Lamin B1 regulates somatic mutations and progression of B-cell malignancies

Somatic hypermutation (SHM) is a pivotal process in adaptive immunity that occurs in the germinal centre and allows B cells to change their primary DNA sequence and diversify their antigen receptors. Here, we report that genome binding of Lamin B1, a component of the nuclear envelope involved in epigenetic chromatin regulation, is reduced during B-cell activation and formation of lymphoid germinal centres. Chromatin immunoprecipitation-Seq analysis showed that kappa and heavy variable immunoglobulin domains were released from the Lamin B1 suppressive environment when SHM was induced in B cells. RNA interference-mediated reduction of Lamin B1 resulted in spontaneous SHM as well as kappa-light chain aberrant surface expression. Finally, Lamin B1 expression level correlated with progression-free and overall survival in chronic lymphocytic leukaemia, and was strongly involved in the transformation of follicular lymphoma. In summary, here we report that Lamin B1 is a negative epigenetic regulator of SHM in normal B-cells and a 'mutational gatekeeper', suppressing the aberrant mutations that drive lymphoid malignancy.

A new in vivo and in vitro B cell lymphoma model, pi-BCL1

We report a new variant of the BCL1 syngeneic mouse B-cell lymphoma model, which we have called pi-BCL1. pi-BCL1 can be established as a syngeneic tumor in BALB/c mice. Tumors can be removed, prepared and easily grown in liquid culture and subsequently transferred back successfully as syngeneic tumors. As a syngeneic tumor pi-BCL1 behave more like a lymphoma with solid tumor masses, than a chronic lymphocytic leukaemia of the original BCL1 model. The immunophenotype and the growth characteristics of the pi-BCL1 and BCL1 tumors appear very similar. Cytologically, pi-BCL1 appears to be a transformation from a small lymphocytic lymphoma to a more diffuse large cell centroblast-like higher-grade lymphoma. We are not aware of any previous reports of such transformation events in a syngeneic animal model of B cell lymphoma. We believe pi-BCL1 provides a useful new tool for the study of B cell lymphoma in vitro and in vivo and enables reduced numbers of tumor passage in mice.

Radioimmunotherapy in the pi-BCL1 B cell lymphoma model: efficacy depends on more than targeted irradiation alone

We report the in vivo radioimmunotherapy (RIT) of a new variant of the BCL1 syngeneic mouse B-cell lymphoma model, pi-BCL1, using a panel of monoclonal antibodies (MoAb) reactive with B cell-associated antigens (CD19, CD22, CD40, MHC II, and idiotype). MoAb were radiolabeled with 131I or used in conjunction with external beam irradiation. When administered early in disease (day 4) 131I-anti-MHC II MoAb produced long term disease free survivors as a result of targeted irradiation alone; the equivalent unlabelled MoAb was non-therapeutic. In contrast, 131I-anti-CD40, and 131I-anti-Idiotype (Id) MoAb administered at day 4 despite targeting irradiation and having intrinsic therapeutic activity as unconjugated antibodies, protected mice for approximately 30 days. The 131I-anti-CD19 and anti-CD22 were therapeutically inactive. Treating later in the disease (day 14, after tumor inoculation) permitted study of the efficacy in the presence of an increased tumor load. An increased tumor burden brought about an expected reduction in therapeutic activity with 131I-anti-MHC II, but surprisingly, 131I anti-CD40 and 131I-anti-Id were able to produce prolonged disease free survival in most mice. This unexpected potency of 131I-anti-CD40 and 131I-anti-Id late in disease appeared to result from the direct cytotoxic action induced by these MoAb. Mechanisms by which these two MoAb operate, in producing long-term disease free survival in animals with advanced disease appear different. Our therapeutic results have important implications for the selection of reagents for RIT and demonstrate that successful treatment with such agents may involve more than simple targeting of irradiation.