A diagnostic challenge-First case of chronic lymphatic leukemia-associated necrotizing sweet syndrome

Sweet syndrome, also known as acute febrile neutrophilic dermatosis, is a rare disorder typically characterized by the clinical triad including a sudden onset of fever, painful skin lesions, and neutrophilia. The histopathological findings are a dense neutrophilic infiltrate and oedema of the dermis and epidermis without evidence of a vasculitis. Besides treatment of the underlying cause, sweet syndrome is typically treated with high-dose corticosteroids leading to a relapse-free response in 70% of patients. However, if left unrecognized or untreated, the condition may lead to serious complications. Here, we report on the case of a 38-year-old patient in whom, under the assumption of the presence of necrotizing fasciitis, exarticulation of the right arm was performed. In the absence of pathogen detection and insufficient response to anti-infective therapies, the diagnosis of a sweet syndrome was assumed and, later, confirmed by an excellent response to high-dose administration of systematic glucocorticoids. The case emphasizes the need to be aware of this rare syndrome, which can be easily misdiagnosed due to its close resemblance to infection and stresses the need of further research to define distinct diagnostic tools.

Distinct Genetically Determined Origins of Myd88/BCL2-Driven Aggressive Lymphoma Rationalize Targeted Therapeutic Intervention Strategies

Genomic profiling revealed the identity of at least 5 subtypes of diffuse large B-cell lymphoma (DLBCL), including the MCD/C5 cluster characterized by aberrations in MYD88, BCL2, PRDM1, and/or SPIB. We generated mouse models harboring B cell-specific Prdm1 or Spib aberrations on the background of oncogenic Myd88 and Bcl2 lesions. We deployed whole-exome sequencing, transcriptome, flow-cytometry, and mass cytometry analyses to demonstrate that Prdm1- or Spib-altered lymphomas display molecular features consistent with prememory B cells and light-zone B cells, whereas lymphomas lacking these alterations were enriched for late light-zone and plasmablast-associated gene sets. Consistent with the phenotypic evidence for increased B cell receptor signaling activity in Prdm1-altered lymphomas, we demonstrate that combined BTK/BCL2 inhibition displays therapeutic activity in mice and in five of six relapsed/refractory DLBCL patients. Moreover, Prdm1-altered lymphomas were immunogenic upon transplantation into immuno-competent hosts, displayed an actionable PD-L1 surface expression, and were sensitive to antimurine-CD19-CAR-T cell therapy, in vivo.

SIGNIFICANCE

Relapsed/refractory DLBCL remains a major medical challenge, and most of these patients succumb to their disease. Here, we generated mouse models, faithfully recapitulating the biology of MYD88-driven human DLBCL. These models revealed robust preclinical activity of combined BTK/BCL2 inhibition. We confirmed activity of this regimen in pretreated non-GCB-DLBCL patients. See related commentary by Leveille et al., p. 8. This article is highlighted in the In This Issue feature, p. 1.

Deregulation and epigenetic modification of BCL2-family genes cause resistance to venetoclax in hematologic malignancies

The BCL2 inhibitor venetoclax has been approved to treat different hematological malignancies. Because there is no common genetic alteration causing resistance to venetoclax in chronic lymphocytic leukemia (CLL) and B-cell lymphoma, we asked if epigenetic events might be involved in venetoclax resistance. Therefore, we employed whole-exome sequencing, methylated DNA immunoprecipitation sequencing, and genome-wide clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 screening to investigate venetoclax resistance in aggressive lymphoma and high-risk CLL patients. We identified a regulatory CpG island within the PUMA promoter that is methylated upon venetoclax treatment, mediating PUMA downregulation on transcript and protein level. PUMA expression and sensitivity toward venetoclax can be restored by inhibition of methyltransferases. We can demonstrate that loss of PUMA results in metabolic reprogramming with higher oxidative phosphorylation and adenosine triphosphate production, resembling the metabolic phenotype that is seen upon venetoclax resistance. Although PUMA loss is specific for acquired venetoclax resistance but not for acquired MCL1 resistance and is not seen in CLL patients after chemotherapy-resistance, BAX is essential for sensitivity toward both venetoclax and MCL1 inhibition. As we found loss of BAX in Richter's syndrome patients after venetoclax failure, we defined BAX-mediated apoptosis to be critical for drug resistance but not for disease progression of CLL into aggressive diffuse large B-cell lymphoma in vivo. A compound screen revealed TRAIL-mediated apoptosis as a target to overcome BAX deficiency. Furthermore, antibody or CAR T cells eliminated venetoclax resistant lymphoma cells, paving a clinically applicable way to overcome venetoclax resistance.

An Autochthonous Mouse Model of Myd88- and BCL2-Driven Diffuse Large B-cell Lymphoma Reveals Actionable Molecular Vulnerabilities

Based on gene expression profiles, diffuse large B cell lymphoma (DLBCL) is sub-divided into germinal center B cell-like (GCB) and activated B cell-like (ABC) DLBCL. Two of the most common genomic aberrations in ABC-DLBCL are mutations in MYD88, as well as BCL2 copy number gains. Here, we employ immune phenotyping, RNA-Seq and whole exome sequencing to characterize a Myd88 and Bcl2-driven mouse model of ABC-DLBCL. We show that this model resembles features of human ABC-DLBCL. We further demonstrate an actionable dependence of our murine ABC-DLBCL model on BCL2. This BCL2 dependence was also detectable in human ABC-DLBCL cell lines. Moreover, human ABC-DLBCLs displayed increased PD-L1 expression, compared to GCB-DLBCL. In vivo experiments in our ABC-DLBCL model showed that combined venetoclax and RMP1-14 significantly increased the overall survival of lymphoma bearing animals, indicating that this combination may be a viable option for selected human ABC-DLBCL cases harboring MYD88 and BCL2 aberrations.

New murine models of aggressive lymphoma

Diffuse large B cell lymphoma (DLBCL) is the most common type of aggressive lymphoma and has traditionally been subdivided into germinal center B cell-like and activated B cell-like DLBCL, using transcriptome profiling. The recent characterization of the genomic landscape of DLBCL revealed the identity of at least five molecularly-defined subclusters of DLBCL. Intriguingly, these different clusters display a different response to frontline, anthracycline-based chemo-immune therapy. Moreover, multiple, potentially actionable genomic aberrations have been identified in these clusters, including EZH2, CREBBP/EP300, and KMT2D mutations, BCL2 overexpression, PTEN inactivation, CD274 rearrangements and others. With this genomic understanding, it is possible to develop autochthonous mouse models, which capture this genomic complexity. These models can serve as pre-clinical platforms to devise molecularly targeted therapeutic intervention strategies. Here, we review the available mouse models of aggressive lymphoma and indicate which compound-mutant mice may be desirable tools to further advance the field of translational lymphoma research.