Extended Data Figure 1. (Related to Figure 1). In vitro validation of the K^bStrep allele.

a) Structural model depicting the topology of the K^bStrep protein during affinity purification. The StrepTagII engagement with Streptactin affinity resin does not interfere with peptide or B2m binding. b) Southern blot analysis of K^bStrep targeted KP* ES cells. c) Representative genotyping for WT/WT, K^bStrep/WT heterozygotes, and K^bStrep/K^bStrep homozygotes. d) Brightfield images of KP and KP/ K^bStrep pancreatic organoids pre- and post- Ad-CMV-Cre mediated transformation ex vivo. e) RT-PCR analysis of KP or KP/K^bStrep pancreatic organoids with or without Cre recombination and with or without IFN-γ treatment. Each row represents a distinct primer set showing no discernable alterations in mRNA splicing with or without StrepTagII activation. f) Representative flow cytometry plots detecting cell surface expression of PD-L1 and StrepTagII at baseline (red) and following Cre activation and IFN-γ treatment (blue). g) Quantification of the median fluorescence intensity (MFI) of StrepTagII staining in KP (orange) and KP/K^bStrep (blue) organoids in control, IFN-γ treated, Cre transformed, and Cre+IFN-γ treated samples. Data are mean ± sem (n=3). Two-sided Student’s t-test. h) Immunoblot analysis of whole cell lysate from KP or KP/K^bStrep PDAC cells after adaptation to 2D following treatment with IFN-γ. i) Immunoblot depicting affinity purification of intact MHC-I with Streptactin resin as evidenced by the co-precipitation of B2m. j) Coomassie staining of samples taken from KP or KP/K^bStrep lysates at various stages of purification. In this experiment, the elution was taken by incubating washed Streptactin resin with SDS-PAGE loading buffer.