Effect of CD3δ Deficiency on Maturation of α/β and γ/δ T-Cell Lineages in Severe Combined Immunodeficiency

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Abstract
The T-cell–receptor complex consists of the α and β or γ and δ variant chains, paired as mutually exclusive heterodimers in association with the invariant chains CD3γ, δ, ε, and ζ. T cells with α and β chains are referred to as α/β T cells, and those with γ and δ chains are called γ/δ T cells. During development, the CD3 protein complex plays an important part in the transition of thymocytes from CD4–CD8– double-negative immature precursors to a CD4+CD8+ double-positive stage and finally to the mature CD4+CD8– or CD4–CD8+ single-positive T cell.1-5 Selective deficiency of CD3 component γ, δ, ε, or ζ in mice, achieved by gene knockout, causes mild-to-severe, although incomplete, blockage of T-cell development.6-10 Similarly, CD3γ or CD3ε deficiency in humans brings about a partial arrest of T-cell maturation and only moderate immunodeficiency.11,12