Fig. 4.

Antigenic peptides loaded onto MHC I via TAPBPR are available to the T cell receptor. MCF-7 cells were treated ±1 µM soluble TAPBPR^WT or TAPBPR^TN5 for 15 min at 37 °C followed by 60-min incubation ±10 nM (A) IMDQK*PFSV, ELAGK*GILTV, LLGRK*SFEV, or RLLQK*TELV; (B) NLVPK*VATV or YLLEK*LWRL; or (C and D) YLLEMLWRL (YLL) followed by staining with the TCR-like mAb L1 specific for YLLEMLWRL/HLA-A2 complexes. (D) The MFI of L1 binding to MCF-7 cells ±SD from three independent experiments. (E) Bar graphs show T cell activity measured by IFN-γ secretion in fluorospot assays of a HLA-A2 restricted NLVPMVATV specific CD8⁺ T cell line when incubated with MCF-7 target cells as treated in B, with the exception that nonfluorescent NLVPMVATV peptide at 100 pM was used. Results are from triplicate wells representative of two independent experiments. Error bars ± SD. Note: In A, B, and E IFN-γ–treated cells were used. Equivalent experiments of B–E were performed using HeLaM-HLA-ABC^KO expressing HLA-A*02:01 and can be found in SI Appendix, Fig. S7. *P ≤ 0.05, ***P ≤ 0.001 using unpaired two-tailed t test.