T lymphocytes (T cells) play critical roles in the regulation of immune responses,
and are responsible for mediating many of the effector mechanisms of the immune
system. For this reason, there has always been a need for assays to measure
accurately the activity of populations of T cells, both in model (animal) systems
and in humans. The expansion of the biotechnology industry has led to a dramatic
increase in the number of novel immunotherapeutics that are being developed
for the treatment of cancer, autoimmune disorders and infectious diseases. This
increase in activity in the field of immunotherapy, coupled with the expense
of clinical trials, has led to renewed interest in methods that accurately assess
T-cell function, as researchers seek to maximise the amount of information that
can be obtained from each clinical study. Assessing the quantitative and qualitative
nature of a T-cell response, for example following vaccination or immunosuppressive
therapy, can provide valuable information about the efficacy of a treatment,
in place of a clinical endpoint. This article reviews some of the established
methods that are used to monitor human T-cell activity, and describes some new
approaches that are in development to increase the speed, sensitivity and relevance
of such methods.