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| Other names | Corynebacterium diphtheriae CRM197 protein |
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| Molar mass | 58.4kD |
CRM197 [1] is a non-toxic mutant of diphtheria toxin, currently used as a carrier protein for polysaccharides and haptens to make them immunogenic. [2] There is some dispute about the toxicity of CRM197, with evidence that it is toxic to yeast cells and some mammalian cell lines. [3]
CRM197 is a genetically detoxified form of diphtheria toxin. A single mutation at position 52, substituting glutamic acid for glycine, causes the ADP-ribosyltransferase activity of the native toxin to be lost. The structural basis for the lack of CRM197 toxicity has recently been elucidated. [4] CRM197 is widely used as a carrier protein for conjugate vaccines. A potential advantage of CRM197 over toxoided proteins is that, because it is genetically detoxified, it retains its full complement of lysine amines for conjugation. There is also evidence suggesting that, compared with tetanus toxoid, there is less carrier-induced suppression of the immune response, especially when there are many individual polysaccharides linked to the same carrier protein. [5] A summary of the uses and properties of CRM197 has been published. [5] CRM197, like diphtheria toxin, is a single polypeptide chain of 535 amino acids (58.4 kDa) consisting of two subunits (linked by disulfide bridges).
The gene for CRM197 has been cloned into Corynebacterium diphtheriae , the bacterium that produces the native toxin. [6] Like the wild type toxin, CRM197 is expressed as a secreted protein at relatively low yields (typically <100 mg/L). Corynebacterium expressed CRM197 is available from several sources, including List Laboratories and Sigma-Aldrich. The low yield and high cost of commercially available native CRM197 has led to efforts to produce CRM197 in other bacteria but this has proven a difficult task until recently.
Three companies have succeeded at manufacturing CRM197 as a recombinant protein. Ligand's wholly-owned subsidiary, Pelican (previously Pfenex), a San Diego–based developer of the Pelican Expression Technology™ production platform, [7] produces the protein ("PeliCRM™") in India at Serum Institute of India Pune using Pseudomonas fluorescens and various proprietary expression technologies for high yield. Fina BioSolutions LLC of Rockville, Maryland has achieved multi-gram/L expression of CRM197 in E. coli (“EcoCRMTM”) as an intracellular, properly folded soluble protein. Fina Biosolutions currently provides the protein for pre-clinical use. Recombinant CRM197 is also made in low-mutation Clean Genome® E. coli by Scarab Genomics LLC where transport of CRM197 into the bacterial cell periplasm enhances its stability and proper folding.
CRM197 is used as a carrier protein in a number of approved conjugate vaccines. Hibtiter™, a vaccine to protect against Haemophilus influenzae type b, approved by the FDA in 1990, was the first conjugate vaccine to use CRM197 (the vaccine was discontinued in 2007). Pfizer's Prevnar, which in 2000 became the first pneumococcal conjugate vaccine to gain FDA approval, comprises polysaccharides from pneumococcal serotypes conjugated to CRM197. A larger number of clinical and pre-clinical conjugate vaccines using CRM197 as the carrier protein are being evaluated. A further example of a vaccine currently in use that is a CRM197 conjugate is the meningitis ACWY vaccine, Menveo, produced by GlaxoSmithKline. [8] In addition, CRM197 made in the Pelican Expression Technology™ platform is used in Merck's VAXNEUVANCE and Serum Institute's Pneumosil.
CRM197 possesses a binding site for EGF receptor heparin-binding epidermal growth factor-like growth factor (HB-EGF), a member of the EGF family. [9] As this receptor is overexpressed on cancer cells, there have been efforts to use CRM197 as an anti-cancer therapy. [10] The cancer immunotherapy company Imugene reported dramatic improvements in antibody titers from its B cell peptide cancer immunotherapy targeting HER2 when it used CRM197 as a carrier protein.[5]
CRM197 is being evaluated as a potential drug delivery fusion protein. The Swiss-based Turing Pharmaceuticals is working on CRM197 fusion constructs with therapeutic proteins of up to 1,000 amino acids in length.[6]
Preclinical studies have shown that CRM197 is also suitable for conjugation and presentation of peptide epitopes, a vaccinal approach that could have applications in Streptococcal infection, [11] cancer, [12] or Alzheimer's disease [13] therapy.
In 1971 Tsuyoshi Uchida, in the laboratory of Alwin Pappenheimer at Harvard, used nitroguanidine to create mutants of diphtheria toxin, which were called Cross Reacting Materials, or CRMs. [14] One of these mutants, called CRM197, interested researchers because its lack of toxicity suggested a better starting material for diphtheria vaccine than the wild-type protein, and the protein was found to enhance the immunogenicity of bacterial polysaccharides. [15] The pharmaceutical company Wyeth took advantage of this immunogenicity in the 1990s when it conjugated seven polysaccharides from Streptococcus pneumoniae to CRM197 to create the original Prevnar vaccine which was FDA approved in February 2000. A 13-polysaccharides Prevnar was FDA-approved in 2010. [16] The meningococcal vaccine Menveo, from Novartis, is four Neisseria meningitidis polysaccharides plus CRM197. This vaccine gained FDA approval in 2010. [17]
An exotoxin is a toxin secreted by bacteria. An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism. They are highly potent and can cause major damage to the host. Exotoxins may be secreted, or, similar to endotoxins, may be released during lysis of the cell. Gram negative pathogens may secrete outer membrane vesicles containing lipopolysaccharide endotoxin and some virulence proteins in the bounding membrane along with some other toxins as intra-vesicular contents, thus adding a previously unforeseen dimension to the well-known eukaryote process of membrane vesicle trafficking, which is quite active at the host–pathogen interface.
Haptens are small molecules that elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response by itself. The mechanisms of absence of immune response may vary and involve complex immunological interactions, but can include absent or insufficient co-stimulatory signals from antigen-presenting cells.
A cancer vaccine, or oncovaccine, is a vaccine that either treats existing cancer or prevents development of cancer. Vaccines that treat existing cancer are known as therapeutic cancer vaccines or tumor antigen vaccines. Some of the vaccines are "autologous", being prepared from samples taken from the patient, and are specific to that patient.
A conjugate vaccine is a type of subunit vaccine which combines a weak antigen with a strong antigen as a carrier so that the immune system has a stronger response to the weak antigen.
Corynebacterium diphtheriae is a Gram-positive pathogenic bacterium that causes diphtheria. It is also known as the Klebs–Löffler bacillus because it was discovered in 1884 by German bacteriologists Edwin Klebs (1834–1912) and Friedrich Löffler (1852–1915). The bacteria are usually harmless unless they are infected by a bacteriophage that carries a gene that gives rise to a toxin. This toxin causes the disease. Diphtheria is caused by the adhesion and infiltration of the bacteria into the mucosal layers of the body, primarily affecting the respiratory tract and the subsequent release of an exotoxin. The toxin has a localized effect on skin lesions, as well as a metastatic, proteolytic effects on other organ systems in severe infections. Originally a major cause of childhood mortality, diphtheria has been almost entirely eradicated due to the vigorous administration of the diphtheria vaccination in the 1910s.
Cancer immunotherapy (immuno-oncotherapy) is the stimulation of the immune system to treat cancer, improving the immune system's natural ability to fight the disease. It is an application of the fundamental research of cancer immunology (immuno-oncology) and a growing subspecialty of oncology.
Pneumococcal polysaccharide vaccine, sold under the brand name Pneumovax 23, is a pneumococcal vaccine that is used for the prevention of pneumococcal disease caused by the 23 serotypes of Streptococcus pneumoniae contained in the vaccine as capsular polysaccharides. It is given by intramuscular or subcutaneous injection.
A toxoid is an inactivated toxin whose toxicity has been suppressed either by chemical (formalin) or heat treatment, while other properties, typically immunogenicity, are maintained. Toxins are secreted by bacteria, whereas toxoids are altered form of toxins; toxoids are not secreted by bacteria. Thus, when used during vaccination, an immune response is mounted and immunological memory is formed against the molecular markers of the toxoid without resulting in toxin-induced illness. Such a preparation is also known as an anatoxin. There are toxoids for prevention of diphtheria, tetanus and botulism.
Immunogenicity is the ability of a foreign substance, such as an antigen, to provoke an immune response in the body of a human or other animal. It may be wanted or unwanted:
Pneumococcal conjugate vaccine is a pneumococcal vaccine made with the conjugate vaccine method and used to protect infants, young children, and adults against disease caused by the bacterium Streptococcus pneumoniae (pneumococcus). It contains purified capsular polysaccharide of pneumococcal serotypes conjugated to a carrier protein to improve antibody response compared to the pneumococcal polysaccharide vaccine. The World Health Organization (WHO) recommends the use of the conjugate vaccine in routine immunizations given to children.
Diphtheria toxin is an exotoxin secreted mainly by Corynebacterium diphtheriae but also by Corynebacterium ulcerans and Corynebacterium pseudotuberculosis, the pathogenic bacterium that causes diphtheria. The toxin gene is encoded by a prophage called corynephage β. The toxin causes the disease in humans by gaining entry into the cell cytoplasm and inhibiting protein synthesis.
Pneumococcal vaccines are vaccines against the bacterium Streptococcus pneumoniae. Their use can prevent some cases of pneumonia, meningitis, and sepsis. There are two types of pneumococcal vaccines: conjugate vaccines and polysaccharide vaccines. They are given by injection either into a muscle or just under the skin.
PEGylation is the process of both covalent and non-covalent attachment or amalgamation of polyethylene glycol polymer chains to molecules and macrostructures, such as a drug, therapeutic protein or vesicle, which is then described as PEGylated. PEGylation affects the resulting derivatives or aggregates interactions, which typically slows down their coalescence and degradation as well as elimination in vivo.
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Peptide-based synthetic vaccines are subunit vaccines made from peptides. The peptides mimic the epitopes of the antigen that triggers direct or potent immune responses. Peptide vaccines can not only induce protection against infectious pathogens and non-infectious diseases but also be utilized as therapeutic cancer vaccines, where peptides from tumor-associated antigens are used to induce an effective anti-tumor T-cell response.
A vaccine dose contains many ingredients very little of which is the active ingredient, the immunogen. A single dose may have merely nanograms of virus particles, or micrograms of bacterial polysaccharides. A vaccine injection, oral drops or nasal spray is mostly water. Other ingredients are added to boost the immune response, to ensure safety or help with storage, and a tiny amount of material is left-over from the manufacturing process. Very rarely, these materials can cause an allergic reaction in people who are very sensitive to them.
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Dan M. Granoff is an infectious disease physician-scientist who was named the 2014 Maurice Hilleman/Merck Laureate by the American Society for Microbiology for outstanding contributions to vaccine discovery and development. Beginning in 2011, Granoff held the Clorox Foundation Endowed Chair and was director of the Center of Immunobiology and Vaccine Development at Children's Hospital Oakland Research Institute. His work increased understanding of basic mechanisms of human immunity to encapsulated bacteria, and furthered development of vaccines against Haemophilus influenzae type B (Hib) and Neisseria meningitidis.
