MONITORING OF LEUKEMIA GROWTH IN A RAT MODEL USING A HIGHLY SENSITIVEASSAY FOR THE DETECTION OF LACZ MARKED LEUKEMIC-CELLS

A very sensitive assay for the detection of LacZ marked cells of an in vitro growing subline of the brown Norway rat myelocytic leukemia (BN ML) model was developed. By combining cytochemical X-gal staining with D-galactose mediated suppression of endogenous background beta-galact ose activity, a detection sensitivity of one leukemic cell per 10(8) n ormal bone marrow cells could be achieved. A detailed analysis of the in vivo growth pattern and kinetics of this cell line is presented. Al so, it is shown that after cyclophosphamide treatment of leukemic rats no leukemic colonies are formed in an agar-colony assay, whereas the leukemic cells remain detectable in the bone marrow for a considerable time period. Eventually, however, all leukemic cells disappear from t he marrow. These findings are discussed in the light of prolonged dete ction of rare leukemic cells in patients in continuing remission.