While the primary cause of inflammatory bowel disease (IBD) development remains unknown, it is widely accepted that the initial events culminate in persistent immune responses with infiltration of immune cells and tissue destruction in the gut. Immune cell populations present within the inflamed bowel wall of IBD patients have been extensively characterized and studied (1;6). Studies focusing on T cells have demonstrated that the mucosa of Crohn's disease (CD) patients is dominated by Th1 cells, while in patients with ulcerative colitis (UC) T helper cells with an atypical Th2 profile, which excessively produce IL-5 and IL-13 but not IL-4, are abundant (7). Furthermore, Th17 cells can be identified in the inflamed lamina propria and these cells are thought to play an important role in the pathophysiology of IBD, although the pathogenic mechanisms of these cells are not yet fully understood (8;9). Treg are also present within the lamina propria and these cells control the effector T cell populations mentioned above. They can be generated through the interaction of local T cells with CD103 expressing dendritic cells and intestinal epithelial cells, respectively (10;11). Moreover, the expression of integrins on the Treg surface (e.g. α4β7) facilitates mucosal migration through their interaction with specific ligands (e.g. MAdCAM1). As such, homing and local expansion of Treg cells create a local Treg pool that is essential for self-tolerance and the support of gut homeostasis (12). In addition, Treg cells are shown to suppress proinflammatory intestinal immune responses in colitis and colitis-associated cancer (13-16) and they are thought to augment intestinal Th17 responses (17). As previous studies have demonstrated insufficient expansion of mucosal Treg cells in IBD patients in comparison to the massive local expansion of effector T cells, it is likely that the relatively low number of Treg cells in IBD patients explains why these cells fail to control excessive immune responses (18).

Experimental colitis studies in mice have demonstrated that colitogenic immune responses can be controlled by increasing the number of mucosal Treg cells and highlight the potential of Treg-based cell therapy in IBD (19). Specifically, co-transfer of naïve CD4+ T cells with Treg both prevents chronic colitis and ameliorates established colitis in severe combined immunodeficiency (SCID) mice (20). Moreover, CD4+ T cells expanded ex vivo in the presence of rapamycin prevent the development of colitis in a naïve CD4+ T cell model in SCID mice. Importantly, the systemic administration of rapamycin alone only partially prevented the development of colonic Inflammation (20). In addition, the adoptive transfer of nTreg cells as well as the adoptive transfer of ex vivo transforming growth factor (TGF)-β-induced Treg (iTreg) suppressed colitis activity in vivo in mouse models (13;15;21). Collectively, these data suggest that Treg cells could be used for therapy of intestinal inflammation in IBD (22).

To allow an adoptive transfer of large numbers of Treg, CD25+ Treg cells are isolated from an autologous leukapheresis product and in vitro expanded during 21 days in the presence of the additives Interleukin-2 (IL-2), rapamycin and anti-CD3/anti-CD28 expander beads. After 21 days of expansion, anti-CD3/anti-CD28 expander beads are removed from the Treg drug product. Next, Treg are frozen in aliquots of 10 Million Treg/mL until further use (5).

Twelve patients, including 10% patient loss, resulting in at least ten treated and fully evaluable patients, will be enrolled in this single-center, open-label, fast-track dose-escalation study. Autologous ex vivo expanded CD4+CD25+CD127-/lo Treg cells will be adoptively transferred in patients with ulcerative colitis with active disease or stable disease under the allowed concomintant therapy at the time of enrollment. The maximal tolerated dose (MTD) is defined as the dose that does not produce more than one dose-limiting toxicity (DLT) among a total of four treated patients at the particular dose level.

The first enrolled patient will receive the initial starting dose of 0.5 x10e6 Treg/kg bodyweight. Adoptive transfer is escalated to the next dose level (1 x 10e6 Treg/kg, 2 x 10e6 Treg/kg, 5 x 10e6/Treg/kg and 10 x 10e6 Treg/kg bodyweight), in a next patient, if no DLT occurs. Consecutive patients will be treated at least four weeks apart to monitor acute severe adverse advents. If a DLT is noted, three additional patients will receive the same dose level. Dose-escalation continues until at least two patients among a cohort of four patients experience a DLT. If two patients among a cohort of four patients experience a DLT, dose de-escalation to the highest previously tolerated dose-level will follow. Three additional patients will receive the highest previously tolerated dose. If a DLT is noted in at least two patients at the tested dose-level, dose de-escalation will continue until less than two patients have experienced a DLT. After successful enrollment at the highest dose-level, five additional patients will be enrolled at the highest dose level to extend safety assessment. If no DLTs or less than two DLTs are experienced at all dose-levels tested, the MTD is not reached. In this case, a maximal administered dose (MAD) is defined.