What MOI Should I Use for a Lentiviral CRISPR Library?

Target MOI 0.1–0.3. At MOI 0.1, roughly 90% of transduced cells carry a single guide; at 0.3, roughly 70%. Both keep the majority of cells interpretable as single-perturbation units.

Higher MOI increases the fraction of cells with multiple guides, which makes any phenotype ambiguous: you cannot say which guide caused it.

The proportion of cells with exactly one integrated guide follows a Poisson distribution. At MOI 0.3:

• • ~22% of cells receive no guide (lost to selection)
• • ~22% receive exactly one... and the remainder receive two or more

At MOI 1.0, fewer than 40% of transduced cells carry a single guide — and in a library where most guides have no effect, double integrants systematically distort hit calling toward combinations.

Two practical methods:

1. Titration with a marker. Transduce a serial dilution of the virus carrying a fluorescent or resistance marker alongside the library; measure the fraction positive by flow cytometry at low dose, and pick the volume giving the target percentage.
2. Colony or viability assay. Under selection, compare colony counts between a fully transduced control and dilutions; the ratio gives the transducing units per cell.

Report the measured MOI and the method. "MOI 0.3" without a measurement is an assumption.

• • Titre varies by batch and cell type. Re-titrate for each new virus prep and each new target line; a titre measured in HEK293 does not transfer to primary cells.
• • Polybrene and spinoculation change effective MOI substantially; keep conditions constant across arms of a screen.
• • Selection timing. Start selection 48–72 hours after transduction; too early kills cells before integration is expressed, too late allows untransduced cells to overgrow.
• • Verify by sequencing. Sequence the integrated cassettes in the transduced pool; the guide distribution should be broad, and the fraction of cells with multiple guides can be estimated from co-occurrence.

Higher MOI is sometimes used to "ensure every cell gets a guide". That goal is met by adequate coverage of transduced cells, not by multiple integrations per cell. If too few cells are transduced, the fix is more cells or better transduction — not a higher MOI.

EDITGENE characterizes transduction conditions per cell line, reports measured MOI and the fraction of single integrants, and validates guide distribution in the transduced pool before a screen begins.

Tell us the library and cell line. Contact EDITGENE to request a project consultation or quote.

The single-integration fractions above follow a Poisson model and will differ with cell type, viral prep, and transduction protocol; measurement in your system is required.

Screens should report measured MOI, transduction efficiency, and integration status rather than nominal values.

• • Shalem O, et al. Genome-scale CRISPR-Cas9 knockout screening in human cells. Science. 2014;343:84–87.
• • Doench JG. Am I ready for CRISPR? A user's guide to genetic screens. Nature Reviews Genetics. 2018;19:67–80.
• • Joung J, et al. Genome-scale CRISPR-Cas9 knockout and transcriptional activation screening. Nature Protocols. 2017;12:828–863.