CD3G or CD3D Knockdown in Mature, but Not Immature, T Lymphocytes Similarly Cripples the Human TCRαβ Complex

The human alpha beta T-cell receptor (TCR) is composed of a variable heterodimer (TCR alpha beta) and three invariant dimers (CD3 gamma epsilon, CD3 delta epsilon, and zeta zeta/CD247(2)). The role of each invariant chain in the stepwise interactions among TCR chains along the assembly is still not fully understood. Despite the high sequence homology between CD3 gamma and CD3 delta, the clinical consequences of the corresponding immunodeficiencies (ID) in humans are very different (mild and severe, respectively), and mouse models do not recapitulate findings in human ID. To try to understand such disparities, we stably knocked down (KD) CD3D or CD3G expression in the human Jurkat T-cell line and analyzed comparatively their impact on TCR alpha beta assembly, transport, and surface expression. The results indicated that TCR ensembles were less stable and CD3 epsilon levels were lower when CD3 gamma, rather than CD3 delta, was scarce. However, both defective TCR ensembles were strongly retained in the ER, lacked zeta zeta/CD247(2), and barely reached the T-cell surface (<11% of normal controls) in any of the CD3 KD cells. This is in sharp contrast to human CD3 gamma ID, whose mature T cells express higher levels of surface TCR (>30% vs. normal controls). CD3 KD of human T-cell progenitors followed by mouse fetal thymus organ cultures showed high plasticity in emerging immature polyclonal T lymphocytes that allowed for the expression of significant TCR levels which may then signal for survival in CD3 gamma, but not in CD3 delta deficiency, and explain the immunological and clinical disparities of such ID cases.

Automated summary

This study investigated the different roles of the invariant chains CD3 gamma and CD3 delta in the assembly of the human αβ T-cell receptor (TCR) and found that deficiencies in CD3 gamma had a greater impact. Deficiencies in CD3 gamma result in higher levels of surface TCR in humans, while deficiencies in CD3 delta lead to a more stable but insufficiently expressed TCR ensemble, retention in the endoplasmic reticulum, and lack of surface expression.