CONTROL OF INTESTINAL ALLOGRAFT REJECTION BY FTY720 AND COSTIMULATION BLOCKADE

Abstract

P1038 Aims: The clinical application of small bowel transplantation (SBTx) is hampered by its pronounced immunogenicity. To date no immunosuppressive protocol has proven to prevent intestinal allograft rejection in mouse models. Therefore, in this study we examined the effects of the novel immunosuppressant FTY-720 and costimulation blockade by an anti-CD40L mAb (MR-1) in a heterotopic model of small bowel transplantation. Methods: SBTx was performed in mice with a full MHC haplotype mismatch (donors: C3H=H-2k; recipients: C57BL/6=H-2b). Recipients were divided into 4 groups: 1, non-treated group; 2, MR1 monotherapy (500 μg iv on day 0, and 500 μg i.p. on days 2, 4 and 7); 3, FTY720 monotherapy (1 mg/kg body weight po for 14 consecutive days after transplantation); 4, FTY720 plus MR1 treated group. Each group contained 6 mice for histological assessment at day 14, and another 6 mice for FACS analysis and histology at day 6 after transplantation. Analyses were performed on donor and recipient mesenteric lymph nodes, Peyer’s Patches, as well as Intraepithelial Lymphocytes (IEL) and Lamina Propria Lymphocytes (LPL) that were purified by differential collagenase digestion. Tissue sections were analyzed by three colour immunofluorescence staining on an Axiovert M200 microscope. Lymphocytes were stained with monoclonal antibodies, and were studied by three-colour flow cytometry on a FACSCalibur (Becton Dickinson). Results: Both FTY720 and MR1 monotherapy were not efficient in alleviating the rejection of mouse intestinal allografts, whereas FTY720 plus MR1 profoundly improved the rejection response both at early (day 6) and later (day 14) time points. In the latter, the infiltration of host lymphocytes was profoundly reduced in graft mesenteric lymph nodes (MLNs), Peyer’s patches (PPs), intraepithelial lymphocytes (IELs), and lamina propria lymphocytes (LPLs) by FTY720 therapy. FTY720 plus MR1 inhibited host CD8+ T cell infiltration in graft LPLs when compared with grafts treated with FTY720 only. Infiltration by CD44+ T cells was inhibited in most of the FTY720 plus MR1 treated grafts (4/6). Additionally, two sub-populations, CD11b+high Gr1+ and CD11b+high Gr1+ cells were decreased in FTY720 treated grafts. Conclusions: FTY720 plus MR1 efficiently delayed intestinal allograft rejection in a mouse model by preventing the infiltration of host lymphocytes, particularly of CD8+ cells.