggesting that the effects were mediated by inhibiting STAT3.

Conclusions:

A very large number of human malignancies and benign diseases have constitutive STAT3 activation. Therefore, the results described here suggest that anti-STAT3 B VHH13 can be developed for therapeutic intervention for cancer cells expressing STAT3 or p-STAT3.

Nanobody-Based Delivery Systems for Diagnosis and Targeted Tumor Therapy

The development of innovative targeted therapeutic approaches are expected to surpass the efficacy of current forms of treatments and cause less damage to healthy cells surrounding the tumor site. Since the first development of targeting agents from hybridoma’s, monoclonal antibodies (mAbs) have been employed to inhibit tumor growth and proliferation directly or to deliver effector molecules to tumor cells. However, the full potential of such a delivery strategy is hampered by the size of mAbs, which will obstruct the targeted delivery system to access the tumor tissue. By serendipity, a new kind of functional homodimeric antibody format was discovered in camelidae, known as heavy-chain antibodies (HCAbs). The cloning of the variable domain of HCAbs produces an attractive minimal-sized alternative for mAbs, referred to as VHH or nanobodies (Nbs). Apart from their dimensions in the single digit nanometer range, the unique characteristics of Nbs combine a high stability and solubility, low immunogenicity and excellent affinity and specificity against all possible targets including tumor markers. This stimulated the development of tumor-targeted therapeutic strategies. Some autonomous Nbs have been shown to act as antagonistic drugs, but more importantly, the targeting capacity of Nbs has been exploited to create drug delivery systems. Obviously, Nb-based targeted cancer therapy is mainly focused toward extracellular tumor markers, since the membrane barrier prevents antibodies to reach the most promising intracellular tumor markers. Potential strategies, such as lentiviral vectors and bacterial type 3 secretion system, are proposed to deliver target-specific Nbs into tumor cells and to block tumor markers intracellularly. Simultaneously, Nbs have also been employed for in vivo molecular imaging to diagnose diseased tissues and to monitor the treatment effects. Here, we review the state of the art and focus on recent developments with Nbs as targeting moieties for drug delivery systems in cancer therapy and cancer imaging.

Institute collection and analysis of Nanobodies (iCAN): a comprehensive database and analysis platform for nanobodies

BACKGROUND

Nanobodies are single-domain antibodies that contain the unique structural and functional properties of naturally-occurring heavy chain in camelidae. As a novel class of antibody, they show many advantages compared with traditional antibodies such as smaller size, higher stability, improved specificity, more easily expressed in microorganisms. These unusual hallmarks make them as promising tools in basic research and clinical practice. Although thousands of nanobodies are known to be published, no single database provides searchable, unified annotation and integrative analysis tools for these various nanobodies.

RESULTS

Here, we present the database of Institute Collection and Analysis of Nanobodies (iCAN). It is built for the aim that addressing the above gap to expand and accelerate the nanobody research. iCAN, as the first database of nanobody, contains the most comprehensive information to date on nanobodies and related antigens. So far, iCAN incorporates 2391 entries which include 2131 from patents and 260 from publications and provides a simple user interface for researchers to retrieve and view the detailed information of nanobodies. In addition to the data collection, iCAN also provides online bioinformatic tools for sequence analysis and characteristic feature extraction.

CONCLUSIONS

In summary, iCAN enables researchers to analyze nanobody features and explore the applications of nanobodies more efficiently. iCAN is freely available at http://ican.ils.seu.edu.cn .

Rituximab as first-line treatment for acquired thrombotic thrombocytopenic purpura

Objective To investigate the efficacy and safety of rituximab (RTX) as first-line treatment of acquired thrombotic thrombocytopenic purpura (aTTP). Methods Twenty-five patients with acute aTTP and/or severe a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) deficiency were admitted to our centre from April 2009 to March 2015. Fourteen patients received RTX plus standard therapy (plasma exchange and corticosteroids) at acute episodes. Haemoglobin, platelet count, schistocytes, lactate dehydrogenase levels, ADAMTS13 activity and its inhibitors, and the ratio of B lymphocytes in the peripheral blood, were monitored. The number of plasma exchange (PEXs), total plasma volume, remission time, relapse ratio, and adverse effects were recorded. Results The median number of PEXs was 5 (2-17) sessions and median total plasma volume was 168.43 ml/kg (62.86-469.52 ml/kg). Patients achieved haematological remission at a median of 15 days (5-22 days), and the median time of immunological remission was 2 weeks (2-8 weeks) with a median follow-up of 13 months (3-61 months). ADAMTS13 activity significantly increased after 2 weeks. The B lymphocyte percentage in peripheral blood was reduced 1 week after the first dose of RTX infusion compared with before treatment (2.21% ± 5.23% vs 18.47% ± 7.34%, P = 0.000 [the result of statistical software]), and began to gradually increase 9 months later. Severe adverse effects and relapsing TTP were not observed during therapy and follow-up. However, one patient who had sustained immunological remission died of severe pneumonia 7 months later. Conclusion Although our study was limited by its small sample number and it was a non-controlled, clinical trial, it showed potential benefits of RTX therapy for acute aTTP. RTX may be administered as a first-line therapy for lowering patients' relapse rate in the long term. Randomized, controlled trials of RTX for aTTP are required.

Therapeutic efficacy of the platelet glycoprotein Ib antagonist anfibatide in murine models of thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP), a potentially fatal blood clot disorder, is primarily caused by severe deficiency of plasma ADAMTS13 activity resulting from acquired autoantibodies. Plasma exchange is the only effective initial therapy. However, the high mortality rate and the complications associated with plasma exchange therapy remain a major concern. To address unmet clinical needs, therapeutic efficacies of anfibatide, a snake venom-derived platelet glycoprotein Ib antagonist, in murine models of spontaneous thrombocytopenia and shigatoxin-induced TTP were determined. A light scattering platelet aggregometry, microfluidic shear-based assay, and murine models of TTP were used in the study. We showed that purified anfibatide inhibits ristocetin- or botrocetin-induced human or murine platelet agglutination in the presence of von Willebrand factor in a concentration-dependent manner. Anfibatide could also dramatically inhibit the adhesion and aggregation of murine and human platelets on a collagen surface under arterial shear stress, in the presence or absence of plasma ADAMTS13 activity. Most importantly, we demonstrated that an intraperitoneal administration of anfibatide at the dose of 60 ng/g body weight twice daily mitigated spontaneous thrombocytopenia and prevented shigatoxin-induced TTP in Adamts13^-/- and disease-susceptible mice (CAST/Ei strain). Thus, we conclude that anfibatide, when administered at the optimal dosage, route, and interval, is efficacious in treating spontaneous and bacterial shigatoxin-induced TTP in the murine models. Our findings may provide the basis for further development of anfibatide for the treatment of acute TTP in humans.

Camelid and shark single domain antibodies: structural features and therapeutic potential

In addition to canonical antibodies composed of heavy and light chains, the adaptive immune systems of camelids and cartilaginous fish comprise heavy-chain only isotypes (HcAb) devoid of light chains, where antigen-binding is mediated exclusively by one variable domain. Due to their inherent favorable attributes, such as high affinity and specificity for their cognate antigen, extraordinary stability, small size and, most importantly, the possibility to complement classical antibodies in terms of 'drugable' target-space, HcAb-derived entities evolved as promising candidates for biomedical applications of which many have already proven to be successful in early stage clinical trials.

Global analysis of VHHs framework regions with a structural alphabet

The VHHs are antigen-binding region/domain of camelid heavy chain antibodies (HCAb). They have many interesting biotechnological and biomedical properties due to their small size, high solubility and stability, and high affinity and specificity for their antigens. HCAb and classical IgGs are evolutionary related and share a common fold. VHHs are composed of regions considered as constant, called the frameworks (FRs) connected by Complementarity Determining Regions (CDRs), a highly variable region that provide interaction with the epitope. Actually, no systematic structural analyses had been performed on VHH structures despite a significant number of structures. This work is the first study to analyse the structural diversity of FRs of VHHs. Using a structural alphabet that allows approximating the local conformation, we show that each of the four FRs do not have a unique structure but exhibit many structural variant patterns. Moreover, no direct simple link between the local conformational change and amino acid composition can be detected. These results indicate that long-range interactions affect the local conformation of FRs and impact the building of structural models.

Generation of Anti-Murine ADAMTS13 Antibodies and Their Application in a Mouse Model for Acquired Thrombotic Thrombocytopenic Purpura

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening thrombotic microangiopathy linked to a deficiency in the metalloprotease ADAMTS13. In the current study, a novel mouse model for acquired TTP was generated to facilitate development and validation of new therapies for this disease. Therefore, a large panel (n = 19) of novel anti-mouse ADAMTS13 (mADAMTS13) monoclonal antibodies (mAbs) of mouse origin was generated. Inhibitory anti-mADAMTS13 mAbs were identified using the FRETS-VWF73 assay. Four mAbs strongly inhibited mADAMTS13 activity in vitro (∼68–90% inhibition). Injecting a combination of 2 inhibitory mAbs (13B4 and 14H7, 1.25 mg/kg each) in Adamts13^+/+ mice resulted in full inhibition of plasma ADAMTS13 activity (96 ± 4% inhibition, day 1 post injection), leading to the appearance of ultra-large von Willebrand factor (UL-VWF) multimers. Interestingly, the inhibitory anti-mADAMTS13 mAbs 13B4 and 14H7 were ideally suited to induce long-term ADAMTS13 deficiency in Adamts13^+/+ mice. A single bolus injection resulted in full ex vivo inhibition for more than 7 days. As expected, the mice with the acquired ADAMTS13 deficiency did not spontaneously develop TTP, despite the accumulation of UL-VWF multimers. In line with the Adamts13^-/- mice, TTP-like symptoms could only be induced when an additional trigger (rVWF) was administered. On the other hand, the availability of our panel of anti-mADAMTS13 mAbs allowed us to further develop a sensitive ELISA to detect ADAMTS13 in mouse plasma. In conclusion, a novel acquired TTP mouse model was generated through the development of inhibitory anti-mADAMTS13 mAbs. Consequently, this model provides new opportunities for the development and validation of novel treatments for patients with TTP. In addition, these newly developed inhibitory anti-mADAMTS13 mAbs are of great value to specifically study the role of ADAMTS13 in mouse models of thrombo-inflammatory disease.

Nanobody-derived nanobiotechnology tool kits for diverse biomedical and biotechnology applications

Owing to peculiar properties of nanobody, including nanoscale size, robust structure, stable and soluble behaviors in aqueous solution, reversible refolding, high affinity and specificity for only one cognate target, superior cryptic cleft accessibility, and deep tissue penetration, as well as a sustainable source, it has been an ideal research tool for the development of sophisticated nanobiotechnologies. Currently, the nanobody has been evolved into versatile research and application tool kits for diverse biomedical and biotechnology applications. Various nanobody-derived formats, including the nanobody itself, the radionuclide or fluorescent-labeled nanobodies, nanobody homo- or heteromultimers, nanobody-coated nanoparticles, and nanobody-displayed bacteriophages, have been successfully demonstrated as powerful nanobiotechnological tool kits for basic biomedical research, targeting drug delivery and therapy, disease diagnosis, bioimaging, and agricultural and plant protection. These applications indicate a special advantage of these nanobody-derived technologies, already surpassing the “me-too” products of other equivalent binders, such as the full-length antibodies, single-chain variable fragments, antigen-binding fragments, targeting peptides, and DNA-based aptamers. In this review, we summarize the current state of the art in nanobody research, focusing on the nanobody structural features, nanobody production approach, nanobody-derived nanobiotechnology tool kits, and the potentially diverse applications in biomedicine and biotechnology. The future trends, challenges, and limitations of the nanobody-derived nanobiotechnology tool kits are also discussed.

[Hemolytic anemia]

Hemolytic anemia can be caused by various hereditary or acquired diseases. Classification is usually based on corpuscular or extracorpuscular defects. Beside the anemia, laboratory testing indicates increased lactate dehydrogenase, unconjugated bilirubin and reticulocytes as well as reduced or absent plasma haptoglobin. Knowledge of further diagnostic procedures (e.g., Coombs test, schistocytes, hemoglobin electrophoresis or flow cytometric analysis) leads in many cases to an underlying disease with differentiated therapeutic options. Autoimmune hemolytic anemia (AIHA) is often associated with diseases as HIV, connective tissue disease, lymphomas or malignant tumors and the hemolytic process is preexisting in many cases. Thrombotic microvascular diseases (e.g., thrombotic thrombocytopenic purpura or hemolytic-uremic syndrome) are further important causes of hemolytic anemia which need immediate diagnosis and treatment.

The VWF-GPIb axis in ischaemic stroke: lessons from animal models

Stroke is a leading cause of death and long-term disability worldwide. Ischaemic stroke is caused by a blood clot that obstructs cerebral blood flow. Current treatment mainly consists of achieving fast reperfusion, either via pharmacological thrombolysis using tissue plasminogen activator or via endovascular thrombectomy. Unfortunately, reperfusion therapy is only available to a limited group of patients and reperfusion injury can further aggravate brain damage. Hence, there is an urgent need for better understanding of ischaemic stroke pathophysiology in order to develop novel therapeutic strategies. In recent years, the pathophysiological importance of von Willebrand factor (VWF) in ischaemic stroke has become clear from both clinical and experimental studies. In particular, binding of VWF to platelet glycoprotein Ib (GPIb) has become an interesting target for ischaemic stroke therapy. Recent insights show that inhibting the VWF-GPIb interaction could result in a pro-thrombolytic activity improving cerebral reperfusion rates and concurrently reducing cerebral ischaemia/reperfusion damage. This review gives an overview of the experimental evidence that illustrates the crucial role of the VWF-GPIb axis in ischaemic stroke.

[Clinical study on Rituximab in the treatment of idiopathic thrombotic thrombocytopenic purpura]

目的

观察利妥昔单抗（RTX）在特发性血栓性血小板减少性紫癜(ITTP)治疗中的价值。

方法

17例ITTP患者中9例采用RTX＋血浆置换＋糖皮质激素治疗（RTX组），8例采用血浆置换+糖皮质激素±免疫抑制剂（对照组）。RTX用法为375 mg/m²每周1次连续4次。监测患者血常规、LDH、ADAMTS13活性及抑制物、外周血B淋巴细胞百分比。观察两组患者的血浆置换次数/总量、缓解时间、复发率及不良反应发生情况。

结果

RTX组、对照组血浆置换次数中位数分别为5(2~8)、6(4~9）次，血浆置换总量中位数分别为9.6(4.0~15.4)、11.2(7.5~14.6)L。RTX组、对照组达到血液学缓解中位时间分别为15(5~20)d、22(7~36)d，达到免疫学缓解中位时间分别为2(2~8)、2(2~4）周。两组患者ADAMTS13活性均在2周后显著回升。RTX组随访期内无复发，对照组4例患者复发。RTX给药前及治疗后1周患者外周血B淋巴细胞百分比差异有统计学意义[(18.39±7.15)％对(2.19±5.11)%，P<0.001], 9个月后逐渐回升，治疗中未观察到RTX相关严重不良反应，但该组1例患者持续免疫学缓解7个月后死于肺部感染。

结论

RTX联合血浆置换和糖皮质激素治疗ITTP，能快速获得血液学甚至免疫学缓解，降低复发率，不良反应少，但需注意防治感染。

Structural insights and biomedical potential of IgNAR scaffolds from sharks

In addition to antibodies with the classical composition of heavy and light chains, the adaptive immune repertoire of sharks also includes a heavy-chain only isotype, where antigen binding is mediated exclusively by a small and highly stable domain, referred to as vNAR. In recent years, due to their high affinity and specificity combined with their small size, high physicochemical stability and low-cost of production, vNAR fragments have evolved as promising target-binding scaffolds that can be tailor-made for applications in medicine and biotechnology. This review highlights the structural features of vNAR molecules, addresses aspects of their generation using immunization or in vitro high throughput screening methods and provides examples of therapeutic, diagnostic and other biotechnological applications.

Nanobodies for targeted treatment of gastric cancer

With the development and application of monoclonal antibody-based targeted therapy drugs in recent years, some achievements have been made in the treatment of gastric cancer; however, because their preparation is relatively complex and expensive, their application is limited. Nanobodies have some advantages over conventional molecular targeted drugs, such as small molecular weight and unique structural features, and provide a new treatment strategy for targeted therapy of gastric cancer. In this paper, we review the nanobodies that have the potential for targeted treatment of gastric cancer.

Acquired thrombotic thrombocytopenic purpura: new therapeutic options and their optimal use

Advances in our understanding of the pathophysiology of both congenital and acquired thrombotic thrombocytopenic purpura (TTP) have led to both an increased understanding of the disease and novel approaches to therapy. The efficacy of rituximab in acquired TTP has led to consideration of rituximab as a prophylactic therapy to prevent relapse of TTP. Novel therapies that target the A1 domain of von Willebrand factor (VWF) to block the formation of microthrombotic disease have also entered clinical study and have demonstrated promise as potential therapeutic options. Additionally, a recombinant ADAMTS13 protease has been developed which may be an important therapeutic option for both congenital and acquired TTP. The development of these new therapeutic options for patients diagnosed with TTP has increased the importance of conducting prospective, randomized studies with these agents to both confirm their efficacy and more importantly understand their most appropriate role in the treatment of patients with TTP.

Single domain antibodies as a powerful tool for high quality surface plasmon resonance studies

Single domain antibodies are recombinantly expressed functional antibodies devoid of light chains. These binding elements are derived from heavy chain antibodies found in camelids and offer several distinctive properties for applications in biotechnology such as small size, stability, solubility, and expression in high yields. In this study we demonstrated the potential of using single domain antibodies as capturing molecules in biosensing applications. Single domain antibodies raised against green fluorescent protein were anchored onto biosensor surfaces by using several immobilization strategies based on Ni2+:nitrilotriacetic acid-polyhistidine tag, antibody-antigen, biotin-streptavidin interactions and amine-coupling chemistry. The interaction with the specific target of the single domain antibodies was characterized by surface plasmon resonance. The immobilized single domain antibodies show high affinities for their antigens with KD = 3-6 nM and outperform other antibody partners as capturing molecules facilitating also the data analysis. Furthermore they offer high resistance and stability to a wide range of denaturing agents. These unique biophysical properties and the production of novel single domain antibodies against affinity tags make them particularly attractive for use in biosensing and diagnostic assays.

Cardiac troponin-I on diagnosis predicts early death and refractoriness in acquired thrombotic thrombocytopenic purpura. Experience of the French Thrombotic Microangiopathies Reference Center

BACKGROUND

Cardiac involvement is a major cause of mortality in patients with thrombotic thrombocytopenic purpura (TTP). However, diagnosis remains underestimated and delayed, owing to subclinical injuries. Cardiac troponin-I measurement (cTnI) on admission could improve the early diagnosis of cardiac involvement and have prognostic value.

OBJECTIVES

To assess the predictive value of cTnI in patients with TTP for death or refractoriness.

PATIENTS/METHODS

The study involved a prospective cohort of adult TTP patients with acquired severe ADAMTS-13 deficiency (< 10%) and included in the registry of the French Reference Center for Thrombotic Microangiopathies. Centralized cTnI measurements were performed on frozen serum on admission.

RESULTS

Between January 2003 and December 2011, 133 patients with TTP (mean age, 48 ± 17 years) had available cTnI measurements on admission. Thirty-two patients (24%) had clinical and/or electrocardiogram features. Nineteen (14.3%) had cardiac symptoms, mainly congestive heart failure and myocardial infarction. Electrocardiogram changes, mainly repolarization disorders, were present in 13 cases. An increased cTnI level (> 0.1 μg L(-1) ) was present in 78 patients (59%), of whom 46 (59%) had no clinical cardiac involvement. The main outcomes were death (25%) and refractoriness (17%). Age (P = 0.02) and cTnI level (P = 0.002) showed the greatest impact on survival. A cTnI level of > 0.25 μg L(-1) was the only independent factor in predicting death (odds ratio [OR] 2.87; 95% confidence interval [CI] 1.13-7.22; P = 0.024) and/or refractoriness (OR 3.03; 95% CI 1.27-7.3; P = 0.01).

CONCLUSIONS

A CTnI level of > 0.25 μg L(-1) at presentation in patients with TTP appears to be an independent factor associated with a three-fold increase in the risk of death or refractoriness. Therefore, cTnI level should be considered as a prognostic indicator in patients diagnosed with TTP.

Animal models for thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a puzzling disorder in many ways. The disease is difficult to diagnose as analogous symptoms are also found in other microangiopathic disorders. Although ADAMTS13 deficiency is generally required to develop TTP, only some patients with severe ADAMTS13 deficiency do spontaneously develop this disease. It is therefore assumed that environmental and/or genetic factors are needed to cause acute TTP. Nevertheless, acute TTP-like symptoms have also been observed in patients with moderate or normal levels of ADAMTS13. The development of animal models for TTP has allowed a closer look at the specific need for ADAMTS13 deficiency and the necessity for additional triggers in the pathophysiology of TTP. Mouse models for congenital TTP and a baboon model for acquired TTP have been generated. These animal models have also proven to be extremely valuable in developing new treatment strategies for TTP. In the current review, we discuss current animal models for TTP, what we have learned from them and how they were used to test new treatment strategies.

Nanobodies: natural single-domain antibodies

Sera of camelids contain both conventional heterotetrameric antibodies and unique functional heavy (H)-chain antibodies (HCAbs). The H chain of these homodimeric antibodies consists of one antigen-binding domain, the VHH, and two constant domains. HCAbs fail to incorporate light (L) chains owing to the deletion of the first constant domain and a reshaped surface at the VHH side, which normally associates with L chains in conventional antibodies. The genetic elements composing HCAbs have been identified, but the in vivo generation of these antibodies from their dedicated genes into antigen-specific and affinity-matured bona fide antibodies remains largely underinvestigated. However, the facile identification of antigen-specific VHHs and their beneficial biochemical and economic properties (size, affinity, specificity, stability, production cost) supported by multiple crystal structures have encouraged antibody engineering of these single-domain antibodies for use as a research tool and in biotechnology and medicine.

Novel antiplatelet agents: ALX-0081, a Nanobody directed towards von Willebrand factor

This manuscript reviews the studies performed with ALX-0081 (INN: caplacizumab), a Nanobody targeting von Willebrand factor, in the context of current antithrombotic therapy in coronary artery disease. ALX-0081 specifically inhibits platelet adhesion to the vessel wall, and may control platelet aggregation and subsequent clot formation without increasing bleeding risk. A substantial number of antithrombotics are aimed at this cascade; however, their generally indiscriminative mode of action can result in a narrow therapeutic window, defined by the risk for bleeding complications, and thrombotic events. Nonclinically, ALX-0081 compared favorably to several antithrombotics. In Phase I studies in healthy subjects and stable angina patients undergoing percutaneous coronary intervention (PCI), ALX-0081 was well tolerated, and effectively inhibited pharmacodynamic markers. Following these results, a phase II study was initiated in high-risk acute coronary syndrome patients undergoing PCI. Based on its mechanism of action, ALX-0081 is also being developed for acquired thrombotic thrombocytopenic purpura.

Antigen and substrate withdrawal in the management of autoimmune thrombotic disorders

Prevailing approaches to manage autoimmune thrombotic disorders, such as heparin-induced thrombocytopenia, antiphospholipid syndrome and thrombotic thrombocytopenic purpura, include immunosuppression and systemic anticoagulation, though neither provides optimal outcome for many patients. A different approach is suggested by the concurrence of autoantibodies and their antigenic targets in the absence of clinical disease, such as platelet factor 4 in heparin-induced thrombocytopenia and β(2)-glycoprotein-I (β(2)GPI) in antiphospholipid syndrome. The presence of autoantibodies in the absence of disease suggests that conformational changes or other alterations in endogenous protein autoantigens are required for recognition by pathogenic autoantibodies. In thrombotic thrombocytopenic purpura, the clinical impact of ADAMTS13 deficiency caused by autoantibodies likely depends on the balance between residual antigen, that is, enzyme activity, and demand imposed by local genesis of ultralarge multimers of von Willebrand factor. A corollary of these concepts is that disrupting platelet factor 4 and β(2)GPI conformation (or ultralarge multimer of von Willebrand factor oligomerization or function) might provide a disease-targeted approach to prevent thrombosis without systemic anticoagulation or immunosuppression. Validation of this approach requires a deeper understanding of how seemingly normal host proteins become antigenic or undergo changes that increase antibody avidity, and how they can be altered to retain adaptive functions while shedding epitopes prone to elicit harmful autoimmunity.