Chronic lymphocytic leukemia cells diversify and differentiate in vivo via a nonclassical Th1-dependent, Bcl-6–deficient process

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Abstract

Xenografting primary tumor cells allows modeling of the heterogeneous natures of malignant diseases and the influences of the tissue microenvironment. Here, we demonstrate that xenografting primary chronic lymphocytic leukemia (CLL) B lymphocytes with activated autologous T cells into alymphoid mice results in considerable CLL B cell division and sizable T cell expansion. Nevertheless, most/all CD5⁺CD19⁺ cells are eventually lost, due in part to differentiation into antibody-secreting plasmablasts/plasma cells. CLL B cell differentiation is associated with isotype class switching and development of new IGHV-D-J mutations and occurs via an activation-induced deaminase-dependent pathway that upregulates IRF4 and Blimp-1 without appreciable levels of the expected Bcl-6. These processes were induced in IGHV-unmutated and IGHV-mutated clones by Th1-polarized T-bet⁺ T cells, not classical T follicular helper (Tfh) cells. Thus, the block in B cell maturation, defects in T cell action, and absence of antigen-receptor diversification, which are often cardinal characteristics of CLL, are not inherent but imposed by external signals and the microenvironment. Although these activities are not dominant features in human CLL, each occurs in tissue proliferation centers where the mechanisms responsible for clonal evolution operate. Thus, in this setting, CLL B cell diversification and differentiation develop by a nonclassical germinal center–like reaction that might reflect the cell of origin of this leukemia.

Authors

Piers E.M. Patten, Gerardo Ferrer, Shih-Shih Chen, Rita Simone, Sonia Marsilio, Xiao-Jie Yan, Zachary Gitto, Chaohui Yuan, Jonathan E. Kolitz, Jacqueline Barrientos, Steven L. Allen, Kanti R. Rai, Thomas MacCarthy, Charles C. Chu, Nicholas Chiorazzi

Synergism of FAK and tyrosine kinase inhibition in Ph⁺ B-ALL

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Abstract

BCR-ABL1⁺ B progenitor acute lymphoblastic leukemia (Ph⁺ B-ALL) is an aggressive disease that frequently responds poorly to currently available therapies. Alterations in IKZF1, which encodes the lymphoid transcription factor Ikaros, are present in over 80% of Ph⁺ ALL and are associated with a stem cell–like phenotype, aberrant adhesion molecule expression and signaling, leukemic cell adhesion to the bone marrow stem cell niche, and poor outcome. Here, we show that FAK1 is upregulated in Ph⁺ B-ALL with further overexpression in IKZF1-altered cells and that the FAK inhibitor VS-4718 potently inhibits aberrant FAK signaling and leukemic cell adhesion, potentiating responsiveness to tyrosine kinase inhibitors, inducing cure in vivo. Thus, targeting FAK with VS-4718 is an attractive approach to overcome the deleterious effects of FAK overexpression in Ph⁺ B-ALL, particularly in abrogating the adhesive phenotype induced by Ikaros alterations, and warrants evaluation in clinical trials for Ph⁺ B-ALL, regardless of IKZF1 status.

Authors

Michelle L. Churchman, Kathryn Evans, Jennifer Richmond, Alissa Robbins, Luke Jones, Irina M. Shapiro, Jonathan A. Pachter, David T. Weaver, Peter J. Houghton, Malcolm A. Smith, Richard B. Lock, Charles G. Mullighan