Targeting BMI-1 to deplete antibody-secreting cells in autoimmunity.

Objectives: B cells drive the production of autoreactive antibody-secreting cells (ASCs) in autoimmune diseases such as Systemic Lupus Erythematosus (SLE) and Sjögren's syndrome, causing long-term organ damage. Current treatments for antibody-mediated autoimmune diseases target B cells or broadly suppress the immune system. However, pre-existing long-lived ASCs are often refractory to treatment, leaving a reservoir of autoreactive cells that continue to produce antibodies. Therefore, the development of novel treatment methods targeting ASCs is vital to improve patient outcomes. Our objective was to test whether targeting the epigenetic regulator BMI-1 could deplete ASCs in autoimmune conditions in vivo and in vitro. Methods: Use of a BMI-1 inhibitor in both mouse and human autoimmune settings was investigated. Lyn -/- mice, a model of SLE, were treated with the BMI-1 small molecule inhibitor PTC-028, before assessment of ASCs, serum antibody and immune complexes. To examine human ASC survival, a novel human fibroblast-based assay was established, and the impact of PTC-028 on ASCs derived from Sjögren's syndrome patients was evaluated. Results: BMI-1 inhibition significantly decreased splenic and bone marrow ASCs in Lyn -/- mice. The decline in ASCs was linked to aberrant cell cycle gene expression and led to a significant decrease in serum IgG3, immune complexes and anti-DNA IgG. PTC-028 was also efficacious in reducing ex vivo plasma cell survival from both Sjögren's syndrome patients and age-matched healthy donors. Conclusion: These data provide evidence that inhibiting BMI-1 can deplete ASC in a variety of contexts and thus BMI-1 is a viable therapeutic target for antibody-mediated autoimmune diseases.

Heterogeneous Tfh cell populations that develop during enteric helminth infection predict the quality of type 2 protective response.

T follicular helper (Tfh) cells are an important component of germinal center (GC)-mediated humoral immunity. Yet, how a chronic type 1 versus protective type 2 helminth infection modulates Tfh-GC responses remains poorly understood. Here, we employ the helminth Trichuris muris model and demonstrate that Tfh cell phenotypes and GC are differentially regulated in acute versus chronic infection. The latter failed to induce Tfh-GC B cell responses, with Tfh cells expressing Τ-bet and interferon-γ. In contrast, interleukin-4-producing Tfh cells dominate responses to an acute, resolving infection. Heightened expression and increased chromatin accessibility of T helper (Th)1- and Th2 cell-associated genes are observed in chronic and acute induced Tfh cells, respectively. Blockade of the Th1 cell response by T-cell-intrinsic T-bet deletion promoted Tfh cell expansion during chronic infection, pointing to a correlation between a robust Tfh cell response and protective immunity to parasites. Finally, blockade of Tfh-GC interactions impaired type 2 immunity, revealing the critical protective role of GC-dependent Th2-like Tfh cell responses during acute infection. Collectively, these results provide new insights into the protective roles of Tfh-GC responses and identify distinct transcriptional and epigenetic features of Tfh cells that emerge during resolving or chronic T. muris infection.

Targeting BMI-1 in B cells restores effective humoral immune responses and controls chronic viral infection.

Ineffective antibody-mediated responses are a key characteristic of chronic viral infection. However, our understanding of the intrinsic mechanisms that drive this dysregulation are unclear. Here, we identify that targeting the epigenetic modifier BMI-1 in mice improves humoral responses to chronic lymphocytic choriomeningitis virus. BMI-1 was upregulated by germinal center B cells in chronic viral infection, correlating with changes to the accessible chromatin landscape, compared to acute infection. B cell-intrinsic deletion of Bmi1 accelerated viral clearance, reduced splenomegaly and restored splenic architecture. Deletion of Bmi1 restored c-Myc expression in B cells, concomitant with improved quality of antibody and coupled with reduced antibody-secreting cell numbers. Specifically, BMI-1-deficiency induced antibody with increased neutralizing capacity and enhanced antibody-dependent effector function. Using a small molecule inhibitor to murine BMI-1, we could deplete antibody-secreting cells and prohibit detrimental immune complex formation in vivo. This study defines BMI-1 as a crucial immune modifier that controls antibody-mediated responses in chronic infection.

The Histone Methyltransferase DOT1L Is Essential for Humoral Immune Responses.

Histone modifiers are essential for the ability of immune cells to reprogram their gene expression during differentiation. The recruitment of the histone methyltransferase DOT1L (disruptor of telomeric silencing 1-like) induces oncogenic gene expression in a subset of B cell leukemias. Despite its importance, its role in the humoral immune system is unclear. Here, we demonstrate that DOT1L is a critical regulator of B cell biology. B cell development is defective in Dot1lf/fMb1Cre/+ mice, culminating in a reduction of peripheral mature B cells. Upon immunization or influenza infection of Dot1lf/fCd23Cre/+ mice, class-switched antibody-secreting cells are significantly attenuated and germinal centers fail to form. Consequently, DOT1L is essential for B cell memory formation. Transcriptome, pathway, and histological analyses identified a role for DOT1L in reprogramming gene expression for appropriate localization of B cells during the initial stage of the response. Together, these results demonstrate an essential role for DOT1L in generating an effective humoral immune response.

Assessing the role of the T-box transcription factor Eomes in B cell differentiation during either Th1 or Th2 cell-biased responses.

Successful T-dependent humoral responses require the production of antibody-secreting plasmablasts, as well as the formation of germinal centers which eventually form high-affinity B cell memory. The ability of B cells to differentiate into germinal center and plasma cells, as well as the ability to tailor responses to different pathogens, is driven by transcription factors. In T cells, the T-box transcription factors T-bet and Eomesodermin (Eomes) regulate effector and memory T cell differentiation, respectively. While T-bet has a critical role in regulating anti-viral B cell responses, a role for Eomes in B cells has yet to be described. We therefore investigated whether Eomes was required for B cell differentiation during either Th1 or Th2 cell-biased immune responses. Here, we demonstrate that deletion of Eomes specifically in B cells did not affect B cell differentiation in response to vaccination, as well as following viral or helminth infection. In contrast to its established role in CD8+ T cells, Eomes did not influence memory B cell differentiation. Finally, the use of an Eomes reporter mouse confirmed the lack of Eomes expression during immune responses. Thus, germinal center and plasma cell differentiation and the formation of isotype-switched memory B cells in response to infection are independent of Eomes expression.