Dr Paula Fernandez, MD/PhD
President, European Society for Clinical Flow Cytometry (ESCCA)
Cancer cells differ from normal in their expression of cellular antigens. Flow cytometry enables us to characterise cells, therefore allowing us to differentiate between types of cells.
Cell types differ from each other by the antigens they express. The profile of antigens expressed on a given cell constitutes its immunophenotype and is a constant characteristic by which cells can be divided into different cell lineages (e.g. red blood cell vs white blood cells), maturation stages (mature cells versus precursor cell) or activation states, among other things.
Normal cells look alike, but not cancer cells – they usually show some type of immunophenotypic deviation. These deviations in immunophenotype not only allow for disease classification at diagnosis, but also detection of remaining tumour cells during therapy.
New tests are being devised and validated to monitor new cellular therapies.
The more, the better
Flow cytometry is a technique used to characterise the immunophenotype of cells. Fluorescently-labelled probes specific for an antigen will bind to cells expressing that specific antigen. The probes will emit light when these cells cross a laser beam – that light is then measured and quantified. Its value is directly related to the number of antigens expressed. The more antigens we can simultaneously test on a single cell, the better we can differentiate between cells, even if the differences in immunophenotype are slight, providing diagnostic tests with specificity. The chance of finding rare cancer cells among normal cells becomes higher the greater the number of cells analysed.
Clinical flow cytometry is a powerful tool that can be exploited to analyse the characteristics of a homogenous cell population in great detail or decipher the composition of a highly complex mixture of cells and any combinations thereof depending on the desired scope of the diagnostic test.
The boundaries in the field of clinical flow cytometry are being pushed hard in many different ways. Within a decade, technical progress on the instrument side has increased the number of simultaneously measured parameters by tenfold and greatly increased the speed of measurements to enable the analysis of millions of cells instead of thousands.
The array of reagents has increased to match these new possibilities. New formulations of reagents and their combination into ready-to-use kits have simplified test conditions. Standardised and validated diagnostic techniques have been adopted by many diagnostic labs, leading to an increase in diagnostic quality.
New tests are being devised and validated to monitor new cellular therapies. New tools for handling and interpreting massively increased data sets are being developed and increasingly deployed in our diagnostic routine. In this rapidly evolving field of clinical flow cytometry, the only constant has been change.