HAEMOPOIETIC STEM CELLSINLEUKAEMIC AKR MICE:THE (AKRxC57BL/6)F1 MOUSE AS AN IN VIVOASSAY SYSTEM

Summary.-Characteristics ofthe AKB6F1 mousestrainmakeit suitable asanassayanimal for quantitating haemopoietic stem cells, or spleen colony-forming units (CFU-S),fromleukaemic AKRmice. Marrowcells harvestedfromleukaemic micewereassayedfor CFU-S in lethally irradiated AKRor AKB6F1 hosts. Survivaltimesand numbers of leukaemiccolony-forming units (L-CFU) in unirradiatedrecipients were used to detect proliferation of transplanted leukaemic cells. In contrast toAKRrecipients, the proliferation of transplanted leukaemiccells wassuppressed in F1 hosts. Injection of marrowcells fromnormalnonleukaemicAKR miceinto AKR and F1 hosts yielded significantly more CFU-Sandspleen 59Fe uptake in F1 than in AKRhosts. In marked contrast, injection of marrow from leukaemic AKRmicesuppressedCFU-Sproliferation inthe F1 recipients. Thus it was possible to quanti-tate CFU-S in marrow containing L-CFU.AKRSPONTANEOUS and transplanted leu-kaemias are often used to measure theeffects of anticancer agents on malignant