Marker tolerant, immunocompetent animals as a new tool for regenerative medicine and long-term cell tracking

Background: Immune- mediated rejection of labeled cells is a
general problem in transplantation studies using cells labeled with
any immunogenic marker, and also in gene therapy protocols. The aim
of this study was to establish a syngeneic model for long-term
histological cell tracking in the absence of immune-mediated
rejection of labeled cells in immunocompetent animals. We used
inbred transgenic Fischer 344 rats expressing human placental
alkaline phosphatase (hPLAP) under the control of the ubiquitous
R26 promoter for this study. hPLAP is an excellent marker enzyme,
providing superb histological detection quality in paraffin and
plastic sections. Results: Transplantation of cells from hPLAP
transgenic (hPLAP-tg) F344 rats into wild-type ( WT) F344
recipients failed because of immune-mediated rejection. Here we
show that this problem can be overcome by inducing tolerance to the
marker gene by transplantation of bone marrow from hPLAP-tg F344
rats into WT F344 hosts after lethal irradiation, or by neonatal
exposure of WT F344 rats to hPLAP-tg F344 cells. As
proof-of-principle, we injected bone marrow cells (BMC) from
hPLAP-tg rats into the knee joint of marker tolerant, bone
marrow-transplanted WT rats, and found successful engraftment and
differentiation of donor cells. In addition, hPLAP-tg BMC injected
intravenously in neonatally tolerized WT F344 hosts could be traced
in lymph nodes, 2 months post-injection. Conclusion: In combination
with the excellent marker hPLAP, marker tolerant animals may open
up new perspectives for all experiments requiring long-term
histological tracking of genetically labeled cells.