HUMAN ALKYLTRANSFERASE-TRANSDUCED MURINE MYELOID PROGENITORS ARE ENRICHED IN-VIVO BY BCNU TREATMENT OF TRANSPLANTED MICE

Retroviral gene transfer into murine hematopoietic pro genitors of the human O(6)alkylguanine-DNA alkyltransferase cDNA, methylguanine methy ltransferase (MGMT) has been shown to result in MGMT expression, incre ased alkyltransferase (AGT) activity, and resistance to 1,3-bis-(2-chl oroethyl) nitrosourea (BCNU) both in vitro and in vivo. In the present study we show that MGMT expressing bone marrow (BM) progenitors can b e selected for in vivo by BCNU administration. MGMT(+) mice treated wi th multiple doses of BCNU and examined 13 to 17 weeks after transplant ation displayed a 2.4-fold increase in the percentage of progenitors w ith evidence of proviral integration (p < 0.0001). Likewise, percent a ge of the BCNU IC50 in these progenitors was 1.8-fold higher than that observed in progenitors of MGMT(+) mice not treated with BCNU (p = 0. 0027) and 3.6-fold higher than in mock transduced progenitors (p < 0.0 01). AGT expression in myeloid cells was 3.8-fold higher in mice treat ed with BCNU than in untreated mice (p = 0.0378) and 64-fold higher th an endogenous AGT levels. These findings demonstrate that after transp lantation with MGMT-transduced BM cells, BCNU treatment enriches for M GMT cells, resulting in an increase in MGMT expression and AGT activit y in vivo. This approach may be used to enrich for transduced hematopo ietic cells in patients after clinical transplantation, to decrease my elosuppression after repeated nitrosourea exposure, and to increase th e proportion of genetically altered hematopoietic cells.