Complement deficiencies limit CD20 monoclonal antibody treatment efficacy in CLL.

Monoclonal antibodies (MAbs) form a central part of chronic lymphocytic leukaemia (CLL) treatment. We therefore evaluated whether complement defects in CLL patients reduced the induction of complement-dependent cytotoxicity (CDC) by using anti-CD20 MAbs rituximab (RTX) and ofatumumab (OFA). Ofatumumab elicited higher CDC levels than RTX in all CLL samples examined, particularly in poor prognosis cohorts (11q- and 17p-). Serum sample analyses revealed that 38.1% of patients were deficient in one or more complement components, correlating with reduced CDC responses. Although a proportion of patients with deficient complement levels initially induced high levels of CDC, on secondary challenge CDC activity in sera was significantly reduced, compared with that in normal human serum (NHS; P<0.01; n=52). In addition, a high CLL cell number contributed to rapid complement exhaustion. Supplementing CLL serum with NHS or individual complement components, particularly C2, restored CDC on secondary challenge to NHS levels (P<0.0001; n=9). In vivo studies revealed that complement components were exhausted in CLL patient sera post RTX treatment, correlating with an inability to elicit CDC. Supplementing MAb treatment with fresh-frozen plasma may therefore maintain CDC levels in CLL patients with a complement deficiency or high white blood cell count. This study has important implications for CLL patients receiving anti-CD20 MAb therapy.

Proteomic analysis reveals a novel mechanism induced by the leukemic oncogene Tel/PDGFRß in stem cells: activation of the interferon response pathways.

Objective proteomic analysis offers opportunities for hypothesis generation on molecular events associated with pathogenesis in stem cells. Relative quantification mass spectrometry was employed to identify pathways affected by Tel/PDGFRß, an oncogene associated with myeloproliferative neoplasia (MPN). Its effects on over 1800 proteins were quantified with high confidence. Of those up-regulated by Tel/PDGFRß several were involved in the interferon gamma (IFNγ) response. To validate these observations we employed embryonic and myeloid stem cells models which revealed Tel/PDGFRß-induced STAT1 up-regulation and activation was responsible for modulating the interferon response. A STAT1 target highly up-regulated was ICSBP, a transcriptional regulator of myeloid and eosinophilic differentiation. ICSBP interacts with CBP/p300 and Ets transcription factors, to promote transcription of additional genes, including the Egr family, key regulators of myelopoiesis. These interferon responses were recapitulated using IFNγ stimulation of stem cells. Thus Tel/PDGFRß induces aberrant IFN signaling and downstream targets, which may ultimately impact the hematopoietic transcriptional factor network to bias myelomonocytic differentiation in this MPN.

Tel/PDGFRbeta inhibits self-renewal and directs myelomonocytic differentiation of ES cells.

The leukemic oncogene Tel/PDGFRbeta, was inducibly expressed in embryonic stem (ES) cells and the phenotypic and molecular changes occurring during hematopoietic differentiation investigated. Expression of Tel/PDGFRbeta resulted in an inability of ES cells to self-renew and caused a significant increase in myelopoiesis with a corresponding decrease in erythropoiesis. Analysis of gene expression patterns indicated a dramatic alteration in the levels of genes associated with self-renewal and differentiation, especially myelomonocytic genes in Tel/PDGFRbeta-expressing cells. This study indicates Tel/PDGFRbeta drives myelopoiesis by altering expression of genes involved in hematopoiesis and demonstrates the potential of this stem cell system to study oncogene-induced pathogenesis.