A capsid antibody is serotype specific unless it is raised against a conserved region, so the reagent and the vector have to be matched before anything is measured. The other half of this work is counting: genome copies, capsid particles and infectious units are three different numbers from the same tube.
rcaav, and what a recombinant vector is
A recombinant vector, written rcaav in some catalogues, carries a transgene between the inverted repeats and none of the viral coding sequence, which is why it cannot replicate without helper functions supplied in production. What matters for a reagent order is which serotype's capsid it wears, since tropism and the antibodies that detect it follow the capsid rather than the genome.
aav5 and the tropism that distinguishes it
aav5 has a distinct receptor use and a strong preference for airway and central nervous tissue, so it is chosen for those rather than for general expression, and its capsid is different enough that many serotype antibodies do not cross react. Pre-existing neutralising antibodies in a population differ by serotype too, which is the reason a programme screens for them.
aav8 and liver directed work
aav8 is the usual choice for liver directed expression and crosses from blood to hepatocytes efficiently, which is why dose comparisons between it and other serotypes are not like for like. Its capsid antibodies are serotype specific. Empty capsid content matters more at high dose, so the measurement that limits a study is often the full to empty ratio rather than the titre.
aav2 as the reference serotype
aav2 is the best characterised serotype and the reference most reagents and protocols were built on, which is why a new capsid is described by how it differs from it. Its receptor is broadly expressed, giving wide but not strong tropism. Most conserved epitope antibodies were raised against it, so cross reactivity claims usually start from this capsid.
An aav titer assay and the three numbers it can give
An aav titer assay reports genome copies by quantitative PCR or droplet digital PCR, capsid particles by an immunoassay, or infectious units by a cell based assay, and the ratios between them are the quality measures rather than nuisances. Nuclease treatment before extraction is what stops unpackaged DNA inflating a genome titre, and a reference material is what makes two laboratories comparable.
An adenovirus vector, and why the distinction matters here
An adenovirus vector is a different platform with a larger cargo, a stronger innate response and no integration, and it is often confused with the smaller parvoviral vectors in a catalogue search. Helper functions for parvoviral production historically came from adenovirus, which is the source of the confusion. Detection reagents for one do not recognise the other.
An rcaav assay and what it is looking for
An rcaav assay tests for replication competent vector, which is a safety attribute rather than a potency one, and it is a cell based amplification and detection method with a stated limit expressed per vector genome. The limit rather than a pass or fail is what a report has to carry, and the assay's sensitivity is what makes that limit meaningful.
aav packaging plasmids and what a set contains
aav packaging plasmids are a set: the vector carrying the transgene between the inverted repeats, a plasmid supplying replication and capsid functions, and a helper supplying the adenoviral genes, and the capsid plasmid decides the serotype. Plasmid grade matters because residual plasmid DNA in the product is a release specification downstream.
Questions people ask about aav antibodies
Will a serotype antibody detect another capsid?
Only if it was raised against a conserved region and says so. Most are serotype specific.
Which titre should be reported?
Whichever the dose was set by, with the assay named. Genome copies, capsid particles and infectious units differ.
Why treat with nuclease before a genome titre?
Unpackaged DNA is otherwise counted, which inflates the titre.