Activated gp130 signaling selectively targets B cell differentiation to induce mature lymphoma and plasmacytoma.

Aberrant activity of the glycoprotein 130 130/JAK/STAT3 (gp130/JAK/STAT3) signaling axis is a recurrent event in inflammation and cancer. In particular, it is associated with a wide range of hematological malignancies, including multiple myeloma and leukemia. Novel targeted therapies have only been successful for some subtypes of these malignancies, underlining the need for developing robust mouse models to better dissect the role of this pathway in specific tumorigenic processes. Here, we investigated the role of selective gp130/JAK/STAT3 activation by generating a conditional mouse model. This model targeted constitutively active, cell-autonomous gp130 activity to B cells, as well as to the entire hematopoietic system. We found that regardless of the timing of activation in B cells, constitutively active gp130 signaling resulted in the formation specifically of mature B cell lymphomas and plasma cell disorders with full penetrance, only with different latencies, where infiltrating CD138+ cells were a dominant feature in every tumor. Furthermore, constitutively active gp130 signaling in all adult hematopoietic cells also led to the development specifically of largely mature, aggressive B cell cancers, again with a high penetrance of CD138+ tumors. Importantly, gp130 activity abrogated the differentiation block induced by a B cell-targeted Myc transgene and resulted in a complete penetrance of the gp130-associated, CD138+, mature B cell lymphoma phenotype. Thus, gp130 signaling selectively provides a strong growth and differentiation advantage for mature B cells and directs lymphomagenesis specifically toward terminally differentiated B cell cancers.

Epitope mapping via selection of anti-FVIII antibody-specific phage-presented peptide ligands that mimic the antibody binding sites.

The most serious complication in today's treatment of congenital haemophilia A is the development of neutralising antibodies (inhibitors) against factor VIII (FVIII). Although FVIII inhibitors can be eliminated by immune tolerance induction (ITI) based on repeated administration of high doses of FVIII, 20-30% of patients fail to become tolerant. Persistence of FVIII inhibitors is associated with increased morbidity and mortality. Data from recent studies provide evidence for a potential association between ITI outcome and epitope specificity of FVIII inhibitors. Nevertheless the determination of epitopes and their clinical relevance has not yet been established. In this study a general strategy for the identification of anti-FVIII antibody epitopes in haemophilia A patient plasma was to be demonstrated. Phage-displayed peptide libraries were screened against anti-FVIII antibodies to isolate specific peptides. Peptide specificity was confirmed by FVIII-sensitive ELISA binding. Peptide residues essential for antibody binding were identified by mutational analysis and epitopes were predicted via FVIII homology search. The proposed mapping strategy was validated for the monoclonal murine antibody (mAb) 2-76. Binding studies with FVIII variants confirmed the location of the predicted epitope at the level of individual amino acids. In addition, anti-FVIII antibody-specific peptide ligands were selected for 10 haemophilia A patients with FVIII inhibitors. Detailed epitope mapping for three of them showed binding sites on the A2, A3 and C2 domains. Precise epitope mapping of anti-FVIII antibodies using antibody-specific peptide ligands can be a useful approach to identify antigenic sites on FVIII.

Fas ligand-mediated immune surveillance by T cells is essential for the control of spontaneous B cell lymphomas.

Loss of function of the tumor suppressor gene PRDM1 (also known as BLIMP1) or deregulated expression of the oncogene BCL6 occurs in a large proportion of diffuse large B cell lymphoma (DLBCL) cases. However, targeted mutation of either gene in mice leads to only slow and infrequent development of malignant lymphoma, and despite frequent mutation of BCL6 in activated B cells of healthy individuals, lymphoma development is rare. Here we show that T cells prevent the development of overt lymphoma in mice caused by Blimp1 deficiency or overexpression of Bcl6 in the B cell lineage. Impairment of T cell control results in rapid development of DLBCL-like disease, which can be eradicated by polyclonal CD8(+) T cells in a T cell receptor-, CD28- and Fas ligand-dependent manner. Thus, malignant transformation of mature B cells requires mutations that impair intrinsic differentiation processes and permit escape from T cell-mediated tumor surveillance.