Coexpression of a Mu Cα and different Hu TCRβ chains in Jurkat-76 lacking endogenous TCRs. To elucidate the propensity of Mu Cα to pair with arbitrary endogenous TCRβ chains (A-B right; 24.5%/3.1%), we introduced the TCRβ chain alone as a negative control (A-B left; 18.5%/0.2%) or the WT Hu TCRα/β chains of the gp100(280-288) specificity (Vβ14) or the Hu CMV pp65(495-503) specificity (Vβ13.1) as positive controls (A-B outmost right; 96.9%/62.2%). In addition, a partially murinized (ie, chimerized in C domains) dcTCR gp100²⁵  was assayed to confirm that Mu Cα T84C pairs with a murinized TCRβ with higher efficacy than with a Hu full-length TCRβ chain (A bottom right; 95.1% vs 24.5%). We used TCR RNA transfection by electroporation as described elsewhere.¹⁹  Surface expression of any monodimer or heterodimer was already monitored next day in flow cytometric analysis with the use of the related anti-TCR Vβ antibody. Mu Cα marginally pairs with an unrelated Hu TCRβ chain (24.5% vs 18.5% and 3.1% vs 0.2%, respectively). In a clinical situation, the tiny fraction of hybrid Mu Cα T84C/Hu TCRβ should be theoretically outcompeted by endogenous TCRα chains which contribute with 2 domains (ie, Vα + Cα) to chain pairing.