Designing and interpreting limiting dilution assays: general principles and applications to the latent reservoir for HIV-1

Limiting dilution assays are commonly used to measure the extent of infection, and in the context of HIV they represent an essential tool for studying latency and potential curative strategies. To assist investigators using dilution assays, we illustrate the major statistical method for estimating the frequency of infected cells (or other infectious units) from assay results, and we offer an online tool for computing this estimate. We then recommend a procedure for optimizing assay design to achieve any desired set of sensitivity and precision goals, subject to experimental constraints. We discuss challenges involved in interpreting experiments in which no viral growth is observed and explain how using alternative measures for viral outgrowth may make measurement of HIV latency more efficient. Finally, we discuss how biological complications – such as probabilistic growth of a small infection in culture – alter interpretations of experimental results.