Polymorphisms in genes involved in regulating follicular helper T cell differentiation predict de novo donor-specific antibody formation after liver transplantation.

BACKGROUND: De novo donor-specific antibodies (dnDSAs) significantly affect the long-term outcomes of liver transplantation (LT), highlighting the importance of risk prediction. Follicular helper T (Tfh) cells have been implicated in dnDSA formation after transplantation. Considering the influence of immune response gene polymorphisms on transplantation outcomes, we investigated the association between polymorphisms in Tfh cell-related genes and dnDSA formation after LT. METHODS: Fifty-three living-donor LT patients were included in this study. Single nucleotide polymorphisms (SNPs) were identified in six Tfh cell-related genes crucial for differentiation and maturation (BCL6, CXCR5, CXCL13, ICOS, CD40L, and IL-21); their association with the development of dnDSA after LT was evaluated. RESULTS: Among the 53 recipients, 9 developed dnDSAs. BCL6 and IL-21 SNPs showed potential associations with dnDSA formation, enabling risk stratification. CONCLUSIONS: Variations in Tfh cell-related genes may predispose individuals to dnDSA formation after LT, emphasizing the importance of genetic factors for predicting post-transplant complications.

Pharmaceutical inhibition of BCL6 ameliorates resistance to imatinib in chronic myeloid leukemia.

The tyrosine kinase inhibitors (TKIs) have improved overall survival of CML (chronic myeloid leukemia) patients and allow them to experience normal life expectancy. However, relapse and drug resistance remain the main challenges in the clinical treatment of CML. The B-cell lymphoma 6 (BCL6) is essential to regulation of multiple function such as immune response and lymphomagenesis in lymph node germinal cells. Recent studies have shown that BCL6 is required for the maintenance of leukemia stem cells in CML, but the expression of Bcl-6 in response to Imatinib and the underlying mechanism are still unclear. Here, we found that BCL6 is expressed at high levels in primary CML bone marrow samples and CML TKI-resistance cell lines. CML cells with higher levels of BCL6 were generally sensitive to treatment with BCL6 inhibitors, BI-3812. Treatment of CML cells with BCL6 inhibitor and TKIs suggested enhanced anti-leukemia activity. In summary, our findings suggest BCL6 as a therapeutic target for the treatment of CML.

Discovery of novel BCL6-Targeting PROTACs with effective antitumor activities against DLBCL in vitro and in vivo.

The transcriptional repressor B cell lymphoma 6 (BCL6) plays a critical role in driving tumorigenesis of diffuse large B-cell lymphoma (DLBCL). However, the therapeutic potential of inhibiting or degrading BCL6 for DLBCL has not been thoroughly understood. Herein, we reported the discovery of a series of novel BCL6-targeting PROTACs based on our previously reported N-phenyl-4-pyrimidinamine BCL6 inhibitors. The optimal compound DZ-837 degraded BCL6 with DC50 values around 600 nM and effectively inhibited the proliferation of several DLBCL cell lines. Further study indicated that DZ-837 induced significant G1 phase arrest and exhibited sustained reactivation of BCL6 downstream genes. In the SU-DHL-4 xenograft model, DZ-837 significantly inhibited tumor growth with TGI of 71.8 % at 40 mg/kg once daily. Furthermore, the combination of DZ-837 with BTK inhibitor Ibrutinib showed synergistic effects and overcame acquired resistance against DLBCL cells. Overall, our findings demonstrate that DZ-837 is an effective BCL6 degrader for DLBCL treatment as a monotherapy or in combination with Ibrutinib.

BCL6 confers resistance to HDAC inhibitors in DLBCL.

Diffuse large B-cell lymphoma (DLBCL) is an aggressive non-Hodgkin lymphoma with limited response to chemotherapy. Histone acetylation is reduced in DLBCL. Chidamide, a histone deacetylase inhibitor, shows promise in lymphomas but needs further investigation for DLBCL. Our study indicated that chidamide effectively suppresses DLBCL both in vitro and in vivo. High-throughput RNA sequencing analysis provided comprehensive evidence that chidamide markedly influences crucial signaling pathways in DLBCL, including the MAPK, MYC and p53 pathway. Additionally, we observed substantial variability in the sensitivity of DLBCL cells to chidamide, and identified that elevated expression of BCL6 might confer resistance to chidamide in DLBCL. Moreover, our investigations revealed that BCL6 inhibited chidamide-induced histone acetylation by recruiting histone deacetylase (HDACs), leading to drug resistance in DLBCL cells. Furthermore, we found that lenalidomide targeted BCL6 degradation through the ubiquitination pathway and restore the sensitivity of drug-resistant DLBCL to chidamide. Collectively, these findings provided valuable insights into the global impact of chidamide on DLBCL and highlight the potential of targeting HDACs as a therapeutic strategy for DLBCL. Identifying BCL6 as a biomarker for predicting the response to chidamide and the combination therapy with BCL6 inhibition has the potential to lead to more personalized and effective treatments for DLBCL patients.

Double-hit primary central nervous system lymphoma with histogenetically proven bone marrow infiltration: a case report and a review of the literature.

Double-hit lymphoma (DHL) formerly referred to high-grade B-cell lymphoma with concurrent MYC and BCL2 or BCL6 rearrangements, however, the updated 2022 World Health Organization Classification (5th edition online) excludes those with MYC and BCL 6 rearrangements from the high-grade category. DHL confined to the central nervous system (CNS), known as double-hit primary CNS lymphoma (DH-PCNSL), is rare with poorly understood clinical features. Here, we report a case of a 64-year-old man with multiple brain tumors diagnosed with DH-PCNSL who showed bone marrow (BM) infiltration early in the clinical course. The histological diagnosis was high-grade B-cell lymphoma with MYC and BCL6 rearrangements. Fluorodeoxyglucose positron emission tomography (FDG-PET) revealed no abnormal accumulation except in the CNS. The patient received whole-brain radiotherapy following the failure of high-dose methotrexate. After completion of radiotherapy, the patient developed thrombocytopenia, and BM biopsy showed infiltration of DHL cells, which were not detected by repeated FDG-PET. This is the first report of DH-PCNSL where identical gene rearrangements were confirmed in both the resected CNS tumor and BM tissue. Patients with DH-PCNSL require careful follow-up because they may be at a potential risk of BM infiltration, which may be undetectable by FDG-PET, particularly early in the disease course.

Enhancement of gemcitabine sensitivity in intrahepatic cholangiocarcinoma through Saikosaponin-a mediated modulation of the p-AKT/BCL-6/ABCA1 axis.

BACKGROUND: Intrahepatic cholangiocarcinoma (ICC) remains a significant challenge in cancer therapy, especially due to its resistance to established treatments like Gemcitabine, necessitating novel therapeutic approaches. METHODS: This study utilized Gemcitabine-resistant cell lines, patient-derived organotypic tumor spheroids (PDOTs), and patient-derived xenografts (PDX) to evaluate the effects of Saikosaponin-a (SSA) on ICC cellular proliferation, migration, apoptosis, and its potential synergistic interaction with Gemcitabine. Techniques such as transcriptome sequencing, Luciferase reporter assays, and molecular docking were employed to unravel the molecular mechanisms. RESULTS: SSA exhibited antitumor effects in both in vitro and PDX models, indicating its considerable potential for ICC treatment. SSA markedly inhibited ICC progression by reducing cellular proliferation, enhancing apoptosis, and decreasing migration and invasion. Crucially, it augmented Gemcitabine's efficacy by targeting the p-AKT/BCL6/ABCA1 signaling pathway. This modulation led to the downregulation of p-AKT and suppression of BCL6 transcriptional activity, ultimately reducing ABCA1 expression and enhancing chemosensitivity to Gemcitabine. Additionally, ABCA1 was validated as a predictive biomarker for drug resistance, with a direct correlation between ABCA1 expression levels and the IC50 values of various small molecule drugs in ICC gene profiles. CONCLUSION: This study highlights the synergistic potential of SSA combined with Gemcitabine in enhancing therapeutic efficacy against ICC and identifies ABCA1 as a key biomarker for drug responsiveness. Furthermore, the introduction of the novel PDOTs microfluidic model provides enhanced insights into ICC research. This combination strategy may provide a novel approach to overcoming treatment challenges in ICC.

Key Functions of the Transcription Factor BCL6 During T-Cell Differentiation.

T lymphocytes consist of several subtypes with distinct functions that help to coordinate an immune response. They are generated within the thymus through a sequential developmental pathway that produces subsets with diverse antigen specificities and functions. Naïve T cells populate peripheral lymphoid organs and are activated upon foreign antigen encounter. While most T cells die soon after activation, a memory population survives and is able to quickly respond to secondary challenges, thus providing long-term immunity to the host. Although cell identity is largely stable and is instructed by cell-specific transcriptional programs, cells may change their transcriptional profiles to be able to adapt to new functionalities. Central to these dynamic processes are transcription factors, which control cell fate decisions, through direct regulation of gene expression. In this book chapter, we review the functions of the transcription factor B-cell lymphoma 6 (BCL6), which directs the fate of several lymphocyte subsets, including helper, cytotoxic, and innate-like T cells, but can also be involved in lymphomagenesis in humans.

BCL6 overexpression in CD4+ T cells induces Tfh-like transdifferentiation and enhances antitumor efficiency of CAR-T therapy in pancreatic cancer.

PDAC is a typical "cold tumor" characterized by low immune cell infiltration and a suppressive immune microenvironment. We previously observed the existence of a rare group of follicular helper T cells (Tfh) that could enhance antitumor immune responses by recruiting other immune cells in PDAC. In this study, we ectopically expressed BCL6 in CD4+ T cells, and successfully induced Tfh-like transdifferentiation in vitro. This strategy provided abundant Tfh-like cells (iTfhs) that can recruit CD8+ T cells like endogenous Tfhs. Subsequently, Chimeric Antigen Receptors (CARs) against both MSL (Mesothelin) and EPHA2 (Ephrin receptor A2) were used to modify iTfh cells, and the CAR-iTfh cells significantly improved infiltration and antitumor cytotoxicity of co-cultured CD8+ T cells. After that, combinatory administration of CAR-iTfh & CAR-CD8 T cell therapy displayed a better effect in repressing the PDAC tumors in xenograft mouse models, compared to conventional CAR-CD4 & CAR-CD8 combinations, and the models received the CAR-iTfh & CAR-CD8 T cells displayed a significantly improved survival rate. Our study revealed the plasticity of Thelper differentiation, expanded the source of Tfh-like cells for cell therapy, and demonstrated a novel and potentially more efficient cellular composition for CAR-T therapy.

Molecular characterization of a rare case of high-grade B-cell lymphoma with MYC, BCL2, BCL6, and CCND1 rearrangements.

Quadruple-hit lymphomas are extremely rare non-Hodgkin lymphomas with a reported dismal prognosis in the few reported cases. A "quadruple hit" has been defined by the presence of concurrent MYC, BCL2, BCL6, and CCND1 chromosomal rearrangements. We report a new case of a quadruple hit lymphoma in a 73-year-old Hispanic man who presented with an enlarging left-sided neck mass. Computed tomography showed a 1.9-cm mass in left the tonsil with bulky cervical lymphadenopathy. The presence of all four chromosomal rearrangements can reportedly occur with disease progression in both diffuse large B-cell lymphomas and mantle cell lymphomas. Further characterization of the tumor by next-generation sequencing may be of benefit to delineate between these two possibilities. Immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and next-generation sequencing were used to confirm and classify the diagnosis. Histologic sections of the cervical lymph node demonstrated an atypical lymphoid infiltrate with large and pleomorphic cells, which were positive for CD20, CD10, BCL1 (Cyclin D1), BCL2, BCL6, and cMYC and negative for CD5 and SOX11 on immunohistochemistry with a Ki-67 proliferative index of 70%. FISH demonstrated MYC, BCL2, BCL6, and CCND1 rearrangements and the diagnosis of high-grade B-cell lymphoma with MYC, BCL2, BCL6, and CCND1 was rendered. Our patient was treated with dose adjusted etoposide, doxorubicin, cyclophosphamide, prednisone, and rituximab chemotherapy and has been in remission for 20 months.

Comparison of serum levels of IL-10 and IL-11 and mRNA expression of IL-10, IL-11, COX-2, BCL6, and ZEB Family in peripheral blood mononuclear cells (PBMC) of women with polycystic ovary syndrome and healthy individuals.

BACKGROUND: The roles of IL-10, IL-11, COX-2, BCL6, ZEB1, and ZEB2 genes in the potential correlation between polycystic ovary syndrome (PCOS), inflammation, and cancer remain controversial. AIMS: This study aimed to compare serum levels of IL-10 and IL-11 and gene expression of IL-10, IL-11, COX-2, BCL6, ZEB1, and ZEB2 in PBMCs of women with PCOS and healthy controls. METHODS: A case-control study included 40 women with PCOS as the case group and 40 healthy women as controls. Group matching for age and BMI was performed. Serum levels of IL-10 and IL-11 were assessed using ELISA, while gene expression was measured using real-time PCR. Parameters were compared between groups, and correlations among gene expression and serum levels were explored. RESULTS: In comparison to healthy women, women with PCOS exhibited a significant decrease in the expression of COX-2 and IL-10 genes (p<0.001), alongside a significant increase in ZEB2 gene expression (p<0.001). There were no significant differences observed in the expression of IL-11, BCL6, and ZEB1 genes. Furthermore, the serum level of IL-10 was significantly lower in women with PCOS compared to the control group (p<0.001), while no significant difference was found in IL-11 levels. Additionally, no significant correlations were identified between gene expression and serum levels. CONCLUSION: In women with PCOS, reduced IL-10 gene expression may indicate inflammation and serve as a diagnostic biomarker. However, conflicting findings on COX-2 expression complicate understanding. Elevated ZEB2 expression in PCOS women may lead to infertility, epithelial-mesenchymal transition, and aggressive phenotypes.

Sequential drug treatment targeting cell cycle and cell fate regulatory programs blocks non-genetic cancer evolution in acute lymphoblastic leukemia.

BACKGROUND: Targeted therapies exploiting vulnerabilities of cancer cells hold promise for improving patient outcome and reducing side-effects of chemotherapy. However, efficacy of precision therapies is limited in part because of tumor cell heterogeneity. A better mechanistic understanding of how drug effect is linked to cancer cell state diversity is crucial for identifying effective combination therapies that can prevent disease recurrence. RESULTS: Here, we characterize the effect of G2/M checkpoint inhibition in acute lymphoblastic leukemia (ALL) and demonstrate that WEE1 targeted therapy impinges on cell fate decision regulatory circuits. We find the highest inhibition of recovery of proliferation in ALL cells with KMT2A-rearrangements. Single-cell RNA-seq and ATAC-seq of RS4;11 cells harboring KMT2A::AFF1, treated with the WEE1 inhibitor AZD1775, reveal diversification of cell states, with a fraction of cells exhibiting strong activation of p53-driven processes linked to apoptosis and senescence, and disruption of a core KMT2A-RUNX1-MYC regulatory network. In this cell state diversification induced by WEE1 inhibition, a subpopulation transitions to a drug tolerant cell state characterized by activation of transcription factors regulating pre-B cell fate, lipid metabolism, and pre-BCR signaling in a reversible manner. Sequential treatment with BCR-signaling inhibitors dasatinib, ibrutinib, or perturbing metabolism by fatostatin or AZD2014 effectively counteracts drug tolerance by inducing cell death and repressing stemness markers. CONCLUSIONS: Collectively, our findings provide new insights into the tight connectivity of gene regulatory programs associated with cell cycle and cell fate regulation, and a rationale for sequential administration of WEE1 inhibitors with low toxicity inhibitors of pre-BCR signaling or metabolism.

[Primary renal triple expressor DLBCL treated with chemotherapy under continuous hemodialysis and filtration support].

A 69-year-old woman was previously treated with antibiotics for suspected pyelonephritis due to fever but showed limited improvement. Contrast-enhanced CT revealed heterogeneous areas of decreased contrast enhancement in both kidneys, along with an elevated soluble level of the IL-2 receptor (5,090 U/ml), and thus the patient was referred to our department for further evaluation. A percutaneous renal biopsy performed due to suspected malignant lymphoma confirmed lymphoma cell infiltration into the renal interstitium. Immunohistochemical staining was positive for MYC/BCL2/BCL6, leading to the diagnosis of stage IVB primary renal triple expressor diffuse large B cell lymphoma (DLBCL). Due to acute kidney injury, continuous hemodiafiltration (CHDF) was initiated, followed by rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) chemotherapy. The patient's renal function improved rapidly, and complete response was achieved after six cycles of R-CHOP. Although DLBCL is a common lymphoma, the primary renal subtype is extremely rare and poses both diagnostic and therapeutic challenges. This case highlights the potential clinical implications of combining CHDF with chemotherapy to achieve complete response despite an initial poor prognosis based on the patient's overall clinical condition and pathology.

Deficiency of CBL and CBLB ubiquitin ligases leads to hyper T follicular helper cell responses and lupus by reducing BCL6 degradation.

Recent evidence reveals hyper T follicular helper (Tfh) cell responses in systemic lupus erythematosus (SLE); however, molecular mechanisms responsible for hyper Tfh cell responses and whether they cause SLE are unclear. We found that SLE patients downregulated both ubiquitin ligases, casitas B-lineage lymphoma (CBL) and CBLB (CBLs), in CD4+ T cells. T cell-specific CBLs-deficient mice developed hyper Tfh cell responses and SLE, whereas blockade of Tfh cell development in the mutant mice was sufficient to prevent SLE. ICOS was upregulated in SLE Tfh cells, whose signaling increased BCL6 by attenuating BCL6 degradation via chaperone-mediated autophagy (CMA). Conversely, CBLs restrained BCL6 expression by ubiquitinating ICOS. Blockade of BCL6 degradation was sufficient to enhance Tfh cell responses. Thus, the compromised expression of CBLs is a prevalent risk trait shared by SLE patients and causative to hyper Tfh cell responses and SLE. The ICOS-CBLs axis may be a target to treat SLE.

BCL6 is a context-dependent mediator of the glioblastoma response to irradiation therapy.

Glioblastoma is a rapidly fatal brain cancer that does not respond to therapy. Previous research showed that the transcriptional repressor protein BCL6 is upregulated by chemo and radiotherapy in glioblastoma, and inhibition of BCL6 enhances the effectiveness of these therapies. Therefore, BCL6 is a promising target to improve the efficacy of current glioblastoma treatment. BCL6 acts as a transcriptional repressor in germinal centre B cells and as an oncogene in lymphoma and other cancers. However, in glioblastoma, BCL6 induced by therapy may not be able to repress transcription. Using a BCL6 inhibitor, the whole proteome response to irradiation was compared with and without BCL6 activity. Acute high dose irradiation caused BCL6 to switch from repressing the DNA damage response to promoting stress response signalling. Rapid immunoprecipitation mass spectrometry of endogenous proteins (RIME) enabled comparison of BCL6 partner proteins between untreated and irradiated glioblastoma cells. BCL6 was associated with transcriptional coregulators in untreated glioblastoma including the known partner NCOR2. However, this association was lost in response to acute irradiation, where BCL6 unexpectedly associated with synaptic and plasma membrane proteins. These results reveal the activity of BCL6 under therapy-induced stress is context-dependent, and potentially altered by the intensity of that stress.

Still Far to Go With Characterisation of Molecular and Genetic Features of Diffuse Large B-Cell Lymphoma in People Living With HIV: A Scoping Review.

Diffuse large B-cell lymphoma (DLBCL) accounts for half of non-Hodgkin lymphoma cases in people living with human immunodeficiency syndrome (PLWH). The interplay of viremia, immune dysregulation and co-infection with oncogenic viruses play a role in pathogenesis of DLBCL in PLWH (HIV-DLBCL). This scoping review aimed to describe the molecular landscape of HIV-DLBCL, investigate the impact of biomarker on clinical outcomes and describe technologies used to characterise HIV-DLBCL. Thirty-two papers published between 2001 and 2023 were included in this review. Samples of HIV-DLBCL were relatively small (16-110). Cohort effects influenced frequencies of molecular characteristics hence their impact on survival was not clear. Molecular features were distinct from HIV-unrelated DLBCL. The most frequently assessed characteristic was cell of origin (81.3% of studies). Somatic mutations were the least researched (6.3% of studies). Overall, biomarker identification in HIV-DLBCL requires broader richer data from larger or pooled samples using more powerful techniques such as next-generation sequencing.

Foveal photoreceptor atrophy, persistent fetal vasculature, congenital cataracts, and microphthalmia in a pediatric patient with BCOR-associated oculo-facio-cardio-dental (OFCD) syndrome.

Purpose: To report a case of oculo-facio-cardio-dental (OFCD) syndrome secondary to a novel BCOR variant in a pediatric patient with congenital cataracts, microphthalmia, persistent fetal vasculature (PFV), focal chorioretinal hyperpigmentation, peripheral retinal avascularity, and foveal photoreceptor atrophy. Observations: A 3-month-old female patient was referred for bilateral congenital cataracts with microphthalmia. Her past medical history was significant for syndactyly of the toes, left bifid rib, atrial septal defect, patent ductus arteriosus, mitral regurgitation, pulmonary hypertension, anemia of prematurity, vesicoureteral reflux, and duodenal atresia. Examination under anesthesia revealed persistent fetal vasculature (PFV) with peripheral avascularity, foveal photoreceptor atrophy, and focal chorioretinal hyperpigmentation. A bilateral lensectomy with anterior vitrectomy and posterior capsulotomy were performed. Genetic testing identified a novel heterozygous pathogenic variant in the BCOR gene (c.1612C > T (p.Gln538Ter)), confirming a diagnosis of OFCD syndrome. Conclusions and importance: This case describes novel posterior segment findings in a patient with OFCD. A detailed examination of both anterior and posterior segments in combination with multimodal imaging should be performed in patients suspected of having OFCD, as this may be critical in determining visual potential and appropriate surgical management.

Epidermal loss of Bcl6 exacerbates MC903-induced atopic dermatitis-like skin inflammation.

Atopic dermatitis (AD) is a chronic inflammatory skin disease where Th2-type immune responses are dominant. In the lesional skin of AD, keratinocytes show differentiation defects and secrete proinflammatory cytokines and chemokines, amplifying Th2-type responses in AD. We previously reported that inducible loss of B-cell lymphoma 6 (Bcl6), a transcription repressor and a master transcriptional regulator of follicular helper T cells and germinal center B cells, in the whole body results in upregulation of Th2-related cytokines in mouse skin. However, the role of Bcl6 in keratinocytes remains to be clarified. Here, we observed that BCL6 positively regulates the expression of keratinocyte differentiation markers and plasma membrane localization of adherence junctional proteins in keratinocyte cell culture. Although keratinocyte-specific loss of Bcl6 alone did not induce AD-like skin inflammation, it aggravates MC903-induced AD-like skin inflammation in mice. In addition, Bcl6 expression is decreased in the epidermis of lesional skin from MC903-induced AD-like skin inflammation in mice. These results strongly suggest that Bcl6 downregulation in keratinocytes contributes to the development and aggravation of AD-like skin inflammation in mice.

High-grade B-cell lymphoma with a quadruple-hit genetic profile including concurrent MYC, BCL2, BCL6, and CCND1 gene rearrangements.

Several reports of concurrent MYC, BCL2, BCL6, and CCND1 rearrangements in high-grade B-cell lymphoma (HGBL) have been recently described. Herein, we aimed to delineate the scope of this entity through a review of HGBL with a "quadruple-hit" genetic profile identified at our institution. We performed a retrospective review (2015-2023) at our institution of B-cell lymphoma (BCL) cases that were evaluated with concurrent MYC, BCL2, and BCL6 break-apart and IGH::MYC and IGH::CCND1 dual-color dual-fusion fluorescence in situ hybridization studies. Of 203 cases meeting inclusion criteria, 2 (1%) with a quadruple-hit genetic profile were identified. Case 1 represented a 59-year-old female with widespread lymphadenopathy and a diagnosis of HGBL who exhibited primary refractoriness to dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin, and rituximab (DA-EPOCH-R) chemotherapy. Case 2 represented a 58-year-old male with mediastinal and abdominal lymphadenopathy and a diagnosis of large BCL who died from disease after 1 cycle of DA-EPOCH-R chemotherapy. Similarly, a literature review of 7 previously reported cases of HGBL with a quadruple-hit profile also demonstrated aggressive disease behavior. Our study adds 2 new cases to the rarely encountered quadruple-hit HGBL, and a brief meta-analysis of the 9 available cases indicates aggressive disease behavior conferred by this constellation of genetic events.

Interleukin-4 downregulates transcription factor BCL6 to promote memory B cell selection in germinal centers.

Germinal center (GC)-derived memory B cells (MBCs) are critical for humoral immunity as they differentiate into protective antibody-secreting cells during re-infection. GC formation and cellular interactions within the GC have been studied in detail, yet the exact signals that allow for the selection and exit of MBCs are not understood. Here, we showed that IL-4 cytokine signaling in GC B cells directly downregulated the transcription factor BCL6 via negative autoregulation to release cells from the GC program and to promote MBC formation. This selection event required additional survival cues and could therefore result in either GC exit or death. We demonstrate that both increasing IL-4 bioavailability or limiting IL-4 signaling disrupted MBC selection stringency. In this way, IL-4 control of BCL6 expression serves as a tunable switch within the GC to tightly regulate MBC selection and affinity maturation.

Mutational, immune microenvironment, and clinicopathological profiles of diffuse large B-cell lymphoma and follicular lymphoma with BCL6 rearrangement.

BCL6-rearrangement (BCL6-R) is associated with a favorable prognosis of follicular lymphoma (FL), but the mechanism is unknown. We analyzed the clinicopathological, immune microenvironment (immune checkpoint, immuno-oncology markers), and mutational profiles of 10 BCL6-R-positive FL, and 19 BCL6-R-positive diffuse large B-cell lymphoma (DLBCL) cases (both BCL2-R and MYC-R negative). A custom-made panel included 168 genes related to aggressive B-cell lymphomas and FL. FL cases were nodal, histological grade 3A in 70%, low Ki67; and had a favorable overall and progression-free survival. DLBCL cases were extranodal in 60%, IPI high in 63%, non-GCB in 60%, EBER-negative; and had a progression-free survival comparable to that of DLBCL NOS. The microenvironment had variable infiltration of M2-like tumor-associated macrophages (TAMs) that were CD163, CSF1R, LAIR1, PD-L1, and CD85A (LILRB3) positive; but had low IL10 and PTX3 expression. In comparison to FL, DLBCL had higher TAMs, IL10, and PTX3 expression. Both lymphoma subtypes shared a common mutational profile with mutations in relevant pathogenic genes such as KMT2D, OSBPL10, CREBBP, and HLA-B (related to chromatin remodeling, metabolism, epigenetic modification, and antigen presentation). FL cases were characterized by a higher frequency of mutations of ARID1B, ATM, CD36, RHOA, PLOD2, and PRPRD (p < 0.05). DLBCL cases were characterized by mutations of BTG2, and PIM1; and mutations of HIST1H1E and MFHAS1 to disease progression (p < 0.05). Interestingly, mutations of genes usually associated with poor prognosis, such as NOTCH1/2 and CDKN2A, were infrequent in both lymphoma subtypes. Some high-confidence variant calls were likely oncogenic, loss-of-function. MYD88 L265P gain-of-function was found in 32% of DLBCL. In conclusion, both BCL6-R-positive FL and BCL6-R-positive DLBCL had a common mutational profile; but also, differences. DLBCL cases had a higher density of microenvironment markers.