Extensive genetic alterations of the HLA region, including homozygous deletions of HLA class II genes in B-cell lymphomas arising in immune-privileged sites

Diffuse large B-cell lymphoma involving the central nervous system: biologic rationale for targeted therapy

Diffuse large B-cell lymphoma (DLBCL) is an aggressive B-cell lymphoma curable even in advanced stages. DLBCL involving the central nervous system (CNS) is more difficult to cure and fewer treatment options exist. Primary CNS lymphoma (PCNSL) refers to aggressive lymphomas confined to the CNS, and are almost always DLBCL. Standard approaches for PCNSL use high-dose methotrexate-based combinations as induction therapy and younger patients often receive dose-intensive consolidation. However, dose-intensive therapies are not suitable for all patients, and older patients have fewer effective treatment options. Patients with relapsed or chemotherapy-refractory disease have a very poor prognosis. Secondary CNS lymphoma (SCNSL) describes aggressive lymphomas involving the CNS at initial presentation or relapses within the CNS after treatment for systemic DLBCL. Isolated CNS relapse is often managed as PCNSL, but patients with synchronous involvement of DLBCL in both the periphery and the CNS pose a unique clinical challenge. Insights into the molecular circuitry of DLBCL have identified distinct genetic subtypes including cases with a predilection for CNS invasion. PCNSL and subsets of SCNSL are characterized by chronically activated B-cell receptor and NFκB signaling along with genetic evidence of immune evasion which may be exploited therapeutically. Improved mechanistic understanding of targetable pathways underpinning CNS lymphomas has led to numerous clinical trials testing targeted agent combinations and immunotherapy approaches with promising early results. Biologically rational strategies may further improve the cure rate of CNS lymphomas, either by overcoming intrinsic or acquired treatment resistance and/or by being broadly applicable to patients of all ages.

Primary testicular lymphoma demonstrates overexpression of the Wilms tumor 1 gene and different mRNA and miRNA expression profiles compared to nodal diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) shows a high degree of clinical and biological heterogeneity. Primary testicular lymphoma (PTL) is an extranodal variant of DLBCL associated with a higher risk of recurrence, including contralateral testicles and central nervous system sanctuary sites. Several molecular aberrations, including somatic mutation of MYD88, CD79B, and upregulation of NF-kB, PDL-1, and PDL-2, are thought to contribute to the pathogenesis and poor prognosis of PTL. However, additional biomarkers are needed that may improve the prognosis and help understand the PTL biology and lead to new therapeutic targets. RNA from diagnostic tissue biopsies of the PTL-ABC subtype and matched nodal DLBCL-ABC subtype patients was evaluated by mRNA and miRNA expression. Screening of 730 essential oncogenic genes was performed, and their epigenetic connections were examined using the nCounter PAN-cancer pathway, and Human miRNA assays with the nCounter System (NanoString Technologies). PTL and nodal DLBCL patients were comparable in age, gender, and putative cell of origin (p > 0.05). Wilms tumor 1 (WT1) expression in PTL exceeded that in nodal DLBCL (>6-fold; p = 0.01, FDR <0.01) and WT1 associated pathway genes THBS4, PTPN5, PLA2G2A, and IFNA17 were upregulated in PTL (>2.0-fold, p < 0.01, FDR <0.01). Additionally, miRNAs targeting WT1 (hsa15a-5p, hsa-miR-16-5p, has-miR-361-5p, has-miR-27b-3p, has-miR-199a-5p, has-miR-199b-5p, has-miR-132-3p, and hsa-miR-128-3p) showed higher expression in PTL compared to nodal DLBCL (≥2.0-fold; FDR 0.01). Lower expression of BMP7, LAMB3, GAS1, MMP7, and LAMC2 (>2.0-fold, p < 0.01) was observed in PTL compared to nodal DLBCL. This research revealed higher WT1 expression in PTL relative to nodal DLBCL, suggesting that a specific miRNA subset may target WT1 expression and impact the PI3k/Akt pathway in PTL. Further investigation is needed to explore WT1's biological role in PTL and its potential as a therapeutic target.

Resistance mechanisms of immune checkpoint inhibition in lymphoma: Focusing on the tumor microenvironment

Immune checkpoint inhibitors (ICIs) have revolutionized the therapeutic strategies of multiple types of malignancies including lymphoma. However, efficiency of ICIs varies dramatically among different lymphoma subtypes, and durable response can only be achieved in a minority of patients, thus requiring unveiling the underlying mechanisms of ICI resistance to optimize the individualized regimens and improve the treatment outcomes. Recently, accumulating evidence has identified potential prognostic factors for ICI therapy, including tumor mutation burden and tumor microenvironment (TME). Given the distinction between solid tumors and hematological malignancies in terms of TME, we here review the clinical updates of ICIs for lymphoma, and focus on the underlying mechanisms for resistance induced by TME, which play important roles in lymphoma and remarkably influence its sensitivity to ICIs. Particularly, we highlight the value of multiple cell populations (e.g., tumor infiltrating lymphocytes, M2 tumor-associated macrophages, and myeloid-derived suppressor cells) and metabolites (e.g., indoleamine 2, 3-dioxygenase and adenosine) in the TME as prognostic biomarkers for ICI response, and also underline additional potential targets in immunotherapy, such as EZH2, LAG-3, TIM-3, adenosine, and PI3Kδ/γ.

Understanding the Immune-Stroma Microenvironment in B Cell Malignancies for Effective Immunotherapy

Cancers, including lymphomas, develop in complex tissue environments where malignant cells actively promote the creation of a pro-tumoral niche that suppresses effective anti-tumor effector T cell responses. Research is revealing that the tumor microenvironment (TME) differs between different types of lymphoma, covering inflamed environments, as exemplified by Hodgkin lymphoma, to non-inflamed TMEs as seen in chronic lymphocytic leukemia (CLL) or diffuse-large B-cell lymphoma (DLBCL). In this review we consider how T cells and interferon-driven inflammatory signaling contribute to the regulation of anti-tumor immune responses, as well as sensitivity to anti-PD-1 immune checkpoint blockade immunotherapy. We discuss tumor intrinsic and extrinsic mechanisms critical to anti-tumor immune responses, as well as sensitivity to immunotherapies, before adding an additional layer of complexity within the TME: the immunoregulatory role of non-hematopoietic stromal cells that co-evolve with tumors. Studying the intricate interactions between the immune-stroma lymphoma TME should help to design next-generation immunotherapies and combination treatment strategies to overcome complex TME-driven immune suppression.

Utilizing cell-based therapeutics to overcome immune evasion in hematologic malignancies

Hematologic malignancies provide a suitable testing environment for cell-based immunotherapies, which were pioneered by the development of allogeneic hematopoietic stem cell transplant. All types of cell-based therapies, from donor lymphocyte infusion to dendritic cell vaccines, and adoptive transfer of tumor-specific cytotoxic T cells and natural killer cells, have been clinically translated for hematologic malignancies. The recent success of chimeric antigen receptor-modified T lymphocytes in B-cell malignancies has stimulated the development of this approach toward other hematologic tumors. Similarly, the remarkable activity of checkpoint inhibitors as single agents has created enthusiasm for potential combinations with other cell-based immune therapies. However, tumor cells continuously develop various strategies to evade their immune-mediated elimination. Meanwhile, the recruitment of immunosuppressive cells and the release of inhibitory factors contribute to the development of a tumor microenvironment that hampers the initiation of effective immune responses or blocks the functions of immune effector cells. Understanding how tumor cells escape from immune attack and favor immunosuppression is essential for the improvement of immune cell-based therapies and the development of rational combination approaches.

Targetable genetic features of primary testicular and primary central nervous system lymphomas

Primary central nervous system lymphomas (PCNSLs) and primary testicular lymphomas (PTLs) are extranodal large B-cell lymphomas (LBCLs) with inferior responses to current empiric treatment regimens. To identify targetable genetic features of PCNSL and PTL, we characterized their recurrent somatic mutations, chromosomal rearrangements, copy number alterations (CNAs), and associated driver genes, and compared these comprehensive genetic signatures to those of diffuse LBCL and primary mediastinal large B-cell lymphoma (PMBL). These studies identify unique combinations of genetic alterations in discrete LBCL subtypes and subtype-selective bases for targeted therapy. PCNSLs and PTLs frequently exhibit genomic instability, and near-uniform, often biallelic, CDKN2A loss with rare TP53 mutations. PCNSLs and PTLs also use multiple genetic mechanisms to target key genes and pathways and exhibit near-uniform oncogenic Toll-like receptor signaling as a result of MYD88 mutation and/or NFKBIZ amplification, frequent concurrent B-cell receptor pathway activation, and deregulation of BCL6. Of great interest, PCNSLs and PTLs also have frequent 9p24.1/PD-L1/PD-L2 CNAs and additional translocations of these loci, structural bases of immune evasion that are shared with PMBL.

Primary testicular lymphoma

Primary testicular lymphoma (PTL) is a rare, clinically aggressive form of extranodal lymphoma. The vast majority of cases are histologically diffuse large B-cell lymphoma, but rarer subtypes are clinically important and must be recognized. In this review, we discuss the incidence, clinical presentation, and prognostic factors of PTL and present a summary of the recent advances in our understanding of its pathophysiology, which may account for the characteristic clinical features. Although outcomes for patients with PTL have historically been poor, significant gains have been made with the successive addition of radiotherapy (RT), full-course anthracycline-based chemotherapy, rituximab and central nervous system–directed prophylaxis. We describe the larger retrospective series and prospective clinical trials and critically examine the role of RT. Although rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone given every 21 days with intrathecal methotrexate and locoregional RT is the current international standard of care, a substantial minority of patients progress, representing an unmet medical need. Finally, we discuss new treatment approaches and recent discoveries that may translate into improved outcomes for patients with PTL.

Partial plasma cell differentiation as a mechanism of lost major histocompatibility complex class II expression in diffuse large B-cell lymphoma

Loss of major histocompatibility complex class II (MHC II) expression is associated with poor patient outcome in diffuse large B-cell lymphoma (DLBCL). As MHC II molecules are lost with plasmacytic differentiation in normal cells, we asked whether MHC II loss in DLBCL is associated with an altered differentiation state. We used gene expression profiling, quantum dots, and immunohistochemistry to study the relationship between MHC II and plasma cell markers in DLBCL and plasmablastic lymphoma (PBL). Results demonstrate that MHC II(-) DLBCL immunophenotypically overlap with PBL and demonstrate an inverse correlation between MHC II and plasma cell markers MUM1, PRDM1/Blimp1, and XBP1s. In addition, MHC II expression is significantly higher in germinal center-DLBCL than activated B cell-DLBCL. A minor subset of cases with an unusual pattern of mislocalized punctate MHC II staining and intermediate levels of mRNA is also described. Finally, we show that PBL is negative for MHC II. The results imply a spectrum of MHC II expression that is more frequently diminished in tumors derived from B cells at the later stages of differentiation (with complete loss in PBL). Our observations provide a possible unifying concept that may contribute to the poor outcome reported in all MHC II(-) B-cell tumors.

The molecular pathogenesis of primary mediastinal large B-cell lymphoma

Primary mediastinal large B-cell lymphoma (PMBCL) is a recognized non-Hodgkin lymphoma entity with unique pathologic, clinical, and molecular characteristics distinct from those of other diffuse large B-cell lymphomas. Immunohistochemical characterization and molecular studies strongly suggest that PMBCL is of germinal center or postgerminal center origin. Pivotal gene expression profiling work defined major deregulated pathway activities that overlap with Hodgkin lymphoma and prompted a more detailed analysis of candidate genes. In particular, the nuclear factor-κB and the Janus Kinase-Signal Transducer and Activator of Transcription signaling pathways are targeted by multiple genomic hits, and constitutive activity of both pathways can be considered molecular hallmark alterations of PMBCL. Moreover, data are emerging giving unique insight into remodeling of the epigenome that affects transcriptional regulation of a multitude of genes. More recently, the tumor microenvironment of PMBCL has shifted into focus based on a number of gene perturbations altering expression of surface molecules that contribute to immune escape. These findings highlight the importance of immune privilege in the pathogenesis of PMBCL and suggest that disrupting crosstalk between the tumor cells and the microenvironment might be a rational new therapeutic target in conjunction with traditional treatment strategies.

Distribution patterns of dendritic cells and T cells in diffuse large B-cell lymphomas correlate with prognoses

PURPOSE

Diffuse large B-cell lymphoma (DLBCL), the most common subtype of non-Hodgkin's lymphomas, accounts for 30% to 40% of all lymphoma cases. However, long-term survival by current chemotherapy was achieved in only 40% of patients, warranting the development of novel therapeutic strategies including T-cell immunotherapy. However, the level of baseline immune activation in DLBCL is unclear.

EXPERIMENTAL DESIGN

The density and distribution of dendritic cells and T cells in 48 cases of primary DLBCL was evaluated by immunohistochemistry.

RESULTS

Increased numbers of intratumoral CD1a+ dendritic cells and increased S100+ cells and CD45RO+ T cells around the edges of the tumors were seen in 10 of 48 (21%), 9 of 48 (19%), and 10 of 48 (21%) cases and these were correlated with a favorable prognosis (P = 0.015; P = 0.070, and P = 0.017, respectively), along with increased granzyme B+ T cells in tumor beds (P = 0.013). Increased peritumoral T cells were correlated with tumor expression of HLA-DR (r = 0.446; P = 0.002). Extranodal lymphomas showed fewer tumor-associated CD45RO+ T cells (r = -0.407; P = 0.001) and less conspicuous dendritic cell infiltrates.

CONCLUSIONS

In DLBCL, the presence of baseline antitumor immune response is associated with favorable clinical outcome, and thus adjuvant T-cell immunotherapy may further boost treatment responses.

Mechanisms and effects of loss of human leukocyte antigen class II expression in immune-privileged site-associated B-cell lymphoma

PURPOSE AND EXPERIMENTAL DESIGN

Loss of human leukocyte antigen (HLA) expression on tumor cells is frequent in diffuse large B-cell lymphoma (DLBCL) arising in immune-privileged sites, such as the testis and central nervous system, and is associated with small homozygous deletions of HLA-DQ/HLA-DR and larger hemizygous deletions of the MHC region. To better understand the significance of down-regulation of HLA class II expression in relation to the homozygous and hemizygous deletions, we analyzed global gene expression patterns in a series of 26 testicular DLBCL after characterization of these deletions.

RESULTS

Low levels of HLA-DR mRNA in whole testicular DLBCL samples were associated with a strong down-regulation of numerous immune-related genes specific for T cells, macrophages, antigen presentation and processing, lymphocyte activation, chemokines and chemokine receptors, and the complement system. The number of CD3+ tumor-infiltrating T cells was also significantly lower in low expressors of HLA-DR mRNA. Interestingly, hemizygous and homozygous deletions in the MHC region did not have any additional effect on global gene expression.

CONCLUSION

In conclusion, we found that loss of HLA class II mRNA expression in testicular DLBCL is associated with a significant change in global gene expression patterns. This effect is independent of the mechanism causing the down-regulation of HLA class II genes in the lymphoma cells.

Patterns of outcome and prognostic factors in primary large-cell lymphoma of the testis in a survey by the International Extranodal Lymphoma Study Group

PURPOSE

To determine clinical features and patterns of outcome of primary testicular diffuse large B-cell lymphomas (DLCL).

PATIENTS AND METHODS

A retrospective international survey of 373 patients with primary testicular DLCL.

RESULTS

Most patients presented with localized disease (stage I to II), and the median age at diagnosis was 66 years (range, 19 to 91 years). Anthracycline-based chemotherapy was administered to 255 patients (68%), and prophylactic intrathecal chemotherapy was given to 68 patients (18%); 133 patients (36%) received prophylactic scrotal radiotherapy. Median overall survival was 4.8 years, and median progression-free survival was 4 years. The survival curves showed no clear evidence of a substantial proportion of cured patients. A favorable international prognostic index score (IPI), no B-symptoms, the use of anthracyclines, and prophylactic scrotal radiotherapy were significantly associated with longer survival at multivariate analysis. However, even for patients with stage I disease and good-risk IPI, the outcome seems worse than what was reported for DLCL at other sites. At a median follow-up of 7.6 years, 195 patients (52%) had relapsed. Extranodal recurrence was reported in 140 cases. Relapses in CNS were detected in 56 patients (15%) up to 10 years after presentation. A continuous risk of recurrence in the contralateral testis was seen in patients not receiving scrotal radiotherapy.

CONCLUSION

Testicular DLCL is characterized by a particularly high risk of extranodal relapse even in cases with localized disease at diagnosis. Anthracycline-based chemotherapy, CNS prophylaxis, and contralateral testicular irradiation seem to improve the outcome. Their efficacy is under evaluation in a prospective clinical trial.