Divergence in CD19-Mediated Signaling Unfolds Intra-Clonal Diversity in Chronic Lymphocytic Leukemia Which Correlates with Disease Progression

Abstract 4570 Emerging data on intra-clonal diversity imply that this phenomenon may play a role in the clinical outcome of patients with chronic lymphocytic leukemia (CLL), where subsets of the CLL clone responding more robustly to external stimuli may gain a growth and survival advantage. Here we report intra-clonal diversity resolved by responses to CD19 engagement in CLL cells, which can be classified into responding (CD19-R) and non-responding (CD19-N) sub-populations. Engagement of CD19 by anti-CD19 antibody rapidly induced cellular aggregation in the CD19-R CLL cells. The CD19-R CLL cells expressed higher surface levels of CD19 and c- myc mRNA and exhibited distinct morphological features. Both sub-populations reacted to IgM stimulation in a similar manner and exhibited similar levels of Akt phosphorylation, pointing to functional signaling divergence within the B-cell receptor. CD19 unresponsiveness was partially reversible, where CD19-N cells spontaneously recover their signaling capacity following incubation in vitro , pointing to possible in vivo CD19-signaling attenuating mechanisms. This concept was supported by the lower CD19-R occurrence in bone marrow-derived samples compared with cells derived from the peripheral blood of the same patients. CLL patients with more than 18.5% of CD19-R cell fraction had a shorter median time to treatment compared to patients with less than 18.5% of CD19-R cell fraction. Conclusions: Divergence in CD19-mediated signaling unfolds both inter-patient and intra-clonal diversity in CLL. This signaling diversity is associated with physiological implications including the location of the cells and disease progression. Disclosures: No relevant conflicts of interest to declare.