T-cell repertoire diversity and clonal expansions in normal and clinical samples.

Improved polymerase chain reaction (PCR)-based methods now permit a more in-depth analysis of the repertoire of T cells recovered in biological samples from mice and humans. At a certain level of resolution, the diversity of the T-cell repertoire can be readily estimated and clonal expansions become easily detectable. As discussed here by Christophe Pannetier, Jos Even and Philippe Kourilsky, these improvements allow a better appreciation of the degree of reproducibility of immune responses, both in mice and humans, and should have a significant impact on clinical investigations.