Recombinant human Fab to glycoprotein D neutralizes infectivity and prevents cell-to-cell transmission of herpes simplex viruses 1 and 2 in vitro

Applications of the phage display technology in molecular biology, biotechnology and medicine

The phage display technology is based on the presentation of peptide sequences on the surface of virions of bacteriophages. Its development led to creation of sophisticated systems based on the possibility of the presentation of a huge variability of peptides, attached to one of proteins of bacteriophage capsids. The use of such systems allowed for achieving enormous advantages in the processes of selection of bioactive molecules. In fact, the phage display technology has been employed in numerous fields of biotechnology, as diverse as immunological and biomedical applications (in both diagnostics and therapy), the formation of novel materials, and many others. In this paper, contrary to many other review articles which were focussed on either specific display systems or the use of phage display in selected fields, we present a comprehensive overview of various possibilities of applications of this technology. We discuss an usefulness of the phage display technology in various fields of science, medicine and the broad sense of biotechnology. This overview indicates the spread and importance of applications of microbial systems (exemplified by the phage display technology), pointing to the possibility of developing such sophisticated tools when advanced molecular methods are used in microbiological studies, accompanied with understanding of details of structures and functions of microbial entities (bacteriophages in this case).

Effector functions are required for broad and potent protection of neonatal mice with antibodies targeting HSV glycoprotein D

Multiple failed herpes simplex virus (HSV) vaccine candidates induce robust neutralizing antibody (Ab) responses in clinical trials, raising the hypothesis that Fc-domain-dependent effector functions may be critical for protection. While neonatal HSV (nHSV) infection results in mortality and lifelong neurological morbidity in humans, it is uncommon among neonates with a seropositive birthing parent, supporting the hypothesis that Ab-based therapeutics could protect neonates from HSV. We therefore investigated the mechanisms of monoclonal Ab (mAb)-mediated protection in a mouse model of nHSV infection. For a panel of glycoprotein D (gD)-specific mAbs, neutralization and effector functions contributed to nHSV-1 protection. In contrast, effector functions alone were sufficient to protect against nHSV-2, exposing a functional dichotomy between virus types consistent with vaccine trial results. Effector functions are therefore crucial for protection by these gD-specific mAbs, informing effective Ab and vaccine design and demonstrating the potential of polyfunctional Abs as therapeutics for nHSV infections.

Progress on Phage Display Technology: Tailoring Antibodies for Cancer Immunotherapy

The search for innovative anti-cancer drugs remains a challenge. Over the past three decades, antibodies have emerged as an essential asset in successful cancer therapy. The major obstacle in developing anti-cancer antibodies is the need for non-immunogenic antibodies against human antigens. This unique requirement highlights a disadvantage to using traditional hybridoma technology and thus demands alternative approaches, such as humanizing murine monoclonal antibodies. To overcome these hurdles, human monoclonal antibodies can be obtained directly from Phage Display libraries, a groundbreaking tool for antibody selection. These libraries consist of genetically engineered viruses, or phages, which can exhibit antibody fragments, such as scFv or Fab on their capsid. This innovation allows the in vitro selection of novel molecules directed towards cancer antigens. As foreseen when Phage Display was first described, nowadays, several Phage Display-derived antibodies have entered clinical settings or are undergoing clinical evaluation. This comprehensive review unveils the remarkable progress in this field and the possibilities of using clever strategies for phage selection and tailoring the refinement of antibodies aimed at increasingly specific targets. Moreover, the use of selected antibodies in cutting-edge formats is discussed, such as CAR (chimeric antigen receptor) in CAR T-cell therapy or ADC (antibody drug conjugate), amplifying the spectrum of potential therapeutic avenues.

Maternally transferred mAbs protect neonatal mice from HSV-induced mortality and morbidity

Neonatal herpes simplex virus (nHSV) infections often result in significant mortality and neurological morbidity despite antiviral drug therapy. Maternally transferred herpes simplex virus (HSV)-specific antibodies reduce the risk of clinically overt nHSV, but this observation has not been translationally applied. Using a neonatal mouse model, we tested the hypothesis that passive transfer of HSV-specific human mAbs can prevent mortality and morbidity associated with nHSV. The mAbs were expressed in vivo via vectored immunoprophylaxis or recombinantly. Through these maternally derived routes or through direct administration to pups, diverse mAbs to HSV glycoprotein D protected against neonatal HSV-1 and HSV-2 infection. Using in vivo bioluminescent imaging, both pre- and post-exposure mAb treatment significantly reduced viral load in mouse pups. Together these studies support the notion that HSV-specific mAb-based therapies could prevent or improve HSV infection outcomes in neonates.

Monoclonal antibody therapy of herpes simplex virus: An opportunity to decrease congenital and perinatal infections

The fetal/neonatal period represents both a unique window of opportunity for interventions as well as vulnerability to a number of viral infections. While Herpesviruses such as herpes simplex virus (HSV) are highly prevalent and typically of little consequence among healthy adults, they are among the most consequential infections of early life. Despite treatment with antiviral drugs, neonatal HSV (nHSV) infections can still result in significant mortality and lifelong neurological morbidity. Fortunately, newborns in our pathogen-rich world inherit some of the protection provided by the maternal immune system in the form of transferred antibodies. Maternal seropositivity, resulting in placental transfer of antibodies capable of neutralizing virus and eliciting the diverse effector functions of the innate immune system are associated with dramatically decreased risk of nHSV. Given this clear epidemiological evidence of reduced risk of infection and its sequelae, we present what is known about the ability of monoclonal antibody therapies to treat or prevent HSV infection and explore how effective antibody-based interventions in conjunction with antiviral therapy might reduce early life mortality and long-term morbidity.

Developing Recombinant Antibodies by Phage Display Against Infectious Diseases and Toxins for Diagnostics and Therapy

Antibodies are essential molecules for diagnosis and treatment of diseases caused by pathogens and their toxins. Antibodies were integrated in our medical repertoire against infectious diseases more than hundred years ago by using animal sera to treat tetanus and diphtheria. In these days, most developed therapeutic antibodies target cancer or autoimmune diseases. The COVID-19 pandemic was a reminder about the importance of antibodies for therapy against infectious diseases. While monoclonal antibodies could be generated by hybridoma technology since the 70ies of the former century, nowadays antibody phage display, among other display technologies, is robustly established to discover new human monoclonal antibodies. Phage display is an in vitro technology which confers the potential for generating antibodies from universal libraries against any conceivable molecule of sufficient size and omits the limitations of the immune systems. If convalescent patients or immunized/infected animals are available, it is possible to construct immune phage display libraries to select in vivo affinity-matured antibodies. A further advantage is the availability of the DNA sequence encoding the phage displayed antibody fragment, which is packaged in the phage particles. Therefore, the selected antibody fragments can be rapidly further engineered in any needed antibody format according to the requirements of the final application. In this review, we present an overview of phage display derived recombinant antibodies against bacterial, viral and eukaryotic pathogens, as well as microbial toxins, intended for diagnostic and therapeutic applications.

Safety, acceptability, and pharmacokinetics of a monoclonal antibody-based vaginal multipurpose prevention film (MB66): A Phase I randomized trial

BACKGROUND

MB66 film is a multipurpose prevention technology (MPT) product with monoclonal antibodies (mAbs) against HIV-1 (VRC01-N) and HSV-1 and 2 (HSV8-N). The mAbs were produced by transient expression in Nicotiana benthamiana (N). We conducted a Phase I clinical trial to assess the safety, pharmacokinetics (PK), and ex vivo efficacy of single and repeated doses of MB66 when used intravaginally.

METHODS AND FINDINGS

The clinical trial enrolled healthy reproductive-aged, sexually abstinent women. In Segment A, 9 women received a single MB66 film which was inserted into the vaginal posterior fornix by a clinician. In Segment B, 29 women were randomly assigned to MB66 (Active) or Placebo film groups and were instructed to insert 1 film vaginally for 7 consecutive days. Visits and clinical sampling occurred predose and at various time points after single and repeated film doses. The primary endpoint was number of adverse events (AEs) Grade 2 or higher related to product use. Secondary endpoints included film dissolution rate, Nugent score (a Gram stain scoring system to diagnose bacterial vaginosis), vaginal pH, post-use survey results, cytokine concentrations in cervicovaginal lavage (CVL) specimens (assessed by Luminex assay), mAb concentrations in vaginal fluid collected from 4 sites (assessed by ELISA), and HIV and HSV neutralization activity of CVL samples ex vivo (assessed by TZM-bl and plaque reduction assay, respectively). The product was generally safe and well tolerated, with no serious AEs recorded in either segment. The AEs in this study were primarily genitourinary in nature with the most commonly reported AE being asymptomatic microscopic hematuria. There were no differences in vaginal pH or Nugent scores or significant increases in levels of proinflammatory cytokines for up to 7 days after film insertion in either segment or between Active and Placebo groups. Acceptability and willingness to use the product were judged to be high by post-use surveys. Concentrations of VRC01-N and HSV8-N in vaginal secretions were assessed over time to generate pharmacokinetic curves. Antibody levels peaked 1 hour postdosing with Active film (median: 35 μg/mL) and remained significantly elevated at 24 hours post first and seventh film (median: 1.8 μg/mL). Correcting for sample dilution (1:20), VRC01-N concentrations ranged from 36 to 700 μg/mL at the 24-hour time point, greater than 100-fold the IC50 for VRC01 (0.32 μg/mL); HSV8-N concentrations ranged from 80 to 601 μg/mL, well above the IC50 of 0.1 μg/m. CVL samples collected 24 hours after MB66 insertion significantly neutralized both HIV-1 and HSV-2 ex vivo. Study limitations include the small size of the study cohort, and the fact that no samples were collected between 24 hours and 7 days for pharmacokinetic evaluation.

CONCLUSIONS

Single and repeated intravaginal applications of MB66 film were safe, well tolerated, and acceptable. Concentrations and ex vivo bioactivity of both mAbs in vaginal secretions were significantly elevated and thus could provide protection for at least 24 hours postdose. However, further research is needed to evaluate the efficacy of MB66 film in women at risk for HIV and HSV infection. Additional antibodies could be added to this platform to provide protection against other sexually transmitted infections (STIs) and contraception.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02579083.

Infectious disease antibodies for biomedical applications: A mini review of immune antibody phage library repertoire

Antibody phage display is regarded as a critical tool for the development of monoclonal antibodies for infectious diseases. The different classes of antibody libraries are classified based on the source of repertoire used to generate the libraries. Immune antibody libraries are generated from disease infected host or immunization against an infectious agent. Antibodies derived from immune libraries are distinct from those derived from naïve libraries as the host's in vivo immune mechanisms shape the antibody repertoire to yield high affinity antibodies. As the immune system is constantly evolving in accordance to the health state of an individual, immune libraries can offer more than just infection-specific antibodies but also antibodies derived from the memory B-cells much like naïve libraries. The combinatorial nature of the gene cloning process would give rise to a combination of natural and un-natural antibody gene pairings in the immune library. These factors have a profound impact on the coverage of immune antibody libraries to target both disease-specific and non-disease specific antigens. This review looks at the diverse nature of antibody responses for immune library generation and discusses the extended potential of a disease-specified immune library in the context of phage display.

Bacteriophages and Their Immunological Applications against Infectious Threats

Bacteriophage therapy dates back almost a century, but the discovery of antibiotics led to a rapid decline in the interests and investments within this field of research. Recently, the novel threat of multidrug-resistant bacteria highlighted the alarming drop in research and development of new antibiotics: 16 molecules were discovered during 1983–87, 10 new therapeutics during the nineties, and only 5 between 2003 and 2007. Phages are therefore being reconsidered as alternative therapeutics. Phage display technique has proved to be extremely promising for the identification of effective antibodies directed against pathogens, as well as for vaccine development. At the same time, conventional phage therapy uses lytic bacteriophages for treatment of infections and recent clinical trials have shown great potential. Moreover, several other approaches have been developed in vitro and in vivo using phage-derived proteins as antibacterial agents. Finally, their use has also been widely considered for public health surveillance, as biosensor phages can be used to detect food and water contaminations and prevent bacterial epidemics. These novel approaches strongly promote the idea that phages and their proteins can be exploited as an effective weapon in the near future, especially in a world which is on the brink of a “postantibiotic era.”

Entry inhibition of HSV-1 and -2 protects mice from viral lethal challenge

The present study focused on inhibition of HSV-1 and -2 replication and pathogenesis in vitro and in vivo, through the selective targeting of the envelope glycoprotein D. Firstly, a human monoclonal antibody (Hu-mAb#33) was identified that could neutralise both HSV-1 and -2 at nM concentrations, including clinical isolates from patients affected by different clinical manifestations and featuring different susceptibility to acyclovir in vitro. Secondly, the potency of inhibition of both infection by cell-free viruses and cell-to-cell virus transmission was also assessed. Finally, mice receiving a single systemic injection of Hu-mAb#33 were protected from death and severe clinical manifestations following both ocular and vaginal HSV-1 and -2 lethal challenge. These results pave the way for further studies reassessing the importance of HSV entry as a novel target for therapeutic intervention and inhibition of cell-to-cell virus transmission.

Recombinant antibodies for diagnostics and therapy against pathogens and toxins generated by phage display

Antibodies are valuable molecules for the diagnostic and treatment of diseases caused by pathogens and toxins. Traditionally, these antibodies are generated by hybridoma technology. An alternative to hybridoma technology is the use of antibody phage display to generate recombinant antibodies. This in vitro technology circumvents the limitations of the immune system and allows—in theory—the generation of antibodies against all conceivable molecules. Phage display technology enables obtaining human antibodies from naïve antibody gene libraries when either patients are not available or immunization is not ethically feasible. On the other hand, if patients or immunized/infected animals are available, it is common to construct immune phage display libraries to select in vivo affinity‐matured antibodies. Because the phage packaged DNA sequence encoding the antibodies is directly available, the antibodies can be smoothly engineered according to the requirements of the final application. In this review, an overview of phage display derived recombinant antibodies against bacterial, viral, and eukaryotic pathogens as well as toxins for diagnostics and therapy is given.

Phage and Yeast Display

Despite the availability of antimicrobial drugs, the continued development of microbial resistance--established through escape mutations and the emergence of resistant strains--limits their clinical utility. The discovery of novel, therapeutic, monoclonal antibodies (mAbs) offers viable clinical alternatives in the treatment and prophylaxis of infectious diseases. Human mAb-based therapies are typically nontoxic in patients and demonstrate high specificity for the intended microbial target. This specificity prevents negative impacts on the patient microbiome and avoids driving the resistance of nontarget species. The in vitro selection of human antibody fragment libraries displayed on phage or yeast surfaces represents a group of well-established technologies capable of generating human mAbs. The advantage of these forms of microbial display is the large repertoire of human antibody fragments present during a single selection campaign. Furthermore, the in vitro selection environments of microbial surface display allow for the rapid isolation of antibodies--and their encoding genes--against infectious pathogens and their toxins that are impractical within in vivo systems, such as murine hybridomas. This article focuses on the technologies of phage display and yeast display, as these strategies relate to the discovery of human mAbs for the treatment and vaccine development of infectious diseases.

Novel therapeutic investigational strategies to treat severe and disseminated HSV infections suggested by a deeper understanding of in vitro virus entry processes

The global burden of herpes simplex virus (HSV) legitimates the critical need to develop new prevention strategies, such as drugs and vaccines that are able to fight either primary HSV infections or reactivations. Moreover, the ever-growing number of patients receiving transplants increases the number of severe HSV infections that are unresponsive to current therapies. Finally, the high global incidence of genital HSV-2 infection increases the risk of perinatal transmission to newborns, in which disseminated infection or central nervous system (CNS) involvement is frequent, with associated high morbidity and mortality rates. There are several key features shared by novel anti-HSV drugs, from currently available optimized drugs to small molecules able to interfere with various virus replication steps. However, several virological aspects of the disease and associated clinical needs highlight why an ideal anti-HSV drug has yet to be developed.

The herpes virus Fc receptor gE-gI mediates antibody bipolar bridging to clear viral antigens from the cell surface

The Herpes Simplex Virus 1 (HSV-1) glycoprotein gE-gI is a transmembrane Fc receptor found on the surface of infected cells and virions that binds human immunoglobulin G (hIgG). gE-gI can also participate in antibody bipolar bridging (ABB), a process by which the antigen-binding fragments (Fabs) of the IgG bind a viral antigen while the Fc binds to gE-gI. IgG Fc binds gE-gI at basic, but not acidic, pH, suggesting that IgG bound at extracellular pH by cell surface gE-gI would dissociate and be degraded in acidic endosomes/lysosomes if endocytosed. The fate of viral antigens associated with gE-gI-bound IgG had been unknown: they could remain at the cell surface or be endocytosed with IgG. Here, we developed an in vitro model system for ABB and investigated the trafficking of ABB complexes using 4-D confocal fluorescence imaging of ABB complexes with transferrin or epidermal growth factor, well-characterized intracellular trafficking markers. Our data showed that cells expressing gE-gI and the viral antigen HSV-1 gD endocytosed anti-gD IgG and gD in a gE-gI-dependent process, resulting in lysosomal localization. These results suggest that gE-gI can mediate clearance of infected cell surfaces of anti-viral host IgG and viral antigens to evade IgG-mediated responses, representing a general mechanism for viral Fc receptors in immune evasion and viral pathogenesis.

Possible future monoclonal antibody (mAb)-based therapy against arbovirus infections

More than 150 arboviruses belonging to different families are known to infect humans, causing endemic infections as well as epidemic outbreaks. Effective vaccines to limit the occurrence of some of these infections have been licensed, while for the others several new immunogens are under development mostly for their improvements concerning safety and effectiveness profiles. On the other hand, specific and effective antiviral drugs are not yet available, posing an urgent medical need in particular for emergency cases. Neutralizing monoclonal antibodies (mAbs) have been demonstrated to be effective in the treatment of several infectious diseases as well as in preliminary in vitro and in vivo models of arbovirus-related infections. Given their specific antiviral activity as well-tolerated molecules with limited side effects, mAbs could represent a new therapeutic approach for the development of an effective treatment, as well as useful tools in the study of the host-virus interplay and in the development of more effective immunogens. However, before their use as candidate therapeutics, possible hurdles (e.g., Ab-dependent enhancement of infection, occurrence of viral escape variants) must be carefully evaluated. In this review are described the main arboviruses infecting humans and candidate mAbs to be possibly used in a future passive immunotherapy.

Non-neutralizing antibodies protect from chronic LCMV infection independently of activating FcγR or complement

Chronic viral infections lead to CD8(+) T cell exhaustion, characterized by impaired cytokine secretion. The presence of the immune-regulatory cytokine IL-10 promotes chronic lymphocytic choriomeningitis virus (LCMV) Clone 13 infection in mice, whereas the absence of IL-10/IL-10R signaling early during infection results in viral clearance and higher percentages and numbers of antiviral, cytokine-producing T cells. However, it is currently unclear which cell populations and effector molecules are crucial to protect against chronic infection. In this study, we demonstrate that antiviral, LCMV-binding, non-neutralizing antibodies are needed, in addition to CD4(+) and CD8(+) T cells, to clear a high-dose LCMV infection in mice, in the absence of IL-10. The interaction between CD4(+) T cells and B cells in B-cell follicles via CD40/CD40L, in addition to class switch and/or somatic hypermutation, is crucial for viral control in the absence of IL-10. Interestingly, transfer of LCMV-binding non-neutralizing antibodies protected recipients from chronic infection. In addition, viral clearance in the absence of IL-10R signaling was independent of activating Fcγ receptors and complement. These data highlight that non-neutralizing antibodies effectively contribute to the control of LCMV infection when present prior to infection, suggesting that the induction of neutralizing antibodies is not implicitly necessary for the generation of successful vaccines.

JC polyomavirus (JCV) and monoclonal antibodies: friends or potential foes?

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease of the central nervous system (CNS), observed in immunodeficient patients and caused by JC virus ((JCV), also called JC polyomavirus (JCPyV)). After the HIV pandemic and the introduction of immunomodulatory therapy, the PML incidence significantly increased. The correlation between the use of natalizumab, a drug used in multiple sclerosis (MS), and the PML development of particular relevance. The high incidence of PML in natalizumab-treated patients has highlighted the importance of two factors: the need of PML risk stratification among natalizumab-treated patients and the need of effective therapeutic options. In this review, we discuss these two needs under the light of the major viral models of PML etiopathogenesis.

Overcoming drug-resistant herpes simplex virus (HSV) infection by a humanized antibody

Despite the availability of antiviral chemotherapy, herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) infections remain a severe global health problem. Of particular concern is the growing incidence of drug resistance in immunocompromised patients, which stresses the urgency to develop new effective treatment alternatives. We have developed a humanized monoclonal antibody (mAb hu2c) that completely abrogates viral cell-to-cell spread, a key mechanism by which HSV-1/2 escapes humoral immune surveillance. Moreover, mAb hu2c neutralized HSV fully independent of complement and/or immune effector cell recruitment in a highly efficient manner. Prophylactic and therapeutic administration of mAb hu2c completely prevented infection-related mortality of severely immunodeficient mice being challenged with a lethal dose of HSV-1. The high neutralization capacity of mAb hu2c was fully maintained toward clinical HSV isolates being multiresistant to standard antiviral drugs, and infection was fully resolved in 7/8 nonobese diabetic/SCID mice being infected with a multidrug resistant HSV-1 patient isolate. Immunohistochemical studies revealed no significant cross-reactivity of the antibody toward human tissues. These features warrant further clinical development of mAb hu2c as an immunotherapeutic compound for the management of severe and particularly drug-resistant HSV infections.

Influenza B-cells protective epitope characterization: a passkey for the rational design of new broad-range anti-influenza vaccines

The emergence of new influenza strains causing pandemics represents a serious threat to human health. From 1918, four influenza pandemics occurred, caused by H1N1, H2N2 and H3N2 subtypes. Moreover, in 1997 a novel influenza avian strain belonging to the H5N1 subtype infected humans. Nowadays, even if its transmission is still circumscribed to avian species, the capability of the virus to infect humans directly from avian reservoirs can result in fatalities. Moreover, the risk that this or novel avian strains could adapt to inter-human transmission, the development of resistance to anti-viral drugs and the lack of an effective prevention are all incumbent problems for the world population. In this scenario, the identification of broadly neutralizing monoclonal antibodies (mAbs) directed against conserved regions shared among influenza isolates has raised hopes for the development of monoclonal antibody-based immunotherapy and "universal" anti-influenza vaccines.

Molecular signatures of hepatitis C virus (HCV)-induced type II mixed cryoglobulinemia (MCII)

The role of hepatitis C virus (HCV) infection in the induction of type II mixed cryoglobulinemia (MCII) and the possible establishment of related lymphoproliferative disorders, such as B-cell non-Hodgkin lymphoma (B-NHL), is well ascertained. However, the molecular pathways involved and the factors predisposing to the development of these HCV-related extrahepatic complications deserve further consideration and clarification. To date, several host- and virus-related factors have been implicated in the progression to MCII, such as the virus-induced expansion of selected subsets of B-cell clones expressing discrete immunoglobulin variable (IgV) gene subfamilies, the involvement of complement factors and the specific role of some HCV proteins. In this review, we will analyze the host and viral factors taking part in the development of MCII in order to give a general outlook of the molecular mechanisms implicated.

Neutralization interfering antibodies: a "novel" example of humoral immune dysfunction facilitating viral escape?

The immune response against some viral pathogens, in particular those causing chronic infections, is often ineffective notwithstanding a robust humoral neutralizing response. Several evasion mechanisms capable of subverting the activity of neutralizing antibodies (nAbs) have been described. Among them, the elicitation of non-neutralizing and interfering Abs has been hypothesized. Recently, this evasion mechanism has acquired an increasing interest given its possible impact on novel nAb-based antiviral therapeutic and prophylactic approaches. In this review, we illustrate the mechanisms of Ab-mediated interference and the viral pathogens described in literature as able to adopt this "novel" evasion strategy.

Ocular distribution, spectrum of activity, and in vivo viral neutralization of a fully humanized anti-herpes simplex virus IgG Fab fragment following topical application

Herpes simplex ocular infection is a major cause of corneal blindness. Local antiviral treatments exist but are associated with corneal toxicity, and resistance has become an issue. We evaluated the biodistribution and efficacy of a humanized anti-herpes simplex virus (anti-HSV) IgG FAb fragment (AC-8; 53 kDa) following repeated topical administration. AC-8 was found in the corneal epithelium, anterior stroma, subepithelial stromal cells, and retinal glial cells, with preferential entry through the ocular limbus. AC-8 was active against 13 different strains of HSV-1, with 50% and 90% mean effective concentrations (MEC(50) and MEC(90), respectively) ranging from 0.03 to 0.13 μg/ml, indicating broad-spectrum activity. The in vivo efficacy of AC-8 was evaluated in a mouse model of herpes-induced ocular disease. Treatment with low-dose AC-8 (1 mg/ml) slightly reduced the ocular disease scores. A greater reduction of the disease scores was observed in the 10-mg/ml AC-8-treated group, but not as much as with trifluridine (TFT). AC-8 treatment reduced viral titers but less than trifluridine. AC-8 did not display any toxicity to the cornea or other structures in the eye. In summary, topical instillation of an anti-HSV FAb can be used on both intact and ulcerated corneas. It is well tolerated and does not alter reepithelialization. Further studies to improve the antiviral effect are needed for AC-8 to be considered for therapeutic use.

Monoclonal antibodies isolated from human B cells neutralize a broad range of H1 subtype influenza A viruses including swine-origin Influenza virus (S-OIV)

The new H1N1 swine-origin influenza virus (S-OIV) strain is a global health problem. The elucidation of the virus-host relationship is crucial for the control of the new infection. Two human monoclonal antibody Fab fragments (HMab) neutralizing the novel H1N1 influenza strain at very low concentrations were cloned before the emergence of S-OIV from a patient who had a broad-range H1N1 serum neutralizing activity. The two HMabs neutralized all tested H1N1 strains, including S-OIV and a swine strain with IC(50) ranging from 2 to 7 microg/ml. Data demonstrate that infection with previously circulating H1N1 strains can elicit antibodies neutralizing S-OIV. Finally, the human genes coding for the neutralizing HMabs could be used for generating full human monoclonal IgGs that can be safely administered being potentially useful in the prophylaxis and the treatment of this human infection.

Evaluation of CD4-CD4i antibody architectures yields potent, broadly cross-reactive anti-human immunodeficiency virus reagents

The envelope glycoprotein of human immunodeficiency virus type 1 (HIV-1) has several adaptations that allow the virus to evade antibody neutralization. Nevertheless, a few broadly cross-reactive neutralizing antibodies as well as reagents containing portions of CD4, the HIV receptor, have demonstrated partial efficacy in suppressing viral replication. One type of reagent designed for improved HIV neutralization fuses the CD4 D1-D2 domains to the variable regions of an antibody recognizing the CD4-induced (CD4i) coreceptor binding site on the gp120 portion of the HIV envelope spike. We designed, expressed, purified, and tested the neutralization potencies of CD4-CD4i antibody reagents with different architectures, antibody combining sites, and linkers. We found that fusing CD4 to the heavy chain of the CD4i antibody E51 yields a bivalent reagent including an antibody Fc region that expresses well, is expected to have a long serum half-life, and has comparable or greater neutralization activity than well-known broadly neutralizing anti-HIV antibodies. A CD4 fusion with the anti-HIV carbohydrate antibody 2G12 also results in a potent neutralizing reagent with more broadly neutralizing activity than 2G12 alone.

Phage display on the base of filamentous bacteriophages: application for recombinant antibodies selection

The display of peptides and proteins on the surface of filamentous bacteriophage is a powerful methodology for selection of peptides and protein domains, including antibodies. An advantage of this methodology is the direct physical link between the phenotype and the genotype, as an analyzed polypeptide and its encoding DNA fragment exist in one phage particle. Development of phage display antibody libraries provides repertoires of phage particles exposing antibody fragments of great diversity. The biopanning procedure facilitates selection of antibodies with high affinity and specificity for almost any target. This review is an introduction to phage display methodology. It presents recombinant antibodies display in more details:, construction of phage libraries of antibody fragments and different strategies for the biopanning procedure.

Recombinant human IgG antibodies against human cytomegalovirus

OBJECTIVE

To study the passive immunization with human monoclonal antibodies as for prophylaxis of human cytomegalovirus (HCMV) infection.

METHODS

Fab monoclonal antibodies to HCMV were recovered by repertoire cloning of mRNA from a HCMV infected individual. Antigen binding specificity, CDR sequence of V(H) and V(L) and neutralizing activity on HCMV AD169 stain were analyzed in vitro. The light and heavy chain Fd fragment genes of Fab antibodies were further cloned into a recombinant baculovirus expression vector pAC-kappa-Fc to express intact IgG. Secreted products were purified with affinity chromatography using protein G.

RESULTS

SDS-PAGE and Western blot confirmed the expression of the intact IgG. Immuno-blotting and -precipitation were used to identify HCMV proteins. One Fab monoclonal antibody recognized a conformational HCMV protein.

CONCLUSION

IgG antibodies can neutralize the HCMV AD169 strain efficiently at a titer of 2.5 microg/mL and may prove valuable for passive immunoprophylaxis against HCMV infection in humans.

Antiherpevirus activity of Artemisia arborescens essential oil and inhibition of lateral diffusion in Vero cells

BACKGROUND

New prophylactic and therapeutic tools are needed for the treatment of herpes simplex virus infections. Several essential oils have shown to possess antiviral activity in vitro against a wide spectrum of viruses.

AIM

The present study was assess to investigate the activities of the essential oil obtained from leaves of Artemisia arborescens against HSV-1 and HSV-2

METHODS

The cytotoxicity in Vero cells was evaluated by the MTT reduction method. The IC50 values were determined by plaque reduction assay. In order to characterize the mechanism of action, yield reduction assay, inhibition of plaque development assay, attachment assay, penetration assay and post-attachment virus neutralization assay were also performed.

RESULTS

The IC50 values, determined by plaque reduction assay, were 2.4 and 4.1 microg/ml for HSV-1 and HSV-2, respectively, while the cytotoxicity assay against Vero cells, as determined by the MTT reduction method, showed a CC50 value of 132 mug/ml, indicating a CC50/IC50 ratio of 55 for HSV-1 and 32.2 for HSV-2. The antiviral activity of A. arborescens essential oil is principally due to direct virucidal effects. A poor activity determined by yield reduction assay was observed against HSV-1 at higher concentrations when added to cultures of infected cells. No inhibition was observed by attachment assay, penetration assay and post-attachment virus neutralization assay. Furthermore, inhibition of plaque development assay showed that A. arborescens essential oil inhibits the lateral diffusion of both HSV-1 and HSV-2.

CONCLUSION

This study demonstrates the antiviral activity of the essential oil in toto obtained from A. arborescens against HSV-1 and HSV-2. The mode of action of the essential oil as antiherpesvirus agent seems to be particularly interesting in consideration of its ability to inactivate the virus and to inhibit the cell-to-cell virus diffusion.

A recombinant human monoclonal antibody to human metapneumovirus fusion protein that neutralizes virus in vitro and is effective therapeutically in vivo

Human metapneumovirus (hMPV) is a recently discovered paramyxovirus that is a major cause of lower-respiratory-tract disease. hMPV is associated with more severe disease in infants and persons with underlying medical conditions. Animal studies have shown that the hMPV fusion (F) protein alone is capable of inducing protective immunity. Here, we report the use of phage display technology to generate a fully human monoclonal antibody fragment (Fab) with biological activity against hMPV. Phage antibody libraries prepared from human donor tissues were selected against recombinant hMPV F protein with multiple rounds of panning. Recombinant Fabs then were expressed in bacteria, and supernatants were screened by enzyme-linked immunosorbent assay and immunofluorescent assays. A number of Fabs that bound to hMPV F were isolated, and several of these exhibited neutralizing activity in vitro. Fab DS7 neutralized the parent strain of hMPV with a 60% plaque reduction activity of 1.1 mug/ml and bound to hMPV F with an affinity of 9.8 x10(-10) M, as measured by surface plasmon resonance. To test the in vivo activity of Fab DS7, groups of cotton rats were infected with hMPV and given Fab intranasally 3 days after infection. Nasal turbinates and lungs were harvested on day 4 postinfection and virus titers determined. Animals treated with Fab DS7 exhibited a >1,500-fold reduction in viral titer in the lungs, with a modest 4-fold reduction in the nasal tissues. There was a dose-response relationship between the dose of DS7 and virus titer. Human Fab DS7 may have prophylactic or therapeutic potential against severe hMPV infection.

Carrier-specificity of a phosphorylcholine-binding antibody requires the presence of the constant domains and is not dependent on the unique VH49 glycine or VH30 threonine residues

Bacterially-produced antibody fragments, such as single-chain Fv (scFv) which comprises the variable regions of the light (VL) and heavy (VH) chains joined together by a short flexible linker, are useful as diagnostic and therapeutic agents. We previously constructed a scFv fragment from a hybridoma antibody (Mab2) but it unexpectedly lacked the unique carrier specificity of the native antibody. Thus, it bound indiscriminately to various phosphorylcholine (PC)-associated antigens, whereas the hybridoma antibody recognized the PC epitope only in the context of the immunizing antigen. Here, we investigated whether the problem was linker-related by changing the linker composition or by deleting it, but these attempts proved futile. Instead, we have constructed a recombinant Fab fragment of the antibody in bacteria that was carrier-specific. This suggests that constant regions are required for the carrier specificity, which presumably helps to mould the fine structure of the antibody combining site or in stabilizing such a structure. Consistent with this global effect is the finding that replacing specific residues in VH with germ-line residues, namely, VH49 glycine and VH30 threonine, both thought previously to be important for the carrier specificity, had no effect on the carrier specificity of the recombinant Fab.

Protective immunity against hepatitis C virus infection

There is increasing evidence that a small percentage of individuals exposed to the hepatitis C virus have the capacity to generate a strong cellular immune response against the virus and avoid persistent infection, and perhaps do so repeatedly after re-exposure. This article reviews the evidence that the responses identified in this unique group of individuals represent the protective immunity that will need to be elicited by hepatitis C virus vaccines.

HCV-hepatocellular carcinoma: new findings and hope for effective treatment

We present here a comprehensive review of the current literature plus our own findings about in vivo and in vitro analysis of hepatitis C virus (HCV) infection, viral pathogenesis, mechanisms of interferon action, interferon resistance, and development of new therapeutics. Chronic HCV infection is a major risk factor for the development of human hepatocellular carcinoma. Standard therapy for chronic HCV infection is the combination of interferon alpha and ribavirin. A significant number of chronic HCV patients who cannot get rid of the virus infection by interferon therapy experience long-term inflammation of the liver and scarring of liver tissue. Patients who develop cirrhosis usually have increased risk of developing liver cancer. The molecular details of why some patients do not respond to standard interferon therapy are not known. Availability of HCV cell culture model has increased our understanding on the antiviral action of interferon alpha and mechanisms of interferon resistance. Interferons alpha, beta, and gamma each inhibit replication of HCV, and the antiviral action of interferon is targeted to the highly conserved 5'UTR used by the virus to translate protein by internal ribosome entry site mechanism. Studies from different laboratories including ours suggest that HCV replication in selected clones of cells can escape interferon action. Both viral and host factors appear to be involved in the mechanisms of interferon resistance against HCV. Since interferon therapy is not effective in all chronic hepatitis C patients, alternative therapeutic strategies are needed to treat chronic hepatitis C patients not responding to interferon therapy. We also reviewed the recent development of new alternative therapeutic strategies for chronic hepatitis C, which may be available in clinical use within the next decade. There is hope that these new agents along with interferon will prevent the occurrence of hepatocellular carcinoma due to chronic persistent hepatitis C virus infection. This review is not inclusive of all important scientific publications due to space limitation.

Construction of human Fab library and isolation of monoclonal Fabs with rabies virus-neutralizing ability

A combinatorial human Fab library was constructed using RNAs from peripheral blood lymphocytes of 6 rabies vaccine-boosted volunteers using pComb3X phagemid vector. The size of the constructed library was approximately 7.0 x 10(7) Escherichia coli transformants. The library was selected against purified rabies virus (RV) virion or purified RV glycoprotein for isolation of phages displaying RVneutralizing human Fab antibody. Among 132 selected clones, two Fab preparations revealed neutralizing activities against RV strain CVS when assayed in the rapid fluorescent focus inhibition test (RFFIT). The Fab preparation EP5G3 exhibited neutralizing activity with an infected cell count reduction of 76% at a dilution of 1: 2, and of 20% at a dilution of 1: 4. The Fab preparation GD2D12 also exhibited neutralizing activity with a 57% reduction at 1: 2 and 41% reduction at 1: 4. In the co-immunoprecipitation using strain CVS, the RV glycoprotein was precipitated in reactions with both Fab preparations. The RV neutralizing ability of the Fab preparations described in the study were not directly correlated with their binding specificity for RV antigens detected by ELISA.

Inhibition of hepatitis C virus nonstructural protein, helicase activity, and viral replication by a recombinant human antibody clone

Hepatitis C virus (HCV) nonstructural protein 3 (NS3), with its protease, helicase, and NTPase enzymatic activities, plays a crucial role in viral replication, and therefore represents an ideal target for the development of anti-viral agents. We have developed a recombinant human antibody (Fab) that reacts with the helicase domain of HCV NS3. The affinity-purified Fab antibody completely inhibited the helicase activity of HCV NS3 at equimolar concentration. To evaluate the effect of the Fab on HCV replication, the clone encoding the Fab gene was put into an expression vector, which converts Fab into a complete IgG1 antibody. Using a DNA-based transfection model, we demonstrated that intracellular expression of this antibody resulted in significant reduction of HCV-negative strand RNA synthesis. Intracellular expression of this antibody into either a stable cell line replicating subgenomic RNA, or a transient full-length HCV replication model, reduced both HCV RNA and viral protein expression. These results support the use of recombinant antibody fragments to inhibit NS3 enzyme as a novel, feasible, and effective approach for inhibiting HCV replication.

Human monoclonal antibody fragment specific for glycoprotein G in herpes simplex virus type 2 with applications for serotype-specific diagnosis

A combinatorial library was used to select a human monoclonal antibody fragment (Fab) with high affinity for G glycoprotein in herpes simplex virus type 2 (HSV-2). Tests with 112 clinical specimens demonstrated successful discrimination between HSV-2 and HSV-1, showing the potential of Fab as a low-cost tool for HSV subtyping in clinical diagnosis.

Production and characterization of a human recombinant monoclonal Fab fragment specific for influenza A viruses

A human recombinant monoclonal Fab fragment that specifically recognizes all the influenza A virus strains tested was produced in transformed Escherichia coli using the phage display technique. No strain of influenza B virus reacted with it. It was purified after four cycles of panning and by a single passage through an immunoaffinity column. About 1 mg of pure monoclonal antibody was obtained from 1 liter of culture medium in 3 working days. The Fab fragment reacted with a viral 27-kDa protein, which could reasonably be a matrix protein. Indirect immunofluorescence tests performed on virus-infected MDCK cells showed that this Fab fragment was at least equally efficient as other commercial monoclonal antibody-based systems in detecting influenza A viral infections. The potential advantages of human recombinant Fabs on murine monoclonal antibodies are discussed.

Expression and assembly of a fully active antibody in algae

Although combinatorial antibody libraries have solved the problem of access to large immunological repertoires, efficient production of these complex molecules remains a problem. Here we demonstrate the efficient expression of a unique large single-chain (lsc) antibody in the chloroplast of the unicellular, green alga, Chlamydomonas reinhardtii. We achieved high levels of protein accumulation by synthesizing the lsc gene in chloroplast codon bias and by driving expression of the chimeric gene using either of two C. reinhardtii chloroplast promoters and 5' and 3' RNA elements. This lsc antibody, directed against glycoprotein D of the herpes simplex virus, is produced in a soluble form by the alga and assembles into higher order complexes in vivo. Aside from dimerization by disulfide bond formation, the antibody undergoes no detectable posttranslational modification. We further demonstrate that accumulation of the antibody can be modulated by the specific growth regime used to culture the alga, and by the choice of 5' and 3' elements used to drive expression of the antibody gene. These results demonstrate the utility of alga as an expression platform for recombinant proteins, and describe a new type of single chain antibody containing the entire heavy chain protein, including the Fc domain.

Antibodies, viruses and vaccines

Neutralizing antibodies are crucial for vaccine-mediated protection against viral diseases. They probably act, in most cases, by blunting the infection, which is then resolved by cellular immunity. The protective effects of neutralizing antibodies can be achieved not only by neutralization of free virus particles, but also by several activities directed against infected cells. In certain instances, non-neutralizing antibodies contribute to protection. Several viruses, such as HIV, have evolved mechanisms to evade neutralizing-antibody responses, and these viruses present special challenges for vaccine design that are now being tackled.

Mapping B-cell epitopes of hepatitis C virus E2 glycoprotein using human monoclonal antibodies from phage display libraries

Clinical and experimental evidence indicates that the hepatitis C virus (HCV) E2 glycoprotein (HCV/E2) is the most promising candidate for the development of an effective anti-HCV vaccine. Identification of the human epitopes that are conserved among isolates and are able to elicit protective antibodies would constitute a significant step forward. This work describes the mapping of the B-cell epitopes present on the surface of HCV/E2, as recognized by the immune system during infection, by the analysis of the reciprocal interactions of a panel of human recombinant Fabs derived from an HCV-infected patient. Three unrelated epitopes recognized by antibodies with no neutralization-of-binding (NOB) activity were identified; a fourth, major epitope was defined as a clustering of minor epitopes recognized by Fabs endowed with strong NOB activity.

Molecular profile of a human monoclonal antibody Fab fragment specific for Epstein-Barr virus gp350/220 antigen

Experimental evidence indicates Epstein Barr virus (EBV) envelope glycoprotein gp350/220 elicits a potent virus neutralizing response in the infected human host that may play an important role in restricting viral pathogenesis. In this study, we report the molecular cloning in combinatorial phage display vectors, of the IgG1 repertoire of an individual naturally infected with EBV, and describe the recovery and characterization of a monoclonal antibody recognizing gp350/220. A detailed understanding of the human antibody response in EBV infection will identify antibodies of potential use in anti-viral prophylaxis and will advance the production of more effective vaccine candidates.

Isolation of the melanoma-associated antigen p23 using antibody phage display

The general responsiveness of human melanoma to immunotherapy has been well established, but active immunotherapy of melanoma has been hampered by insufficient information on the immunogenicity of melanoma-associated Ags in patients. In this study, we isolated a recombinant phage-Fab clone (A10-5) from a phage-Fab library derived from the B cells of a melanoma patient in remission after immunotherapy. Purified A10-5 Fab bound at high levels to cultured melanoma cell lines and to tissue sections of metastatic and vertical growth phase primary melanoma, but not to radial growth phase primary melanoma, nevi, or normal skin. A10-5 Fab bound to both the surface and the cytoplasm of cultured melanoma cells, but only to the cytoplasm of cultured fibroblasts. Western blot analysis revealed A10-5 Fab reactivity with a 33- and a 23-kDa glycoprotein under nonreducing conditions, and with a 23-kDa protein only under reducing conditions. A cDNA with an open reading frame predicted to encode a 23-kDa protein was cloned by screening a melanoma cell cDNA library with A10-5 Fab. This protein (p23) is the human homologue of the murine tumor transplantation Ag P198 that interacts with the cytoplasmic domain of ErbB-3 expressed by melanoma cells. Thus, the Ab phage display method has identified a novel, stage-specific melanoma-associated Ag that may have therapeutic and diagnostic value.

Inactivation of HSV-1 and HSV-2 and prevention of cell-to-cell virus spread by Santolina insularis essential oil

The essential oil obtained in toto from Santolina insularis was investigated for its antiviral activity on herpes simplex type 1 (HSV-1) and type 2 (HSV-2) in vitro. The IC(50) values, determined by plaque reduction assays, were 0.88 and 0.7 microg/ml for HSV-1 and HSV-2, respectively, while the CC(50) determined by the MTT test on Vero cells was 112 microg/ml, indicating a CC(50)/IC(50) ratio of 127 for HSV-1 and 160 for HSV-2. Results obtained by plaque reduction assays also indicated that the antiviral activity of S. insularis was principally due to direct virucidal effects. Antiviral activity against HSV-1 and HSV-2 was not observed in a post-attachment assay, and attachment assays indicated that virus adsorption was not inhibited. Up to 80% inhibition of HSV-1 was achieved at the concentration of 40 microg/ml by yield reduction assay. Furthermore, reduction of plaque formation assays also showed that S. insularis essential oil inhibits cell-to-cell transmission of both HSV-1 and HSV-2.

Localization of a passively transferred human recombinant monoclonal antibody to herpes simplex virus glycoprotein D to infected nerve fibers and sensory neurons in vivo

A human recombinant monoclonal antibody to herpes simplex virus (HSV) glycoprotein D labeled with the fluorescent dye Cy5 was administered to mice infected in the cornea with HSV type 1 (HSV-1). The distribution of such antibody in the corneas and trigeminal ganglia of the mice was then investigated by confocal microscopy. The antibody was detected on HSV-infected nerve fibers in the cornea--identified by colocalization with HSV antigens and the neuritic markers neurofilament, GAP-43, synapsin-1, and CNPase--and on the perikarya of sensory neurons in the HSV-1-infected neurons in ipsilateral trigeminal ganglia. Antibodies have been shown to be effective against many neurotropic viruses, often in the absence of obvious cell damage. Observations from experimental HSV infections suggest that antibodies could act in part by interfering with virus expression in the ganglia and/or with axonal spread. The present results provide morphological evidence of the localization of antiviral antibodies at anatomical sites relevant to such putative antibody-mediated protective actions and suggest that viral glycoproteins are accessible to antibodies on infected nerve fibers and sensory neurons.

Neutralizing antibodies inhibit axonal spread of herpes simplex virus type 1 to epidermal cells in vitro

The ability of antibodies to interfere with anterograde transmission of herpes simplex virus (HSV) from neuronal axons to the epidermis was investigated in an in vitro model consisting of human fetal dorsal root ganglia innervating autologous skin explants in a dual-chamber tissue culture system. The number and size of viral cytopathic plaques in epidermal cells after axonal transmission from HSV type 1 (HSV-1)-infected dorsal root ganglionic neurons were significantly reduced by addition to the outer chamber of neutralizing polyclonal human sera to HSV-1, of a human recombinant monoclonal group Ib antibody to glycoprotein D (gD), and of rabbit sera to HSV-1 gB and gD but not by rabbit anti-gE or anti-gG. A similar pattern of inhibition of direct infection of epidermal cells by these antibodies was observed. High concentrations of the monoclonal anti-gD reduced transmission by 90%. Rabbit anti-gB was not taken up into neurons, and human anti-gD did not influence spread of HSV in the dorsal root ganglia or axonal transport of HSV antigens when applied to individual dissociated neurons. These results suggest that anti-gD and -gB antibodies interfere with axonal spread of HSV-1, possibly by neutralizing HSV during transmission across an intercellular gap between axonal termini and epidermal cells, and thus contribute to control of HSV spread and shedding. Therefore, selected human monoclonal antibodies to protective epitopes might even be effective in preventing epidermis-to-neuron transmission during primary HSV infection, especially neonatal infection.

pFab-CMV, a single vector system for the rapid conversion of recombinant Fabs into whole IgG1 antibodies

We have constructed a single vector system for the rapid conversion of recombinant Fabs into whole IgG1 antibodies and their expression in eukaryotic cells. This vector, named pFab-CMV, utilizes the same unique cloning sites present on the pComb3 phagemid thus allowing for the direct subcloning of light chains and heavy chain Fd regions. pFab-CMV also allows for the expression of recombinant Fabs in eukaryotic cells by removal of a cassette containing part of the hinge, CH2 and CH3 sequences. Stable cell lines are rapidly obtained with pFab-CMV by NEO selection without the need for co-transfection of heavy and light chain expressing vectors.

Cloning the antibody response in humans with inflammatory CNS disease: isolation of measles virus-specific antibodies from phage display libraries of a subacute sclerosing panencephalitis brain

We have developed a strategy to identify the disease-relevant antigens in a chronic inflammatory CNS disease exhibiting intrathecally expressed oligoclonal IgG. Using subacute sclerosing panencephalitis (SSPE), a chronic inflammatory measles virus infection of the brain as a model system, we constructed a phage display antibody Fab library from the amplified products of IgG expressed in the brain. Selection of the library against measles virus-infected cell lysates yielded four distinct Fabs which, by ELISA and by immunostaining, reacted specifically with measles virus-infected cells. Three Fabs immunoprecipitated a 72 kDa protein from infected cell cultures corresponding to the measles virus phosphoprotein. The fourth Fab immunoprecipitated and recognized by immunoblotting a 60 kDa protein corresponding to the measles virus nucleoprotein. The results demonstrate that functional antibodies from an inflammatory CNS disease can be expressed in bacteria and used to identify disease-relevant antigens. This approach could be applied to chronic inflammatory CNS diseases of unknown cause such as multiple sclerosis.