SCFV PHAGE DISPLAY

What are the benefits of using scFv antibodies ?

Single-chain variable fragment (scFv) are very small (25 kDa) recombinant proteins, corresponding to the smallest functional antigen-binding domain of an antibody. They contain a variable light chain (VL) and a variable heavy chain (VH) linked together with a flexible peptide linker of about 3.5 nm in length. These antibody fragments are highly flexible and soluble thanks to hydrophilic Gly/Ser and Glu/Lys residues, respectively. scFv are characterized by several features making them a valuable tool in research and clinical applications. Some of these features include:

• Fast cell/tissue penetrance & clearance – The small size of these antibodies helps them penetrating easily cells and tissues and readily cross the blood-brain barrier. For the same reason, these antibodies are easily cleared from tissues (short half-life). These two characteristics make them a valuable tool for in vivo studies, mainly in diagnostic studies as the tissue needs to be cleared quickly, to minimize the healthy tissue exposure to radionuclei during imaging studies.
• Easy storage – Thanks to their high stability, scFv antibodies can be easily stored at 4°C for up to several years.
• Reduced immunogenicity – scFv antibodies lack the Fc region, leading to low immunogenicity when administered in vivo. This makes them a better therapeutic agents compared to traditional full-length monoclonal antibodies for many applications.
• Easy screening – Recombinant antibodies are small enough to be screened with in vitro phage display methods
• Easy and cheap production – These proteins, being small, make them easy to produce in “simple” systems, for instance, in E. coli which is a very simple and very cost-effective solution and allows for a large production of scFv antibodies.
• No animal uses – In vitro selection and production of scFv antibodies avoids animal immunization.

scFv applications in Research and clinics

• Useful tools to Study Protein Functions
  scFv antibodies have been shown to be an efficient tool to study the protein loss-of-function and to elucidate the protein function. In fact, these antibody fragments can be used as silencing tools, and be targeted to a full protein or only to a part of it, thus facilitating studies of protein fragment function.
• Cancer therapy
  scFv fragments are characterized by a very good tissue penetration ability. This makes them a tool of choice in the drug administration in solid tumors, as conventional monoclonal antibodies have poor tissue penetration abilities due to their big size (150 kDa). Moreover, recent studies have also demonstrated that scFv fragments can also be used as recombinant immunotoxins (RIT) and carry out cytotoxic drugs aiming to cancer cell killing. Furthermore, scFv fragment can be used in cancer immunotherapy, using them as vaccines to target immunogenic tumors.
• Neurodegenerative diseases
  Thanks to their small size and high solubility, making them easy to cross the blood brain barrier, scFv antibodies have emerged as a powerful tool in the Alzheimer’s Disease (AD) treatment. AD treatments aim at reducing the amyloid plaque formation by targeting the Aβ peptide, which aggregates and forms these neurotoxic species. It was shown that scFv targeting Aβ in a transgenic mouse model of AD led to a reduction of amyloid plaques and improved cognitive impairment in AD mouse models.
  scFv are also used in the Huntington’s Disease (HD), another neurodegenerative disease characterized by abnormal folding and a proteolytic cleavage of the mutant huntingtin protein (mHTT), leading to formation of aggregates. scFv-targeting mHTT aggregates have been generated and preferentially bind to specific regions in the mHTT fragments leading to the mHTT aggregate reduction.
• In vivo imaging tracers
  scFv antibodies are a powerful tool for in vivo imaging, helping to visualize the location and distribution of specific targets within deep tissues. In fact, thanks to their small size, these small antibody fragments can be conjugated to, fluorescent moieties, radionuclei or nanoparticles and can be followed by different imaging techniques. Moreover, scFv antibodies have the ability to readily penetrate and to be easily cleared from tissues, and thus minimizes the exposure of healthy tissue, which makes them an ideal imaging tool among other antibody fragments, especially for in vivo diagnostic applications. When they are conjugated to supramagnetic iron oxide nanoparticles (SPIONSs), scFv have a great utility in magnetic resonance imaging (MRI) as they increase its sensitivity, for instance, they help to distinguish between healthy and cancerous cells by increasing the contrast between these two cell types.
• Vehicles to deliver drugs and nanoparticles
  Thanks to their high specific recognition of the protein target as well as their small size enabling them to easily penetrate deep tissues, scFv antibodies are used as vehicles to deliver some drugs, siRNA or toxins to specific target cells/tissues, making them a valuable tool in immunotherapeutic field.