VPEP-established oral T _RM are durably maintained following cohousing with pet shop mice. (A) Enumeration of OT-I T cells isolated from the indicated tissues of VPEP mice following >2 mo of cohousing (CoH) with pet shop mice. Data represent two independent experiments with N = 2–3 mice per experiment. (B) Representative flow cytometry plots concatenated from three mice from one of two independent experiments, highlighting phenotype of oral OT-I T cells in SPF vs. cohoused VPEP memory mice. (C) Left: Enumeration of total endogenous CD8⁺ T cells and percentage of endogenous CD8⁺ T cells expressing CD103 and CD69 in VPEP mice housed under SPF conditions (orange) or cohoused for >2 mo with pet shop mice (purple). Right: Enumeration of total endogenous CD4⁺ T cells and percentage of endogenous CD4⁺ T cells expressing CD103 and CD69 in VPEP mice housed under SPF conditions or cohoused for >2 mo. All dots represent individual mice. *, P < 0.05; **, P < 0.01 as determined by an unpaired Student’s t test between SPF and CoH groups.