100％感染需要多少病毒顆粒？

What is multiplicity of infection?

MOI是感染因子與感染目標的比率。在許多情況下，它是指在特定空間（例如細胞培養孔）中病毒顆粒與靶細胞的比率。

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.

MOI =	Infectious Agents	=	Viral Particles
	Infection Targets		Target Cells

如果將一千萬個病毒添加到一百萬個細胞中，則MOI為10，而感染一個細胞的病毒顆粒的平均概率為10。

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.

MOI =	Viral Particles
	Target Cells

MOI =	10 million viral particles
	1 million cells

MOI = 10

A simple sample calculation

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 10⁶ IU/ml and you are delivering to 1 x 10⁵ cells, what volume of virus will you need for your project?

假設您希望將MOI設置為10，如果您的病毒效價為1 x 106 IU / ml，並且要傳遞給1 x 105個細胞

We’ll use the following calculation:

MOI =	Virus Titer X Virus Volume
	Total Cell Number

10 =	1 x 106 IU/ml X ?
	1 x 105 cells

  = 1 ml

So you will need 1.0 ml of virus to achieve an MOI of 10.

Factors that can affect your MOI

So, based on the 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: dividing or non-dividing
• the characteristics of the virus: lentivirus, adenovirus, etc.
• the transduction efficiency
• your application: transducing a packaging cell line for virus production, generating a stable cell line for protein production, etc.

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 <1 is typically recommended. This is because passaging baculoviruses at higher MOIs increases the possibility of transferring large amounts of defective, non-infectious viruses.

AAV, in contrast, requires MOI ranges of 10,000 to 500,000.

Essentially, if the MOI is too high, it can cause cytotoxicity or other undesired effects. If the MOI is too low, it will not achieve 100% infection.

Do a pilot experiment to find your optimal MOI

So, how do you determine the optimal MOI for your experiment? Simply perform a pilot experiment using a reporter virus on your target cell line!

General workflow:

Step 1: Select 6 MOI conditions to test
For example, using a GFP Lentivirus, design a range of MOIs to use, let’s say, 6 conditions ranging from MOIs 1, 2, 5, 10, 15, and 30. It is typically better to test a lower MOI range to avoid cytotoxicity at the higher MOIs. A good starting point would be to reference commonly used MOI for cancer cells and devise the range around the suggested MOI.

Step 2: Infect your target cells and record results

After you have infected your cells, allow the appropriate time to pass before evaluating the fluorescence. For lentiviruses, this is generally 48 -72 hours post infection. Next, record the fluorescence at the various MOIs to determine your transduced cell percentage.

Step 3: Select the minimum MOI at which all the cells are expressing the transgene.

Here is an example of how your results may look like. In this case, a minimum MOI of 10 is required for 100% infection of the target cells.

If your cells are naturally harder to transduce, there are transduction enhancers such as polybrene or our ViralMax Transduction Enhancers to increase infectivity performance.

Summary Video (Duration: 5 min)

We hope you found this blog post helpful in determining the optimal conditions for transduction of your virus to your target cells. At abm, we offer a ready-to-use collection of Lenti-, AAV, Adeno, and Retroviruses for any human, mouse, and rat gene! Browse our collection of tools and resources for gene expression today!

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