Viral Vector Multiplicity of Infection

Vector Dose

Multiplicity of infection (MOI) 3.0

Copies needed to transduce 1

Cell monolayer size 8 × 8

Readouts

Predicted transduced

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Measured transduced

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Mean vector copies / cell (target vs. landed)

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Legend

0 copies landed

Below threshold

Transduced (≥ threshold)

Falling vector particle

How it works

When a fixed dose of viral vector particles is added to a dish of N cells, particles land on cells essentially at random. If the average number of particles per cell is the multiplicity of infection (MOI), the number of particles landing on any one cell follows a Poisson distribution:

P(k particles on a cell) = MOI^k · e^(−MOI) / k!

A cell only becomes transduced once it has received at least a threshold number m of functional vector genomes (many real vectors need more than one copy before enough transgene product accumulates, especially before second-strand synthesis or concatemerization completes). The predicted transduced fraction is:

P(transduced) = 1 − Σ (k = 0 to m−1) MOI^k · e^(−MOI) / k!

m = 1 (classic single-hit case): P(transduced) = 1 − e^(−MOI)

MOI slider — sets the average vector dose per cell; the total particle count seeded (MOI × cell count) is placed uniformly at random across the monolayer, exactly as pipetting a titred vector stock onto a dish would.
Copies needed — the minimum vector genomes (m) a cell must receive before it counts as transduced.
Monolayer size — the number of target cells N; larger N makes the measured fraction converge more tightly to the Poisson prediction (law of large numbers).
Apply Vector Dose — reseeds a fresh random particle placement and replays the "infection" as particles fall onto the monolayer.

Real-world relevance: this is the exact calculation vector-production and gene-therapy labs use to choose a dose — e.g. "MOI 3" for a lentiviral or AAV prep — so that a target percentage of cells receive at least one (or several) copies of the therapeutic gene, while keeping the vector genome burden per cell (and manufacturing cost) as low as possible.

Vector genomes seeded: 0 | landed: 0

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Viral Vector Multiplicity of Infection: Poisson Transduction Statistics