Clinical utility of the lymphocyte proliferation assay, an in vitro functional readout of the adaptive immune response

Despite great advancements in the discovery of genetic variants underlying inborn errors of immunity, functional assessment of the immunological profile of patients in routine clinical practice remains challenging. The lymphocyte proliferation assay using 3H-thymidine incorporation has been the gold standard for decades for functional evaluation of T cells in the clinical laboratory, however, recently developed flow cytometric methods allowing for single cell analysis provide non-radioactive alternatives. Understanding the technical and analytical challenges of test development, validation and maintenance is essential for correct interpretation and test utilization, to assure appropriate and timely patient care. This review will discuss the technological aspects, validation and clinical utilization of in vitro lymphocyte proliferation assays performed in the clinical immunology laboratory, providing a diagnostic readout for T lymphocyte function, an essential hallmark of a functional cellular immune response, and allowing for the detection of impaired responses such as in patients with functional T cell defects.