Addressing the immunological barriers to regenerative medicine: differentiation and characterisation of dendritic cells derived from induced pluripotent stem cells

Induced pluripotent stem cells (iPS cells) have shown great promise in the newly-developing field of regenerative medicine. Recently, however, there have been conflicting reports regarding their immunogenicity, even when derived in an autologous fashion, due to the ectopic expression of certain developmental antigens. Dendritic cells (DC) are professional antigen presenting cells and therefore serve as potential tools for modulating the immune response, particularly with respect to acceptance of stem cell-derived tissues. We hypothesised that DC differentiated from iPS cells, so-called ipDC, may have the capacity to induce tolerance to tissues differentiated from the same parent iPS cell line. As a first step towards this goal, we have derived iPS cells from both embryonic and adult mouse fibroblasts, developed protocols for their differentiation along the DC lineage and characterised the resulting DC both phenotypically and functionally, using bone-marrow derived-DC (bmDC) for comparison. Furthermore, their potential for inducing tolerance as a function of regulatory T cell induction has also been explored. Our data suggest that, although ipDC are able to function in a similar manner to bmDC both in vitro and in vivo, they display important differences with respect to cytokine production and MHC class II expression which may reflect their early embryonic origin and render them pro-tolerogenic. One application for this novel population of DC might be the induction of tolerance to autologous iPS cell-derived tissues. In order to assess the need for tolerance under such circumstances, we have investigated the reported immunological rejection of iPS cells when transplanted syngeneically. Although we were unable to corroborate previous findings showing immunological rejection of iPS cells under such circumstances, we were able to show that the formation of teratomas from iPS cells is a stochastic and very variable process, unlike their generation from ES cells. Importantly, we were able to exclude the involvement of any antigen-specific component to the failure of teratoma survival by inducing blanket tolerance to iPS cell-derived tissues, using a cocktail of non-depleting monoclonal antibodies specific for CD4, CD8 and CD40L. This is the first reported study deriving dendritic cells from mouse iPS cells and demonstrating their extensive characterisation. Additionally, the work presented in this thesis adds to the growing body of evidence of the immunological properties of iPS cells with our work demonstrating that they appear not to attract an adaptive immune response but, however, show significant heterogeneity with respect to their ability to engraft in vivo.