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

Abstract

Genomic profiling revealed the identity of at least 5 subtypes of 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- and mass cytometry analyses to demonstrate that Prdm1- or Spib-altered lymphomas display molecular features consistent with pre-memory 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 out 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 anti-murine-CD19-CAR-T cell therapy, in vivo.

An inducible Cd79b mutation confers ibrutinib sensitivity in mouse models of Myd88-driven diffuse large B-cell lymphoma

“…We previously described murine models of human C5/MCD DLBCL that are driven by B-cell–specific expression of Myd88 p.L252P ( Myd88 c.-p.L252P [ M] , orthologous position of the human MYD88 p.L265P mutation), conditional overexpression of BCL2 from the Rosa26 locus ( Rosa26 LSL.BCL2.IRES.GFP [ B] ), and homozygous deletion of Prdm1 ( Prdm1 fl/fl [ PP] ). 18 , 19 , 20 B-cell specificity was achieved through the use of a Cd19 Cre allele ( C ).…”

“…To assess the effects of introducing a B-cell–specific Cd79b ITAM mutation into the MBC and PPMBC models, 18 , 19 , 20 we generated 79-MBC and 79-PPMBC mice. These animals were born at expected Mendelian ratios and displayed an overall survival (OS) that was indistinguishable from the MBC and PPMBC parental strains ( Figure 1 A-B).…”

“…The generation of the Myd88 cond.p.L252P and Rosa26 LSL.BCL2-IRES-GFP alleles has been described previously. 18 , 19 , 20 The Prdm1 flox and Cd19 Cre alleles were purchased from The Jackson Laboratory. 22 , 23 …”

“…Treatment studies were performed as described previously. 18 In brief, animals were defined as lymphoma-bearing as soon as a lesion >150 μL or splenomegaly >500 μL and a robust volume increase were detectable by magnetic resonance imaging (MRI) in 2 consecutive scans. After lymphoma diagnosis, ibrutinib (MedChem Tronica) was administered daily by oral gavage for 3 weeks as a suspension in 0.4% methylcellulose at 30 mg/kg body weight, then via drinking water until death.…”

“…We previously reported the generation of mouse models of Myd88 -driven DLBCL. 18 , 19 , 20 These models were constructed through the combination of B-cell–specific expression of oncogenic Myd88 and BCL2 together with the deletion of Prdm1 or overexpression of Spib . Although these models, specifically the Cd19 Cre /wt ; Myd88 c.-p.L252P/wt ; Rosa26 LSL.BCL2.IRES.GFP/wt ; Prdm1 fl/fl model, captured central transcriptomic and surface marker features of C5/MCD DLBCL, they lacked co-occurring Cd79b mutations, which significantly cocluster with M YD 88 p.L265P in human C5 DLBCL.…”