Induction of Donor-Specific T-Cell Hyporesponsiveness Using Dexamethasone-Treated Dendritic Cells in Two Fully Mismatched Rat Kidney Transplantation Models Annelein M. Stax, 1 Kyra A. Gelderman, 1 Nicole Schlagwein, 1 Maria C. Essers, 1 Sylvia W. A. Kamerling, 1 Andrea M. Woltman, 1,2 and Cees van Kooten 1,3 Background: Dendritic cells (DC) can exert powerful immune stimulatory as well as regulatory functions and are therefore important tools for therapeutic strategies. Dexamethasone (Dex) was previously shown to inhibit DC mat- uration and to induce regulatory properties both in vitro and in vivo. Here, we investigated the immunoregulatory role of DexDC in two different rat acute rejection models of kidney transplantation. Methods: Rat DC were generated from BN and DA bone marrow in the presence of the corticosteroid, Dex. The function of Dex-modulated DC was analyzed in vitro and in vivo, using a BN to LEW and a DA to LEW renal transplantation model in the absence of other forms of immunosuppression. T cells of transplanted rats were isolated and restimulated with donor mature DC (lipopolysaccharide [LPS] or CD40L activated). T-cell responsiveness was analyzed by proliferative capacity and IFN- production. Results: Stimulation of Dex-modulated rat DC with LPS resulted in normal IL-10 production, whereas synthesis of IL-12 was impaired. In accordance, the capacity of LPS-DexDC to stimulate T-cell activation was decreased. In both renal transplantation models, treatment with donor-derived LPS-DexDC induced a significant donor-specific T-cell hyporesponse. However, pretreatment did not result in a prolonged graft survival. Conclusions: In two fully mismatched kidney transplantation models, donor-derived LPS-DexDC induce a donor- specific T-cell hyporesponse. However, in this setting allograft survival was not improved, suggesting an important role for T cells with indirect alloreactivity. Understanding the underlying mechanism involved in the rejection process will improve the development of a cell-based immunotherapy. Keywords: Dexamethasone, Dendritic cells, Rat, Kidney transplantation, T-cell hyporesponsiveness. (Transplantation 2008;86: 1275–1282) O rgan transplantation is one of the most important ther- apies for end-stage organ failure. In the past, immuno- suppressive therapy has led to significant improvement in short-term survival rates for solid-organ allografts. Unfortu- nately, the use of nonspecific immunosuppression has many adverse side-effects like an increased rate of malignancy and infections (1,2). To prevent these side-effects and to improve transplantation outcome, the development of new treatment strategies is necessary. In this respect, development of a ther- apy, which can induce donor-specific tolerance in the absence of continuous immunosuppression, is the ultimate goal in transplantation research. Dendritic cells (DC) are bone marrow-derived antigen presenting cells (APC) and have the potential to induce both immunity and tolerance, and are therefore a good candidate for cell-based therapy. Under steady-state conditions imma- ture DC (iDC) have the capacity to internalize antigens. In the presence of pathogens, DC mature and acquire the capacity to induce an immunogenic response. In contrast, when self an- tigens are endocytosed in the absence of danger signals, DC induce a tolerogenic response (3, 4). Previous studies have indeed shown that DC inducing tolerogenic responses are phenotypically immature or semi-immature (5). The effect of iDC as a cellular treatment to induce transplant tolerance has been studied in different transplan- tation models (6). Treatment of recipients with donor- derived iDC-induced allogeneic T-cell hyporesponsiveness and prolonged allograft survival in heart allograft models (7, 8). These studies indicate that donor-derived iDC can modulate recipient’s immune response. Because iDC can easily mature on danger signals, there is a risk that once injected into the recipient donor-derived iDC will mature. Matured donor- derived DC may subsequently interfere or even counteract with tolerance induction. It may therefore be important to use donor-derived DC, which are blocked in the maturation process. Various compounds including Dexamethasone (Dex), IL-10, and Vitamin D 3 can influence the maturation status of DC and these modulated DC were strongly ham- pered in their T-cell stimulatory capacity (9 –14). Different modes of activation, including proinflammatory cytokines, lipopolysaccharide (LPS), or CD40L, demonstrated a ham- pered up-regulation of major histocompatibility complex (MHC) and costimulatory molecules on Dex-treated DC This work was supported by the EU grants QLRT-2001-01215 LSHB-CT- 2004-512090 (RISET) and Dutch Kidney Foundation (KSPB 07.003). 1 Department Nephrology, Leiden University Medical Center, Leiden, The Netherlands. 2 Currently, Department of Gastroenterology and Hepatology, Erasmus Medical Center, Rotterdam, The Netherlands. 3 Address correspondence to: Cees van Kooten, Ph.D., Department of Ne- phrology C3-P, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands. E-mail: kooten@lumc.nl Received 23 April 2008. Revision requested 8 May 2008. Accepted 25 July 2008. Copyright © 2008 by Lippincott Williams & Wilkins ISSN 0041-1337/08/8609-1275 DOI: 10.1097/TP.0b013e31818a6682 Transplantation • Volume 86, Number 9, November 15, 2008 1275