KbStrep knock-in mice have an inverted StrepTagII, flanked by two pairs of inward-facing heterospecific Lox sites, inserted into intron 1 of the histocompatibility 2, K1, K region (H2-K1) gene. H2-K1 is involved in antigen processing and presentation of endogenous peptide antigens. Upon cre induction, recombination of the Lox sites results in the inversion of the StrepTagII into the correct transcriptional orientation which ultimately incorporates the StrepTagII onto the mature H2-K1 protein. This inversion is not reversible. Mice that are homozygous for this allele are viable and fertile. When KbStrep mice are bred to Sftpc-CreERT2 mice (Stock No. <a href="https://www.jax.org/strain/028054">028054</a>), the StrepTagII is inverted after tamoxifen administration and is presented on the cell surface of alveolar type 2 cells in healthy lung tissue of resulting mice, enabling the purification of intact MHC-I complexes. When KbStrep mice are crossed to C57BL/6J KrasLSL-G12D/+ Trp53fl/fl mice (Stock No. <a href="https://www.jax.org/strain/032435">032435</a>), administration of cre recombinase activates oncogenic KrasG12D with simultaneous biallelic deletion of Trp53 and activation of the StrepTagII, which enables the purification of MHC-I complexes specifically from cancer cells in the tumor microenvironment in vivo.

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KbStrep knock-in mice have an inverted StrepTagII, flanked by two pairs of inward-facing heterospecific Lox sites, inserted into intron 1 of the H2-K1 gene. Upon cre induction, recombination of the Lox sites results in the inversion of the StrepTagII into the correct transcriptional orientation. These mice may be useful for the selective purification of MHC-I peptide antigens from cell type(s) of interest from intact tissues.

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