ALBERT

Description: The prognosis of chronic lymphocytic leukemia (CLL) depends on different markers, including cytogenetic aberrations, oncogenic mutations, and mutational status of the immunoglobulin (Ig) heavy-chain variable (IGHV) gene. The number of IGHV mutations distinguishes mutated (M) CLL with a markedly superior prognosis from unmutated (UM) CLL cases. In addition, B cell antigen receptor (BCR) stereotypes as defined by IGHV usage and complementarity-determining regions (CDRs) classify ∼30% of CLL cases into prognostically important subsets. Subset 2 expresses a BCR with the combination of IGHV3-21–derived heavy chains (HCs) with IGLV3-21–derived light chains (LCs), and is associated with an unfavorable prognosis. Importantly, the subset 2 LC carries a single-point mutation, termed R110, at the junction between the variable and constant LC regions. By analyzing 4 independent clinical cohorts through BCR sequencing and by immunophenotyping with antibodies specifically recognizing wild-type IGLV3-21 and R110-mutated IGLV3-21 (IGLV3-21R110), we show that IGLV3-21R110–expressing CLL represents a distinct subset with poor prognosis independent of IGHV mutations. Compared with other alleles, only IGLV3-21*01 facilitates effective homotypic BCR–BCR interaction that results in autonomous, oncogenic BCR signaling after acquiring R110 as a single-point mutation. Presumably, this mutation acts as a standalone driver that transforms IGLV3-21*01–expressing B cells to develop CLL. Thus, we propose to expand the conventional definition of CLL subset 2 to subset 2L by including all IGLV3-21R110–expressing CLL cases regardless of IGHV mutational status. Moreover, the generation of monoclonal antibodies recognizing IGLV3-21 or mutated IGLV3-21R110 facilitates the recognition of B cells carrying this mutation in CLL patients or healthy donors.

Description: Chronic lymphocytic leukemia (CLL) is characterized by the existence of subsets of patients with (quasi)identical, stereotyped B cell receptor immunoglobulins (BcR IG). Patients in certain major stereotyped subsets often display remarkably consistent clinicobiological profiles, suggesting that the study of BcR IG 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 IG stereotypy and major subsets, as well as the existence of higher-order connections between individual subsets. In order 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.

Description: Chronic lymphocytic leukemia (CLL) is preceded by monoclonal B cell lymphocytosis (MBL), characterized by the presence of monoclonal CLL-like B cells in the peripheral blood, yet at lower numbers than those required for the diagnosis of CLL. MBL is distinguished into low-count (LC-MBL) and high-count (HC-MBL), based on the number of circulating CLL-like cells. While the former does not virtually progress into a clinically relevant disease, the latter may evolve into CLL at a rate of 1% per year. In CLL, genomic studies have led to the discovery of recurrent gene mutations that drive disease progression. These driver mutations may be detected in HC-MBL and even in multipotent hematopoietic progenitor cells from CLL patients, suggesting that they may be essential for CLL onset. Using whole-genome sequencing (WGS) we profiled LC-MBL and HC-MBL cases but also CLL patients with stable lymphocytosis (range: 39.8-81.8*109 CLL cells/l) for 〉10 years (hereafter termed indolent CLL). This would refine our understanding of the type of genetic aberrations that may be involved in the initial transformation rather than linked to clinical progression as is the case for most, if not all, CLL driver mutations. To this end, we whole-genome sequenced CD19+CD5+CD20dim cells from 6 LC-MBL, 5 HC-MBL and 5 indolent CLL cases; buccal control DNA and polymorphonuclear (PMN) cells were analysed in all cases. We also performed targeted deep-sequencing on 11 known driver genes (ATM, BIRC3, MYD88, NOTCH1, SF3B1, TP53, EGR2, POT1, NFKBIE, XPO1, FBXW7) in 8 LC-MBL, 13 HC-MBL and 7 indolent CLL cases and paired PMN samples. Overall similar mutation signatures/frequencies were observed for LC/HC-MBL and CLL concerning i) the entire genome; with an average of 2040 somatic mutations observed for LC-MBL, 2558 for HC-MBL and 2400 for CLL (186 for PMN samples), as well as ii) in the exome; with an average of non-synonymous mutations of 8.9 for LC-MBL, 14.6 for HC-MBL, 11.6 for indolent CLL (0.9 for PMN samples). Regarding putative CLL driver genes, WGS analysis revealed only 2 somatic mutations within NOTCH1, and FBXW7 in one HC-MBL case each. After stringent filtering, 106 non-coding variants (NCVs) of potential relevance to CLL were identified in all MBL/CLL samples and 4 NCVs in 2/24 PMN samples. Seventy-two of 110 NCVs (65.5%) caused a potential breaking event in transcription factor binding motifs (TFBM). Of these, 29 concerned cancer-associated genes, including BTG2, BCL6 and BIRC3 (4, 2 and 2 samples, respectively), while 16 concerned genes implicated in pathways critical for CLL e.g. the NF-κB and spliceosome pathways. Shared mutations between MBL/CLL and their paired PMN samples were identified in all cases: 2 mutations were located within exons, whereas an average of 15.8 mutations/case for LC-MBL, 8.2 for HC-MBL and 9 for CLL, respectively, concerned the non-coding part. Finally, 16 sCNAs were identified in 9 MBL/CLL samples; of the Döhner model aberrations, only del(13q) was detected in 7/9 cases bearing sCNAs (2 LC-MBL, 3 HC-MBL, 2 indolent CLL). Targeted deep-sequencing analysis (coverage 3000x) confirmed the 2 variants detected by WGS, i.e. in NOTCH1 (n=1) and FBXW7 (n=1), while 4 subclonal likely damaging variants were detected with a VAF 10 years display similar low genomic complexity and absence of exonic driver mutations, assessed both with WGS and deep-sequencing, underscoring their common low propensity to progress. On the other hand, HC-MBL comprising cases that may ultimately evolve into clinically relevant CLL can acquire exonic driver mutations associated with more dismal prognosis, as exemplified by subclonal driver mutations detected by deep-sequenicng. The existence of NCVs in TFBMs targeting pathways critical for CLL prompts further investigation into their actual relevance to the clinical behavior. Shared mutations between CLL and PMN cells indicate that some somatic mutations may occur before CLL onset, likely at the hematopoietic stem-cell level. Their potential oncogenic role likely depends on the cellular context and/or microenvironmental stimuli to which the affected cells are exposed. Disclosures Stamatopoulos: Novartis: Honoraria, Research Funding; Janssen: Honoraria, Other: Travel expenses, Research Funding; Gilead: Consultancy, Honoraria, Research Funding; Abbvie: Honoraria, Other: Travel expenses. Ghia:Adaptive: Consultancy; Gilead: Consultancy, Honoraria, Research Funding, Speakers Bureau; Abbvie: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Speakers Bureau; Roche: Honoraria, Research Funding.

Description: The IGHV4-34 gene is very frequent (~10%) in the B cell receptor immunoglobulin (BcR IG) gene repertoire of chronic lymphocytic leukemia (CLL). Over 30% of IGHV4-34 CLL cases can be assigned to different subsets with stereotyped BcR IG. The largest is subset #4 which represents ~1% of all CLL and ~10% of IGHV4-34 CLL and is considered a prototype for indolent disease. The BcR IG of a great majority (~85%) of IGHV4-34 CLL cases carry a significant load of somatic hypermutation (SHM), often with distinctive SHM patterns. This holds especially true for stereotyped subsets and is suggestive of particular modes of interactions with the selecting antigen(s). In detail, subsets #4 and #16, both involving IgG-switched cases (IgG-CLL), exhibit the greatest sequence similarity in SHM profiles, whereas they differ in this respect from IgM/D subsets #29 and #201. Prompted by these observations, here we explored the extent that these subset-biased SHM profiles in different IGHV4-34 stereotyped subsets were reflected in distinct demographics, clinical presentation, genomic aberrations and outcomes. Within a multi-institutional series of 20,331 CLL patients, 1790 (8.8%) expressed IGHV4-34 BcR IG. Following established bioinformatics approaches for the identification of BcR IG stereotypy, 573/1790 IGHV4-34 CLL cases (32%) were assigned to stereotyped subsets; of these, 340 cases (19% of all IGHV4-34 CLL and 60% of stereotyped IGHV4-34 cases) belonged to subsets #4, #16, #29 and #201, all concerning IGHV-mutated CLL (M-CLL). Clinicobiological information was available for 275/340 patients: #4, n=150; #16, n=44; #29, n=39; and #201, n=42. Comparisons between subsets revealed no differences in gender and age distribution. Interestingly, however, 36-43% of each subset cases were young for CLL (defined as patients aged ≤55 years), which is higher compared to general CLL cohorts, where young patients generally account for ~25% of cases. In contrast, significant differences were identified between subsets regarding: (i) disease stage at diagnosis, with 〉90% of IgG subsets #4 and #16 diagnosed at Binet stage A versus 83% in subset #201 and 74% in subset #29 (p=0.029); (ii) CD38 expression, ranging from 1% in subset #4 to 10% in subset #201 (p=0.013); (iii) the distribution of del(13q), peaking at a remarkable 92% in subset #29 versus only 37% in subset #16 (p

Description: Key Points Low-count and high-count monoclonal B-cell lymphocytosis (MBL) have distinct immunogenetic signatures, with only the latter resembling CLL. Rather than a true premalignant condition, low-count MBL may merely reflect immune senescence or result from persistent antigen stimulation.

Description: Immunoglobulin (IG) G-switched chronic lymphocytic leukemia (G-CLL) is highly enriched for 3 stereotyped CLL subsets, utilizing either the IGHV4-34 gene, namely mutated subsets #4 and #16, or the IGHV4-39 gene, namely unmutated subset #8. These subsets, collectively accounting for ~30% of all G-CLL, are not represented within the common IgM/D variant, thus prompting speculations about distinct ontogenetic origin and/or immune triggering, as well as raising questions regarding the timing of class-switch recombination (CSR) in relation to malignant transformation. Considering the above, we sought to investigate the potential existence of B cells expressing clonotypic mu transcripts within the bulk of IgG-switched CLL cells in cases assigned to the aforementioned subsets. Using high-throughput next-generation sequencing (NGS, MiSeq Illumina), we interrogated the IgM+ B-cell repertoire of CLL subset #4 (n=8), subset #16 (n=1) and subset #8 (n=2) for the presence of clonotypic mu transcripts. PCR amplicons were generated from cDNA using a set of IGHV4/IGHM primers. The paired-end Illumina protocol allowed sequencing of the complementarity determining region 3 (CDR3) twice/read, thus increasing the accuracy of results. For 3/8 subset #4 cases multiple blood samples of the same time point were analyzed as reproducibility controls. A purpose-built bioinformatics algorithm was developed for raw NGS data processing, which included: (i) quality filtering of reads; (ii) merging of paired-end reads via local alignment; (iii) preparation of filtered-in fasta sequences for submission to the IMGT/HighV-QUEST tool; and, (iv) IMGT/HighV-QUEST metadata mining for subset-specific B-cell receptor (BcR) IG rearrangements. Subset-specific CDR3 motifs were defined according to established criteria. Overall, 7,125,958 IGHV-IGHD-IGHJ-IGHC rearrangements (189,988-673,835/sample) were included in the search for stereotyped motifs, corresponding to 1,056,967 distinct clonotypes (i.e. BcR IG rearrangements with a particular IGHV gene and amino acid CDR3 sequence) (7,163-123,276/sample, median=76,109). Regarding subset #4, 7/8 cases exhibited mu transcripts of subset #4-specific IG rearrangements ("subset #4 M-clonotypes"); by definition, these rearrangements utilized the IGHV4-34/IGHJ6 genes and had identical CDR3 length (20 amino acids), however their CDR3 amino acid composition varied (2-75 distinct subset #4 M-clonotypes/sample, median=8). In 5/7 cases these subset #4 M-clonotypes were characterized by CDR3s that were identical and/or highly similar (≤2 amino acid differences, ≥ 90% identity) to the CDR3 of the IgG-switched CLL clone. The M-clonotypes expressing CDR3s identical to those of the IgG-switched CLL clone represented the most expanded subset #4 M-clonotype within the sample, while the less expanded, "satellite" clonotypes may represent subclones that were selected against due to lower affinity with the driving antigen. The possibility that these “satellite” clonotypes derive from PCR and/or sequencing error cannot be a priori excluded, however replicate sample analysis produced identical subset #4 M-clonotypes in all cases tested, thus raising confidence in the accuracy of the data. Analysis of the subset #16 case yielded similar results, i.e. 2 subset #16 M-clonotypes, one of which was identical to the IgG-switched clonotypic BcR IG. Both subset #8 cases also carried subset #8 M-clonotypes, yet only one case exhibited an M-clonotype with a CDR3 identical to that of the respective G-CLL clone. Interestingly, this M-clonotype was accompanied by many highly similar, less expanded “satellite” clonotypes (n=109), raising the possibility that SHM may be occurring in (pre-)CLL clones carrying truly unmutated IGHV genes, but pass unnoticed due to negative selection. Although their actual frequency cannot be conclusively determined due to the inherent limitations of PCR-based NGS analysis, subset-specific rearrangements represented a very minor fraction of the sequenced IGHV4/IGHM clonotypes in all cases tested (median frequency 0.04%). Overall, our findings suggest that while CLL clones are primed prior to CSR for malignant transformation on the basis of their BcR IG features, G-CLL quickly transits through CSR either because full-blown malignant transformation occurs at a later time point, or because CSR offers a selective advantage to the malignant clone. Disclosures No relevant conflicts of interest to declare.

Description: Chronic idiopathic neutropenia (CIN) is an acquired disorder of granulopoiesis characterized by prolonged neutropenia, mainly affecting middle-age females of the HLA-DRB1*1302 type. The defective hematopoiesis in CIN can be mainly attributed to accelerated Fas-mediated death of the CD34+/CD33+ granulocytic progenitors, secondary to an inflammatory bone marrow (BM) microenvironment. Crucial to CIN pathogenesis are the increased numbers of activated T cells identified in both peripheral blood (PB) and BM of CIN patients, supporting an immune pathogenesis. Using Sanger sequencing, we previously reported that the T-cell receptor (TR) gene repertoire in CIN is skewed, indicating antigen selection in CIN ontogeny. However, the analytical depth afforded by Sanger sequencing is limited, hindering definitive conclusions. In order to obtain a truly comprehensive view into the role of antigen drive in CIN, using next generation sequencing (NGS) we interrogated the TR repertoire of 13 patients (8 females, 5 males) included in our previous study as well as a healthy female. TRBV-TRBD-TRBJ gene rearrangements were amplified according to the BIOMED2 protocol on either genomic DNA or cDNA isolated from CD8+ cells of PB (n=4) or BM (n=10) samples. PCR products were used as a substrate for paired-end sample preparation (Illumina) and subjected to NGS on the MiSeq Illumina Platform. The raw NGS data were preprocessed with a dedicated pipeline for this purpose, including: (i) quality filtering of each read; (ii) merging of paired-end reads via local alignment; (iii) preparation of fasta files for submission to the IMGT/High V-QUEST tool; and, (iv) IMGT/High V-QUEST metadata analysis, interpretation and visualization. Overall, 6,196,980 TRBV-TRBD-TRBJ gene rearrangements were analyzed (130,020-1,037,680 /case) of which 5,317,609 were productive since they used functional TRBV genes and also carried in-frame CDR3. Rearrangements with identical TRBV gene usage and CDR3 sequence were defined as clonotypes. For repertoire analyses, clonotypes rather than single rearrangement sequences were considered. Overall, 553,145 unique clonotypes were identified (median 39,510; range 7,732-172,253/case), of which 408,744 represented singletons. All clonotypes from the Sanger analysis were detected by NGS as well. Among the 46 functional TRBV genes identified, the most frequent were: TRBV29-1 (13.9%), TRBV19 (6.7%), TRBV12-3 (5.6%), TRBV6-5 (5.4%), TRBV27 (4.9%) and TRBV6-1 (4.0%), collectively accounting for 40,5% of the TRBV repertoire; the TRBV29-1 gene predominated in 9/13 CIN cases. All CIN cases were found to carry distinct expanded clonotypes (median 10,314; range 2,279-40,245/case). The predominant clonotype ranged in frequency from 5.25 to 20.2% of the total clonotypes observed in each case. This contrasts significantly (p

Description: Abstract 536 Introduction: Mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL) are B-cell malignancies of different postulated origin, genetics, clinical presentation and prognosis. Several studies have reported that both MCL and CLL individually exhibit aberrant methylation in comparison to normal B-cells. However, a comprehensive comparison of the methylation profiles of these two B-cell disorders has not been performed yet. This strategy has the potential to identify cellular pathways and genes that are specifically targeted in each disease. Methods: We applied the genome-wide Illumina Infinium HumanMethylation27 BeadChip array (Illumina, San Diego, USA) which measures methylation levels at 27,578 CpG dinucleotides covering 14,495 genes, to compare the methylation profiles in: (i) 20 MCL cases; and, (ii) 30 CLL cases, 15 each with unmutated stereotyped subset #1 (IGHV1-5-7/IGKV1(D)-39) B cell receptors (BCRs) or mutated stereotyped subset #4 (IGHV4-34/IGKV2-30) BCRs, where these two subsets represent prototypes of unmutated and mutated CLL. The methylation status for each detected CpG site ranged between 0.1 (completely unmethylated) to 1 (completely methylated). Results: As expected, major differences in methylation patterns between MCL and CLL were observed. When the methylation profiles of the two entities were compared, 51 genes were identified as differentially methylated in all comparisons (MCL versus both CLL subsets combined and each subset separately). Among the 19 genes highly methylated in MCL were six (32%) homeobox or homeodomain-containing transcription factors (e.g. POU4F1, PITX3), whereas genes enhancing cell proliferation and tumor progression such as MERTK and CAMP were hypomethylated in MCL. Of the 32 genes hypermethylated in CLL were six pro-apoptotic genes, including DYRK2 and CYFIP2, the tumor suppressor PRDM2 and the cell cycle regulator CCND1. Conclusions: We report for the first time disease-biased methylation profiles for different functional classes of genes in MCL or CLL. Homeobox genes were highly methylated in MCL, whereas CLL was characterized by methylation of apoptosis-related genes. The identified differences in global methylation profiles between MCL and CLL may assist in unfolding distinct epigenetic silencing mechanisms involved in the pathogenesis of these B-cell malignancies. Disclosures: No relevant conflicts of interest to declare.

Description: Immunoglobulin heavy chain variable gene (IGHV) replacement or "VH replacement" (VHR) modifies a rearranged IGHV-D-J sequence by replacing the original IGHV gene with another. This process leaves a detectible "footprint" at the IGHV-D junction of the existing sequence. Roughly 33% of chronic lymphocytic leukemia (CLL) cases exhibit stereotyped B cell receptors (BCRs) often characterized by signature VH CDR3 amino acids. Various mechanisms have been put forth to account for stereotypy in CLL. An overarching hypothesis is that the stereotyped BCRs are antigen driven. Within this concept, a variety of mechanisms could lead to the signatures including somatic mutations and addition/deletion of nucleotides at junctional regions. Here we explore the possibility that VHR provides another mechanism to account for some of the stereotyped rearrangements and some of their signature VH CDR3 amino acid residues in CLL. We examined IG sequences of 26,642 CLL cases and ~16 million healthy controls (HC) to find relic footprints as indicators of VHR. This was done using the VHRFA program developed by Lin Huang et al (PLoS ONE, 2013), as well as our own program which duplicates the VHRFA results but is better able to process large numbers of sequences. The frequency of VHR was similar in CLL and HC (11.6 and 11.9%, respectively). Focusing solely on CLL sequences to define a relationship between VHR and stereotypy, we found highly significant differences in VHR frequencies between stereotyped (n=8,568) and non-stereotyped cases (n=18,074), with stereotyped cases exhibiting VHR at a greatly reduced frequency (7.7% vs. 13.5%, respectively). When comparing VHR frequencies between stereotyped cases and non-stereotyped cases that used the same IGHV, we found that the number of subsets with low VHR exceeded those with elevated VHR ~2:1, accounting for the overall VHR in stereotyped cases being lower than non-stereotyped cases. Further restricting comparisons of stereotyped subsets to non-stereotyped cohorts by matching VH CDR3 length led to similar conclusions. Within stereotyped cases there was a wide distribution of VHR, ranging from 55.6% to 0.1%. Restricting VH CDR3 lengths to "short" (5 - ≤13), "medium" (13.1 - ≤20) and "long" (20.1 - ≤28), the corresponding VHR increased monotonically with length (1.1, 8.2, and 11.9% respectively). Notably, subsets showing elevated VH replacement included better prognosis subsets, #4, 77 and 201 (23.8, 22.1, and 28.6%, respectively). Among low VHR frequency subsets were those associated with worse prognosis, #1, 2, 5, 6, 8, 9 and 10 (VHR frequencies: 0.2, 0.1, 0.9, 2.3, 7.7, 9.0 %, respectively). This was most strikingly exhibited by subsets #1 and #2, both of which comprise patients with poor clinical courses. Each of these sets of sequences displayed virtually no examples of VHR (0.2 and 0.1%, respectively). This might be predicted because these two subsets have relatively short VH CDR3 lengths (subset #1: 13 aa; subset #2: 9 aa), based on the length association mentioned above. Detailed analyses of the presence of footprints and the position of these in the rearranged IGHV-D-J indicated that for some subsets, certain signature VH CDR3 amino acids could be the result of VHR. For example in subset #201, sequence analysis suggests that VHR is responsible for an arginine and for a glutamine in the 5' portion of the VH CDR3. Similarly, VHR may craft the characteristic glutamine on the 5' end of the subset #6 VH CDR3. Thus, our studies indicate that, as a whole, CLL IGHV-D-J sequences use VHR at a frequency comparable to that of normal B cells and significantly less than that of non-stereotyped rearrangements. However, certain stereotyped cases are dramatically enriched for evidence of VHR. Moreover among these cases, the footprints found in the VH CDR3s of stereotyped cases can be shown to directly code for signature amino acids in VH CDR3s. Finally, stereotyped cases with high levels of VHR tend to be those with better clinical courses, whereas those worse outcome stereotyped cases exhibit less evidence for this process. This latter finding is consistent with the concept that VHR is one of the molecular mechanisms used by developing B cells to edit BCRs having high affinity for autoantigens. Since many CLL BCRs are autoreactive, including those found to have high levels of VHR such as subset #4, this implies a fundamental defect in tolerance mechanisms in those normal B cells that eventually became leukemic. Disclosures Agathangelidis: Gilead: Research Funding. Hadzidimitriou:Janssen: Honoraria, Research Funding; Gilead: Research Funding; Abbvie: Research Funding. Ghia:AbbVie, Inc: Honoraria, Research Funding; Acerta: Honoraria, Research Funding; BeiGene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Gilead: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Sunesis: Honoraria, Research Funding. Stamatopoulos:Gilead: Honoraria, Research Funding; Abbvie: Honoraria, Research Funding; Janssen: Honoraria, Research Funding. Chiorazzi:AR Pharma: Equity Ownership; Janssen, Inc: Consultancy.