Highly Efficient Stable Expression of Indoleamine 2,3 Dioxygenase Gene in Primary Fibroblasts

Indoleamine 2,3-dioxygenase (IDO) is a monomeric, heme-containing enzyme that catalyzes the rate limiting step of conversion of tryptophan to kynurenine [1]. Recently, tryptophan catabolism has been implicated in immunological tolerance. One theory proposes that degradation of tryptophan suppresses T cell proliferation by reducing the availability of this essential amino acid in local tissue environments, thereby sensitizing T cells to apoptosis [2]. Another theory suggests that the major tryptophan metabolite, kynurenine, suppresses immune reactivity through direct interaction with effector T lymphocytes [3]. The immunomodulatory effects of tryptophan deficiency and excess kynurenine caused by IDO are of particular interest in the field of transplantation [4].A critical aspect of an immunological intervention using IDO is the requirement to achieve effective expression of this gene. However, genetic manipulation by non-viral transfection approaches has been challenging due to the issues of low transfection efficiency, loss of cell viability, and difficulty in obtaining stable transfection [5,6]. Previously, we have shown that by using dermal fibroblasts transduced with an IDO-expressing adenoviral vector, IDO functions as a local immunosuppressive factor [7], and local expression of IDO suppresses islet allogeneic immune response in mouse islet transplantation [8]. Furthermore, we have used the local immunosuppressive effect of IDO in the development of a non-rejectable skin substitute [9]. These findings demonstrate that IDO has considerable potential for immunoregulation and induction of immunotolerance in transplantation.Nevertheless, the immunogenicity and transient gene expression of adenoviral vectors may hinder its clinical use in transplantation. Thus, in order to sustain the efficacy of IDO activity in the local environment of transplanted organ, it is essential to prolong the expression of functional IDO protein. In fact, it was shown that lentiviral vect