A virosome is a drug or vaccine delivery mechanism consisting of unilamellar phospholipid membrane (either a mono- or bi-layer)

vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features ...

incorporating virus derived proteins to allow the virosomes to fuse with target cells.

Virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

es are infectious agents that can replicate in their host organism, however virosomes do not replicate. The properties that virosomes share with viruses are based on their structure; virosomes are essentially safely modified viral envelopes that contain the phospholipid membrane and surface glycoproteins. As a drug or vaccine delivery mechanism they are biologically compatible with many host organisms and are also biodegradable. The use of reconstituted virally derived proteins in the formation of the virosome allows for the utilization of what would otherwise be the immunogenic properties of a live-attenuated virus, but is instead a safely killed virus. A safely killed virus can serve as a promising

vector Vector most often refers to: * Euclidean vector, a quantity with a magnitude and a direction * Disease vector, an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematics a ...

because it won't cause infection and the viral structure allows the virosome to recognize specific components of its target cells.

Virosomes structure

Virosomes are vehicles that have a spherical shape with a phospholipid mono/bilayer membrane. Inside of the virosome, there is a central cavity that holds the therapeutic molecules such as nucleic acids, proteins, and drugs. On the surface of the virosome, there can be different types of

glycoprotein Glycoproteins are proteins which contain oligosaccharide (sugar) chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known a ...

s. Glycoproteins are a type of protein that have an oligosaccharide chain bonded to amino acid chains. The different types of glycoproteins on the surface of the virosome increases the specificity of the target cells because the surface glycoproteins help with recognition as well as the attachments of the virosomes to their target cells. In the case of the influenza virosome, the glycoproteins are

antigen In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

haemagglutinin The term hemagglutinin (alternatively spelt ''haemagglutinin'', from the Greek , 'blood' + Latin , 'glue') refers to any protein that can cause red blood cells (erythrocytes) to clump together (" agglutinate") ''in vitro''. They do this by bindin ...

, and

neuraminidase Exo-α-sialidase (, sialidase, neuraminidase; systematic name acetylneuraminyl hydrolase) is a glycoside hydrolase that cleaves the glycosidic linkages of neuraminic acids: : Hydrolysis of α-(2→3)-, α-(2→6)-, α-(2→8)- glycosidic linkag ...

. Antigens are molecules that triggers an immune response when targeted by a specific antibody that corresponds to the shape of the antigen. Haemagglutinin is a viral glycoprotein that causes red blood cell agglutination. Neuraminidase are enzymes that break glycosidic linkages. The size and surface molecules presented on of the virosome can be modified so that it can target different types of cells.

Virosome applications

Virosomes deliver antigens and therapeutic agents to their targeted cells. Virosomes can act as immunopotentiating agents and as agents of targeted drug delivery. Virosomes as immunopotentiating agents activate cell mediated and humoral immune responses. Virosomes are suspended in saline buffers and are administered through respiratory, parenteral, intravenous, oral, intramuscular, and topical routes.

Influenza virosomes

In contrast to

liposome A liposome is a small artificial vesicle, spherical in shape, having at least one lipid bilayer. Due to their hydrophobicity and/or hydrophilicity, biocompatibility, particle size and many other properties, liposomes can be used as drug deliver ...

s, virosomes contain functional viral envelope

s: influenza virus

hemagglutinin The term hemagglutinin (alternatively spelt ''haemagglutinin'', from the Greek , 'blood' + Latin , 'glue') refers to any protein that can cause red blood cells (erythrocytes) to clump together (" agglutinate") ''in vitro''. They do this by bindin ...

(HA) and

(NA) intercalated in the

phospholipid Phospholipids are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...

bilayer membrane. They have a typical mean diameter of 150 nm. Essentially, virosomes represent reconstituted empty

influenza virus ''Orthomyxoviridae'' () is a family of negative-sense RNA viruses. It includes nine genera: '' Alphainfluenzavirus'', '' Betainfluenzavirus'', '' Gammainfluenzavirus'', '' Deltainfluenzavirus'', '' Isavirus'', '' Mykissvirus'', '' Quaranjavir ...

envelopes, devoid of the

nucleocapsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or ma ...

including the

genetic material Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nucleic aci ...

of the source

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

Non-influenza virosomes

They are also being considered for

HIV-1 The subtypes of HIV include two main subtypes, known as HIV type 1 (HIV-1) and HIV type 2 (HIV-2). These subtypes have distinct genetic differences and are associated with different epidemiological patterns and clinical characteristics. HIV-1 e ...

vaccine research. They were used as a drug carrier mechanism for experimental cancer therapies.

Benefits and challenges

The benefits of virosomes are that the specific structure and small size help with the precision of target cells. The phospholipid membrane protects the virosome from adverse reactions in the body and the membrane allows the virosome to be biocompatible and biodegradable in the body. The challenges of virosomes are the rapid detection and activation of the immune response against the viral glycoproteins, which can result in a decrease of the virosomes. However, glycoproteins can still induce a prophylactic response against the virus, which helps with establishing virosomes as vaccine delivery systems. If the virosome is administered into the bloodstream, the virosome can disintegrate. However, if the virosome can reach the target quickly enough, the drug delivery will still happen. There are some challenges with virosomes, but there are ways in which the virosome can still help activate the immune response.

References

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External links

"What are virosomes?"

"Virosome based vaccine"
Vaccination