New lines of GFP transgenic rats relevant for regenerative medicine and gene therapy.

Adoptive cell transfer studies in regenerative research and identification of genetically modified cells after gene therapy in vivo require unequivocally identifying and tracking the donor cells in the host tissues, ideally over several days or for up to several months. The use of reporter genes allows identifying the transferred cells but unfortunately most are immunogenic to wild-type hosts and thus trigger rejection in few days. The availability of transgenic animals from the same strain that would express either high levels of the transgene to identify the cells or low levels but that would be tolerant to the transgene would allow performing long-term analysis of labelled cells. Herein, using lentiviral vectors we develop two new lines of GFP-expressing transgenic rats displaying different levels and patterns of GFP-expression. The "high-expresser" line (GFP(high)) displayed high expression in most tissues, including adult neurons and neural precursors, mesenchymal stem cells and in all leukocytes subtypes analysed, including myeloid and plasmacytoid dendritic cells, cells that have not or only poorly characterized in previous GFP-transgenic rats. These GFP(high)-transgenic rats could be useful for transplantation and immunological studies using GFP-positive cells/tissue. The "low-expresser" line expressed very low levels of GFP only in the liver and in less than 5% of lymphoid cells. We demonstrate these animals did not develop detectable humoral and cellular immune responses against both transferred GFP-positive splenocytes and lentivirus-mediated GFP gene transfer. Thus, these GFP-transgenic rats represent useful tools for regenerative medicine and gene therapy.