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case_images: (A) Findings on bowel ultrasound (proximal descending colon). (B) Findings on colonoscopy (sigmoid colon) (C) Findings on histopathology (H/E staining, 10x magnification).
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case_images: On ultrasound, we noted a discontinuous pancolitis with bowel wall thickening and hyperemia ( Figure 1A ). A subsequent colonoscopy confirmed discontinuous pancolitis with redness, swelling, fibrin exudates, and erosions ( Figure 1B ). However, it revealed signs of chronic inflammation of the colon mucosa with crypt distortions and some crypt abscesses ( Figure 1C ). CAR+ and CAR- T cells in the peripheral blood showed that a subset of the CAR T cells expresses the gut-homing receptor alpha4beta7 and that alpha4beta7-expressing cells are enriched within CAR+ compared to CAR- T cells ( Figure 2B ,  Supplementary Figure 1 ). Consistently, we observed a substantial enrichment of CAR T cells in the colon lamina propria ( Figure 2C ).
case_images: (A) Immunohistochemistry of a colon biopsy for CD3 (10x magnification). (B) Flow cytometry of peripheral blood T cells expressing the chimeric antigen receptor (CAR) or not. The frequency of alpha4+beta7+ cells is indicated. CAR T cells were analyzed as previously described. Briefly, peripheral blood mononuclear cells were isolated by density centrifugation, stained with CD19 CAR detection reagent, washed twice and stained with Biotin antibody (both Miltenyi Biotec, Bergisch-Gladbach, Germany), 7-AAD (BD Biosciences) and a standardized panel of antibodies against CD45, CD3, CD4, CD8 (all BD Biosciences, Heidelberg, Germany), alpha4 integrin and beta7 integrin (both Biolegend). Gating strategies are depicted in the 
  Supplementary Figure 1
  . Data were acquired on a LSRFortessa (BD Biosciences) and analyzed by Kaluza software v2.1 (Beckman Coulter, Krefeld, Germany). (C) Flow cytometry of peripheral blood (left) and lamina propria (right) T cells. The frequency of CAR+ cells is indicated.
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case_images: Figure 2A ). Flow cytometry of CAR+ and CAR- T cells in the peripheral blood showed that a subset of the CAR T cells expresses the gut-homing receptor alpha4beta7 and that alpha4beta7-expressing cells are enriched within CAR+ compared to CAR- T cells ( Figure 2B ,  Supplementary Figure 1 ). Consistently, we observed a substantial enrichment of CAR T cells in the colon lamina propria ( Figure 2C ). There was no correlation of diarrhea with CAR+ T cell frequencies in the peripheral blood ( Supplementary Figure 2 ) and, interestingly, resolution occurred following a two-week course of antibiotic treatment with empiric levofloxacin plus vancomycin followed by linezolid for bacteremia due to central venous line infection.