Flow Cytometric Analysis of TCR Vβ Repertoire in Patients with 22q11.2 Deletion Syndrome

In 22q11.2 deletion patients, the normal decrease in T lymphocyte counts after 1–2 years is blunted such that relatively T lymphocyte numbers increase over early childhood, probably via post‐thymic expansion of peripheral lymphocytes. This may leave less T lymphocyte receptor (TCR) diversity than when derived from naive thymic emigrants. We analysed TCR Vβ repertoire on 27 22q11.2 chromosome deletion patients. No patient had infection at sampling. CD3+CD4+ recent thymic emigrants (RTEs) were identified by CD45RA and CD31 expression. TCR Vβ repertoire was determined using four‐colour flow cytometry. Patients and controls showed significant TCR Vβ family usage differences between CD3+CD4+ and CD3+CD4− T lymphocyte subpopulations. Vβ family abnormalities (±3 SD of controls) were identified in 18/27 (67%) patients and 12/47 (25%) controls. In patients, the magnitude of expansions was increased, with some Vβ families representing 37% of the cells present in the subpopulations. There was a significant increase in frequency of abnormalities in CD3+CD4+ (P