T lymphocyte development in the absence of CD3 epsilon or CD3 gamma delta epsilon zeta

CD3 gamma, delta, epsilon, and zeta proteins together with the pre-TCR alph a-chain (pT alpha) and a rearranged TCR beta-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 pT alpha and TCR bet a-chains in prothymocytes and are expressed intracellularly in precursor NK cells, suggesting that the CD3 complex may function independent of pT alph a and TCR beta. In this report, both the role of CD3 epsilon exclusively, a nd the role of CD3 proteins collectively, in thymocyte and NK cell developm ent were examined. In a mouse strain termed epsilon(Delta P), a neomycin ca ssette inserted within the CD3 epsilon promoter abolishes CD3 epsilon and d elta expression and also abolishes CD3 gamma expression in all but a small minority (less than or equal to 1%) of prothymocytes. These prothymocytes b ecame deficient in CD3 epsilon alone upon reconstitution of CD3 delta expre ssion and were severely, but not completely, arrested at the DN stage, as s mall numbers of double positive thymocytes were detected. In de facto CD3 g amma delta epsilon zeta(null) mice generated by crossing the epsilon(Delta P) mice with CD3 zeta(-/-) mice, thymopoiesis were arrested at the CD44(-)C D25(+) DN stage as observed in RAG(-/-) mice, DJ and VDJ recombination at t he TCR beta locus was functional, and normal numbers of Mt cells were detec ted, Together, the findings demonstrate that during thymocyte development, the CD3 complex collectively is not essential until the critical CD44(-)CD2 5(+) DN stage in which pre-TCR begins to function, whereas CD3 epsilon is c ritical for the assembly of pre-TCR, Moreover, CD3 proteins are dispensable for NK cell development.