CD103+CTL accumulate within the graft epithelium during clinical renal allograft rejection

Background. We have previously reported that activated CD8+TCR alpha beta+ cells that express high levels of the beta7 integrin CD103 (formerly alpha (E), MLA) are present at the graft site during clinical renal allograft rejection. This observation potentially provides new insight into the mechanisms underlying renal allograft destruction because the ligand of CD103 is the epithelial cell-specific molecule E-cadherin, which is known to be expressed by critical graft functional elements such as the renal tubular epithelium. We herein used combined fluorescence-activated cell sorter (FACS) and immunohistochemical (IHC) analyses of transplant nephrectomy (TN) specimens to demonstrate that CD103+ cytolytic T lymphocytes (CTLs) specifically home to the graft epithelium during rejection episodes. Methods. Serial sections of TN specimens undergoing histologically confirmed cellular rejection (n=7) were stained with anti-CD8 or anti-CD103 and were scored for the presence of positively stained cells within the tubular basement membrane. Freshly isolated graft-infiltrating lymphocytes were subjected to three-color FACS analyses to define the extended phenotypic characteristics of CD103+ cells detected by IHC. Results. CD103+ cells in all specimens were biased towards an intratubular localization. On average, the percentage of CD103+ cells with an intraepithelial localization was 52.2 +/- 13.1 compared to 12.0 +/-3.5 for pan CD8+ cells (mean +/- SE, n=5). FACS analyses confirmed that CD103+ cells detected by IHC exhibited the salient characteristics of CD8+ CTLs (large CD8+TCR alpha beta+ CD62L(-)CD11a(hi)perforin+). The CD103- subset of graft-infiltrating CD8 cells also exhibited a CTL phenotype, but these were predominantly restricted to the graft interstitium. Conclusions. These data implicate CD103 as a homing receptor that targets graft-infiltrating CD8+ CTLs to the graft epithelium. Given the strong association of tubulitis with clinical rejection, these data are consistent with a role for the CD103+ CTL subset as an effector mechanism in renal allograft destruction.