Single-chain antibodies produced by phage display against the C-terminal 19 kDa region of merozoite surface protein-1 of Plasmodium yoelii reduce parasite growth following challenge

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.

Using two phases of the CD4 T cell response to blood-stage murine malaria to understand regulation of systemic immunity and placental pathology in Plasmodium falciparum infection

Plasmodium falciparum infection and malaria remain a risk for millions of children and pregnant women. Here, we seek to integrate knowledge of mouse and human T helper cell (Th) responses to blood-stage Plasmodium infection to understand their contribution to protection and pathology. Although there is no complete Th subset differentiation, the adaptive response occurs in two phases in non-lethal rodent Plasmodium infection, coordinated by Th cells. In short, cellular immune responses limit the peak of parasitemia during the first phase; in the second phase, humoral immunity from T cell-dependent germinal centers is critical for complete clearance of rapidly changing parasite. A strong IFN-γ response kills parasite, but an excess of TNF compared with regulatory cytokines (IL-10, TGF-β) can cause immunopathology. This common pathway for pathology is associated with anemia, cerebral malaria, and placental malaria. These two phases can be used to both understand how the host responds to rapidly growing parasite and how it attempts to control immunopathology and variation. This dual nature of T cell immunity to Plasmodium is discussed, with particular reference to the protective nature of the continuous generation of effector T cells, and the unique contribution of effector memory T cells.

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.”

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.

Development of anti-infectives using phage display: biological agents against bacteria, viruses, and parasites

The vast majority of anti-infective therapeutics on the market or in development are small molecules; however, there is now a nascent pipeline of biological agents in development. Until recently, phage display technologies were used mainly to produce monoclonal antibodies (MAbs) targeted against cancer or inflammatory disease targets. Patent disputes impeded broad use of these methods and contributed to the dearth of candidates in the clinic during the 1990s. Today, however, phage display is recognized as a powerful tool for selecting novel peptides and antibodies that can bind to a wide range of antigens, ranging from whole cells to proteins and lipid targets. In this review, we highlight research that exploits phage display technology as a means of discovering novel therapeutics against infectious diseases, with a focus on antimicrobial peptides and antibodies in clinical or preclinical development. We discuss the different strategies and methods used to derive, select, and develop anti-infectives from phage display libraries and then highlight case studies of drug candidates in the process of development and commercialization. Advances in screening, manufacturing, and humanization technologies now mean that phage display can make a significant contribution in the fight against clinically important pathogens.

Human recombinant antibodies againstTrypanosoma cruziribosomal P2βprotein

Patients with chronic Chagas' Heart Disease (cChHD) develop an antibody response that is suspected to be involved in the cardiac pathogenesis. The response againstTrypanosoma cruziribosomal P proteins is of particular interest, as these antibodies can cross-react with host cardiac receptors causing electrophysiological alterations. To better understand the humoral anti-P response we constructed a single-chain variable fragment library derived from a cChHD patient. The variable heavy and light regions were amplified from bone-marrow RNA and subcloned into the vector pComb3X. The phage library was subsequently panned againstT. cruziribosomal P2βprotein (TcP2β). We obtained 3 different human recombinant antibodies that specifically reacted with TcP2βin ELISA and Western blots. Two of them reacted with the C-terminal region of TcP2β, peptide R13, as the recombinant autoanti-P antibodies from Systemic Lupus Erythematosus (SLE) patients. Interestingly, the third one was specific for TcP2βbut did not recognize R13, confirming the specific nature of the anti-P response in Chagas disease. Neither sequence nor VH usage similarities between Chagas and SLE anti-P autoantibodies were observed. Herein, the first human mAbs against TcP2βhave been obtained and characterized showing that the humoral anti-P response is directed against the parasite and does not include an autoimmune component.

Baculovirus-based nasal drop vaccine confers complete protection against malaria by natural boosting of vaccine-induced antibodies in mice

Blood-stage malaria parasites ablate memory B cells generated by vaccination in mice, resulting in diminishing natural boosting of vaccine-induced antibody responses to infection. Here we show the development of a new vaccine comprising a baculovirus-based Plasmodium yoelii 19-kDa carboxyl terminus of merozoite surface protein 1 (PyMSP1(19)) capable of circumventing the tactics of parasites in a murine model. The baculovirus-based vaccine displayed PyMSP1(19) on the surface of the virus envelope in its native three-dimensional structure. Needle-free intranasal immunization of mice with the baculovirus-based vaccine induced strong systemic humoral immune responses with high titers of PyMSP1(19)-specific antibodies. Most importantly, this vaccine conferred complete protection by natural boosting of vaccine-induced PyMSP1(19)-specific antibody responses shortly after challenge. The protective mechanism is a mixed Th1/Th2-type immunity, which is associated with the Toll-like receptor 9 (TLR9)-dependent pathway. The present study offers a novel strategy for the development of malaria blood-stage vaccines capable of naturally boosting vaccine-induced antibody responses to infection.

Development and implementation of a single-chain Fv antibody for specific detection of Bacillus anthracis spores

A single-chain Fv (scFv) antibody was developed and applied for efficient and specific detection of Bacillus anthracis spores. The antibody was isolated from a phage display library prepared from spleens of mice immunized with a water-soluble extract of the outer membrane of the B. anthracis spore (exosporium). The library (7 x 10(6) PFU) was biopanned against live, native B. anthracis ATCC delta14185 spores suspended in solution, resulting in the isolation of a unique soluble scFv antibody. The antibody was affinity purified and its affinity constant (3 x 10(8) +/- 1 x 10(8) M(-1)) determined via flow cytometry (FCM). Preliminary characterization of scFv specificity indicated that the scFv antibody does not cross-react with representatives of some phylogenetically related Bacillus spores. The potential use of scFv antibodies in detection platforms was demonstrated by the successful application of the soluble purified scFv antibody in enzyme-linked immunosorbent assays, immunofluorescence assays, and FCM.

Phage display: a useful tool for malaria research?

Defining the molecular intricacies of malaria pathogenesis is a vital area of medical and scientific research. Sophisticated methods have been developed to identify and characterise host-parasite interactions that are important in infection. Phage display involves the combinatorial display of proteins or peptides on the surface of bacteriophage. The technology provides an invaluable tool for screening diverse libraries for polypeptides that have a high affinity for a given target. Phage display in malaria research has proven successful, not only in mapping the protein-protein interactions that are important in Plasmodium biology, but also in the identification of molecules that might be exploited in the design of therapeutic agents or vaccines.

Long-lasting protective immune response to the 19-kilodalton carboxy-terminal fragment of Plasmodium yoelii merozoite surface protein 1 in mice

Merozoite surface protein 1 (MSP1) is the major protein on the surface of the plasmodial merozoite, and its carboxy terminus, the 19-kDa fragment (MSP1(19)), is highly conserved and effective in induction of a protective immune response against malaria parasite infection in mice and monkeys. However, the duration of the immune response has not been elucidated. As such, we immunized BALB/c mice with a standard four-dose injection of recombinant Plasmodium yoelii MSP1(19) formulated with Montanide ISA51 and CpG oligodeoxynucleotide (ODN) and monitored the MSP1(19)-specific antibody levels for up to 12 months. The antibody titers persisted constantly over the period of time without significant waning, in contrast to the antibody levels induced by immunization with Freund's adjuvant, where the antibody levels gradually declined to significantly lower levels 12 months after immunization. Investigation of immunoglobulin G (IgG) subclass longevity revealed that only the IgG1 antibody level (Th2 type-driven response) decreased significantly by 6 months, while the IgG2a antibody level (Th1 type-driven response) did not change over the 12 months after immunization, but the boosting effect was seen in the IgG1 antibody responses but not in the IgG2a antibody responses. After challenge infection, all immunized mice survived with negligibly patent parasitemia. These findings suggest that protective immune responses to MSP1(19) following immunization using oil-based Montanide ISA51 and CpG ODN as an adjuvant are very long-lasting and encourage clinical trials for malaria vaccine development.

Plasmodium falciparum: immunization with MSP1-42 induced non-inhibitory antibodies that have no blocking activities but enhanced the potency of inhibitory anti-MSP1-42 antibodies

Hyperimmunization with Plasmodium falciparum MSP1-42 could induce antibodies that have little or no parasite growth inhibitory activities. These antisera had no blocking activities as determined by their ability to interfere with the in vitro activities of growth inhibitory anti-MSP1-42 sera. Equally important, they enhanced the potency of growth inhibitory anti-MSP1-42 sera.

Plasmodium falciparum anti-MSP1-19 antibodies induced by MSP1-42 and MSP1-19 based vaccines differed in specificity and parasite growth inhibition in terms of recognition of conserved versus variant epitopes

The C-terminal 42 kDa fragment (MSP1-42) and its smaller 19 kDa subfragment (MSP1-19) of the Plasmodium falciparum merozoite surface protein, MSP1, are leading candidate malaria vaccines. Since the targets of protective immunity lie within the MSP1-19, we compared the anti-MSP1-19 antibodies induced by vaccination with recombinant MSP1-42 and MSP1-19. The specificities of the antibody responses were analyzed using five recombinant MSP1-19s expressing different naturally occurring variant amino acid residues. We observed dramatic differences in the specificities of the anti-MSP1-19 antibodies induced by the two vaccines. MSP1-42 consistently induced crossreactive antibodies; whereas the antibodies induced by recombinant MSP1-19 were highly variable among animals in terms of recognition of conserved versus variant epitopes. Of the variant residues examined, only a subset significantly contributed as part of immunogenic B epitopes. MSP1-42 consistently induced potent growth inhibitory antibodies that recognized conserved epitopes, leading to efficient inhibition of heterologous parasites. In contrast, MSP1-19 induced strong inhibitory antibody responses in only a subset of animals studied. In some of the MSP1-19 immunized animals, inhibition of homologous parasites may be due to recognition of inhibitory epitopes associated with the homologous variant residues, and the induction of antibodies to conserved inhibitory epitopes may not be efficiently achieved. These data suggest an advantage of using MSP1-42 over MSP1-19 based vaccines.

Antigenicity and immunogenicity of the N-terminal 33-kDa processing fragment of the Plasmodium falciparum merozoite surface protein 1, MSP1: implications for vaccine development

The Plasmodium falciparum merozoite surface protein 1 (MSP1), MSP1-42 and MSP1-19 are protective malaria vaccines. MSP1-42 is cleaved to form MSP1-33 and MSP1-19. The role of MSP1-33 in immunity is unclear. We investigated the antibody responses to MSP1-33; and to MSP1-33Trunc, in which major conserved sequences were excised. While anti-MSP1-33 antibodies were subdominant in the anti-MSP1-42 responses, immunizations with MSP1-33 or MSP1-33Trunc induced high levels of antibodies reactive with MSP1-42 or whole merozoites. Anti-MSP1-33 and anti-MSP1-33Tunc antibodies crossreacted with both allelic forms of MSP1-42. Anti-MSP1-33 sera were ineffective in inhibiting parasite growth in vitro; but they significantly enhanced the activities of sub-optimal concentrations of the inhibitory anti-MSP1-42 sera. Thus, immunization strategies with MSP1-based vaccines may benefit from co-induction of anti-MSP1-33 responses to enhance efficacy and potency.

Antibody- and Fc-receptor-based therapeutics for malaria

Abs (antibodies) are complex glycoproteins that play a crucial role in protective immunity to malaria, but their effectiveness in mediating resistance can be enhanced by genetically engineered modifications that improve on nature. These Abs also aid investigation of immune mechanisms operating to control the disease and are valuable tools in developing neutralization assays for vaccine design. This review explores how this might be achieved.

A survey of the year 2002 commercial optical biosensor literature

We have compiled 819 articles published in the year 2002 that involved commercial optical biosensor technology. The literature demonstrates that the technology's application continues to increase as biosensors are contributing to diverse scientific fields and are used to examine interactions ranging in size from small molecules to whole cells. Also, the variety of available commercial biosensor platforms is increasing and the expertise of users is improving. In this review, we use the literature to focus on the basic types of biosensor experiments, including kinetics, equilibrium analysis, solution competition, active concentration determination and screening. In addition, using examples of particularly well-performed analyses, we illustrate the high information content available in the primary response data and emphasize the impact of including figures in publications to support the results of biosensor analyses.

Novel antimalarial antibodies highlight the importance of the antibody Fc region in mediating protection

Parasite drug resistance and difficulties in developing effective vaccines have precipitated the search for alternative therapies for malaria. The success of passive immunization suggests that immunoglobulin (Ig)-based therapies are effective. To further explore the mechanism(s) by which antibody mediates its protective effect, we generated human chimeric IgG1 and IgA1 and a single-chain diabody specific for the C-terminal 19-kDa region of Plasmodium yoelii merozoite surface protein 1 (MSP119), a major target of protective immune responses. These novel human reagents triggered in vitro phagocytosis of merozoites but, unlike their parental mouse IgG2b, failed to protect against parasite challenge in vivo. Therefore, the Fc region appears critical for mediating protection in vivo, at least for this MSP119 epitope. Such antibodies may serve as prototype therapeutic agents, and as useful tools in the development of in vitro neutralization assays with Plasmodium parasites.