Myeloablation enhances engraftment of transduced murine hematopoietic cells, but does not influence long-term expression of the transgene

To investigate to what extent myeloablation, graft size, and ex vivo manipulation influence the engraftment and long-term survival of transduced murine hematopoietic cells, groups of C57BL/6J (CD45.2) mice receiving total body irradiation (TBI) (1-9 Gy) or no irradiation were transplanted with either transduced bone marrow (BM) cells, at two cell doses, or with fresh BM cells from B6/SJL (CD45. 1) congenic mice. Short (40 days) and long-term (5 months) engraftment and transgene expression were measured by FACS analysis. No donor cells were detected in the hematopoietic tissues of non-myeloablated mice, whereas in the irradiated animals, levels of engraftment correlated well with the dose of TBI administered. Similar percentages of transgene-expressing cells were found in the grafted hematopoietic cells of all groups of mice, regardless of the dose of TBI administered or the level of engraftment achieved. This suggests that the engrafted animals could become tolerant to the transgene product (enhanced green fluorescent protein, EGFP). Our results indicate that TBI facilitates the engraftment of manipulated hematopoietic cells in a dose-dependent manner, that mice engrafted with EGFP(+) hematopoietic cells probably acquire tolerance to EGFP, and that increasing the graft size and reducing the ex vivo manipulation required for retroviral gene transfer of hematopoietic cells also enhances their engrafting potential.