Figure 2.

Impact of circulating monocytes on murine CLL development. (a) The absolute number of classical and non-classical monocytes were measured according to their surface expression of CD14, Gr1 and CD43 in the peripheral blood of leukemic mice at the end stage of disease in both primary disease (right panel) and adoptive transfer (left panel) models. For each cohort, the median tumor load (% CD5+CD19+ of total lymphocytes) is given. In the primary disease model, circulating total monocyte numbers are increased in TCL1-tg (n=5) and GK/TCL1-tg (n=9) mice compared with age-matched littermate controls (WT, n=13; GK, n=7) (left panel; TCL-tg vs WT, P<0.0001; GK/TCL1-tg vs WT, P<0.0001). Similarly, in the adoptive transfer model, total monocyte numbers are increased at the end stage of disease in both GK mice (n=7) and WT littermates (n=5), compared with pre-engraftment levels (n=8 and 7, respectively) (right panel; WT pre-adoptive transfer vs leukemic P=0.001; GK pre-adoptive transfer vs leukemic, P=0.0002). (b) Treatment of both GK mice and their WT littermate controls with clodronate-loaded liposomes (Clodrosome) resulted in the selective depletion of non-classical monocytes compared with treatment with control liposomes (Encapsome). WT mice treated with Encapsome (n=5) vs Clodrosome (n=5), P<0.0001; GK treated with Encapsome (n=5) vs Clodrosome (n=5), P=0.0002. The depletion of the non-classical monocyte fraction resulted in a reduction in total circulating monocyte numbers (WT Encapsome vs Clodrosome, P=0.0095; GK Encapsome vs Clodrosome, P=0.0067). (c) Concomittant with the depletion of non-classical monocytes, tumor development was significantly delayed in engrafted WT or GK mice that had been treated with Clodrosome (top panel; GK Encapsome vs Clodrosome at week 7, P<0.0001) and the onset of tumor development paralleled the recovery of the circulating non-classical monocytes subset (bottom panel; GK Encapsome vs Clodrosome at week 7, P=0.0011). *P<0.05, **P<0.01 and ***P<0.001; n.s., not significant.