Combination ofCTLA4-FasL gene transfer and allogeneic bone marrow transplantation led to durable macrochimerism and donor-specific tolerance in mouse model

Mixed hemopoietic chimerism is capable of inducing donor specific tolerance, thus eliminating the chronic immunosuppressive therapy following organ trans- plantation. As yet no safe and effective tolerance protocol is available for clinical implementation. Here we describe an alternative nonmyeloablative based strategy of using a single injection of recombination adenovirus vector encoding CTLA4-FasL fusing gene and donor bone marrow cells to promote durable mixed macrochimerism (>20% on 140 d). Chimeras exhibited robust donor-specific tolerance, as evi- denced by acceptance of fully allogeneic skin grafts (the mean survival time (MST)>200 d) and rejection of third- party skin grafts in a normal manner (MST<10 d). In this model, the frequencies of helper T lymphocyte precursor (HTLp) and cytotoxic T lymphocyte precursor (CTLp) were greatly reduced on day 14 after transplantation, suggesting that CTLA4-FasL led to rapid systemic peripheral tolerance to facilitate the bone marrow engraftment, while both HTLp and CTLp remained at low level only in recipient mice with mixed chimerism on day 140 after transplantation, demon- strating that long-term skin grafts tolerance was associated with stable mixed chimerism, and central deletion of donor specific T cell may be the main mechanism for tolerance maintenance.