Engraftment of retroviral EGFP-transduced bone marrow in mice prevents rejection of EGFP-transgenic skin grafts

We have investigated whether a state of tolerance toward EGFP-expressing skin tissue can be induced by prior establishment of EGFP molecular chimerism by transplant of gene-transduced bone marrow in mice. Irradiated (10 Gy) C57BL/6J mice were transplanted with bone marrow cells transduced with two different retroviral vectors encoding EGFP. EGFP-transduced, mock-transduced, and age-matched control mice received skin grafts from both C57BL/6 EGFP-transgenic (B6-EGFP. Tg) and MHC-mismatched B10.A donor mice at 8, 29, or 39 weeks after bone marrow transplantation. Although 14 of 17 control mice rejected EGFP.Tg skin grafts within 100 days, 24 of 25 mice receiving EGFP-expressing bone marrow cells accepted their B6-EGFP.Tg grafts out to 200 days after skin grafting, including animals with undetectable levels of EGFP expression in blood cells. The EGFP-transduced animals rejected third-party grafts from MHC-mismatched mice within 20 days, indicating that acceptance of the EGFP-expressing skin grafts was the result of the induction of specific and operational immune tolerance. Thus, our data indicate that (a) EGFP-expressing tissue elicits an immunological rejection in C57BL/6 mice and (b) tolerance can be induced by engrafting relatively small numbers of EGFP-transduced hematopoietic cells. These experiments utilizing EGFP as an immunogen point to the wider therapeutic potential of employing transplantation of gene-transduced hematopoietic cells for establishing immunological tolerance and thereby preventing rejection of gene-corrected cells and tissues.