Transplantation

To determine the fate of hematopoietic cell populations, we have transplanted either whole kidney marrow, or FACS isolated subpopulations into recipient zebrafish. Because of graft rejection, injections can be done either into the sinus cavernosus of d2 embryonic recipients (i.e. prior to immunocompetence), or into sublethally irradiated adult recipients (see Fig. 1). FACS isolation of subpopulations can either be based on light scatter characteristics, or on lineage-specific expression of a fluorescent transgene (see Fig.2 and FACS section). We found that longterm repopulating cells (LTRC) reside in the zebrafish kidney. These LTRC can give rise to erythroid cells (evidenced by donor derived GATA-1 GFP expression), as well as T cells (lck::GFP expression), conclusively demonstrating that they are capable of supporting primitive and definitive hematopoiesis (Fig. 3 lower panels). Engraftment of T cells was sustained for more than six months, suggesting that true stem cells have been transplanted along with the kidney marrow. Sequential transplantations are underway. Following transplantation of thymocytes we observed homing to the thymus, but only short-term repopulation activity was contained in this population (see Fig. 3, 2 top panels). We have also transplanted malignant cells from our leukemia models (Figure 4). The left panel in Fig. 4 shows the abdominal injection site 7 days after transplantation. Two transplanted individuals are shown in the right panel 21 days post transplantation; the red arrowhead points to the injection site in the fish on top. Note the massive expansion of GFP-positive transplanted cells. Serial transplantation leads to increasingly aggressive behavior of transplanted T-ALL cells.