αβTCR targeting to Trac can bypass β-selection via transient γδTCR expression 2721

Abstract Description Thymocyte maturation is a tightly controlled process of TCR gene rearrangement that generates T cells with a broad repertoire and minimal self-reactivity. Thymocytes that successfully rearrange Tcrb are permitted to progress to Tcra rearrangement through a process called β-selection. We previously demonstrated that targeting an exogenous TCR to the Trac locus in murine zygotes, referred to as TCR exchange (TRex) mice, results in physiological T cell development and function. TRex mice contain T cells that primarily express the exogenous TCR of interest. A minority of T cells from TRex mice can co-express endogenous and exogenous TCRβ, raising the hypothesis that endogenous Tcrb rearrangement is required for Trac-integrated TCR expression and TRex T cell maturation. To evaluate this, we generated TRex mice lacking endogenous Tcrb. We show that most TRex thymocytes proceed through β-selection when endogenous Tcrb is intact. However, in the absence of endogenous Tcrb, γδTCR serves as a surrogate for thymocytes to mature along a pathway canonically thought to be exclusive to αβ T cells. Evaluations in mixed bone marrow chimeras confirm that γδTCR can bypass β-selection for T cells to rearrange Tcra. Mature T cells from TRex mice lacking endogenous Tcrb exhibit enhanced functionality compared to T cells from TRex mice with intact Tcrb. Collectively, we delineate two routes for αβ T cell maturation and build on a new platform for studying antigen-specific T cell populations. Funding Sources 5T32CA009138 Topic Categories Hematopoiesis and Immune System Development (HEM)