PIM1 and CD79B Mutation Status Impacts the Outcome of Primary Diffuse Large B-Cell Lymphoma of the CNS

Excessive activation?induced cytidine deaminase accumulated by proteasome inhibitors rescues abnormal class switch in activated B?cell?like diffuse large B?cell lymphoma

Activation-induced cytidine deaminase (AID) is an enzyme that plays a crucial role in mediating somatic hypermutation and class-switch recombination (CSR). It has been found to be associated with aberrant immunoglobulin CSR in activated B-cell-like diffuse large B-cell lymphoma (ABC-DLBCL). In the present study, MG132, a potent proteasome and calpain inhibitor, induced significant cell death in ABC-DLBCL cells and inhibited the growth of ABC-DLBCL cell xenograft tumors. The results also showed that MG132 induced AID accumulation by impairing proteasome degradation of AID. Excessive endogenous AID accumulation was observed in both AID-deficient and C57/BL6 wild-type mice treated with MG132, and apparent CSR of IgM to IgG1, IgG3 and IgE. Upon stimulation of cytokines such as LPS and/or IL-4, ABC-DLBCL cells also showed a noticeable increase in CSR of IgM to IgG1, IgG3 and IgE with decreased AID protein levels. The present study demonstrates that MG132 can induce AID accumulation, which in turn restores dysfunctional CSR in ABC-DLBCL. Using MG132 as a tool, the present study elucidates the anti-lymphoma effect of proteasome inhibitors on ABC-DLBCL by rescuing the abnormal AID-induced CSR.

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.

Updates of primary central nervous system lymphoma

Lymphoma occurring in the central nervous system is considered primary central nervous system lymphoma (PCNSL), usually without systematic lesions. Over the last few decades, a deep understanding of PCNSL has been lacking due to the low incidence rate, and the overall survival and progression-free survival of patients with PCNSL are lower than those with other types of non-Hodgkin lymphoma. Recently, there have been several advancements in research on PCNSL. Advances in diagnosis of the disease are primarily reflected in the promising diagnostic efficiency of novel biomarkers. Pathogenesis mainly involves abnormal activation of nuclear factor kappa-B signaling pathways, copy number variations, and DNA methylation. Novel therapies such as Bruton's tyrosine kinase inhibitors, immunomodulatory drugs, immune checkpoint inhibitors, and phosphoinositide 3-kinase/mammalian target of rapamycin inhibitors are being evaluated as possible treatment options for PCNSL, especially for relapsed/refractory (R/R) cases. Several clinical trials also indicated the promising feasibility and efficacy of chimeric antigen receptor T-cell therapy for selected R/R PCNSL patients. This review focuses on discussing recent updates, including the diagnosis, pathogenesis, and novel therapy of PCNSL.

Deciphering the Prognostic Significance of MYD88 and CD79B Mutations in Diffuse Large B-Cell Lymphoma: Insights into Treatment Outcomes

BACKGROUND

The clinical and genetic characteristics, as well as treatment outcomes, of diffuse large B-cell lymphoma (DLBCL) patients with different MYD88 and CD79B mutation status merit further investigation.

OBJECTIVE

This study aims to investigate the distinctions in clinical manifestations, genetic characteristics, and treatment outcomes among MYD88-CD79Bco-mut, MYD88/CD79Bsingle-mut, and MYD88-CD79Bco-wt DLBCL patients.

PATIENTS AND METHODS

Clinical and genetic characteristics, along with treatment outcomes among 2696 DLBCL patients bearing MYD88-CD79Bco-mut, MYD88/CD79Bsingle-mut, and MYD88-CD79Bco-wt treated with R-CHOP/R-CHOP-like regimens from the Cancer Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College and six external cohorts were analyzed. Potential molecular mechanisms were investigated through Gene Set Enrichment Analysis and xCell methodology.

RESULTS

In the MCD subtype, patients with MYD88-CD79Bco-mut showed comparable progression-free survival (PFS) and overall survival (OS) compared to MYD88/CD79Bsingle-mut or MYD88-CD79Bco-wt. However, in the non-MCD subtype, patients with MYD88-CD79Bco-mut exhibited significantly inferior OS than MYD88/CD79Bsingle-mut or MYD88-CD79Bco-wt, while there was no significant OS difference between MYD88/CD79Bsingle-mut and MYD88-CD79Bco-wt (median OS: 68.8 [95% CI 22-NA] vs NA [95% CI 112-NA] vs 177.7 [95% CI 159-NA] months; MYD88-CD79Bco-mut vs MYD88/CD79Bsingle-mut: p = 0.02; MYD88-CD79Bco-mut vs MYD88-CD79Bco-wt: p = 0.03; MYD88/CD79Bsingle-mut vs MYD88-CD79Bco-wt: p = 0.33). Regarding patients with MYD88-CD79Bco-mut, there was no significant difference in PFS and OS between the MCD and non-MCD subtypes. Within the MYD88-CD79Bco-mut group, patients with PIM1mut had better PFS than PIM1wt (median PFS: 8.34 [95% CI 5.56-NA] vs 43.8 [95% CI 26.4-NA] months; p = 0.02). Possible mechanisms contributing to the superior PFS of PIM1mut patients may include activated lymphocyte-mediated immunity and interferon response, a higher proportion of natural killer T cells and plasmacytoid dendritic cells, as well as suppressed angiogenesis and epithelial-mesenchymal transition, along with lower fibroblast and stromal score.

CONCLUSIONS

In the MCD subtype, patients with MYD88-CD79Bco-mut showed comparable PFS and OS compared to MYD88/CD79Bsingle-mut or MYD88-CD79Bco-wt, while in the non-MCD subtype, they exhibited significantly inferior OS. There was no significant disparity in PFS and OS of MYD88-CD79Bco-mut between the MCD and non-MCD subtypes. The presence of PIM1mut within the MYD88-CD79Bco-mut group correlated with better PFS, which may result from an intricate interplay of immune processes and tumor microenvironment alterations.

Pathology and new insights in central nervous system lymphomas

PURPOSE OF REVIEW

Primary central nervous system lymphoma (PCNSL) is a rare central nervous system (CNS) malignancy, which represents a heterogenous group of tumors. Among PCNSL, diffuse large B-cell lymphoma of the CNS (CNS-DLBCL) represents the most common tumor type. Multiomics studies have recently revealed the complex genomic landscape of these rare diseases. These findings lead to a potential new molecular and epigenetic classification.

RECENT FINDINGS

Our review is focused on CNS-DLBCL in immunocompetent patients. CNS-DLBCL are derived from self-reactive/polyreactive precursor cells. An early molecular event such as MYD88 mutation leads to escape elimination of precursor cells, which, by a dysregulated GC reaction, acquire auto-/polyreactivity of the B-cell tumoral cells for antigens physiologically expressed in the CNS. Most of CNS-DLBCL tumor cells harbor a non-GCB, ABC-like immunophenotype associated with a late GC (exit) B-cells genotype by gene expression profiling. Various mechanisms of genetic alterations are involved in the pathogenesis of PCNSL, including point mutations [nonsomatic hypermutation (SHM), aberrant SHM (aSHM)], SHM/aSHM, chromosome copy gains or losses, and DNA hypermethylation. Constitutive NFκB activation plays a key role in lymphoma cell proliferation and survival by dysregulation of toll-like receptor (mutations of CARD11 and MYD88 ), BCR ( CD79B ), JAK-STAT, and NFκB signaling pathways.

SUMMARY

Multiomics approaches have succeeded to substantially improve the understanding of the pathogenesis, as well as the molecular and epigenetic events in PCNSL. Challenges remain due to the obvious heterogeneity of CNS-DLBCL, and improvement is needed for their classification.

Whole-Genome/Exome Sequencing Uncovers Mutations and Copy Number Variations in Primary Diffuse Large B-Cell Lymphoma of the Central Nervous System

Background/objective: Identification of key genetic alterations is of importance in the targeted therapies of primary central nervous system lymphoma (PCNSL). However, only a small number of studies have been carried out in PCNSL. In this study, we further described the genetic mutations and copy number variations (CNVs) in PCNSL patients using whole-genome/exome sequencing (WGS/WES), as well as revealed their associations with patients’ clinicopathological features and prognosis.

Methods: Tumor specimens from 38 patients with primary diffuse large B-cell lymphoma of the central nervous system (CNS DLBCL) were enrolled to WGS (n = 24) or WES (n = 14). The CNVs and mutations of 24 samples (WGS) and 38 samples (WGS/WES) were characterized, respectively. The associations between CNVs and mutations with the overall survival rates of PCNSL patients were also evaluated.

Results: The most common mutations were identified in IGLL5 (68%), PIM1 (63%), MYD88 (55%), CD79B (42%), BTG2 (39%), PCLO (39%), KMT2D (34%), and BTG1 (29%) genes. Among the mutated genes, EP300, ETV6, and HIST1H1E mutations were exclusively detected in the elderly, while DUSP2 mutations were associated with the immune microenvironment indicators. In addition, KMT2D mutation was associated with a poor prognosis. In addition, 488 CNVs including 91 gains and 397 deletions were observed across 24 samples from WGS results. Notably, 1q31.3 amplification was closely associated with the poor prognosis of PCNSL patients.

Conclusion: This study further characterizes the genomic landscape of primary CNS DLBCL using WGS/WES, which provides insight into understanding the pathogenesis of PCNSL and fosters new ideas for the targeted treatment of PCNSL.