This strain is a Tcra gene deletion model in which homozygous B6-Tcra KO mice with αβ T-cell receptor deficiency have thymuses lacking CD4+CD8- and CD4-CD8+ cells, and approximately 1.5% of thymocytes express γδ T-cell receptors. homozygous B6-Tcra KO mice are developmentally normal and fertile, but mortality increases after 6 months, and few mice survive beyond one year.