Nonsense CD247 mutations show dominant-negative features in TCR expression and function

Abstract

Background The invariant TCRζ/CD247 homodimer is crucial for TCR/CD3 expression and signaling through its three immunoreceptor tyrosine‐based activation motifs (ITAMs). Homozygous null mutations in CD247 lead to immunodeficiency, while carriers exhibit 50% reduced surface CD3. It is unclear whether carriers of other CD247 variants show dominant-negative effects.

Objective To analyze and model the potential impact on TCR expression and function of heterozygous nonsense CD247 mutations found in patients with signs of immunodeficiency or autoimmunity.

Methods Jurkat T cells, either wild-type (WT) or CRISPR/Cas9-edited CD247-deficient (ZKO), were lentivirally transduced with wild-type CD247 or mutations ablating one (Q142X), two (Q101X), or three (Q70X) ITAMs.

Results Three patients from unrelated families were studied. Two heterozygous nonsense CD247 mutations were identified (p.Y152X and p.Q101X), which affected ITAM-3 and ITAM-2+3, respectively. Both mutations were associated with low surface CD3 expression, normal intracellular CD247 levels using a transmembrane-specific antibody but very low intracellular CD247 levels using an ITAM-3-specific one, suggesting the presence of truncated variants in T cells. Transduction of the mutations lacking 1, 2, or 3 ITAMs into ZKO could not restore normal surface CD3 expression (only 60%, 22% and 10%, respectively), whereas in WT they reduced it (to 39%, 19% and 9% of normal levels), and both effects were ITAM number dependent. All six transfectants showed reduced CD69 induction (25-50%), indicating that they were unable to signal downstream properly neither isolated nor associated with wild-type CD247.

Conclusion Our results suggest that CD247 variants lacking ITAMs due to nonsense, but not null, mutations are defective for normal TCR assembly and exert a dominant-negative effect on TCR expression and signaling in vitro. This, in turn, may correlate with clinical features in vivo.