T Lymphocyte Development in the Absence of CD3ε or CD3γδεζ

Abstract CD3γ, δ, ε, and ζ proteins together with the pre-TCR α-chain (pTα) and a rearranged TCR β-chain assemble to form the pre-TCR that controls the double negative (DN) to double positive (DP) stages of thymopoiesis. The CD3 proteins are expressed before pTα and TCR β-chains in prothymocytes and are expressed intracellularly in precursor NK cells, suggesting that the CD3 complex may function independent of pTα and TCRβ. In this report, both the role of CD3ε exclusively, and the role of CD3 proteins collectively, in thymocyte and NK cell development were examined. In a mouse strain termed εΔP, a neomycin cassette inserted within the CD3ε promoter abolishes CD3ε and δ expression and also abolishes CD3γ expression in all but a small minority (≤1%) of prothymocytes. These prothymocytes became deficient in CD3ε alone upon reconstitution of CD3δ expression and were severely, but not completely, arrested at the DN stage, as small numbers of double positive thymocytes were detected. In de facto CD3γδεζnull mice generated by crossing the εΔP mice with CD3ζ−/− mice, thymopoiesis were arrested at the CD44−CD25+ DN stage as observed in RAG−/− mice, DJ and VDJ recombination at the TCRβ locus was functional, and normal numbers of NK cells were detected. Together, the findings demonstrate that during thymocyte development, the CD3 complex collectively is not essential until the critical CD44−CD25+ DN stage in which pre-TCR begins to function, whereas CD3ε is critical for the assembly of pre-TCR. Moreover, CD3 proteins are dispensable for NK cell development.