Anti-CD47 antibody synergizes with rituximab to promote phagocytosis and eradicate non-Hodgkin lymphoma.

Monoclonal antibodies are standard therapeutics for several cancers including the anti-CD20 antibody rituximab for B cell non-Hodgkin lymphoma (NHL). Rituximab and other antibodies are not curative and must be combined with cytotoxic chemotherapy for clinical benefit. Here we report the eradication of human NHL solely with a monoclonal antibody therapy combining rituximab with a blocking anti-CD47 antibody. We identified increased expression of CD47 on human NHL cells and determined that higher CD47 expression independently predicted adverse clinical outcomes in multiple NHL subtypes. Blocking anti-CD47 antibodies preferentially enabled phagocytosis of NHL cells and synergized with rituximab. Treatment of human NHL-engrafted mice with anti-CD47 antibody reduced lymphoma burden and improved survival, while combination treatment with rituximab led to elimination of lymphoma and cure. These antibodies synergized through a mechanism combining Fc receptor (FcR)-dependent and FcR-independent stimulation of phagocytosis that might be applicable to many other cancers.

Efficient chimeric antigen receptor targeting of a central epitope of CD22.

Chimeric antigen receptor (CAR) T-cell therapy has had considerable success in the treatment of B-cell malignancies. Targeting the B-lineage marker CD19 has brought great advances to the treatment of acute lymphoblastic leukemia and B-cell lymphomas. However, relapse remains an issue in many cases. Such relapse can result from downregulation or loss of CD19 from the malignant cell population or expression of alternate isoforms. Consequently, there remains a need to target alternative B-cell antigens and diversify the spectrum of epitopes targeted within the same antigen. CD22 has been identified as a substitute target in cases of CD19-negative relapse. One anti-CD22 antibody-clone m971-targets a membrane-proximal epitope of CD22 and has been widely validated and used in the clinic. Here, we have compared m971-CAR with a novel CAR derived from IS7, an antibody that targets a central epitope on CD22. The IS7-CAR has superior avidity and is active and specific against CD22-positive targets, including B-acute lymphoblastic leukemia patient-derived xenograft samples. Side-by-side comparisons indicated that while IS7-CAR killed less rapidly than m971-CAR in vitro, it remains efficient in controlling lymphoma xenograft models in vivo. Thus, IS7-CAR presents a potential alternative candidate for the treatment of refractory B-cell malignancies.

Mechanism of CD79A and CD79B Support for IgM+ B Cell Fitness through B Cell Receptor Surface Expression.

The BCR consists of surface-bound Ig and a heterodimeric signaling unit comprised of CD79A and CD79B. Upon cognate Ag recognition, the receptor initiates important signals for B cell development and function. The receptor also conveys Ag-independent survival signals termed tonic signaling. Although the requirement of a CD79A/CD79B heterodimer for BCR complex assembly and surface expression is well established based on mice models, few studies have investigated this in human mature B cells. In this study, we found that human tonsillar B cells with high surface expression of IgM or IgG had potentiated BCR signaling compared with BCRlow cells, and high IgM expression in germinal center B cells was associated with reduced apoptosis. We explored the mechanism for IgM surface expression by CRISPR/Cas9-induced deletion of CD79A or CD79B in four B lymphoma cell lines. Deletion of either CD79 protein caused loss of surface IgM in all cell lines and reduced fitness in three. From two cell lines, we generated stable CD79A or CD79B knockout clones and demonstrated that loss of CD79A or CD79B caused a block in N-glycan maturation and accumulation of immature proteins, compatible with retention of BCR components in the endoplasmic reticulum. Rescue experiments with CD79B wild-type restored surface expression of CD79A and IgM with mature glycosylation, whereas a naturally occurring CD79B G137S mutant disrupting CD79A/CD79B heterodimerization did not. Our study highlights that CD79A and CD79B are required for surface IgM expression in human B cells and illuminates the importance of the IgM expression level for signaling and fitness.

Combinatorial CAR design improves target restriction.

CAR T cells targeting the B lymphocyte antigen CD19 have led to remarkable clinical results in B cell leukemia and lymphoma but eliminate all B lineage cells, leading to increased susceptibility to severe infections. As malignant B cells will express either immunoglobulin (Ig) light chain κ or λ, we designed a second-generation CAR targeting Igκ, IGK CAR. This construct demonstrated high target specificity but displayed reduced efficacy in the presence of serum IgG. Since CD19 CAR is insensitive to serum IgG, we designed various combinatorial CAR constructs in order to maintain the CD19 CAR T cell efficacy, but with IGK CAR target selectivity. The Kz-19BB design, combining CD19 CAR containing a 4-1BB costimulatory domain with an IGK CAR containing a CD3zeta stimulatory domain, maintained the target specificity of IgK CAR and was resistant to the presence of soluble IgG. Our results demonstrate that a combinatorial CAR approach can improve target selectivity and efficacy.

Human Germinal Center B Cells Differ from Naïve and Memory B Cells in CD40 Expression and CD40L-Induced Signaling Response.

CD40 expression is required for germinal center (GC) formation and function, but the kinetics and magnitude of signaling following CD40 engagement remain poorly characterized in human B cells undergoing GC reactions. Here, differences in CD40 expression and signaling responses were compared across differentiation stages of mature human tonsillar B cells. A combination of mass cytometry and phospho-specific flow cytometry was used to quantify protein expression and CD40L-induced signaling in primary human naïve, GC, and memory B cells. Protein expression signatures of cell subsets were quantified using viSNE and Marker Enrichment Modeling (MEM). This approach revealed enriched expression of CD40 protein in GC B cells, compared to naïve and memory B cells. Despite this, GC B cells responded to CD40L engagement with lower phosphorylation of NFκB p65 during the first 30 min following CD40L activation. Before CD40L stimulation, GC B cells expressed higher levels of suppressor protein IκBα than naïve and memory B cells. Following CD40 activation, IκBα was rapidly degraded and reached equivalently low levels in naïve, GC, and memory B cells at 30 min following CD40L. Quantifying CD40 signaling responses as a function of bound ligand revealed a correlation between bound CD40L and degree of induced NFκB p65 phosphorylation, whereas comparable IκBα degradation occurred at all measured levels of CD40L binding. These results characterize cell-intrinsic signaling differences that exist in mature human B cells undergoing GC reactions. © 2019 International Society for Advancement of Cytometry.

Distinct patterns of B-cell receptor signaling in non-Hodgkin lymphomas identified by single-cell profiling.

Kinases downstream of B-cell antigen receptor (BCR) represent attractive targets for therapy in non-Hodgkin lymphoma (NHL). As clinical responses vary, improved knowledge regarding activation and regulation of BCR signaling in individual patients is needed. Here, using phosphospecific flow cytometry to obtain malignant B-cell signaling profiles from 95 patients representing 4 types of NHL revealed a striking contrast between chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) tumors. Lymphoma cells from diffuse large B-cell lymphoma patients had high basal phosphorylation levels of most measured signaling nodes, whereas follicular lymphoma cells represented the opposite pattern with no or very low basal levels. MCL showed large interpatient variability in basal levels, and elevated levels for the phosphorylated forms of AKT, extracellular signal-regulated kinase, p38, STAT1, and STAT5 were associated with poor outcome. CLL tumors had elevated basal levels for the phosphorylated forms of BCR-signaling nodes (Src family tyrosine kinase, spleen tyrosine kinase [SYK], phospholipase Cγ), but had low α-BCR-induced signaling. This contrasted MCL tumors, where α-BCR-induced signaling was variable, but significantly potentiated as compared with the other types. Overexpression of CD79B, combined with a gating strategy whereby signaling output was directly quantified per cell as a function of CD79B levels, confirmed a direct relationship between surface CD79B, immunoglobulin M (IgM), and IgM-induced signaling levels. Furthermore, α-BCR-induced signaling strength was variable across patient samples and correlated with BCR subunit CD79B expression, but was inversely correlated with susceptibility to Bruton tyrosine kinase (BTK) and SYK inhibitors in MCL. These individual differences in BCR levels and signaling might relate to differences in therapy responses to BCR-pathway inhibitors.

Human c-SRC kinase (CSK) overexpression makes T cells dummy.

Adoptive cell therapy with T-cell receptor (TCR)-engineered T cells represents a powerful method to redirect the immune system against tumours. However, although TCR recognition is restricted to a specific peptide-MHC (pMHC) complex, increasing numbers of reports have shown cross-reactivity and off-target effects with severe consequences for the patients. This demands further development of strategies to validate TCR safety prior to clinical use. We reasoned that the desired TCR signalling depends on correct pMHC recognition on the outside and a restricted clustering on the inside of the cell. Since the majority of the adverse events are due to TCR recognition of the wrong target, we tested if blocking the signalling would affect the binding. By over-expressing the c-SRC kinase (CSK), a negative regulator of LCK, in redirected T cells, we showed that peripheral blood T cells inhibited anti-CD3/anti-CD28-induced phosphorylation of ERK, whereas TCR proximal signalling was not affected. Similarly, overexpression of CSK together with a therapeutic TCR prevented pMHC-induced ERK phosphorylation. Downstream effector functions were also almost completely blocked, including pMHC-induced IL-2 release, degranulation and, most importantly, target cell killing. The lack of effector functions contrasted with the unaffected TCR expression, pMHC recognition, and membrane exchange activity (trogocytosis). Therefore, co-expression of CSK with a therapeutic TCR did not compromise target recognition and binding, but rendered T cells incapable of executing their effector functions. Consequently, we named these redirected T cells "dummy T cells" and propose to use them for safety validation of new TCRs prior to therapy.

Patterns of constitutively phosphorylated kinases in B cells are associated with disease severity in common variable immunodeficiency.

Patients with common variable immunodeficiency (CVID) constitute a clinically and immunologically heterogeneous group characterized by B-cell dysfunction with hypogammaglobulinemia and defective immunoglobulin class switch of unknown etiology. Current classification systems are insufficient to achieve precise disease management. Characterization of signaling pathways essential for B-cell differentiation and class switch could provide new means to stratify patients. We evaluated constitutive and induced signaling by phospho-specific flow cytometry in 26 CVID patients and 18 healthy blood donors. Strong responses were induced both in CVID and healthy donor B cells upon activation. In contrast, constitutive phosphorylation levels of STAT3,-5,-6, Erk, PLC-γ and Syk were significantly increased in CVID B cells only. Hierarchical clustering revealed a subgroup of CVID patients with elevated constitutive phosphorylation of Syk and PLC-γ. All these patients had non-infectious complications, indicating that a distinct phosphorylation pattern of kinases in B cells identifies a clinically important subgroup of CVID patients.

Defective IL-4 signaling in T cells defines severe common variable immunodeficiency.

Common variable immunodeficiency (CVID) is defined by hypogammaglobulinemia and B-cell dysfunction, with significant clinical and immunological heterogeneity. Severe non-infectious complications, such as autoimmunity, granulomatous disease and splenomegaly, constitute a major cause of morbidity in CVID patients. T cells are generally regarded important for development of these clinical features. However, while T-cell abnormalities have been found in CVID patients, functional characteristics of T cells corresponding to well-defined clinical subtypes have not been identified. As common γ-chain cytokines play important roles in survival and differentiation of T cells, characterization of their signaling pathways could reveal functional differences of clinical relevance. We characterized CVID T cells functionally by studies of cytokine-induced signaling, and correlated the findings to defined clinical subtypes. Peripheral blood T cells from 29 CVID patients and 19 healthy donors were analyzed for i) phenotype, ii) cytokine-induced (interleukin (IL)-2, IL-4, IL-7 and IL-21) phosphorylation of signal transducer and activator of transcription (STAT) 3, STAT5 and STAT6, and iii) T-helper (Th)1/Th2 polarization. Expression of IL-4 receptor and downstream signaling molecules was measured. A subgroup of CVID patients (n = 7) was identified by impaired IL-4-induced p-STAT6 in naive and memory CD4 and CD8 T cells. This corresponded to patients with the largest accumulation of severe (non-infectious) complications. The signaling defect persisted over years and was not due to constitutively activated p-STAT6. The CD4 T cells were strongly Th1-skewed, but IL-4 signaling was impaired independently of Th status. However, IL-4Rα and Janus kinase (JAK) 1 mRNA levels were significantly lower than in normal donors, providing a likely mechanism for the defective IL-4-induced p-STAT6 and Th1-bias. In conclusion, we identified a subgroup of CVID patients with defective IL-4 signaling in T cells, with severe clinical features of inflammation and autoimmunity.

Whole-genome integrative analysis reveals expression signatures predicting transformation in follicular lymphoma.

Transformation of follicular lymphoma (FL) to a more aggressive disease is associated with rapid progression and death. Existing molecular markers for transformation are few and their clinical impact is limited. Here, we report on a whole-genome study of DNA copy numbers and gene expression profiles in serial FL biopsies. We identified 698 genes with high correlation between gene expression and copy number, and the molecular network most enriched for these cis-associated genes. This network includes 14 cis-associated genes directly related to the nuclear factor κB (NF-κB) pathway. For each of these 14 genes, the correlated NF-κB target genes were identified and corresponding expression scores were defined. The scores for 6 of the cis-associated NFκB pathway genes (BTK, IGBP1, IRAK1, ROCK1, TMED7-TICAM2, and TRIM37) were significantly associated with transformation. The results suggest that genes regulating B-cell survival and activation are involved in transformation of FL.

Content of endothelial progenitor cells in autologous stem cell grafts predict survival after transplantation for multiple myeloma.

Multiple myeloma (MM) is considered an incurable B cell malignancy, although many patients can benefit from high-dose therapy with autologous stem cell transplantation (ASCT) as a first-line treatment. In non-Hodgkin lymphoma (NHL), ASCT is usually performed after relapse with curative intent. Disease progression is often associated with increased angiogenesis, in which endothelial progenitor cells (EPC) may have a central role. Here, we investigated the clinical impact of EPC levels in peripheral blood stem cell (PBSC) autografts for MM and NHL patients who received ASCT. EPC were identified by flow cytometry as aldehyde dehydrogenase(hi) CD34(+) vascular endothelial growth factor receptor 2(+) CD133(+) cells in both MM and NHL autografts. In MM, there was a positive correlation between EPC percentage and serum (s)-ß2-microglobulin levels (r(2) = .371, P = .002). Unlike for NHL patients, MM patients with high numbers of infused EPC (EPC cells per kilogram) during ASCT had significant shorter progression-free survival (PFS) (P = .035), overall survival (P = .044) and time to next treatment (P = .009). In multivariate analysis, EPC cells per kilogram was a significant independent negative prognostic indicator of PFS (P = .03). In conclusion, the presence of high number of EPC in PBSC grafts is associated with adverse prognosis after ASCT in MM.

Hierarchy in somatic mutations arising during genomic evolution and progression of follicular lymphoma.

Follicular lymphoma (FL) is currently incurable using conventional chemotherapy or immunotherapy regimes, compelling new strategies. Advances in high-throughput sequencing technologies that can reveal oncogenic pathways have stimulated interest in tailoring therapies toward actionable somatic mutations. However, for mutation-directed therapies to be most effective, the mutations must be uniformly present in evolved tumor cells as well as in the self-renewing tumor-cell precursors. Here, we show striking intratumoral clonal diversity within FL tumors in the representation of mutations in the majority of genes as revealed by whole exome sequencing of subpopulations. This diversity captures a clonal hierarchy, resolved using immunoglobulin somatic mutations and IGH-BCL2 translocations as a frame of reference and by comparing diagnosis and relapse tumor pairs, allowing us to distinguish early versus late genetic eventsduring lymphomagenesis. We provide evidence that IGH-BCL2 translocations and CREBBP mutations are early events, whereas MLL2 and TNFRSF14 mutations probably represent late events during disease evolution. These observations provide insight into which of the genetic lesions represent suitable candidates for targeted therapies.

High PD-1 expression and suppressed cytokine signaling distinguish T cells infiltrating follicular lymphoma tumors from peripheral T cells.

Defects in T-cell function in patients with cancer might influence their capacity to mount efficient antitumor immune responses. Here, we identified highly reduced IL-4-, IL-10-, and IL-21-induced phosphorylation of STAT6 and STAT3 in tumor-infiltrating T cells (TILs) in follicular lymphoma (FL) tumors, contrasting other non-Hodgkin lymphoma TILs. By combining phospho-protein-specific flow cytometry with several T-cell markers, we identified that CD4(+)CD45RO(+)CD62L(-) FL TILs were largely nonresponsive to cytokines, in contrast to the corresponding autologous peripheral blood subset. We observed differential expression of the inhibitory receptor PD-1 in FL TILs and peripheral blood T cells. Furthermore, CD4(+)PD-1(hi) FL TILs, containing T(FH) and non-T(FH) cells, had lost their cytokine responsiveness, whereas PD-1 TILs had normal cytokine signaling. However, this phenomenon was not tumor specific, because tonsil T cells were similar to FL TILs. FL tumor cells were negative for PD-1 ligands, but PD-L1(+) histiocytes were found within the T cell-rich zone of the neoplastic follicles. Disruption of the microenvironment and in vitro culture of FL TILs could restore cytokine signaling in the PD-1(hi) subset. Because FL TILs in vivo probably receive suppressive signals through PD-1, this provides a rationale for testing PD-1 Ab in combination with immunotherapy in patients with FL.

Disruption of KLHL6 Fuels Oncogenic Antigen Receptor Signaling in B-cell Lymphoma.

Pathomechanisms that activate oncogenic B-cell receptor (BCR) signaling in diffuse large B-cell lymphoma (DLBCL), are largely unknown. Kelch-like family member 6 (KLHL6) encoding a substrate-adapter for Cullin-3-RING E3 ubiquitin-ligase (CRL) with poorly established targets is recurrently mutated in DLBCL. By applying high-throughput protein interactome screens and functional characterization, we discovered that KLHL6 regulates BCR by targeting its signaling subunits CD79A and CD79B. Loss of physiological KLHL6 expression pattern was frequent among the MCD/C5-like activated B-cell DLBCLs and was associated with higher CD79B levels and dismal outcome. Mutations in the BTB domain of KLHL6 disrupted its localization and heterodimerization, and increased surface BCR levels and signaling, whereas Kelch domain mutants had the opposite effect. Malfunctions of KLHL6 mutants extended beyond proximal BCR signaling with distinct phenotypes from KLHL6 silencing. Collectively, our findings uncover how recurrent mutations in KLHL6 alter BCR signaling and induce actionable phenotypic characteristics in DLBCL.

Prediction of survival in diffuse large B-cell lymphoma based on the expression of 2 genes reflecting tumor and microenvironment.

Several gene-expression signatures predict survival in diffuse large B-cell lymphoma (DLBCL), but the lack of practical methods for genome-scale analysis has limited translation to clinical practice. We built and validated a simple model using one gene expressed by tumor cells and another expressed by host immune cells, assessing added prognostic value to the clinical International Prognostic Index (IPI). LIM domain only 2 (LMO2) was validated as an independent predictor of survival and the "germinal center B cell-like" subtype. Expression of tumor necrosis factor receptor superfamily member 9 (TNFRSF9) from the DLBCL microenvironment was the best gene in bivariate combination with LMO2. Study of TNFRSF9 tissue expression in 95 patients with DLBCL showed expression limited to infiltrating T cells. A model integrating these 2 genes was independent of "cell-of-origin" classification, "stromal signatures," IPI, and added to the predictive power of the IPI. A composite score integrating these genes with IPI performed well in 3 independent cohorts of 545 DLBCL patients, as well as in a simple assay of routine formalin-fixed specimens from a new validation cohort of 147 patients with DLBCL. We conclude that the measurement of a single gene expressed by tumor cells (LMO2) and a single gene expressed by the immune microenvironment (TNFRSF9) powerfully predicts overall survival in patients with DLBCL.

Signaling pathways in lymphoma: pathogenesis and therapeutic targets.

Lymphoma is the fifth most common cancer in the USA. Most lymphomas are classified as non-Hodgkin's lymphoma, and nearly 95% of these cancers are of B-cell origin. B-cell receptor (BCR) surface expression and BCR functional signaling are critical for survival and proliferation of both healthy B cells, as well as most B-lymphoma cells. Agents that inhibit various components of the BCR signaling pathway, as well as parallel signaling pathways, are currently in clinical trials for the treatment of various lymphoma subtypes, including those targeting isoforms of PI3K, mTOR and BTK. In this review, we describe the signaling pathways in healthy mature B cells, the aberrant signaling in lymphomatous B cells and the rationale for clinical trials of agents targeting these pathways as well as the results of clinical trials to date. We propose that the entry into a kinase inhibitor era of lymphoma therapy will be as transformative for our patients as the advent of the antibody or chemotherapy era before it.

B-cell signaling networks reveal a negative prognostic human lymphoma cell subset that emerges during tumor progression.

Human tumors contain populations of both cancerous and host immune cells whose malignant signaling interactions may define each patient's disease trajectory. We used multiplexed phospho-flow cytometry to profile single cells within human follicular lymphoma tumors and discovered a subpopulation of lymphoma cells with impaired B cell antigen receptor (BCR) signaling. The abundance of BCR-insensitive cells in each tumor negatively correlated with overall patient survival. These lymphoma negative prognostic (LNP) cells increased as tumors relapsed following chemotherapy. Loss of antigen receptor expression did not explain the absence of BCR signaling in LNP tumor cells, and other signaling responses were intact in these cells. Furthermore, BCR signaling responses could be reactivated in LNP cells, indicating that BCR signaling is not missing but rather specifically suppressed. LNP cells were also associated with changes to signaling interactions in the tumor microenvironment. Lower IL-7 signaling in tumor infiltrating T cells was observed in tumors with high LNP cell counts. The strength of signaling through T cell mediator of B cell function CD40 also stratified patient survival, particularly for those whose tumors contained few LNP cells. Thus, analysis of cell-cell interactions in heterogeneous primary tumors using signaling network profiles can identify and mechanistically define new populations of rare and clinically significant cells. Both the existence of these LNP cells and their aberrant signaling profiles provide targets for new therapies for follicular lymphoma.

Diversity of intratumoral regulatory T cells in B-cell non-Hodgkin lymphoma.

Tumor-infiltrating regulatory T cells (Tregs) contribute to an immunosuppressive tumor microenvironment. Despite extensive studies, the prognostic impact of tumor-infiltrating Tregs in B-cell non-Hodgkin lymphomas (B-NHLs) remains unclear. Emerging studies suggest substantial heterogeneity in the phenotypes and suppressive capacities of Tregs, emphasizing the importance of understanding Treg diversity and the need for additional markers to identify highly suppressive Tregs. Here, we applied single-cell RNA sequencing and T-cell receptor sequencing combined with high-dimensional cytometry to decipher the heterogeneity of intratumoral Tregs in diffuse large B-cell lymphoma and follicular lymphoma (FL), compared with that in nonmalignant tonsillar tissue. We identified 3 distinct transcriptional states of Tregs: resting, activated, and unconventional LAG3+FOXP3- Tregs. Activated Tregs were enriched in B-NHL tumors, coexpressed several checkpoint receptors, and had stronger immunosuppressive activity compared with resting Tregs. In FL, activated Tregs were found in closer proximity to CD4+ and CD8+ T cells than other cell types. Furthermore, we used a computational approach to develop unique gene signature matrices, which were used to enumerate each Treg subset in cohorts with bulk gene expression data. In 2 independent FL cohorts, activated Tregs was the major subset, and high abundance was associated with adverse outcome. This study demonstrates that Tregs infiltrating B-NHL tumors are transcriptionally and functionally diverse. Highly immunosuppressive activated Tregs were enriched in tumor tissue but absent in the peripheral blood. Our data suggest that a deeper understanding of Treg heterogeneity in B-NHL could open new paths for rational drug design, facilitating selective targeting to improve antitumor immunity.

Bone morphogenetic proteins inhibit CD40L/IL-21-induced Ig production in human B cells: differential effects of BMP-6 and BMP-7.

Bone morphogenetic proteins (BMPs) are members of the TGF-ß superfamily. TGF-ß can affect class switch recombination in human B cells, but whether BMPs also play a role have not been tested. We investigated the functional effects of exogenously added BMPs on CD27(-) naive and CD27(+) memory B cells from healthy donors. BMP-2, -4, -6 and -7 inhibited CD40L/IL-21-induced production of IgM, IgG and IgA. BMP-6 reduced Ig production by 70% in memory B cells and more than 55% in naive B cells, whereas the other BMPs were slightly less potent. We observed a striking difference in functional effects between the structurally similar BMP-6 and BMP-7, as BMP-6 mainly inhibited plasmablast differentiation, and BMP-7 mainly induced apoptosis. In memory B cells, BMP-6 upregulated expression of DNA-binding protein inhibitor genes, but potently inhibited CD40L/IL-21-induced upregulation of the transcription factor XBP1, necessary for the late stages of plasmacytic differentiation. Expression of transcription factors regulating earlier stages (IRF4, PRDM1) was not affected by BMP-6. Taken together, these results show that BMPs are potent suppressors of naive and memory B cells.