Subunit vaccine

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A subunit vaccine is a vaccine that contains purified parts of the pathogen that are antigenic, or necessary to elicit a protective immune response. [1] [2] A "subunit" vaccine doesn't contain the whole pathogen, unlike live attenuated or inactivated vaccine, but contains only the antigenic parts such as proteins, polysaccharides [1] [2] or peptides. Because the vaccine doesn't contain "live" components of the pathogen, there is no risk of introducing the disease, and is safer and more stable than vaccine containing whole pathogens. [1] Other advantages include being well-established technology and being suitable for immunocompromised individuals. [2] Disadvantages include being relatively complex to manufacture compared to some vaccines (such as RNA vaccine), possibly requiring adjuvants and booster shots, and requiring time to examine which antigenic combinations may work best. [2]

Contents

Mechanism

Subunit vaccines contain fragments of the pathogen, such as protein or polysaccharide, whose combinations are carefully selected to induce a strong and effective immune response. Because the immune system interacts with the pathogen in a limited way, the risk of side effects is minimal. [2] An effective vaccine would elicit the immune response to the antigens and form memory that allows quick recognition of the pathogens and quick response to future infections. [1]

A drawback is that the specific antigens used in a subunit vaccine may lack pathogen-associated molecular patterns which are common to a class of pathogen. These molecular structures may be used by immune cells for danger recognition, so without them, the immune response maybe weaker. Another drawback is that the antigens do not infect cells, so the immune response to the subnit vaccines may only be antibody-mediated, not cell-mediated, and as a result, is weaker than those ellicited by other types of vaccines. To increase immune response, adjuvants may be used with the subunit vaccines, or booster doses may be required. [2]

Types

Summary of subunit vaccine types [1] [2]
TypesDescriptionExamples
Protein subunit contains isolated proteins from pathogens (virus or bateria) hepatitis B, acellular pertussis vaccines
Polysaccharide contains chains of polysaccharides (sugar molecules) found in the pathogen's capsule such as cell walls of some bacteria pneumococcal polysaccharide vaccine, meningococcal vaccine preventing diseases from Neisseria meningitidis group A, C, W-135, and Y
Conjugate contains polysaccharide chains bound to carrier proteins, such as diphtheria and tetanus toxoid, to boost the immune response pneumococcal conjugate vaccine, haemophilus influenzae type b conjugate vaccine, meningococcal conjugate vaccine

Protein subunit

A protein subunit is a single protein molecule that assembles (or "coassembles") with other protein molecules to form a protein complex.[ citation needed ]

One method of production of protein-based subunits involves isolation of a specific protein from a virus and administering this by itself. A weakness of this technique is that isolated proteins can be denatured.[ citation needed ] A second method of making a subunit vaccine involves putting an antigen's gene from the targeted virus or bacterium into another virus (virus vector), yeast (yeast vector), as in the case of the hepatitis B vaccine [3] or attenuated bacterium (bacterial vector) to make a recombinant virus or bacteria to serve as the important component of a recombinant vaccine (called a recombinant subunit vaccine). The recombinant vector that is genomically modified will express the antigen. The antigen (one or more subunits of protein) is extracted from the vector. [3] Just like the highly successful subunit vaccines, the recombinant-vector-produced antigen will be of little to no risk to the patient. This is the type of vaccine currently in use for hepatitis B, [3] and it is experimentally popular, being used to try to develop new vaccines for difficult-to-vaccinate-against viruses such as ebolavirus and HIV. [4]

Polysaccharide subunit

Vi capsular polysaccharide vaccine (ViCPS) against typhoid caused by the Typhi serotype of Salmonella enterica. [5] Instead of being a protein, the Vi antigen is a bacterial capsule polysacchide, made up of a long sugar chain linked to a lipid. [6] Capsular vaccines like ViCPS tend to be weak at eliciting immune responses in children. Making a conjugate vaccine by linking the polysacchide with a toxoid increases the efficacy. [7]

Conjugate vaccine

A conjugate vaccine is a type of 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.[ citation needed ]

Peptide subunit

A peptide-based subunit vaccine employs a peptide instead of a full protein.[ citation needed ]

Virus-like particles

Virus-like particle (VLP) vaccines use VLPs, which are proteins that mimic real virus particles. [8] They generally consist of proteins assembled into the natural shape of the virus' outer shell (capsid).[ citation needed ]

Advantages and disadvantages

Advantages

Disadvantages

Related Research Articles

Antigen Molecule triggering an immune response (antibody production) in the host

In immunology, an antigen (Ag) is a molecule or molecular structure that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. The term antigen originally referred to a substance that is an antibody generator. Antigens can be proteins, peptides, polysaccharides, lipids, nucleic acids, or other biomolecules.

Vaccine Pathogen-derived preparation that provides acquired immunity to an infectious disease

A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future. Vaccines can be prophylactic, or therapeutic. Some vaccines offer full sterilizing immunity, in which infection is prevented completely.

DNA vaccine Vaccine containing DNA

A DNA vaccine is a type of vaccine that transfects a specific antigen-coding DNA sequence into the cells of an organism as a mechanism to induce an immune response.

HIV vaccine development In-progress vaccinations that may prevent or treat HIV infections

A HIV vaccine is potential vaccine that could be either a preventive vaccine or a therapeutic vaccine, which means it would either protect individuals from being infected with HIV or treat HIV-infected individuals.

In biology, immunity is the capability of multicellular organisms to resist harmful microorganisms. Immunity involves both specific and nonspecific components. The nonspecific components act as barriers or eliminators of a wide range of pathogens irrespective of their antigenic make-up. Other components of the immune system adapt themselves to each new disease encountered and can generate pathogen-specific immunity.

Exotoxin

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.

Polyclonal antibodies (pAbs) are antibodies that are secreted by different B cell lineages within the body. They are a collection of immunoglobulin molecules that react against a specific antigen, each identifying a different epitope.

Conjugate vaccine Type of vaccine

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.

Virus-like particles (VLPs) are molecules that closely resemble viruses, but are non-infectious because they contain no viral genetic material. They can be naturally occurring or synthesized through the individual expression of viral structural proteins, which can then self assemble into the virus-like structure. Combinations of structural capsid proteins from different viruses can be used to create recombinant VLPs. VLPs derived from the Hepatitis B virus (HBV) and composed of the small HBV derived surface antigen (HBsAg) were described in 1968 from patient sera. VLPs have been produced from components of a wide variety of virus families including Parvoviridae, Retroviridae, Flaviviridae, Paramyxoviridae and bacteriophages. VLPs can be produced in multiple cell culture systems including bacteria, mammalian cell lines, insect cell lines, yeast and plant cells.

Malaria vaccine Vaccine that is used to prevent malaria

A malaria vaccine is a vaccine that is used to prevent malaria. The only approved vaccine, as of 2021, is RTS,S, known by the brand name Mosquirix. It requires four injections.

The Vi capsular polysaccharide vaccine is a typhoid vaccine recommended by the World Health Organization for the prevention of typhoid. The vaccine was first licensed in the US in 1994 and is made from the purified Vi capsular polysaccharide from the Ty2 Salmonella Typhi strain; it is a subunit vaccine.

Ty21a

Ty21a is a live attenuated bacterial vaccine that protects against typhoid. First licensed in Europe in 1983 and in the United States in 1989, it is an orally administered, live-attenuated Ty2 strain of S. Typhi in which multiple genes, including the genes responsible for the production of Vi, have been deleted so as to render it harmless but nevertheless immunogenic. It is one of the three typhoid vaccines currently recommended by the World Health Organization.

Immune stimulating complexes (ISCOMs) are spherical open cage-like structures that are spontaneously formed when mixing together cholesterol, phospholipids and Quillaja saponins under a specific stoichiometry. The complex displays immune stimulating properties and is thus mainly used as a vaccine adjuvant in order to induce a stronger immune response and longer protection.

Typhoid vaccines are vaccines that prevent typhoid fever. Several types are widely available: typhoid conjugate vaccine (TCV), Ty21a and Vi capsular polysaccharide vaccine (ViPS). They are about 30 to 70% effective in the first two years, depending on the specific vaccine in question. The Vi-rEPA vaccine has been shown to be efficacious in children.

A hepatitis C vaccine, a vaccine capable of protecting against the hepatitis C virus (HCV), is not yet available. Although vaccines exist for hepatitis A and hepatitis B, development of an HCV vaccine has presented challenges. No vaccine is currently available, but several vaccines are currently under development.

Inactivated vaccine Vaccine using a killed version of a disease pathogen

An inactivated vaccine is a vaccine consisting of virus particles, bacteria, or other pathogens that have been grown in culture and then killed to destroy disease-producing capacity. In contrast, live vaccines use pathogens that are still alive. Pathogens for inactivated vaccines are grown under controlled conditions and are killed as a means to reduce infectivity and thus prevent infection from the vaccine.

Peptide-based synthetic vaccines, also called epitope 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.

Edward Thomas Ryan

Edward T. (Thomas) Ryan is an American microbiologist, immunologist, and physician at Harvard University and Massachusetts General Hospital. Ryan served as President of the American Society of Tropical Medicine and Hygiene from 2009 to 2010. Ryan is Professor of Immunology and Infectious Diseases at the Harvard T.H. Chan School of Public Health, Professor of Medicine at Harvard Medical School, and Director of Global Infectious Diseases at the Massachusetts General Hospital. Ryan's research and clinical focus has been on infectious diseases associated with residing in, immigrating from, or traveling through resource-limited areas. Ryan is a Fellow of the American Society of Microbiology, the American Society of Tropical Medicine and Hygiene, the American College of Physicians, and the Infectious Diseases Society of America.

Vaccine ingredients Ingredients used in a vaccine dose

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.

A genetic vaccine is a vaccine that contains nucleic acids such as DNA or RNA that lead to protein biosynthesis of antigens within a cell. Genetic vaccines thus include DNA vaccines, RNA vaccines and viral vector vaccines.

References

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  8. Noad R, Roy P (2003-09-01). "Virus-like particles as immunogens". Trends in Microbiology. 11 (9): 438–444. doi:10.1016/S0966-842X(03)00208-7. ISSN   0966-842X. PMID   13678860.
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