Modelling CLL cell and T-cell Migration in a Dynamic Circulating Model of CLL

We have recently developed a novel circulating model of chronic lymphocytic leukaemia (CLL) that mimics the transient interactions that take place between circulating lymphocytes and vascular endothelium. Here we show that both normal and malignant lymphocytes actively underwent transendothelial migration. Furthermore, seeding of CXCL12-secreting MRC5 cells into the extravascular space (EVS) resulting in significantly enhanced CLL cell migration (P = 0.024) but no increase in T-cell migration. Both CLL cells and T-cells recovered from the EVS showed evidence of activation markers and entry into cell cycle as demonstrated by increased Ki-67 expression (P<0.0001). We subsequently established that CLL cell Ki-67 expression was dependent on the presence of T-cells, as depletion of the T-cells from the circulating compartment significantly inhibited Ki-67 induction (P = 0.003). It is worthy of note that as a proportion of all circulating peripheral blood mononuclear cells, CD3+ T-cells migrated significantly more than CD19+ CLL cells (P = 0.02). This seems likely to be promoted by CLL cell secretion of T-cell attracting chemokines CCL3 (298pg/m1±197.5) and CCL4 (56pg/m1±115.6) in our model. Interestingly, CD38+ CLL samples showed elevated levels of CCL3 and CCL4 suggesting that increased T-cell recruitment may contribute to the inferior clinical outcomes seen in these patients. Taken together the data presented here highlight the requirement of T-cells in the pathology of CLL.