Multiplicity of Infection (MOI): What is it and how do I calculate it?

Multiplicity of Infection (MOI): What is it and how do I calculate it?


So you’ve packaged your DNA into a virus
and you’re ready to infect your cells! But, how many viral particles are required
for 100% infection? In this video, we’ll explain the concept
of Multiplicity of Infection or MOI and take you through how to determine the best MOI
for your experiment. In a nutshell, MOI is the ratio of infectious
agents to infection targets. In many cases, it is the ratio of viral particles
to target cells in a defined space, such as a cell culture well. For example, if you add 10 million viruses
to 1 million cells, you’d have an MOI of 10 and an average probability of 10 viral
particles infecting one cell. Let’s do a quick example calculation! Let’s say you’d like to achieve an MOI
of 10. If your virus titer is 1 x 10^6 infection units
per ml and you are delivering to 1 x 10^5 cells, what volume of virus will you need for your
project? You will need 1.0 ml of virus. So, based on this simple definition of MOI,
you would expect that if your MOI was one, then each cell would be infected by one virus. But the reality is not as simple! Why? Imagine yourself throwing 100 tennis balls
into a room that has 100 buckets. Theoretically, there is one ball for every
bucket. But in reality, the chance of every bucket
getting 1 ball is very low! There are other factors to consider, such
as do the buckets have backboards that would make it easier to make the shot? Similarly, there are factors that can affect
how easily viruses can infect their target cells, such as the current state of your cell
line – whether it is dividing or non-dividing, the characteristics of the virus – whether
it is a lentivirus or adenovirus, the transduction efficiency, and your application – whether
you are transducing a packaging cell line for virus production or a stable cell line
for protein production. For example, if the cell is in a non-dividing
state, a higher MOI may be needed to achieve optimal transduction efficiency. This is the case when infecting neuronal cells
such as SH-SY5Y with lentiviruses for gene delivery where a much higher MOI of 10-50
can be required. On the other hand, when it comes to infecting
insect cells such as Sf9 cells with baculovirus for viral production, a low MOI of


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