Higher-order connections between stereotyped subsets: implications for improved patient classification in CLL.

Chronic lymphocytic leukemia (CLL) is characterized by the existence of subsets of patients with (quasi)identical, stereotyped B-cell receptor (BcR) immunoglobulins. Patients in certain major stereotyped subsets often display remarkably consistent clinicobiological profiles, suggesting that the study of BcR immunoglobulin stereotypy in CLL has important implications for understanding disease pathophysiology and refining clinical decision-making. Nevertheless, several issues remain open, especially pertaining to the actual frequency of BcR immunoglobulin stereotypy and major subsets, as well as the existence of higher-order connections between individual subsets. To address these issues, we investigated clonotypic IGHV-IGHD-IGHJ gene rearrangements in a series of 29 856 patients with CLL, by far the largest series worldwide. We report that the stereotyped fraction of CLL peaks at 41% of the entire cohort and that all 19 previously identified major subsets retained their relative size and ranking, while 10 new ones emerged; overall, major stereotyped subsets had a cumulative frequency of 13.5%. Higher-level relationships were evident between subsets, particularly for major stereotyped subsets with unmutated IGHV genes (U-CLL), for which close relations with other subsets, termed "satellites," were identified. Satellite subsets accounted for 3% of the entire cohort. These results confirm our previous notion that major subsets can be robustly identified and are consistent in relative size, hence representing distinct disease variants amenable to compartmentalized research with the potential of overcoming the pronounced heterogeneity of CLL. Furthermore, the existence of satellite subsets reveals a novel aspect of repertoire restriction with implications for refined molecular classification of CLL.

Clonal evolution in chronic lymphocytic leukemia is associated with an unmutated IGHV status and frequently leads to a combination of loss of TP53 and TP53 mutation.

BACKGROUND: Chromosomal abnormalities and gene mutations determine the prognosis of patients with chronic lymphocytic leukemia (CLL). Genetic lesions can be acquired by clonal evolution (CE) likely correlating with clinical progression. METHODS AND RESULTS: Samples of 169 CLL patients were analyzed for cytogenetic clonal evolution (CCE) and CE affecting the genes TP53 and SF3B1. Moreover, the mutational status of IGHV and the clinical outcome was evaluated. CCE was observed in 35% of CLL patients. The most frequently gained cytogenetic aberration was a deletion of TP53. Acquired TP53 deletion was more frequent in patients with SF3B1 mutations compared to those without (19% vs. 7%). CCE showed a tendency to occur more frequently in patients with an aberrant karyotype at first investigation than in patients with a normal karyotype. In 73% of patients with CCE (p = 0.002) and 92% of patients with CE affecting the genes TP53 and SF3B1 (p < 0.001) an unmutated IGHV status was present. CCE and CE affecting the genes TP53 and SF3B1 were significantly associated with each other (p < 0.001). In 7% of patients, CE resulted in the co-occurrence of TP53 deletion and TP53 mutation resulting in a significantly shorter overall survival. CONCLUSIONS: The most frequently gained cytogenetic aberration during CCE was a deletion of TP53, which was associated with SF3B1 mutations. Moreover, CCE was associated with an unmutated IGHV status. Our results indicate the importance of re-evaluation of the TP53 status during the course of the disease to ensure correct treatment guidance.

Cytogenetic complexity in chronic lymphocytic leukemia: definitions, associations, and clinical impact.

Recent evidence suggests that complex karyotype (CK) defined by the presence of ≥3 chromosomal aberrations (structural and/or numerical) identified by using chromosome-banding analysis (CBA) may be relevant for treatment decision-making in chronic lymphocytic leukemia (CLL). However, many challenges toward the routine clinical application of CBA remain. In a retrospective study of 5290 patients with available CBA data, we explored both clinicobiological associations and the clinical impact of CK in CLL. We found that patients with ≥5 abnormalities, defined as high-CK, exhibit uniformly dismal clinical outcomes, independently of clinical stage, TP53 aberrations (deletion of chromosome 17p and/or TP53 mutations [TP53abs]), and the expression of somatically hypermutated (M-CLL) or unmutated immunoglobulin heavy variable genes. Thus, they contrasted with CK cases with 3 or 4 aberrations (low-CK and intermediate-CK, respectively) who followed aggressive disease courses only in the presence of TP53abs. At the other end of the spectrum, patients with CK and +12,+19 displayed an exceptionally indolent profile. Building upon CK, TP53abs, and immunoglobulin heavy variable gene somatic hypermutation status, we propose a novel hierarchical model in which patients with high-CK exhibit the worst prognosis, whereas those with mutated CLL lacking CK or TP53abs, as well as CK with +12,+19, show the longest overall survival. Thus, CK should not be axiomatically considered unfavorable in CLL, representing a heterogeneous group with variable clinical behavior. High-CK with ≥5 chromosomal aberrations emerges as prognostically adverse, independent of other biomarkers. Prospective clinical validation is warranted before ultimately incorporating high-CK in risk stratification of CLL.

Tailored approaches grounded on immunogenetic features for refined prognostication in chronic lymphocytic leukemia.

Chronic lymphocytic leukemia (CLL) patients with differential somatic hypermutation status of the immunoglobulin heavy variable genes, namely mutated or unmutated, display fundamental clinico-biological differences. Considering this, we assessed prognosis separately within mutated (M-CLL) and unmutated (U-CLL) CLL in 3015 patients, hypothesizing that the relative significance of relevant indicators may differ between these two categories. Within Binet A M-CLL patients, besides TP53 abnormalities, trisomy 12 and stereotyped subset #2 membership were equivalently associated with the shortest time-to-first-treatment and a treatment probability at five and ten years after diagnosis of 40% and 55%, respectively; the remaining cases exhibited 5-year and 10-year treatment probability of 12% and 25%, respectively. Within Binet A U-CLL patients, besides TP53 abnormalities, del(11q) and/or SF3B1 mutations were associated with the shortest time-to-first-treatment (5- and 10-year treatment probability: 78% and 98%, respectively); in the remaining cases, males had a significantly worse prognosis than females. In conclusion, the relative weight of indicators that can accurately risk stratify early-stage CLL patients differs depending on the somatic hypermutation status of the immunoglobulin heavy variable genes of each patient. This finding highlights the fact that compartmentalized approaches based on immunogenetic features are necessary to refine and tailor prognostication in CLL.

Identification of prognostic parameters in CLL with no abnormalities detected by chromosome banding and FISH analyses.

Chronic Lymphocytic Leukaemia (CLL) is a heterogeneous disease with a clinical course dependent on cytogenetic features. However, in 15-20% of cases both chromosome banding and fluorescence in situ hybridisation analyses do not show any kind of abnormality. With the aim to identify dependable molecular prognostic factors in this subgroup, we performed a comprehensive analysis on 171 patients including genomic arrays (comparative genomic hybridisation and single nucleotide polymorphism), immunoglobulin heavy chain variable region genes (IGHV) status, flow cytometry and targeted sequencing. Genomic arrays detected 73 aberrations in 39 patients (23%). Most frequently, patients had 1 aberration (25/171; 15%), while 14 patients (8%) had at least 2 aberrations. IGHV status was unmutated in 53/171 (31%) patients. SF3B1 was the most frequently mutated gene (26/171 patients; 15%), followed by NOTCH1 (15/171; 9%). At univariate analysis, an adverse impact on time to treatment (TTT) was evident for SF3B1 mutations, higher white blood cell count, higher CLL cells percentage by flow cytometry, CD38 positivity, IGHV unmutated status and at least 2 genomic array abnormalities. Of these, SF3B1 mutations, CLL cells percentage, IGHV unmutated status and number of genomic array aberrations maintained their impact in multivariate analysis. In conclusion, by integrating genomic and molecular data, we identified patients at higher risk for treatment need.

Gain of chromosome 21 or amplification of chromosome arm 21q is one mechanism for increased ERG expression in acute myeloid leukemia.

In acute myeloid leukemia (AML), acquired genomic gains and losses are common and lead to altered expression of genes located within or nearby the affected regions. Increased expression of the ETS-related transcription factor gene ERG has been described in myeloid malignancies with chromosomal rearrangements involving chromosome band 21q22, but also in cytogenetically normal AML, where it is associated with adverse prognosis. In this study, fluorescence in situ hybridization on interphase nuclei disclosed an amplification of the ERG gene (more than six copies) in 33 AML patients with structural rearrangements of 21q22. Array comparative genomic hybridization of these cases disclosed a minimal amplified region at the position 39.6-40.0 Mbp from pter that harbors ERG as the only gene. Analysis by quantitative real-time reverse transcription polymerase chain reaction revealed significantly higher ERG mRNA expression in these patients and in a group of 95 AML patients with complete or partial gain of chromosome 21 (three to six copies) compared with 351 AML patients without gain of chromosome 21. Quantification of ERG DNA copy numbers revealed a strong correlation with ERG mRNA expression. Furthermore, in patients with gain of chromosome 21, higher ERG expression was found to be associated with RUNX1 mutations. Our results suggest that acquired gain of chromosome 21 or amplification of chromosome arm 21q is one mechanism contributing to increased ERG expression in AML.

Investigation of 305 patients with myelodysplastic syndromes and 20q deletion for associated cytogenetic and molecular genetic lesions and their prognostic impact.

In patients with myelodysplastic syndromes (MDS), sole 20q deletion [del(20q)] is a recurrent favourable abnormality. We studied additional molecular and cytogenetic lesions and their prognostic impact in 305 MDS patients with del(20q) (229 males/76 females; 29-90 years). All patients were investigated by cytomorphology and chromosome banding analysis (CBA), subsets by fluorescence in situ hybridization, molecular mutation screening, and array comparative genomic hybridization (aCGH). By aCGH (n = 30), the minimal common deleted region (CDR) was flanked by PTPRT (20q13·11) and EYA2 (20q13·12). 210 (68·9%) patients had 'early MDS' without blast increase, 95 (31·1%) 'advanced' MDS with blast increase (5-19%). Additional chromosomal abnormalities (ACAs) were detected in 88/305 (28·9%) patients. Patients with advanced MDS more frequently had ACAs (P = 0·003) and had a higher mean number of ACAs (P = 0·020) and of molecular mutations (P = 0·060). Spliceosome mutations were frequent (U2AF1: n = 31/155; 20·0%; SRSF2: n = 31/159; 19·5%; SF3B1mut: n = 8/159; 5·0%). ASXL1mut (25/153; 16·3%) were associated with advanced MDS (P = 0·001). Presence of ≥3 ACAs (P = 0·003) and ASXL1mut (P = 0·002) were associated with worse 2-year survival. In conclusion, the cytogenetic subgroup of MDS with del(20q) has a good prognosis but may be further subclassified by additional cytogenetic and molecular lesions. U2AF1mut is overrepresented in MDS with del(20q), and ASXL1mut is prognostically adverse.

T cell receptor gene repertoire profiles in subgroups of patients with chronic lymphocytic leukemia bearing distinct genomic aberrations.

Background: Microenvironmental interactions of the malignant clone with T cells are critical throughout the natural history of chronic lymphocytic leukemia (CLL). Indeed, clonal expansions of T cells and shared clonotypes exist between different CLL patients, strongly implying clonal selection by antigens. Moreover, immunogenic neoepitopes have been isolated from the clonotypic B cell receptor immunoglobulin sequences, offering a rationale for immunotherapeutic approaches. Here, we interrogated the T cell receptor (TR) gene repertoire of CLL patients with different genomic aberration profiles aiming to identify unique signatures that would point towards an additional source of immunogenic neoepitopes for T cells. Experimental design: TR gene repertoire profiling using next generation sequencing in groups of patients with CLL carrying one of the following copy-number aberrations (CNAs): del(11q), del(17p), del(13q), trisomy 12, or gene mutations in TP53 or NOTCH1. Results: Oligoclonal expansions were found in all patients with distinct recurrent genomic aberrations; these were more pronounced in cases bearing CNAs, particularly trisomy 12, rather than gene mutations. Shared clonotypes were found both within and across groups, which appeared to be CLL-biased based on extensive comparisons against TR databases from various entities. Moreover, in silico analysis identified TR clonotypes with high binding affinity to neoepitopes predicted to arise from TP53 and NOTCH1 mutations. Conclusions: Distinct TR repertoire profiles were identified in groups of patients with CLL bearing different genomic aberrations, alluding to distinct selection processes. Abnormal protein expression and gene dosage effects associated with recurrent genomic aberrations likely represent a relevant source of CLL-specific selecting antigens.

Indeterminate and oncogenic potential: CHIP vs CHOP mutations in AML with NPM1 alteration.

In AML patients, recurrent mutations were shown to persist in remission, however, only some have a prognostic value and persistent mutations might therefore reflect a re-established premalignant state or truly active disease causing relapse. We aimed to dissect the nature of co-mutations in NPM1 mutated AML where the detection of NPM1 transcripts allows highly specific and sensitive detection of complete molecular remission (CMR). We analysed 150 consecutive patients who achieved CMR following intensive treatment by next generation sequencing on paired samples at diagnosis, CMR and relapse (38/150 patients). Patients with persistence or the acquisition of non-DTA (DNMT3A, TET2, ASXL1) mutations at CMR (23/150 patients, 15%) have a significantly worse prognosis (EFS HR = 2.7, p = 0.003; OS HR = 3.6, p = 0.012). Based on clonal evolution analysis of diagnostic, CMR and relapse samples, we redefine pre-malignant mutations and include IDH1, IDH2 and SRSF2 with the DTA genes in this newly defined group. Only the persistence or acquisition of CHOP-like (clonal hematopoiesis of oncogenic potential) mutations was significantly associated with an inferior outcome (EFS HR = 4.5, p = 0.0002; OS HR = 5.5, p = 0.002). Moreover, the detection of CHOP-like mutations at relapse was detrimental (HR = 4.5, p = 0.01). We confirmed these findings in a second independent whole genome sequencing cohort.

Prognostic relevance of RUNX1 mutations in T-cell acute lymphoblastic leukemia.

The runt-related transcription factor 1, RUNX1, is crucial in the development of myeloid and lymphoid cell lineages and has been reported to be mutated in myeloid malignancies in approximately 30% of cases. In this study, the mutational status of RUNX1 was investigated in 128 acute lymphoblastic leukemia patients. We detected a mutation rate of 18.3% (13 of 71) in patients with T-cell acute lymphoblastic leukemia, 3.8% (2 of 52) in patients with B-cell acute lymphoblastic leukemia and no mutation (0 of 5) in patients with natural killer cell leukemia, respectively. In T-cell acute lymphoblastic leukemia patients, RUNX1 mutations were significantly associated with higher age (P=0.017) and lower white blood cell count (P=0.038). Moreover, an inferior outcome was observed in the subgroup of early T-cell acute lymphoblastic leukemia patients carrying RUNX1 mutations for overall survival (P=0.043). In conclusion, RUNX1 mutations are an important novel biomarker for a comprehensive characterization of T-cell acute lymphoblastic leukemia with poor prognostic impact and have implications for use also in monitoring disease.

Cytogenetic and molecular genetic characterization of KMT2A-PTD positive acute myeloid leukemia in comparison to KMT2A-Rearranged acute myeloid leukemia.

To define the biological differences in acute myeloid leukaemia (AML) with KMT2A gene involvements and their prognostic impact, we compared 190 de novo AML patients at diagnosis, 95 harbouring KMT2A-rearrangement (KMT2Ar) and 95 KMT2A-PTD by performing cytogenetic and molecular genetic analyses. Both AML subtypes had an unfavourable outcome, particularly in patients > 60 years. Patients with KMT2Ar were younger compared to patients with KMT2A-PTD (mean 52 vs 65 years, p < 0.001) and had a higher rate of additional cytogenetic abnormalities (ACA) (46% vs 25% of cases). In both groups, occurrence of ACA did not influence the overall survival (OS). Regarding molecular genetics, 66% of patients with KMT2Ar and 99% of patients with KMT2A-PTD had additional gene mutations. In multivariate analysis, KRAS mutations and 10p12 rearrangement resulted as adverse prognostic factors in KMT2Ar subgroup. In the KMT2A-PTD group, apart from age, only the occurrence of DNMT3A non-R882 mutations correlated with shorter OS.

Molecular characterization of AML with RUNX1-RUNX1T1 at diagnosis and relapse reveals net loss of co-mutations.

AML with RUNX1-RUNX1T1 fusion is a WHO entity with a favorable outcome following intensive chemotherapy. The absence of RUNX1-RUNX1T1 transcripts in remission defines complete molecular response and correlates with a superior survival. However, a significant proportion of patients still relapses and defining molecular risk factors that identify patients at diagnosis or at molecular remission that are at risk of relapse could help tailor treatment strategies for those high risk patients. Here, we analyze a cohort of 94 patients that reach a molecular remission (MR) following intensive treatment and identify 21 patients that relapse despite achieving MR. Using targeted sequencing of 63 genes implicated in hematologic malignancies we show that at diagnosis patients who relapse following MR have a higher burden of co-mutated genes than patients that do not relapse (median = 2 vs median = 0; P = 0.0156). This resulted in a relapse free survival rate of 65% vs 86% at 2 years, respectively (≥1 co-mutation vs no co-mutation, P = 0.02) with a trend for inferior overall survival (n.s.). Applying sensitive sequencing to reassess mutations at relapse in paired samples of 17/21 patients we demonstrate a net loss of co-mutations at relapse: median 2 (range 0-5) vs 1 (0-4) at diagnosis and relapse (P = 0.048). At relapse more patients had no detected co-mutation compared to diagnosis (47% vs 17%, P = 0.034). Co-mutations at diagnosis, therefore, might represent a general susceptibility of the AML clone to acquire mutations and the true nature of 2nd hit mutations that drive leukemia has to be defined for AML with RUNX1-RUNX1T1 fusion.

NPM1 mutated AML can relapse with wild-type NPM1: persistent clonal hematopoiesis can drive relapse.

Acute myeloid leukemia (AML) with NPM1 mutation (NPM1 mut) defines a World Health Organization entity. Absence of minimal residual disease (MRD) following induction chemotherapy is associated with an excellent prognosis. Data are conflicting on NPM1 mut AML relapsing with wild-type NPM1 (NPM1 wt ). We analyzed 104 paired samples of NPM1 mut AML patients with relapse and identified 14/104 that relapsed with NPM1 wt AML. Blood counts at diagnosis differed significantly between patients with NPM1 mut and NPM1 wt relapse (median white blood cell count, 30 vs 3 × 109/L, P = .008; platelet count, 66 vs 128 × 109/l, P = .018). NPM1 mut relapse occurred significantly earlier than NPM1 wt relapse (14 vs 43 months, P = .004). At diagnosis, FLT3-ITD were more frequent in patients with NPM1 mut relapse (P = .029), whereas DNMT3A mutations were more frequent in patients with NPM1 wt relapse (P = .035). Sequencing analysis of paired samples at diagnosis, molecular remission, and NPM1 wt relapse identified cooccurring mutations that persist from diagnosis throughout remission and at relapse, suggestive of a preexisting clonal hematopoiesis. We provide evidence that AML relapsing with NPM1 wt is a distinct disease and that initial leukemia and relapse potentially arise from a premalignant clonal hematopoiesis.