Normal Germinal Center Research Articles

Molecular Determinants of Sensitivity to Polatuzumab Vedotin in Diffuse Large B-Cell Lymphoma.

Polatuzumab vedotin (Pola-V) is an antibody-drug conjugate directed to the CD79B subunit of the B-cell receptor (BCR). When combined with conventional immunochemotherapy, Pola-V improves outcomes in diffuse large B-cell lymphoma (DLBCL). To identify determinants of Pola-V sensitivity, we used CRISPR-Cas9 screening for genes that modulated Pola-V toxicity for lymphomas or the surface expression of its target, CD79B. Our results reveal the striking impact of CD79B glycosylation on Pola-V epitope availability on the lymphoma cell surface and on Pola-V toxicity. Genetic, pharmacological, and enzymatic approaches that remove sialic acid from N-linked glycans enhanced lymphoma killing by Pola-V. Pola-V toxicity was also modulated by KLHL6, an E3 ubiquitin ligase that is recurrently inactivated in germinal center derived lymphomas. We reveal how KLHL6 targets CD79B for degradation in normal and malignant germinal center B cells, thereby determining expression of the surface BCR complex. Our findings suggest precision medicine strategies to optimize Pola-V as a lymphoma therapeutic. Significance: These findings unravel the molecular basis of response heterogeneity to Pola-V and identify approaches that might be deployed therapeutically to enhance the efficacy of CD79B-specific tumor killing. In addition, they reveal a novel post-translational mechanism used by normal and malignant germinal center B cells to regulate expression of the BCR. See related commentary by Leveille, p. 1577 See related article by Meriranta et al.

Abstract PO-034: Targeting metabolic plasticity and flexibility via SIRT3 inhibition to restrain nucleotides availability in DLBCLs

Abstract Cancer cells need metabolic adaptations to survive in hostile environment such as low nutrient and drug treatment conditions. DLBCLs (Diffuse large B cell lymphoma) originate from a metabolic competitive/challenging environment of germinal center (GC) when B cells undergo positive selections against antigens. However, it is largely unknown whether and how metabolic flexibility (the ability to use different nutrients) and plasticity (the ability to process the same nutrient differently) contribute to DLBCLs. Our previous study identified that SIRT3, the only mitochondrial protein deacetylase, is critical to survival and proliferation of DLBCLs by promoting glutaminolysis. Our mitochondrial localized SIRT3 inhibitor, YC8-02, has pan-toxicity to all DLBCL cells tested regardless of different subtypes with somatic mutations. Here, we observed glucose as an alternative nutrient source to compensate in the TCA cycle in SIRT3 deficient cells. DLBCLs exhibited resistance to SIRT3 inhibition in high glucose condition, while SIRT3 inhibited DLBCLs highly depend on glucose metabolism. The combination of YC8-02 with glucose metabolism inhibitors induces synergistic killing to DLBCLs. As glucose is the main carbon source of cells, it is unknown how DLBCLs manage the flexibility of using glucose for different purposes. Using in vivo metabolic imaging (MALDI), we observed that, in contrast to normal GC B cells, lymphomas specifically use the glucose for de novo nucleotide synthesis. SIRT3 inhibition decreased nucleotide levels in DLBCL cells in vitro and in vivo. The metabolic flux tracing showed that DLBCL cells requires SIRT3 activity to activate a glucose/serine/one-carbon metabolism pathway for de novo nucleotide biosynthesis, and Inhibition of SIRT3 decreased the glucose and serine being used for nucleotides in DLBCLs. Serine as another potent source for nucleotides can rescue DLBCLs from SIRT3 inhibition. Furthermore, we validated that overexpression of enzymes, like MTHFD2, in one carbon metabolism pathway can rescue the proliferation in SIRT3 deficient cells. High nucleotides levels in medium also help DLBCLs survival in YC8-02 treatments. To overcome the metabolic flexibility on environmental nucleotides, we used inhibitors of nucleoside transporters (ENT1/2), dipyridamole and draflazine, which can synergize with YC8-02 to kill DLBCLs in vitro and eradicate systemic lymphomas in vivo. In summary, our results illustrate that DLBCLs with active SIRT3 exhibit metabolic plasticity by repurposing glucose to nucleotide biosynthesis, while lymphoma cells can also reply on metabolic flexibility to manage nutrient usage and gain extracellular nucleotides for survival under SIRT3 inhibition. Our combination treatment SIRT3 and ENT inhibitors can be a promising therapy for DLBCLs by restraining their metabolic plasticity and flexibility. Citation Format: Meng Li, Noel R Park, Chris Chin, Coraline Mlynarczyk, Hening Lin, Shawn Davidson, Ari M Melnick. Targeting metabolic plasticity and flexibility via SIRT3 inhibition to restrain nucleotides availability in DLBCLs [abstract]. In: Proceedings of the Fourth AACR International Meeting on Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2024 Jun 19-22; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2024;5(3_Suppl):Abstract nr PO-034.

Outcome of patients with primary CNS lymphoma treated with methotrexate based regimens: A retrospective study.

e19051 Background: Primary central Nervous system Lymphoma is an aggressive Non-Hodgkins Lymphoma with 5-year survival of only 30 percent. Few studies have addressed the comparison of induction treatment regimens with various risk stratification groups with no consensus on the optimal methotrexate dose for best complete overall response and survival outcome. Our retrospective study compares induction treatment regimens, identifies different risk stratification factors, and provides insight into the best induction treatment regimen with determination of optimal methotrexate dose. Methods: Design: Retrospective Primary Outcomes: Complete response rate, overall survival rate with risk stratification based on histology, Ki-67, and initial albumin level. Results: 77 patients 18 years of age and older with PCNSL at NCC and LAC between June 2015 and July 2022 were included in the study. Overall, 50% of patients were treated with CALGB50202 induction regimen,19% with R-MPV,12 % with De-Angelis regimen. CALGB 50202 has the highest survival rate of 63.4% followed by R-MPV with 22% survival rate followed by De-Angelis regimen with 0% survival rate with chi-square test P-value < 0.001 during the study period. Similarly, CALGB 50202 has the highest CR rate of 61.9% followed by R-MPV with CR rate of 16% followed by De-Angelis regimen with the lowest CR rate of 2.4%.CR rate comparison is statistically significant with P-value of < 0.0001. The study assessed optimum methotrexate dose. The mean and median total methotrexate dose in patients who were alive during the study period was 74.3 grams and 81.7 grams respectively as compared to mean value of 34.2 grams and median of 19.3 grams in patients who died with a p-value of 0.0019.Comparing survival based on histology as germinal center versus non-germinal center PCNSL, the later has higher mortality rate of 64.7 % as compared to 11.8 % in patient with germinal center PCNSL.Ki-67 was assessed as >80% and <80%.Among patients who were alive during the study period,48.8% have Ki-67 > 80% as compared to only 12.2%.On the other hand, among the patients who died,47.1% of patients have Ki-67 <80%,indicating lower ki-67 associated a lower survival outcome as depicted on the Kaplan Meier curve with P-value of 0.004. Patients with normal initial albumin have a higher chance of survival (78%) vs 22% in the group with low albumin level with p-value of 0.0005. Conclusions: CALGB 50202 had the highest CR and survival rates followed by R-MPV regimen in patients with primary CNS lymphoma. The total dose of methotrexate patient receives was an important factor for survival and CR and the optimal total methotrexate dose was 70-80 grams. Normal initial albumin, high Ki-67, and germinal center histology favored better survival.

Abstract 1154: Spatial profiling of the tumor microenvironment in head and neck squamous cell carcinoma revealed immune cell type infiltration into the TME as a predictor of immunotherapy response

Abstract Background: Immunotherapy has shown promising results in advanced head and neck cancer patients, however, only a subset of patients are responsive to immune checkpoint blockade therapy. The molecular and cellular characterization of the tumor microenvironment (TME) may reveal clues as to why some head and neck tumors are responsive or resistant to the therapy. Methods: Formalin-fixed paraffin-embedded (FFPE) tissue samples were collected from 34 patients at two major Queensland Hospitals with advanced head and neck squamous cell carcinoma (HNSCC), prior to immunotherapy. To investigate the cellular and molecular characteristics of the HNSCC TME, we used the Nanostring GeoMx Digital Spatial Profiler (DSP) spanning modules in an immune-oncology panel, which included immune cell typing and profiling, cell death, PI3K/AKT signaling, drug target, immune activation, and pan tumor protein biomarkers. A deeper structural analysis was performed using the Nanostring whole transcriptome atlas (WTA) panel of tertiary lymphoid structures (TLSs) and germinal centers (GCs). Results: Out of 34 patients, 3 had a complete response (CR), 7 had a partial response (PR), 5 had stable disease (SD), and 19 had progressive disease (PD), based on the Response Evaluation Criteria in Solid Tumors (RECIST). When we compared patient responders (patients with CR, PR, and SD) to patient non-responders (patients with PD), we found that the former had a higher infiltration of immune cell type markers representatives of CD8+ T cells, dendritic cells, and macrophages, into their tumor microenvironment than the latter. Then, to investigate differentially expressed genes between patients with complete response and patients with partial response to immunotherapy, we performed DE analyses and we found that patients with PR had higher Ki-67 expression than those with CR. Spatial transcriptomic mapping of TLS’s (peripheral, intra-tumoral) and normal germinal centers revealed interferon pathway enrichment in the TLS’s. In a subset, these appear to be linked with HPV viral infection. Conclusion: In this study, we found that immune cell type infiltration into the tumor microenvironment of head and neck cancers could be predictive of response to immunotherapy. Furthermore, it was revealed that patients with a high expression of Ki-67 might be less likely to respond completely to immunotherapy. Spatially resolved whole transcriptome analysis of HNSCC tissues revealed the presence of tertiary lymphoid structures with a higher enrichment of interferon pathway genes. Citation Format: Habib Sadeghirad, Chin Wee Tan, Ning Liu, James Monkman, Caroline Cooper, Ken O’Byrne, Melissa Davis, Brett Hughes, Arutha Kulasinghe. Spatial profiling of the tumor microenvironment in head and neck squamous cell carcinoma revealed immune cell type infiltration into the TME as a predictor of immunotherapy response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1154.

Abstract P04: Role of glucocorticoid receptor in normal and malignant germinal center B cells

Abstract We have reported that super-enhancers (SEs) are specifically hypermutated by Activation-Induced Deaminase (AID)-induced Aberrant Somatic Hypermutation in >90% of diffuse large B cell lymphoma (DLBCL) cases (Bal et al. Nature 2022). Analysis of 122 primary DLBCL biopsies and cell lines identified more than 80 SEs that are recurrently hypermutated, with an average of 12 hypermutated SE/case. Hypermutated SEs are predominantly linked to genes encoding regulators of B cell development and well-known lymphoma oncogenes, including BCL6, BCL2 and CXCR4. We showed that specific hotspot mutations prevent binding and transcriptional downregulation by transcriptional repressors leading to target gene dysregulation. Among these, hypermutation of the SEs linked to BCL2 and CXCR4 abrogates the binding of the glucocorticoid receptor (GR)/transcription factor encoded by NR3C1. As a result, BCL2 and CXCR4 escape GR-mediated transcriptional repression leading to their de-regulated expression in germinal center (GC) B cells. Together with the observation that the NR3C1 gene is genetically inactivated in a small fraction of DLBCL, and the relevance of glucocorticoid-based therapy in DLBCL, these results prompted a comprehensive analysis of the role of GR in normal and malignant B cells. We report that GR is detectable in the nucleus of the great majority of GC B cells, suggesting that it is active as a transcription factor. Similarly, DLBCL primary cases (including GCB-, ABC- and unclassified DLBCL) display GR nuclear expression. Analysis of a conditional GC-specific Nr3c1 knock-out (KO) mouse model showed that GC B cells form normally in the absence of Nr3c1. However, the transcriptional profile of Nr3c1-KO GC B cells was significantly altered compared to wild-type cells. By integrating the GR binding profile obtained in normal human GC B cells with the transcripts differentially expressed in Nr3c1-KO GC B cells, we identified a set of about 2,000 genes that are directly modulated by GR during the GC reaction. Pathway enrichment analysis showed that GR controls several signaling pathways, suggesting a modulatory role on the BCR and CXCR4 pathways. In addition, GR targets display a significant overlap with the BCL6 transcriptional network, suggesting a cooperative role in GC B cell development. Notably, GR was shown to regulate pathways involved in plasma cell differentiation, while repressing targets associated with memory B cell development. In DLBCL cases, several NR3C1 binding sites are recurrently targeted by mutations, suggesting that genetic impairment of GR activity is heterogeneous and extends beyond CXCR4 and BCL2. Together, these data support a role for the glucocorticoid pathway in GC physiology. Recurrent inactivation of the NR3C1 gene or part of its transcriptional regulatory program may contribute to DLBCL pathogenesis, with implications for presently unknown specific roles of glucocorticoids in the therapeutic regimens for DLBCL. Citation Format: Clarissa Corinaldesi, Antony B Holmes, Elodie Bal, Laura Pasqualucci, Katia Basso, Riccardo Dalla-Favera. Role of glucocorticoid receptor in normal and malignant germinal center B cells [abstract]. In: Proceedings of the Blood Cancer Discovery Symposium; 2024 Mar 4-6; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2024;5(2_Suppl):Abstract nr P04.

Phosphorylation of hnRNP A1-Serine 199 Is Not Required for T Cell Differentiation and Function.

hnRNP A1 is an important RNA-binding protein that influences many stages of RNA processing, including transcription, alternative splicing, mRNA nuclear export, and RNA stability. However, the role of hnRNP A1 in immune cells, specifically CD4+ T cells, remains unclear. We previously showed that Akt phosphorylation of hnRNP A1 was dependent on TCR signal strength and was associated with Treg differentiation. To explore the impact of hnRNP A1 phosphorylation by Akt on CD4+ T cell differentiation, our laboratory generated a mutant mouse model, hnRNP A1-S199A (A1-MUT) in which the major Akt phosphorylation site on hnRNP A1 was mutated to alanine using CRISPR Cas9 technology. Immune profiling of A1-MUT mice revealed changes in the numbers of Tregs in the mesenteric lymph node. We found no significant differences in naive CD4+ T cell differentiation into Th1, Th2, Th17, or T regulatory cells (Tregs) invitro. In vivo, Treg differentiation assays using OTII-A1-Mut CD4+ T cells exposed to OVA food revealed migration and homing defects in the A1-MUT but no change in Treg induction. A1-MUT mice were immunized with NP- keyhole limpet hemocyanin, and normal germinal center development, normal numbers of NP-specific B cells, and no change in Tfh numbers were observed. In conclusion, Akt phosphorylation of hnRNP A1 S199 does not play a role in CD4+ T cell fate or function in the models tested. This hnRNP A1-S199A mouse model should be a valuable tool to study the role of Akt phosphorylation of hnRNP A1-S199 in different cell types or other mouse models of human disease.

FcγRIIB modulates splenic germinal center response against immune subversion during acute influenza A virus infection

BackgroundB cells are essential for providing humoral protection against acute influenza A virus (IAV) infection. FcγRIIB, a regulator of antibody (Ab) production, influences immune responses during pathogen infections, but its specific impact on humoral protection and B cell-mediated responses against IAV remains unclear. MethodsTo investigate FcγRIIB's role in host defense and B cell function during acute IAV infection, we generated mice with systemic FcγRIIB deficiency, functional impairment, and B cell-specific FcγRIIB deletion. We infected these mice with PR8 (H1N1) or Hkx31 (H3N2) IAVs and evaluated body weight preservation, survival rates, Ab production, viral neutralization, Ab affinity maturation, and germinal center B cell development. ResultsMice lacking FcγRIIB or with impaired function showed improved protection, preserved body weight, and increased survival rates during IAV infection. Notably, mice with haploinsufficient FcγRIIB function displayed protective effects. Selective deficiency of FcγRIIB in B cells led to enhanced Ab production, resulting in elevated IAV-specific Abs in the serum with superior viral neutralizing potency. However, the impact on the affinity maturation index of virus-specific Abs was modest. Accordingly, FcγRIIB-deficient B cells maintained normal germinal center B cell development during IAV infection, whereas wild-type mice exhibited delayed differentiation. ConclusionOur research underscores the pivotal role of FcγRIIB in host defense and B cell-mediated immunity during acute IAV infection. Additionally, our discoveries hold implications for antiviral treatments, particularly during the initial stages of IAV infection, aimed at enhancing the host's humoral immune response.

CD79 Expression Is Associated with Cell-of-Origin and Outcome in Diffuse Large B-Cell Lymphoma

Introduction: CD79B is a target of polatuzumab vedotin, an antibody-drug conjugate, which significantly improved the prognosis of both previously untreated and relapsed/refractory patients with diffuse large B-cell lymphoma (DLBCL). However, the biological and clinical significance of CD79B protein and gene expression have not been fully explored in DLBCL, thus we aimed at examining these relationships. Methods: We retrospectively analyzed de novo DLBCL patients, who were diagnosed and received rituximab-based immunochemotherapy from 2008 through 2018 in the Okayama Hematology Study Group from Japan. Immunohistochemistry (IHC) staining was performed using a CD79B antibody (AT107-2), and protein expression was assessed based on H-score as described in a previous study (Sehn LH et al. JCO 2020), integrating with publicly available representative bulk RNA sequencing DLBCL datasets (BCC cohort from Ennishi D et al. JCO 2019 and NCI cohort from Schmitz R et al. NEJM 2018). We also performed CD8 and MHC class-I IHC to evaluate the tumor microenvironment. Gene expression profile-based cell-of-origin (COO) classification was performed including double-hit signature (DHITsig), recently renamed the dark zone signature (DZsig), using the NanoString DLBCL90 assay. In addition, simultaneous epitope and transcriptome measurement in single cells from lymphoid tissues was conducted. Results: CD79B IHC was evaluable in 576 cases. DLBCL90 assay classified the entire cohort into 293 ABC (50.9 %), 189 GCB (32.8 %), 31 DZsig-positive (5.4 %) and 63 unclassified (10.9 %). Furthermore, we dichotomized the cohort into 288 CD79B high cases and 288 CD79B low cases according to the median CD79B H-score. A dynamic range of CD79B protein expression was observed across COO, where ABC-DLBCL showed the lowest values followed by GCB-DLBCL and DZsig-positive-DLBCL, in ascending order (Kruskal-Wallis test, P < .00001; Figure A). Indeed, CD79B low cases were significantly enriched in ABC-DLBCL (58 %) compared to GCB-DLBCL (26 %) and DZsig-positive-DLBCL (2 %), respectively (Chi-squared test, P < .001). Consistently, we revealed that CD79B expression was the lowest in ABC-DLBCL compared to GCB-DLBCL and DZsig-positive-DLBCL at the transcriptomic level (Kruskal-Wallis test, P = .011 for BCC cohort and P = .022 for NCI cohort). In addition, we identified different CD79B staining patterns, composed of 433 with cytoplasmic pattern (75 %), 86 with membranous pattern (14.9 %), and 52 cases being IHC negative. These patterns significantly varied across COO (Fisher's exact test, P = .015) and CD79B H-score was the highest in the membranous pattern followed by the cytoplasmic pattern (Kruskal-Wallis test, P < .0001). Of note, the composition of CD8 positive T-cells in CD79B low tumors was significantly higher than that of CD79B high tumors (Wilcoxon rank sum test, P < .0001). However, MHC class-I expression was decreased in CD79B low cases compared to CD79B high (Wilcoxon rank sum test, P = .0002), suggesting an immune escape mechanism with downregulation of MHC class-I in the presence of cytotoxic T-cells, which is often seen in solid cancers. Significant association of CD79B expression with COO further prompted us to evaluate CD79B expression in normal germinal center B cells. Notably, the single-cell simultaneous epitope and transcriptome analysis (CITEseq, n = 2) and single-cell RNAseq analysis (n = 6) of reactive lymph nodes revealed that both CD79B gene and protein expression were the lowest in cells exhibiting plasmablastic signatures, followed by light zone and dark zone B cells (Kruskal-Wallis test, P < .0001; Figure B), supporting the relation of CD79B expression to COO subtype in DLBCL. Regarding prognostic impact, CD79B low group had significantly poorer prognosis in the entire DLBCL cohort (Log-rank test, P = .0005 for overall survival (OS) and P = .008 for progression-free survival (PFS)) and in ABC-DLBCL (Log-rank test, P = .003 for OS and P = .031 for PFS). Moreover, CD79B protein expression was significantly associated with OS after adjusting for International Prognostic Index in the entire DLBCL cohort (Cox regression model; P = .035). Conclusion: Our study identifies distinct CD79B expression patterns across COO subtypes, with CD79B low cases enriched in ABC-DLBCL and demonstrating poorer prognosis, suggesting its potential as a prognostic marker and for targeted therapies.

Localization of DC-SIGN Expressing Cells in Follicular Lymphoma

The high incidence of unusual mannose-rich glycans on the expressed surface immunoglobulins of follicular lymphoma (FL) suggests a pathogenic role for this modification. While lectin-mediated signaling has been proposed to provide trophic support to FL cells, the localization of the lectins has not been extensively characterized. Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin (DC-SIGN) is a mannose-selective lectin named for its expression on classic marrow-derived dendritic cells. In vitro, recombinant DC-SIGN induces signaling in primary FL cells. The nodules of Follicular lymphoma (nFL) are the neoplastic counterparts of normal germinal centers (GC). Both GC and nFL contain variable numbers of centrocytic and/or centroblastic B cells, T-cells, and follicular dendritic cells (FDCs), but macrophages are typically found only in GC. Although termed “follicular dendritic cells”, FDCs are thought to be derived from non-blood stem-cells, potentially pericytes. Therefore, nFL lack classic dendritic cells and macrophages so it is unclear what cells in FL could express DC-SIGN. Therefore, we systematically characterized FDC and DC- SIGN localization in sixteen FL and nine Follicular hyperplasia (FH) lymph nodes. Using flow cytometry of disaggregated FL nodes, we were not able to identify a specific cell population expressing DC-SIGN. However, using immunohistochemistry and Immunofluorescence methods, we identified nine cases of FH and five cases of FL (n=5/16) with DC-SIGN and FDC co-localization. Immunohistochemical stains of the FDCs using CD23 and CD21 showed that the follicular dendritic structures were disrupted in almost all the FL cases assessed showing either a peripheral crescentic staining or broken FDC meshwork within the follicle. We identified five cases of FL with an average of more than four well visualized and complete FDC structures staining per low power field (4X) while the remaining cases had an average of less than two complete FDC network staining. There was near complete absence of CD21 positive FDCs meshwork identified in 50% of the FL cases compared to only one case lacking CD23 positive FDCs structure staining. In contrast, FH cases (n=9) showed complete staining of the FDC meshwork within the follicles with both CD21/CD23. For FH, the average number of complete FDC staining with CD23 was 18 while an average of 10 complete FDC meshworks stained with CD21. Furthermore, immunofluorescence imaging analysis showed different pattern of localization of CD23 positive FDC with DC-SIGN with between the two conditions. In FH, DC-SIGN and CD23 colocalization was identified mainly in the light zone. For FL, we observed that DC-SIGN overlap with CD23 localized in the intra-follicular areas and co-localized with CD163 (M2 macrophages) in the inter-follicular zones. Confocal imaging confirmed colocalization of CD23 and DC-SIGN on FDCs with close association to MUM1-positive B cells in both GC and nFL. Additional analysis also showed that 80% (n=5) of the cases which had more than four complete FDC structures staining with CD23 co-localized with DC-SIGN in the intra-follicular areas and the cases with complete FDC network disruption did not. There was no significant relationship identified between the extent of FDC networks and the fraction of non-neoplastic B cells in the FL cases. In summary, our data show that DC-SIGN is expressed on FDCs in FL and FH even though FDCs are not the marrow-derived DCs for which DC-SIGN is named. Furthermore, localization of DC-SIGN to the follicle suggests a potential role for the microenvironment in the pathogenesis of FL and possible therapeutic target.

T-Cell Signaling Mediates the Epigenetic Priming of Germinal Center B-Cell Plasticity and Stem Functionality

Chemo-immunotherapy can prolong life expectancy of patients with Diffuse Large B-cell Lymphomas (DLBCL). However, the emergence of donor-derived lymphoma cases after stem cell transplantation and the relapse of a third of DLBCL patients, strongly suggests the existence of persisting lymphoma repopulating cells (LRC) with stem-like functionality. This apparently controversial concept arises from the fact that DLBCLs originate from mature rather than progenitor cells. Identifying the biological and epigenetic features of these elusive LRC, and how they arise from normal germinal center (GC) B cells, is therefore critical and remains underexplored. Although fully mature, GC B cells naturally manifest remarkable phenotypic plasticity as compared to other cell types. We hypothesized that this plasticity reflects stem-like programming and functionality. Along these lines, we found that GC B cells are uniquely enriched for pluripotent stem cell transcriptional signatures, and increased chromatin accessibility at stem cell enhancers. We reasoned that the capacity to undergo induced Pluripotent Stem Cells (iPSC) reprogramming could serve as a surrogate assay for stem-like plasticity. Therefore, we investigated the potential of GC B cells to form iPSCs using a doxycycline-dependent mouse strain that enables the inducible expression of Yamanaka transcription factors (TF) in any given cell. Strikingly, GC B cells isolated from our mice manifested a 10-fold (p<0.0001) increase in iPSC reprogramming as compared to other mature B cells. GC B cells are a heterogenous mix of functionally distinct subpopulations. Using single cell RNA-seq and iPSC assays in sorted cells, we noted that the rare population (~3%) of GC B cells selected by T-cell help manifested the stem-like transcriptional profile and iPSC reprogramming phenotype. Moreover, blocking T-cell help during the GC reaction in vivo using CD40 blockade abrogated iPSC forming capacity. Lymphoma-associated EZH2 Y641F mutations impair GC B-cell interactions with T FH cells due to aberrant repression of immune synapse genes. Accordingly, EZH2 Y641F GC B cells manifested loss of the iPSC phenotype. T-cell help induces MYC in GC B cells. However, induction of MYC in mature naïve B cells did not confer them with iPSC potential indicating that other mechanisms must be at play. Lymphoma-associated Btg1 Q36Hmutations confer fitness in GC B cells by enhancing their response to T-cell help. Reciprocal to EZH2 Y641F, Btg1 Q36Hmutant GC B cells manifested further significant increase in iPSC formation. Performing multi-ome (simultaneous single-cell RNAseq and ATACseq) studies in GC B cells revealed massive gain in chromatin accessibility of bona fide stem cell super-enhancers in GC B cells that received T-cell help. There was also a reduced accessibility at genes that maintain B-cell lineage (e.g. Pax5) and GC phenotypes (e.g. Foxo1). Finally, lymphoma-associated Histone 1 mutations induce upregulation of stem cell programs in GCs and could enhance iPSC reprogramming in fibroblasts. We therefore hypothesized that H1 deficiency would overcome the GC dependency on T-cells for their plasticity phenotype. Indeed, increased iPSC formation occurred across all GC subpopulations in H1 C/E-/- (HIST1C/HIST1E knockout) mice. We speculate that restricting plasticity to B cells under selection by T cells, limits the potential for GC B cells to acquire high levels of plasticity, hence reducing the potential for these cells to initiate lymphomas. Consistent with this notion, we found that DLBCL patients enriched for these stem cell signatures manifested inferior clinical outcomes.

Tumor-Infiltrating Normal B Cells Revealed by Immunoglobulin Repertoire Clonotype Analysis Are Highly Prognostic and Crucial for Antitumor Immune Responses in DLBCL.

Tumor-infiltrating B lymphocytes (TIL-B) have demonstrated prognostic and predictive significance in solid cancers. In this study, we aimed to distinguish TIL-Bs from malignant B-cells in diffuse large B-cell lymphoma (DLBCL) and determine the clinical and biological significance. A total of 269 patients with de novo DLBCL from the International DLBCL R-CHOP Consortium Program were studied. Ultra-deep sequencing of the immunoglobulin genes was performed to determine B-cell clonotypes. The frequencies and numbers of TIL-B clonotypes in individual repertoires were correlated with patient survival, gene expression profiling (GEP) data, and frequencies of DLBCL-infiltrating immune cells quantified by fluorescent multiplex IHC at single-cell resolution. TIL-B abundance, evaluated by frequencies of normal B-cell clonotypes in the immunoglobulin repertoires, remarkably showed positive associations with significantly better survival of patients in our sequenced cohorts. DLBCLs with high versus low TIL-B abundance displayed distinct GEP signatures, increased pre-memory B-cell state and naïve CD4 T-cell state fractions, and higher CD4+ T-cell infiltration. TIL-B frequency, as a new biomarker in DLBCL, outperformed the germinal center (GC) B-cell-like/activated B-cell-like classification and TIL-T frequency. The identified TIL-B-high GEP signature, including genes upregulated during T-dependent B-cell activation and those highly expressed in normal GC B cells and T cells, showed significant favorable prognostic effects in several external validation cohorts. TIL-B frequency is a significant prognostic factor in DLBCL and plays a crucial role in antitumor immune responses. This study provides novel insights into the prognostic determinants in DLBCL and TIL-B functions with important therapeutic implications.

17th International Conference on Malignant Lymphoma, Palazzo dei Congressi, Lugano, Switzerland, 13 - 17 June, 2023.

Introduction: CD79B is a target of polatuzumab vedotin, an antibody–drug conjugate, which may improve the prognosis of both previously untreated and relapsed/refractory patients with diffuse large B-cell lymphoma (DLBCL). However, the biological and clinical significance of CD79B protein and gene expression in DLBCL is largely unknown. Methods: We retrospectively analyzed de novo DLBCL patients, who were diagnosed and received rituximab-based immunochemotherapy from 2008 through 2018 in the Okayama Hematology Study Group from Japan. Immunohistochemistry (IHC) staining was performed using a CD79B antibody (AT107-2), and protein expression was assessed based on H-score according to a previous study (Sehn L et al. JCO 2020). We also performed gene expression profile-based cell-of-origin (COO) classification, including double-hit signature (DHITsig) which has been renamed to dark zone signature (DZsig) (Waleed A et al. Blood 2022), using the NanoString DLBCL90 assay. Results: CD79B IHC expression was evaluable in 602 cases. We idefined two groups according to median H-score of CD79B expression: CD79Bhigh and CD79Blow. The COO subtypes were assigned as follows: 308 patients (51%) with activated B-cell-like (ABC)-DLBCL, 196 (33%) with germinal center B-cell-like (GCB)-DLBCL, 32 (5%) with DZsig-pos DLBCL and 66 (11%) with unclassified (UNC). H-score of CD79B was the lowest in patients with ABC-DLBCL followed by GCB-DLBCL and DZsig-pos DLBCL in ascending order (Kruskal–Wallis test P < .00001; Figure A). Indeed, CD79Blow tumors were significantly enriched in ABC-DLBCL (57%) compared to GCB-DLBCL (40%) and DZsig-pos DLBCL (22%), respectively (both, P < .001). Consistently, using publicly available DLBCL datasets (Schmitz et al. NEJM 2018 and Ennishi et al. JCO 2019), we revealed that CD79B gene expression was the lowest in ABC-DLBCL compared to GCB- and DHITsig-DLBCL (Kruskal–Wallis test P = .01; Figure B and C). The association of CD79B expression with COO prompted us to evaluate CD79B expression in normal germinal center B cells. Notably single-cell transcriptomic analyses of six reactive lymphoid tissues from publicly available datasets revealed that the lowest expression of CD79B was found in plasmablasts followed by light zone B cells and dark zone B cells in ascending order (Kruskal–Wallis test P < .0001), supporting the differential expression of CD79Baccording to COO subtype. CD79Blow group had significantly shorter overall survival (OS) in the total DLBCL cohort (log-rank, P < .001) and within ABC-DLBCL (P = .001, Figure D and E). Moreover, CD79B protein expression was significantly associated with OS after adjusting for International Prognostic Index in the total cohort (Cox regression model; P< .001). Keywords: Aggressive B-cell non-Hodgkin lymphoma, Diagnostic and Prognostic Biomarkers Conflicts of interests pertinent to the abstract. K. Sunami Honoraria: Celgene, Sanofi, BMS, Ono, Janssen Research funding: Takeda, AbbVie, GSK, Chugai, Otsuka, MSD, Novartis, Astellas Amgen, Pfizer, Parexel, Kyowa Kirin, Symbio, Agios Y. Hiramatsu Honoraria: Chugai Pharmaceutical Co, Nippon Shinyaku Co, Bristol Myers Squibb, Sanofi K.K. I. Yoshida Honoraria: Kyowa Kirin, Chugai, Eisai, Jannsen, Nippon-shinyaku, Otsuka, Symbio, Takeda, Sumitomo Pharma, Meiji Research funding: Kyowa Kirin, Chugai Y. Maeda Research funding: Chugai, Nippon-shinyaku Other remuneration: Chugai, Eisai, Otsuka, Kyowa Kirin, Takeda D. W. Scott Consultant or advisory role: Abbvie, AstraZeneca, Janssen, Incyte Honoraria: AstraZeneca Research funding: Janssen, Roche/Genentech D. Ennishi Honoraria: Chugai, Eisai, Kyowa Kirin Research funding: Nipponshinyaku, Chugai

The germinal center in the pathogenesis of B cell lymphomas.

The adaptive immune system has evolved to allow effective responses against a virtually unlimited number of invading pathogens. This process requires the transient formation of germinal centers (GC), a dynamic environment that ensures the generation and selection of B cells capable to produce antibodies with high antigen affinity, or to maintain the memory of that antigen for life. However, this comes at a cost, as the unique events accompanying the GC reaction pose a significant risk to the genome of B cells, which must endure elevated levels of replication stress, while proliferating at high rates and undergoing DNA breaks introduced by somatic hypermutation and class switch recombination. Indeed, the genetic/epigenetic disruption of programs implicated in normal GC biology has emerged as a hallmark of most B cell lymphomas. This improved understanding provides a conceptual framework for the identification of cellular pathways that could be exploited for precision medicine approaches.

KMT2D acetylation by CREBBP reveals a cooperative functional interaction at enhancers in normal and malignant germinal center B cells.

Heterozygous inactivating mutations of the KMT2D methyltransferase and the CREBBP acetyltransferase are among the most common genetic alterations in B cell lymphoma and co-occur in 40 to 60% of follicular lymphoma (FL) and 30% of EZB/C3 diffuse large B cell lymphoma (DLBCL) cases, suggesting they may be coselected. Here, we show that combined germinal center (GC)-specific haploinsufficiency of Crebbp and Kmt2d synergizes invivo to promote the expansion of abnormally polarized GCs, a common preneoplastic event. These enzymes form a biochemical complex on select enhancers/superenhancers that are critical for the delivery of immune signals in the GC light zone and are only corrupted upon dual Crebbp/Kmt2d loss, both in mouse GC B cells and in human DLBCL. Moreover, CREBBP directly acetylates KMT2D in GC-derived B cells, and, consistently, its inactivation by FL/DLBCL-associated mutations abrogates its ability to catalyze KMT2D acetylation. Genetic and pharmacologic loss of CREBBP and the consequent decrease in KMT2D acetylation lead to reduced levels of H3K4me1, supporting a role for this posttranslational modification in modulating KMT2D activity. Our data identify a direct biochemical and functional interaction between CREBBP and KMT2D in the GC, with implications for their role as tumor suppressors in FL/DLBCL and for the development of precision medicine approaches targeting enhancer defects induced by their combined loss.

Crebbp Kat Domain Missense Mutations Alter Its Dynamic Loading Onto Chromatin and Create a Transcription Factor Sink

The CREBBP gene encodes a lysine acetyltransferase (KAT) and is one of the most frequently mutated genes in follicular lymphoma (FL) and diffuse large B-cell lymphoma (DLBCL). However, the spectrum of mutations is significantly different between these two diseases, with significantly higher fractions of nonsense/frameshift mutations in DLBCL and comparatively higher fractions of lysine acetyltransferase (KAT) domain point mutations (KAT-PM) in FL. Among KAT domain mutations, multiple hotspots can be observed with R1446 (14%), Y1482 (3%) and Y1503 (7%) being the most frequently mutated residues. We have previously shown that CREBBP R1446C mutations lead to a more profound loss of histone acetylation and gene expression compared to biallelic knock-out (KO) of the CREBBP highlighting a potential dominant-negative function of R1446C via an unknown mechanism. We have also performed biochemical and structural analysis of KAT domain mutations and observed that R1446C mutations result in a partial loss of function (pLOF), whereas Y1482N and Y1503C mutations are catalytically dead. Here, we report the molecular characterization of CRISPR-engineered isogenic cell lines (RL, HT, 293T) bearing biallelic KO, R1446C, Y1482N or Y1503C mutations, or WT CREBBP, using CUT&RUN analysis of CREBBP and EP300 loading, histone marks (H3K27Ac, H3K4me1, H3K4me2, H3K27me3), and ATAC and RNA sequencing for chromatin accessibility and gene expression, respectively. Western blot analysis showed significant reduction of H3K27Ac and H3K18Ac in all point-mutants with no alteration of CREEBP or its paralog EP300 expression. Principal component analysis (PCA) of H3K27Ac and gene expression data revealed that KO cells were most similar to WT, and all KAT-PM cells clustered separately to WT and KO cells. Notably, R1446C (partial LOF) cells reproducibly clustered separately from Y1482N and Y1503C (catalytically dead), and differential analysis identified both shared and R1446C- or Y1482N/Y1503-specific losses of H3K27Ac in all cell lines, suggesting that the degree of loss in catalytic activity rendered by different KAT domain point mutations may be associated with distinct molecular phenotypes. In order to investigate the mechanism by which KAT-PMs drive more severe molecular changes compared to biallelic KO, we investigate the redundant role of EP300 using CUT&RUN analysis of EP300 loading. CREBBP-bound active enhancers (H3K4me1+ H3K27Ac+) showed a significant increase in EP300 loading in cells with CREBBP KO compared to WT. However, we observed a slight decrease in EP300 loading within KAT-PM cells, indicating that the presence of mutant CREBBP protein prevents the redundant activity of EP300. We speculated that this may be due to mutant CREBBP residing on chromatin in an inactive state and preventing loading of EP300. We therefore analyzed CREBBP loading over CREBBP-bound active enhancers in WT cells that had significant reductions of H3K27Ac in KAT-PMs. Surprisingly, we observed a significant reduction in CREBBP loading over these regions, with a greater loss of CREBBP loading in catalytically dead mutants (Y1482N/Y1503C) compared to the partial LOF mutant (R1446C). We therefore characterized patterns of CREBBP loading during normal germinal center B-cell development by analyzing purified tonsillar naïve B-cells, centroblasts and centrocytes. We observed that CREBBP is dynamically loaded onto chromatin during the centroblast-to-centrocyte transition, indicating that loss of chromatin-bound CREBBP in KAT-PMs may be due to a failure of mutant CREBBP to load onto these sites. We next performed transcription factor (TF) motif enrichment analysis and identified a significant enrichment of key TFs such as BACH2 and IRF4 in regions with failed CREBBP loaded and EP300 compensation, indicating that CREBBP may bind these transcription factors and act as a sink that prevents redundant EP300 activity. We validated this using tetracycline-inducible over-expression of IRF4 in KAT-PM cells, which increased EP300 loading and H3K27Ac over IRF4 binding sites. Collectively, our results indicate that CREBBP KAT-PMs prevent the redundant activity of EP300 in a manner proportionally to their relative loss of catalytic activity, by preventing the dynamic loading of CREBBP onto chromatin and acting as a transcription factor sink.

Abstract A05: Olfactory receptors as a new therapeutic target in lymphomas

Abstract Background. Diffuse large B cell lymphoma (DLBCL) and mantle cell lymphoma (MCL) are aggressive lymphomas in which up to 40% of patients are still in need of therapy. G protein-coupled receptors (GPCRs) are integral membrane proteins that mediate cellular responses to endogenous and exogenous stimuli and are implicated in the pathophysiology of various diseases: CXCR3/4/5, S1PR1/2/3, or GPR34 are GPCRs already studied in lymphomas. The olfactory receptors (ORs) are also GPCRs, initially identified and characterized for their expression in olfactory cells but now shown to be expressed in various tissues. OR51E1 is known as prostate-specific G protein-coupled receptor 2 (PSGR2) due to its expression in prostate cancer, OR2B6 and OR2W3 are expressed in breast cancer, and OR51E1 in melanoma. Here, we studied OR13A1 in lymphoma cell lines and clinical specimens. Methods. RNA-Seq and real-time PCR for evaluating the expression of ORs in lymphoma cell lines. Gene expression data for clinical samples were obtained from public datasets. OR13A1 silencing was performed with both siRNAs (OCI-Ly1 and U2932) and doxycycline-inducible shRNAs (U2932 and VAL); viability was assessed after 3 days using MTT and even longer with live imaging. Computer modelling was performed using available ligands for the murine orthologue Olfr211. Results. Various ORs were expressed across a large panel of B cell lymphoma cell lines. In particular, OR13A1 was expressed in 35/47 cell lines and, mostly, derived from DLBCL and MCL. Among DLBCL, the expression was higher in cell lines derived from the germinal center (GC) B-cell type (GCB) rather than from activated B cell like (ABC) DLBCL (P value = 0.03). A similar pattern was observed in DLBCL patients: higher expression in GCB than ABC and in EZB than MCD (P &amp;lt; 0.001). OR13A1 also appeared higher in normal GC cells than in naïve and memory B cells. OR13A1 expression appears to identify GCB DLBCL (P value = 0.009) and MCL (P value = 0.006) patients with inferior outcome. Silencing of OR13A1 with siRNAs in GCB and ABC DLBCL cells (OCI-Ly1 and U2932) caused &amp;gt; 50% reduction in cell viability, and downregulation of pERK levels. Viability data were confirmed using a doxycycline-inducible shRNA system and an Incucyte live cell imaging instrument. Natural compounds reported as ligands for the murine orthologue Olfr211 or in silico identified to bind as agonists (ex: tyramine) increased cell line growth and compounds predicted to bind as antagonists (ex: cyclohexanone) decreased the cell viability in the presence but not in the absence of the GPCR. Conclusion. OR13A1 gene appeared more abundantly expressed in lymphomas compared to others ORs, in particular it was more expressed in MCL and in GCB DLBCL with a possible impact on clinical outcome. Genetic and chemical experiments showed that this GPCR has an essential function in lymphoma cells and represents a novel therapeutic target. Citation Format: Giulio Sartori, Luciano Cascione, Milos Matkovic, Hiro Matsunami, Andrea Cavalli, Francesco Bertoni. Olfactory receptors as a new therapeutic target in lymphomas [abstract]. In: Proceedings of the Third AACR International Meeting: Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2022 Jun 23-26; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2022;3(5_Suppl):Abstract nr A05.

Peyer's patch TH17 cells are dispensable for gut IgA responses to oral immunization.

T helper 17 (TH17) cells located at the Peyer's patch (PP) inductive site and at the lamina propria effector site of the intestinal immune system are responsive to both pathogenic and commensal bacteria. Their plasticity to convert into follicular helper T (TFH) cells has been proposed to be central to gut immunoglobulin A (IgA) responses. Here, we used an IL-17A fate reporter mouse and an MHC-II tetramer to analyze antigen-specific CD4+ T cell subsets and isolate them for single-cell RNA sequencing after oral immunization with cholera toxin and ovalbumin. We found a TFH-dominated response with only rare antigen-specific TH17 cells (<8%) in the PP. A clonotypic analysis provided little support that clonotypes were shared between TFH and TH17 cells, arguing against TH17 plasticity as a major contributor to TFH differentiation. Two mouse models of TH17 deficiency confirmed that gut IgA responses to oral immunization do not require TH17 cells, with CD4CreRorcfl/fl mice exhibiting normal germinal centers in PP and unperturbed total IgA production in the intestine.

P1285: IN VIVO IMPACT OF ABERRANT OVEREXPRESSION OF C-REL NF-ΚB SUBUNIT IN GERMINAL CENTER B-LYMPHOCYTES: A TUMOR ONCOGENIC EVENT IN GCB-DLBCLS

Background: Diffuse large B-cell lymphomas (DLBCLs) are the most NF-κB-related aggressive non-Hodgkin’s lymphomas. DLBCLs are clinically, molecularly and genetically heterogeneous, suggesting different oncogenic mechanisms. Gene-expression profiling studies led to the proposal of two main cell-of-origin molecular subtypes known as germinal center B-cell-like (GCB) DLBCLs, and activated B-cell like (ABC) DLBCLs. With the Lymphoma Study Association LYSA, we previously published that strong c-Rel DNA-binding activity was mostly found in GCBs and was associated with increased REL mRNA expression. These cases with both overexpression of REL mRNA and c-Rel related gene expression profile were correlated with various recurrent GCB-DLBCLs genetic events, including REL gains, BCL2 translocation, MEF2B, EZH2, CREBBP, and TNFRSF14 mutations and with the EZB GCB genetic subtype. Aims: We propose that c-Rel is a major oncogene of GCB-DLBCLs. We speculate that c-Rel confers a selective advantage in the germinal center (GC)-specific environment. We wish to study the consequences of aberrant overexpression and activation of c-Rel in vivo that could promote tumorigenesis in DLBCL precursor cells by disrupting the normal dynamics of B-cell development in the GC. Methods: We have generated the fl_STOP-REL mouse model: the murine REL transgene preceded by a STOP-Neomycin cassette flanked of loxP sites was introduced in Rosa26 locus on chromosome 6. The REL transgene is followed by an IRES to allow YFP marker concomitant expression. To reach GC B-cell specific expression, we used AID_Cre-ert2 mice: the Cre-ert2 transgene was at the AICDA gene locus on chromosome 6. On the same chromosome, the tdTomato marker preceded by a STOP cassette flanked by loxP sites was introduced at the Rosa26 locus. A pool of REL overexpressing GC B-cell was generated after tamoxifen administration and T-cell-dependent antigen stimulation with sheep red blood cells (SRBC). The fate of these YFP and tdTomato positive GC B-cells was followed over-time until 8 months. The first four months, a SRBC immune booster was performed to maintain the GCs. Results: As expected, our model fl_STOP-REL | AID_Cre-ert2 (i.e. REL mice) allowed for in vivo competition between c-Rel overexpressing (tdTomato+/YFP+) and normal (tdTomato+/YFP-) GC B-cells. In blood, the percentage of YFP positive B-lymphocytes among the tdTomato positive cells was increased over-time: 30% at 14 days, 65% at 2 months and about 80% at 8 months. From blood, spleen and lymph nodes, phenotyping analysis by flow cytometry of REL/YFP positive B-cells indicated an activated profile compared to normal GC-derived B-cells: CD19+, IgM+, IgD-, CD21+, CD80+, and B220low. At 8 months after generation of GC B-cells pool, approximatively 3-5% of B-cells were tdTomato and YFP positives in spleen of REL mice, whereas tdTomato positives cells in control mice were rare hardly detectable (less than 0.8%). Altogether, our result indicated that c-Rel reprograms B-cell to be activated and to better survive in vivo for very long time. Image:Summary/Conclusion: We bring strong experimental arguments showing that increased c-Rel expression in GC B-cell favors their survival for several months, and would thus be a primary event. We suspect that additional oncogenic events are probably needed for tumor clonal expansion such as BCL2, EZH2, CREBBP, TNFRSF14 and/or c-Myc dysregulation.

Unveiling the Role of the Tumor Microenvironment in the Treatment of Follicular Lymphoma.

Simple SummaryFollicular lymphoma is the most common type of indolent non-Hodgkin lymphoma and is characterized by its heterogeneity and variable course. In addition to tumor cells, the immune microenvironment plays a fundamental role in the pathogenesis of the disease. Despite advances in treatment, responses vary among patients, and outcomes are often unpredictable: a subset of high-risk patients will be refractory to standard treatments or will develop a high-grade histology. In this review, we try to understand the crosstalk between follicular lymphoma B-cells and the tumor microenvironment as well as its impact on prognosis and the risk of transformation. We also highlight recent findings related to novel therapies developed to treat this complex disease, in which genetic mutations and microenvironment cells play a key role.Follicular lymphomas (FL) are neoplasms that resemble normal germinal center (GC) B-cells. Normal GC and neoplastic follicles contain non-neoplastic cells such as T-cells, follicular dendritic cells, cancer associated fibroblasts, and macrophages, which define the tumor microenvironment (TME), which itself is an essential factor in tumor cell survival. The main characteristics of the TME in FL are an increased number of follicular regulatory T-cells (Treg) and follicular helper T-cells (Tfh), M2-polarization of macrophages, and the development of a nodular network by stromal cells that creates a suitable niche for tumor growth. All of them play important roles in tumor angiogenesis, inhibition of apoptosis, and immune evasion, which are key factors in tumor progression and transformation risk. Based on these findings, novel therapies have been developed to target specific mutations present in the TME cells, restore immune suppression, and modulate TME.

A nodular type of mantle cell lymphoma in the nasopharynx.

Mantle cell lymphoma (MCL) is a subtype of B-cell lymphoma derived from CD5-positive antigen-naïve pre-germinal center B-cells within the mantle zone that surrounds normal germinal center follicles. MCL comprises approximately 5 to 10% of all lymphomas. Tonsil is the most common location of MCL in the head and neck region, followed by the nasopharynx. Primary MCL involving the nasopharynx is extremely rare. Its clinical course is very aggressive with frequent relapses after conventional chemotherapy. It always presents as a protruding mass on the mucosal lining of the pharyngeal cavity. Here, we report a new nodular type of MCL in the nasopharynx. Endoscopically, this case showed multiple nodular lesions of primary MCL on the nasopharyngeal mucosa. This unique finding has not been reported yet in the English literature. These lesions should be differentiated from simple pharyngeal infections or benign lymphoid hyperplasia in the nasopharynx.