Flow cytometry and the future of vaccine development.

Vaccine research increasingly aims to understand the fundamental mechanisms of protection afforded by licensed and candidate vaccines. Historically, nearly all licensed vaccines have relied on measures of humoral immunity to provide correlates of protection, but cellular immunity is important for protection afforded by some vaccines and will be required for vaccines against TB and malaria. Common means of assessing vaccine-induced immune responses include measuring the frequency and functions of antigen-specific lymphocytes. While diverse assays can provide this information, flow cytometry is unique in its ability to simultaneously report other features of antigen-specific cellular responses. Here, we review the application of flow cytometry to characterizing three areas of immune responses to vaccines or diseases. First, analysis of cellular (T-cell) responses is more mature: polychromatic flow cytometric analysis of T-cell function has already yielded important insight into correlates of protection. Second, antibody and antigen-specific B-cell detection by flow cytometry are being actively developed; to date, these assays are not yet widely used. Finally, flow cytometry can also be used to analyze the contribution of innate immunity to vaccine efficacy and disease pathogenesis.