Journal of Cellular Biochemistry 88:223–226 (2003) Analogs of 1a,25-Dihydroxyvitamin D 3 as Pluripotent Immunomodulators Evelyne van Etten, Brigitte Decallonne, Lieve Verlinden, Annemieke Verstuyf, Roger Bouillon, and Chantal Mathieu* Laboratory for Experimental Medicine and Endocrinology, Catholic University of Leuven, Leuven, Belgium Abstract The active form of vitamin D 3 , 1,25(OH) 2 D 3 , is known, besides its classical effects on calcium and bone, for its pronounced immunomodulatory effects that are exerted both on the antigen-presenting cell level as well as directly on the T lymphocyte level. In animal models, these immune effects of 1,25(OH) 2 D 3 are reflected by a strong potency to prevent onset and even recurrence of autoimmune diseases. A major limitation in using 1,25(OH) 2 D 3 in clinical immune therapy are the adverse side effects on calcium and on bone. TX527 (19-nor-14,20-bisepi-23-yne-1,25(OH) 2 D 3 ) is a structural 1,25(OH) 2 D 3 analog showing reduced calcemic activity associated with enhanced in vitro and in vivo immunomodulating capacity compared to the mother-molecule. Indeed, in vitro TX527 is more potent that 1,25(OH) 2 D 3 in redirecting differentiation and maturation of dendritic cells and in inhibiting phytohemagglutinin-stimulated T lym- phocyte proliferation. In vivo, this enhanced potency of TX527 is confirmed by a stronger potential to prevent type 1 diabetes in nonobese diabetic (NOD) mice and to prolong the survival of syngeneic islets grafts, both alone and in combination with cyclosporine A, in overtly diabetic NOD mice. Moreover, these in vivo effects of TX527 are obtain- ed without the adverse side effects observed for 1,25(OH) 2 D 3 itself. We believe therefore that TX527 is a poten- tially interesting candidate to be considered for clinical intervention trails in autoimmune diseases. J. Cell. Biochem. 88: 223–226, 2003. ß 2002 Wiley-Liss, Inc. Key words: structural analogs of 1,25(OH) 2 D 3 ; dendritic cell differentiation; T lymphocyte proliferation; NOD mouse; type 1 diabetes Receptors for the active form of vitamin D 3 , 1,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ), are present in monocytes, monocyte-derived cells and (T- and B-) lymphocytes [Veldman et al., 2000]. Moreover, activated macrophages them- selves are able to produce 1,25(OH) 2 D 3 in a regulated fashion. Regulation of the enzyme responsible for the final and rate-limiting step in the synthesis of the active 1,25(OH) 2 D 3 (25(OH)D 3 -1-a-hydroxylase) is, however, com- pletely different in macrophages than in kidney cells [Overbergh et al., 2000]. In vivo, in animal models, administration of 1,25(OH) 2 D 3 has important immune effects, such as prolongation of graft survival (of for example pancreatic islets, heart, liver and skin) and prevention of autoimmune diseases (in experimental models such as autoimmune diabetes, experimental autoimmune encephalomyelitis and collagen- induced arthritis) [Mathieu and Adorini, 2002]. This effect is achieved through its actions on dendritic cells (DC; inhibition of antigen pre- sentation and modulation of cytokine produc- tion), being the central antigen-presenting cells in the immune system, as well as directly on T lymphocytes (inhibition of proliferation and cytokine production) [Mathieu and Adorini, 2002]. Clinical applications of 1,25(OH) 2 D 3 in immune therapy can only be considered when the adverse side effects on calcium and bone can be avoided. This has been achieved through the design of structural analogs of 1,25(OH) 2 D 3 [Bouillon et al., 1995; Verstuyf et al., 2000] showing a reduced calcemic activity often asso- ciated with an enhanced capacity, when com- pared to the mother-molecule, to modulate the immune system in vitro, on DC and T lympho- cytes, and in vivo. ß 2002 Wiley-Liss, Inc. *Correspondence to: Chantal Mathieu, Laboratory of Experimental Medicine and Endocrinology, Catholic Uni- versity of Leuven, Herestraat 49, 3000 Leuven, Belgium. E-mail: chantal.mathieu@med.kuleuven.ac.be Received 20 June 2002; Accepted 24 June 2002 DOI 10.1002/jcb.10329