Richter syndrome: novel insights into the biology of transformation.

Although the genetic landscape of chronic lymphocytic leukemia (CLL) has been broadly profiled by large-scale sequencing studies performed over the past decade, the molecular basis of the transformation of CLL into aggressive lymphoma, or Richter syndrome (RS), has remained incompletely characterized. Recent advances in computational methods of clonal deconvolution, as well as extensive sample collection efforts in this rapidly progressive malignancy, have now enabled comprehensive analysis of paired CLL and RS samples and have led to multiple new studies investigating the genetic, transcriptomic, and epigenetic origins of RS. In parallel, new genetically engineered and xenograft mouse models have provided the opportunity for gleaning fresh biological and mechanistic insights into RS development and stepwise evolution from antecedent CLL. Altogether, these studies have defined RS driver lesions and CLL risk lesions and identified pathways dysregulated in transformation. Moreover, unique molecular subtypes of RS have been revealed, including a disease marked by profound genomic instability with chromothripsis/chromoplexy and whole genome duplication. Novel profiling approaches, including single-cell DNA and transcriptome sequencing of RS biopsy specimens and cell-free DNA profiling of patient plasma, demonstrate promise for the timely identification of RS clones and may translate to noninvasive identification and early diagnosis of RS. This review summarizes the recent scientific advances in RS and supports the integrated study of human genomics with mouse modeling to provide an advanced understanding of the biological underpinnings of transformation. These recent studies have major implications for much-needed novel therapeutic strategies for this still largely incurable malignancy.

Venetoclax plus dose-adjusted R-EPOCH for Richter syndrome.

Richter syndrome (RS) of chronic lymphocytic leukemia (CLL) is typically chemoresistant, with a poor prognosis. We hypothesized that the oral Bcl-2 inhibitor venetoclax could sensitize RS to chemoimmunotherapy and improve outcomes. We conducted a single-arm, investigator-sponsored, phase 2 trial of venetoclax plus dose-adjusted rituximab, etoposide, prednisone, vincristine, cyclophosphamide, and doxorubicin (VR-EPOCH) to determine the rate of complete response (CR). Patients received R-EPOCH for 1 cycle, then after count recovery, accelerated daily venetoclax ramp-up to 400 mg, then VR-EPOCH for up to 5 more 21-day cycles. Responders received venetoclax maintenance or cellular therapy off-study. Twenty-six patients were treated, and 13 of 26 (50%) achieved CR, with 11 achieving undetectable bone marrow minimal residual disease for CLL. Three additional patients achieved partial response (overall response rate, 62%). Median progression-free survival was 10.1 months, and median overall survival was 19.6 months. Hematologic toxicity included grade ≥3 neutropenia (65%) and thrombocytopenia (50%), with febrile neutropenia in 38%. No patients experienced tumor lysis syndrome with daily venetoclax ramp-up. VR-EPOCH is active in RS, with deeper, more durable responses than historical regimens. Toxicities from intensive chemoimmunotherapy and venetoclax were observed. Our data suggest that studies comparing venetoclax with chemoimmunotherapy to chemoimmunotherapy alone are warranted. This trial was registered at www.clinicaltrials.gov as #NCT03054896.

A multi-cohort phase 1b trial of rituximab in combination with immunotherapy doublets in relapsed/refractory follicular lymphoma.

Antibodies targeting PD-1 or 4-1BB achieve objective responses in follicular lymphoma (FL), but only in a minority of patients. We hypothesized that targeting multiple immune receptors could overcome immune resistance and increase response rates in patients with relapsed/refractory FL. We therefore conducted a phase 1b trial testing time-limited therapy with different immunotherapy doublets targeting 4-1BB (utomilumab), OX-40 (ivuxolimab), and PD-L1 (avelumab) in combination with rituximab among patients with relapsed/refractory grade 1-3A FL. Patients were enrolled onto 2 of 3 planned cohorts (cohort 1 - rituximab/utomilumab/avelumab; cohort 2 - rituximab/ivuxolimab/utomilumab). 3+3 dose escalation was followed by dose expansion at the recommended phase 2 dose (RP2D). Twenty-four patients were enrolled (16 in cohort 1 and 9 in cohort 2, with one treated in both cohorts). No patients discontinued treatment due to adverse events and the RP2D was the highest dose level tested in both cohorts. In cohort 1, the objective and complete response rates were 44% and 19%, respectively (50% and 30%, respectively, at RP2D). In cohort 2, no responses were observed. The median progression-free survivals in cohorts 1 and 2 were 6.9 and 3.2 months, respectively. In cohort 1, higher density of PD-1+ tumor-infiltrating T-cells on baseline biopsies and lower density of 4-1BB+ and TIGIT+ T-cells in on-treatment biopsies were associated with response. Abundance of Akkermansia in stool samples was also associated with response. Our results support a possible role for 4-1BB agonist therapy in FL and suggest that features of the tumor microenvironment and stool microbiome may be associated with clinical outcomes (NCT03636503).

Hodgkin lymphoma arising in patients with chronic lymphocytic leukemia: outcomes from a large multi-center collaboration.

Chronic lymphocytic leukemia (CLL) patients who develop Hodgkin lymphoma (HL) have limited survival. No current therapeutic standard of care exists. We conducted a multi-center retrospective study of patients with Hodgkin Transformation (HT) of CLL. Clinicobiologic characteristics, treatment type, and survival outcomes were analyzed and compared with historic case series. Ninety-four patients were identified. Median age at HT was 67 years (range, 38-85). Median time from CLL diagnosis to HT was 5.5 years (range, 0-20.2). Prior to HT, patients received a median of 2 therapies for CLL (range, 0-12). As initial therapy for HT, 61% (n=62) received ABVD-based regimens (adriamycin, bleomycin, vinblastine, and dacarbazine). Seven (7%) patients received hematopoietic cell transplantation (HCT) while in first complete remission (CR1). The median number of treatments for HT per patient was 1 (range, 0-5) with 59 (61%) patients only receiving one line of therapy. After HT, patients had a median follow-up of 1.6 years (range, 0-15.1). Two-year overall survival (OS) after HT diagnosis was 72% (95%CI 62-83%). The patients who received standard ABVD-based therapy had a median OS of 13.2 years. Although limited by small sample size, the patients who underwent HCT for HT in CR1 had a similar 2-year OS (n=7; 67%) compared to patients who did not undergo HCT for HT in CR1 (n=87; 72%; p=0.46). In this multi-center study, HT patients treated with ABVD-based regimens had prolonged survival supporting the use of these regimens as standard of care for these patients.

The molecular map of CLL and Richter's syndrome.

Clonal expansion of B-cells, from the early stages of monoclonal B-cell lymphocytosis through to chronic lymphocytic leukemia (CLL), and then in some cases to Richter's syndrome (RS) provides a comprehensive model of cancer evolution, notable for the marked morphological transformation and distinct clinical phenotypes. High-throughput sequencing of large cohorts of patients and single-cell studies have generated a molecular map of CLL and more recently, of RS, yielding fundamental insights into these diseases and of clonal evolution. A selection of CLL driver genes have been functionally interrogated to yield novel insights into the biology of CLL. Such findings have the potential to impact patient care through risk stratification, treatment selection and drug discovery. However, this molecular map remains incomplete, with extant questions concerning the origin of the B-cell clone, the role of the TME, inter- and intra-compartmental heterogeneity and of therapeutic resistance mechanisms. Through the application of multi-modal single-cell technologies across tissues, disease states and clinical contexts, these questions can now be addressed with the answers holding great promise of generating translatable knowledge to improve patient care.

A multicenter study of venetoclax-based treatment for patients with Richter transformation of chronic lymphocytic leukemia.

ABSTRACT: Patients with chronic lymphocytic leukemia (CLL) who develop Richter transformation (RT) have a poor prognosis when treated with chemoimmunotherapy regimens used for de novo diffuse large B-cell lymphoma. Venetoclax, a BCL2 inhibitor, has single-agent efficacy in patients with RT and is potentially synergistic with chemoimmunotherapy. In this multicenter, retrospective study, we evaluated 62 patients with RT who received venetoclax-based treatment outside of a clinical trial, in combination with a Bruton tyrosine kinase inhibitor (BTKi; n=28), rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone (R-CHOP) (n=13), or intensive chemoimmunotherapy other than R-CHOP (n=21). The best overall and complete response rates were 36%/25%, 54%/46%, and 52%/38%, respectively. The median progression-free and overall survival estimates for the same treatment groups were 4.9/14.3 months, 14.9 months/not reached, and 3.3/9 months, respectively. CLL with del(17p) was associated with a lower complete response rate in the total cohort (odds ratio [OR] 0.15; 95% confidence interval [CI] 0.04-0.6; p=0.01) and venetoclax-naïve subgroup (OR 0.13; 95%CI 0.02-0.66; p=0.01). TP53 mutated CLL was associated with a lower complete response rate (OR 0.15; 95%CI 0.03-0.74; p=0.02) and shorter progression-free survival (hazard ratio 3.1; 95%CI 1.21-7.95; p=0.02) only in venetoclax-naïve subgroup. No other clinical or baseline characteristics, including prior venetoclax treatment for CLL, showed statistically significant association with outcomes. Grade 3-4 neutropenia and thrombocytopenia events were most frequent with intensive chemoimmunotherapy + venetoclax; grade 3-4 infection rates were similar across treatment groups. In this difficult-to-treat RT patient population, venetoclax-based combination regimens achieved high response rates, with durable remission and survival observed in a subset of patients.

Anti-CD19 Chimeric Antigen Receptor T-Cell Therapy for Richter Transformation: An International, Multicenter, Retrospective Study.

PURPOSE: Outcomes for Richter transformation (RT) are poor with current therapies. The efficacy and safety of anti-CD19 chimeric antigen receptor T-cell therapy (CAR-T) for RT are not established. METHODS: We performed an international multicenter retrospective study of patients with RT who received CAR-T. Patient, disease, and treatment characteristics were summarized using descriptive statistics, and modeling analyses were used to determine association with progression-free survival (PFS) and overall survival (OS). PFS and OS were estimated from the date of CAR-T infusion. RESULTS: Sixty-nine patients were identified. The median age at CAR-T infusion was 64 years (range, 27-80). Patients had a median of four (range, 1-15) previous lines of therapy for CLL and/or RT, including previous Bruton tyrosine kinase inhibitor and/or BCL2 inhibitor therapy in 58 (84%) patients. The CAR-T product administered was axicabtagene ciloleucel in 44 patients (64%), tisagenlecleucel in 17 patients (25%), lisocabtagene maraleucel in seven patients (10%), and brexucabtagene autoleucel in one patient (1%). Eleven patients (16%) and 25 patients (37%) experienced grade ≥3 cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome, respectively. The overall response rate was 63%, with 46% attaining a complete response (CR). After a median follow-up of 24 months, the median PFS was 4.7 months (95% CI, 2.0 to 6.9); the 2-year PFS was 29% (95% CI, 18 to 41). The median OS was 8.5 months (95% CI, 5.1 to 25.4); the 2-year OS was 38% (95% CI, 26 to 50). The median duration of response was 27.6 months (95% CI, 14.5 to not reached) for patients achieving CR. CONCLUSION: CAR-T demonstrates clinical efficacy for patients with RT.

Telomere phenotypes in females with heterozygous mutations in the dyskeratosis congenita 1 (DKC1) gene.

Dyskeratosis congenita (DC) is a telomere-mediated syndrome defined by mucocutaneous features. The X-linked mode of inheritance accounts for half the cases, and is thought to predominantly manifest in childhood as bone marrow failure. We identified two male probands who presented in the fifth decade with idiopathic pulmonary fibrosis and cancer. Their pedigrees displayed consecutively affected generations. Five of six females (83%) manifested mucocutaneous features of DC, and two had wound-healing complications. No mutations in autosomal dominant telomere genes were present, but exome sequencing revealed novel variants in the X-chromosome DKC1 gene that predicted missense mutations in conserved residues, p.Thr49Ser and p.Pro409Arg. Variants segregated with the telomere phenotype, and affected females were heterozygotes, showing skewed X-inactivation. Telomerase RNA levels were compromised in cells from DKC1 mutation carriers, consistent with their pathogenic role. These findings indicate that females with heterozygous DKC1 mutations may be at increased risk for developing penetrant telomere phenotypes that, at times, may be associated with clinical morbidity.

Syndrome complex of bone marrow failure and pulmonary fibrosis predicts germline defects in telomerase.

Mutations in the essential telomerase components hTERT and hTR cause dyskeratosis congenita, a bone marrow failure syndrome characterized by mucocutaneous features. Some (~ 3%) sporadic aplastic anemia (AA) and idiopathic pulmonary fibrosis cases also carry mutations in hTERT and hTR. Even though it can affect clinical outcome, because the mutation frequency is rare, genetic testing is not standard. We examined whether the cooccurrence of bone marrow failure and pulmonary fibrosis in the same individual or family enriches for the presence of a telomerase mutation. Ten consecutive individuals with a total of 36 family members who fulfilled these criteria carried a germline mutant telomerase gene (100%). The mean age of onset for individuals with AA was significantly younger than that for those with pulmonary fibrosis (14 vs 51; P < .0001). Families displayed autosomal dominant inheritance and there was an evolving pattern of genetic anticipation, with the older generation primarily affected by pulmonary fibrosis and successive generations by bone marrow failure. The cooccurrence of AA and pulmonary fibrosis in a single patient or family is highly predictive for the presence of a germline telomerase defect. This diagnosis affects the choice of bone marrow transplantation preparative regimen and can prevent morbidity.

DLBCL arising from indolent lymphomas: How are they different?

Transformation to diffuse large B-cell lymphoma (DLBCL) is a recognized, but unpredictable, clinical inflection point in the natural history of indolent lymphomas. Large retrospective studies highlight a wide variability in the incidence of transformation across the indolent lymphomas and the adverse outcomes associated with transformed lymphomas. Opportunities to dissect the biology of transformed indolent lymphomas have arisen with evolving technologies and unique tissue collections enabling a growing appreciation, particularly, of their genetic basis, how they relate to the preceding indolent lymphomas and the comparative biology with de novo DLBCL. This review summarizes our current understanding of both the clinical and biological aspects of transformed lymphomas and the outstanding questions that remain.

A phase 2 study of nivolumab combined with ibrutinib in patients with diffuse large B-cell Richter transformation of CLL.

Richter transformation (RT) is a rare complication of chronic lymphocytic leukemia (CLL) that has dismal outcomes. Upregulation of PD-1/PD-L1 drives immunological evasion in patients with RT. We hypothesized that combining nivolumab, a PD-1 blocking antibody, with the BTK inhibitor (BTKi) ibrutinib could potentiate tumor-cell killing. We conducted an investigator-initiated phase 2 clinical trial to assess the efficacy of combined nivolumab and ibrutinib in patients with diffuse large B-cell lymphoma (DLBCL) RT and CLL. Patients included were ≥18 years of age with adequate hepatic and renal function. Patients received nivolumab every 2 weeks of a 4-week cycle for a maximum of 24 cycles. A standard dose ibrutinib was initiated from cycle 2 onward and continued daily until progression. For patients who were already on ibrutinib at the time of study entry, the same was continued while nivolumab was initiated. A total of 24 patients with RT with a median age of 64.5 years (range, 47-88) were enrolled. Ten patients (42%) had received prior treatment for RT and 13 patients (54%) had received a prior BTKi. A total of 10 patients (42%) responded with a median duration of response of 15 months. The median overall survival was 13 months. Four of 24 (17%) patients had checkpoint inhibition-related immunological toxicities. In the CLL cohort, 10 patients were enrolled, of whom 3 patients converted from partial to complete remission; 1 patient had a grade 2 immunological toxicity. Combined nivolumab and ibrutinib is an active regimen for patients with DLBCL RT with an overall response rate of 42%. Given the limited treatment options for patients with RT, checkpoint inhibition provides a potential therapeutic option. This trial is registered at www.clinicaltrials.gov as #NCT02420912.

Interim Positron Emission Tomography During Frontline Chemoimmunotherapy for Follicular Lymphoma.

While most patients with follicular lymphoma (FL) have excellent outcomes with frontline chemoimmunotherapy (CIT), a subset of patients will experience early progression, which is associated with poor subsequent outcomes. Novel biomarkers are needed to identify high-risk patients earlier. We hypothesized that interim positron emission tomography (PET) would predict progression-free survival (PFS) in this population. We retrospectively identified 128 patients with grade 1-3A FL who had an interim PET after 2-4 cycles of frontline CIT at 2 academic centers. PET scans were analyzed using Deauville score (DS) and change in maximum standardized uptake value (ΔSUVmax). Interim PET DS was a significant predictor of PFS (P < 0.003). Patients with a DS of 3 had outcomes similar to those of patients with a DS of 4, so were categorized as PET-positive for additional analyses. Interim PET remained a strong predictor of PFS (DS 3-5, hazard ratio [HR] 2.4, P = 0.006) in a multivariable analysis and was also an early predictor of both a positive end-of-treatment PET (P < 0.001) and progression of disease within 24 months (POD24) (P = 0.006). An optimal ΔSUVmax cutoff of 75% was selected using the bootstrap method. ΔSUVmax <75% was also a significant predictor of PFS on univariable and multivariable analyses (HR 2.8, P < 0.003). In a separate cohort of 50 patients with high-grade FL, interim PET interpreted using either DS (P < 0.001) or ΔSUVmax75% (P = 0.034) was also a significant predictor of inferior PFS. In conclusion, interim PET is an independent predictor of PFS and may be useful as a tool for response-adapted treatment strategies in FL.

In Vivo Modeling of CLL Transformation to Richter Syndrome Reveals Convergent Evolutionary Paths and Therapeutic Vulnerabilities.

Transformation to aggressive disease histologies generates formidable clinical challenges across cancers, but biological insights remain few. We modeled the genetic heterogeneity of chronic lymphocytic leukemia (CLL) through multiplexed in vivo CRISPR-Cas9 B-cell editing of recurrent CLL loss-of-function drivers in mice and recapitulated the process of transformation from indolent CLL into large cell lymphoma [i.e., Richter syndrome (RS)]. Evolutionary trajectories of 64 mice carrying diverse combinatorial gene assortments revealed coselection of mutations in Trp53, Mga, and Chd2 and the dual impact of clonal Mga/Chd2 mutations on E2F/MYC and interferon signaling dysregulation. Comparative human and murine RS analyses demonstrated tonic PI3K signaling as a key feature of transformed disease, with constitutive activation of the AKT and S6 kinases, downmodulation of the PTEN phosphatase, and convergent activation of MYC/PI3K transcriptional programs underlying enhanced sensitivity to MYC/mTOR/PI3K inhibition. This robust experimental system presents a unique framework to study lymphoid biology and therapy. SIGNIFICANCE: Mouse models reflective of the genetic complexity and heterogeneity of human tumors remain few, including those able to recapitulate transformation to aggressive disease histologies. Herein, we model CLL transformation into RS through multiplexed in vivo gene editing, providing key insight into the pathophysiology and therapeutic vulnerabilities of transformed disease. This article is highlighted in the In This Issue feature, p. 101.

Minimal residual disease in patients with diffuse large B-cell lymphoma undergoing autologous stem cell transplantation.

Improved biomarkers are required to guide the optimal use of autologous stem cell transplantation (ASCT) in patients with relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL). We hypothesized that minimal residual disease (MRD) identified using immunoglobulin high-throughput sequencing in apheresis stem cell (ASC) samples, post-ASCT peripheral blood mononuclear cell (PBMC), and plasma samples could predict relapse. We studied 159 patients with R/R DLBCL who underwent ASCT, of whom 98 had an ASC sample and 60 had post-ASCT surveillance samples. After a median post-ASCT follow-up of 60 months, the 5-year progression-free survival (PFS) was 48%. MRD was detected in of 23/98 (23%) ASC samples and was associated with very poor PFS (5-year PFS 13% vs 53%, P < .001) and inferior overall survival (52% vs 68%, P = .05). The sensitivity and specificity of ASC MRD positivity for progression and death were 36% and 93%, respectively. Positive ASC MRD remained a significant predictor of PFS in multivariable analysis (hazard ratio [HR], 3.7; P < .001). Post-ASCT surveillance MRD testing of plasma, but not PBMC samples, reliably identified patients with an impending relapse. A positive plasma MRD result was associated with inferior PFS (HR, 3.0; P = .016) in a multivariable analysis. The median lead time from MRD detection to relapse was 62 days (range, 0-518 days). In conclusion, the detection of MRD in ASC samples is associated with a very high risk of relapse, justifying alternative treatment strategies or trials of novel consolidation options in these patients. Furthermore, post-ASCT MRD monitoring may facilitate the evaluation of the early initiation of treatment at molecular relapse. This trial has been registered at www.clinicaltrials.gov as #NCT02362997.

ZNF683 marks a CD8+ T cell population associated with anti-tumor immunity following anti-PD-1 therapy for Richter syndrome.

Unlike many other hematologic malignancies, Richter syndrome (RS), an aggressive B cell lymphoma originating from indolent chronic lymphocytic leukemia, is responsive to PD-1 blockade. To discover the determinants of response, we analyze single-cell transcriptome data generated from 17 bone marrow samples longitudinally collected from 6 patients with RS. Response is associated with intermediate exhausted CD8 effector/effector memory T cells marked by high expression of the transcription factor ZNF683, determined to be evolving from stem-like memory cells and divergent from terminally exhausted cells. This signature overlaps with that of tumor-infiltrating populations from anti-PD-1 responsive solid tumors. ZNF683 is found to directly target key T cell genes (TCF7, LMO2, CD69) and impact pathways of T cell cytotoxicity and activation. Analysis of pre-treatment peripheral blood from 10 independent patients with RS treated with anti-PD-1, as well as patients with solid tumors treated with anti-PD-1, supports an association of ZNF683high T cells with response.

Evolutionary history of transformation from chronic lymphocytic leukemia to Richter syndrome.

Richter syndrome (RS) arising from chronic lymphocytic leukemia (CLL) exemplifies an aggressive malignancy that develops from an indolent neoplasm. To decipher the genetics underlying this transformation, we computationally deconvoluted admixtures of CLL and RS cells from 52 patients with RS, evaluating paired CLL-RS whole-exome sequencing data. We discovered RS-specific somatic driver mutations (including IRF2BP2, SRSF1, B2M, DNMT3A and CCND3), recurrent copy-number alterations beyond del(9p21)(CDKN2A/B), whole-genome duplication and chromothripsis, which were confirmed in 45 independent RS cases and in an external set of RS whole genomes. Through unsupervised clustering, clonally related RS was largely distinct from diffuse large B cell lymphoma. We distinguished pathways that were dysregulated in RS versus CLL, and detected clonal evolution of transformation at single-cell resolution, identifying intermediate cell states. Our study defines distinct molecular subtypes of RS and highlights cell-free DNA analysis as a potential tool for early diagnosis and monitoring.

Short telomeres are sufficient to cause the degenerative defects associated with aging.

Telomerase function is critical for telomere maintenance. Mutations in telomerase components lead to telomere shortening and progressive bone marrow failure in the premature aging syndrome dyskeratosis congenita. Short telomeres are also acquired with aging, yet the role that they play in mediating age-related disease is not fully known. We generated wild-type mice that have short telomeres. In these mice, we identified hematopoietic and immune defects that resembled those present in dyskeratosis congenita patients. When mice with short telomeres were interbred, telomere length was only incrementally restored, and even several generations later, wild-type mice with short telomeres still displayed degenerative defects. Our findings implicate telomere length as a unique heritable trait that, when short, is sufficient to mediate the degenerative defects of aging, even when telomerase is wild-type.

Decreased dyskerin levels as a mechanism of telomere shortening in X-linked dyskeratosis congenita.

Dyskeratosis congenita (DC) is a premature ageing syndrome characterised by short telomeres. An X-linked form of DC is caused by mutations in DKC1 which encodes dyskerin, a telomerase component that is essential for telomerase RNA stability. However, mutations in DKC1 are identifiable in only half of X-linked DC families. A four generation family with pulmonary fibrosis and features of DC was identified. Affected males showed the classic mucocutaneous features of DC and died prematurely from pulmonary fibrosis. Although there were no coding sequence or splicing variants, genome wide linkage analysis of 16 individuals across four generations identified significant linkage at the DKC1 locus, and was accompanied by reduced dyskerin protein levels in affected males. Decreased dyskerin levels were associated with compromised telomerase RNA levels and very short telomeres. These data identify decreased dyskerin levels as a novel mechanism of DC, and indicate that intact dyskerin levels, in the absence of coding mutations, are critical for telomerase RNA stability and for in vivo telomere maintenance.