ALBERT

Description: CLL develops from a small fraction of dividing monoclonal CD5+ B cells. The size and rate of growth of this proliferative fraction (PF) correlates inversely with time-to-first-treatment and directly with poor outcome prognostic markers. Furthermore, since the dividing cells upregulate DNA mutators such as AID and APOBEC family members, the PF has a greater propensity for acquiring new DNA abnormalities that can lead to more lethal disease. Hence, cells of the PF are important targets for therapy for patients with worst outcome category. The PF (CXCR4DimCD5Bright) differs by more than 1000 genes from the resting fraction (RF, CXCR4Bright CD5Dim); these genes relate to replication, migration, and regulation of gene expression. Some of these genes are also preferentially expressed in the PF of U-CLL cases. One such gene is Musashi 2 (MSI2). MSI2 regulates gene expression by binding consensus sequences of mRNA and blocking protein translation. High MSI2 expression is involved in proliferation of normal and malignant stem cells, tumorigenesis, and poor outcome. In CLL, high MSI2 mRNA expression has been identified in patients with worse prognosis. Nevertheless, nothing is known about the function of MSI2 in CLL cells. Therefore, we report studies of the biological role of MSI2 in B-CLL cells and its possible association with B-cell proliferation and CLL disease progression. First, we evaluated MSI2 protein levels by flow cytometry in CD19+CD5- and CD19+CD5+ cells from healthy donors (HDs; n=25) and in CD19+CD5+ from CLL patients (n=55). Higher MSI2 expression was observed in CLL than HD B cells, whereas no differences were found in CD19+CD5+ and CD19+CD5- cells from HDs. Also, MSI2 protein levels were higher in U-CLL than M-CLL, and M-CLL B cells express more MSI2 than HDs. Finally, MSI2 protein levels correlated with CD38, a CLL poor prognosis marker, suggesting MSI2 associates with poor prognosis in CLL. Within the leukemic clone, we observed 25% more MSI2 in the PF than the Int (defined as CXCR4intCD5int) and 15% more in the Int than the RF (PF〉Int 〉RF). The PF contains 40% more MSI2 than the RF, suggesting the highest amounts of MSI2 protein are in dividing and recently-divided cells. Since CLL B cell proliferation occurs in the microenvironment of lymphoid organs, presumably delivered by external signals, we tested whether such signals could stimulate MSI2 expression. Results indicate that CD40L+IL4 and Toll-like 9 stimulation plus IL15 (TLR9+IL5) increase MSI2 synthesis in vitro 1.4 and 1.8 fold, respectively. The increases are associated with the appearance of phospho ERK and AKT. Also, inhibition of AKT signaling by a PI3K inhibitor decreases MSI2 levels, suggesting AKT is involved in MSI2 synthesis. In this regard, signals from the microenvironment inducing cell growth and proliferation promote MSI2 synthesis in B cells from CLL patients. In addition, cells entering the cell cycle (Ki-67+ cells, those incorporating the thymidine analogue EdU, and cells in S, G2 and M cell cycle phases) express higher MSI2 levels than quiescent cells. Furthermore, dividing cells contain higher MSI2 levels than non-dividing cells as determined by CFSE dilution. These results suggest that cells entering the cell cycle or recently dividing have greater MSI2 expression. Since high MSI2 levels associate with cell proliferation and its inhibition is said to promote apoptosis, we studied the effect of MSI2 downregulation in the CLL MEC1 cell line to determine if MSI2 is a potential therapeutic target for CLL. Our findings show that siRNAs decrease MSI2 mRNA (80%) and protein (40%) levels compared to negative controls. Downregulation of MSI2 in MEC1 led to cleaved caspase 3, TRAIL R1 and R2, FADD, TNFR1, P21, P27, phosho-p53, and decreased levels of inhibitors of apoptosis such as cIAP2 and survivin. Hence these data suggest downregulation of MSI2 in CLL cells could induce apoptosis. Thus, MSI2 levels are higher in B cells from poor outcome patients and also in the dividing/divided cells of the PF before and after stimulation. Also, MSI's downregulation induces apoptosis of CLL cell line. Therefore, we propose that MSI2 is a valuable target for therapeutic intervention. Inhibiting its function and its role in cell proliferation will likely abort clonal evolution and disease progression, and make CLL an even more chronic and manageable condition. Disclosures No relevant conflicts of interest to declare.

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: 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.

Description: Lenalidomide (Revlimid®), a thalidomide analogue, is an orally administered second generation immunomodulator with anti-angiogenic and anti-neoplastic properties. Initial studies treating patients with chronic lymphocytic leukemia (CLL) suggest that lenalidomide can have considerable efficacy and that its mode of action is mainly indirect, affecting non-malignant cells in the microenvironment, in particular T lymphocytes. Because a recently described xenograft model for CLL has highlighted the importance of CLL-derived, autologous T cells in promoting leukemic B-cell engraftment and growth in vivo, we have studied the influence of lenalidomide on the expansion of CLL B- and T-lymphocytes in this model. After an initial 12 day culture of FACS-isolated CLL-derived T cells with or without anti-CD3/CD28 beads plus IL-2 (30 IU/ml), T lymphocytes were transferred into alymphoid NSG mice via the retro-orbital plexus (day 0). On day 7, CLL cells were delivered retro-orbitally. These recipient animals are referred to as “T + PBMC mice”. Mice that did not receive T cells on day 0 but were given CLL PBMCs at day 7, with or without lenalidomide, served as controls (“PBMC only mice”). Recipient mice received lenalidomide (10mg/kg/day) or vehicle control daily by gavage starting at day 0. All mice were sacrificed at day 28 (28 days after T-cell and 21 days after B-cell transfer), and blood, spleen, and bone marrow were collected. On this material, four analyses were performed: [1] level of human CD45+ cell engraftment; [2] numbers and types of CLL-derived T cells; [3] numbers of CLL B cells; and [4] levels of cytokines reflective of Th1 and Th2 immune responses. There was a clear enhancement in human hematopoietic (CD45+) cell engraftment in those mice exposed to lenalidomide. This was most marked for the PBMC only mice (vehicle: 10.64%; lenalidomide: 38.53%), although it was also evident for T + PBMC mice (vehicle: 55.96%; lenalidomide: 69.65%). T-cell phenotyping was carried out, before and after cell culture and also at sacrifice. Prior to culture, CLL samples contained on average ∼96% CD5+CD19+ cells and ∼3% CD5+CD19- cells; for the latter, ∼67% were CD4+ and ∼33% CD8+. After 12-day culture, these percentages remained largely unchanged. However, the numbers and types of T cells recovered from the spleens at sacrifice were quite different after in vivo exposure to lenalidomide. For the PBMC only, the percentages of CD4+ and CD8+ cells in the spleens differed somewhat based on lenalidomide exposure (CD4: Vehicle 86% vs. Lenalidomide 61%; CD8: Vehicle 10% vs. Lenalidomide 28%). However, this change was dramatic for the T + PBMC mice (CD4: Vehicle 64.1% vs. Lenalidomide 28.9%; CD8: Vehicle 34% vs. Lenalidomide 62%). Furthermore, when the CD8+ cells from these animals were subsetted based on antigen-experience and function, it appeared that lenalidomide exposure had led to the outgrowth of a greater number of effector memory (CD45RO+ CD62L-) than central memory (CD45RO+ CD62L+) T-cells. For CLL-derived B cells, the numbers differed, based not only on lenalidomide exposure but also on prior in vitro activation. Specifically, in PBMC only mice, the addition of lenalidomide led to increased numbers of CLL B cells in the spleen (Vehicle: 7.81% vs. Lenalidomide: 14%). Conversely, in the T + PBMC mice, the numbers of B cells decreased (Vehicle: 2.36% vs. Lenalidomide: 0.34%). An analysis of Th1 and Th2-related cytokines in the plasmas of the mice at sacrifice revealed a fall in IL-4, IL-5, and IL-10 and a marked increase in IFNg, consistent with a Th2 to Th1 transition. The above data suggest that administration of lenalidomide permits greater engraftment of human hematopoietic cells in alymphoid mice. Although this enhancement involves all members of the hematopoietic lineage, T cells, in particular CD8+ effector memory T cells, emerge in excess over time. This CD8 expansion is associated with diminished levels of CLL B cells suggesting that the decrease is due to T-cell mediated cytolysis. In contrast, in the absence of prior T-cell activation, CLL T cells appear to support better CLL B-cell growth. These findings suggest that lenalidomide alters B-cell expansion in vivo depending on the activation and differentiation state of the autologous T-cell compartment. They also implicate the generation of cytolytic T cells as one mechanism whereby lenalidomide leads to clinical improvement in CLL. Disclosures: Allen: Celgene Corporation: Honoraria.

Description: B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the progressive accumulation of mature B cells. The growth and accumulation of B-CLL cells requires survival and migratory signals from endogenously produced cytokines and chemokines, many of which are supplied by stromal cells. In this comparative study we analyzed the expression, as a function of B-CLL disease, of a set of inflammatory and immune cytokines and chemokines known to regulate the growth, survival and/or trafficking of B cells. Serum cytokines were measured in 87 B-CLL patients and in 32 healthy subjects using a combination of multiplex cytokine bead and protein array technologies. A subset of cytokines and chemokines were found to be significantly elevated in serum from B-CLL patients as compared to healthy age-matched controls: IL-17 (p

Description: The human IGHV4-34 gene encodes antibodies which are intrinsically autoreactive when the VH domain is unmutated. Therefore, B cells expressing IGHV4-34 B-cell receptor immunoglobulins (BcR IG) are normally under close scrutiny in order to avoid unwanted autoreactivity, especially against DNA. The IGHV4-34 gene is frequently utilized in chronic lymphocytic leukemia (CLL), where, typically, it shows a high load of somatic hypermutation (SHM). We have previously reported distinctive SHM patterns amongst IGHV4-34 CLL, especially for subsets with stereotyped BcR IG. However, although a large number of cases (~2000) was previously studied, since even the largest subsets account for only ~3% of CLL, meaningful conclusions could not be reached for smaller subsets. Here we revisit this issue in a series of 16,528 CLL cases and focus on IGHV4-34 expressing subsets: #4 (IGHV4-34/IGHD5-18/IGHJ6 | 156 cases, 0.9%); #11 (IGHV4-34/IGHD3-10/IGHJ4 | 16 cases, 0.1%); #16 (IGHV4-34/IGHD2-15/IGHJ6 | 41 cases, 0.25%); #29 (IGHV4-34/IGHD: unassignable/IGHJ3 | 39 cases, 0.24%); and #201 (IGHV4-34/IGHD: unassignable/IGHJ3 | 43 cases 0.26%). Focusing on codons 27-104 within the VH domain (from CDR1-IMGT to FR3-IMGT), we calculated the sequence distance between subsets and the corresponding IGHV4-34 germline sequence based on a pairwise qualitative and quantitative comparison of the respective amino acid composition. The minimum distance calculated, and hence the greatest identity, was observed between subsets #4 and #16, both concerning IgG-switched cases (IgG-CLL), which is notable given the overall rarity of IgG-CLL. In contrast, the maximum distance, implying the least identity, was between subsets #16 and #201, the latter concerning IgM/D-CLL. Extreme variations between subsets were noted in codons spanning the entire VH domain. This result is consistent with our finding of a subset-biased distribution of mutations over the VH domain. More specifically, while subsets #11, #16, #29 and #201 had a lower frequency of mutations within VH CDR1 compared to VH CDR2, the exact opposite was seen in subset #4, with 40% of mutations in VH CDR1 versus 27% in VH CDR2. In addition, subsets #4, #11, #16 and #29 had a similar distribution of mutations in VH FR2 and VH FR3, in contrast to subset #201 that showed a preference for VH FR3 over VH FR2. Consequently, we noted that certain positions were targeted in a subset-specific manner e.g. codon 28 in VH CDR1 was heavily targeted in subsets #4 (68.6%) and #16 (87.8%), with most cases carrying an acidic amino acid (AA) introduced by SHM, glycine to glutamic acid, G〉E: 51.3% for subset #4 and 78% for subset #16. The high prevalence of acidic AA introduced by SHM in these subsets is notable considering the electropositive nature of their VH CDR3 (especially of subset #4), strongly recalling edited anti-DNA antibodies. Interestingly, the G〉E change was identified at a much lower frequency in other IGHV4-34 subsets: 18.75% for subset #11; 2.6% for subset #29; 7% for subset #201, all of which carried electronegative VH CDR3. Further, we noted that certain positions were heavily targeted in all subsets e.g. 56-86% targeting for SHM at codon 92 in VH FR3 where serine is encoded by the agc triplet, the ”hottest of hotspots”. This result could be viewed as sequence- rather than subset-dependent and linked to the molecular features of this codon, which is supported by the low targeting of codon 93 (0-6%), also encoding serine by the tct triplet. Other positions were targeted in all subsets but at vastly different frequencies e.g. codon 64 was targeted in 37.8% in subset #4 rising to 100% in subset #29. Finally, positions heavily targeted by SHM in certain subsets were unmutated in other subsets e.g. codon 36 in VH CDR1 remained unmutated in subset #16, in contrast 76.9% of subset #29 were mutated at this position resulting in an AA change. In conclusion, we document different spectra of SHM and AA changes between stereotyped IGHV4-34 CLL subsets. The finding of subset-biased, recurrent AA changes at certain codons indicates that the respective progenitor cells may have responded in a specific manner to the selecting antigen(s), despite expressing the same IGHV gene, indicating a functional purpose for these modifications. This is exemplified by the molecular characteristics of the recurrent AA changes in subset #4, thereby offering interesting pathogenetic hints. Disclosures No relevant conflicts of interest to declare.

Description: Background. Chronic lymphocytic leukemia (CLL) is a prototypic microenvironment-dependent B-cell malignancy, in which neoplastic B cells co-evolve with a supportive tissue microenvironment to promote leukemia cell survival, growth, and drug-resistance. Within the microenvironment, hematopoietic and non-hematopoietic stromal and tumor cells produce factors that recruit circulating monocytes to tumor sites and induce differentiation into macrophages. Mirroring the Th1/Th2 paradigm, cells of monocyte-macrophage lineage reprogram their functions in response to environmental signals, undergoing M1 (classical) or M2 (alternative) activation, which represent extremes of a broad continuum of functional states. Classical M1 cells (activated by IFNs and TLR) are involved as inducer and effectors cells in polarized Th1 responses and as effectors of resistance against intracellular parasites and tumors. In contrast, M2 cells (activated by IL4 and IL13) are poor at antigen presentation, suppress Th1 adaptive immunity, actively scavenge debris, contribute to the dampening of inflammation, promote angiogenesis and tissue remodeling, and support tumor progression. One way to distinguish the two types of macrophages is based on surface antigen expression: M1-like cells up-regulate Fcg receptors I, II, III such as CD16, CD32 and CD64, whereas M2-like macrophages display abundant levels of CD23, CD163, and scavenger receptors (e.g. MCR1). Understanding the microenvironment and the crosstalk between B-CLL cells and their tissue neighbors can give insight into disease biology and for therapy. Aim. To investigate if the CLL milieu, contained within serum, influences monocyte-to-macrophage differentiation, promoting an anti (M2)- or pro (M1)- inflammatory microenvironment. Methods. Monocytes from healthy donors were isolated using Monocytes Isolation Kit II (Miltenyi) and cultured in Ultra-Low Attachment plates with 10% normal human AB serum or 10% CLL-derived serum -/+ IL4 or IFNg for 3 days. Macrophages were stained for CD23, CD64, CD32, MRC1, CD14, CD16, and data were acquired with a BD LSRII flow cytometer and analyzed by FlowJo V7.2.4 software. Results. Normal monocytes were differentiated to macrophages in vitro in the presence of sera from 24 untreated CLL patients with different prognostic factors (genomic aberrations, % CD38 and IGHVmutational status). About 45% of the CLL sera (N=10; 6 M-CLL, 4 U-CLL) drove macrophage maturation toward an M2-like phenotype, as assessed by surface expression of CD23, CD64, CD32, CD36, MRC1, etc. These 10 sera induced higher CD23 expression after 3 days in culture compared to AB human serum, whereas the levels of M1-specific markers (CD64 and CD32) did not change relative to the control. Interestingly all of these 10 CLL sera came from patients bearing 13q14 Δ (N=5), 17p13 Δ (N=3) or a combination of these (13q14 Δ + 17p13 Δ; N=1) and 17p13 Δ + trisomy12; N=1)). On the contrary, no increase in CD23 expression was detected in presence of sera from patients with 11q22 Δ (N=1) alone or in combination with 13q14 Δ (13q14 + 11q22 Δ; N=5). Of note, treatment with a neutralizing mAb specific for IL-4 did not block the CLL serum induced up-regulation of CD23 (N=2). In a parallel set of studies, normal monocytes were incubated with each of the 24 CLL sera in combination with the M1 promoting cytokine, IFNg or the M2 promoting cytokine, IL4. In all cases IL4 induced CD23 up-regulation and an M2 phenotype. Paradoxically, IFNg, which normally induces an M1 phenotype, also induced an M2 phenotype (i.e., enhanced CD23 expression) when co-cultured with sera from a subset patients (N=8; 6 M-CLL and 2 U-CLL). Of note, the IFNg stimulatory effect on CD23 expression was observed with a different set of sera from those that directly stimulated CD23 expression. Furthermore, CD64 expression did change after incubation with IFNg + CLL serum in 6 of 8 cases, yielding another unusual (CD23+CD64+) macrophage phenotype. The 2 sera that did not yield such hybrids were from M-CLL patients. Conclusions. Sera from CLL patients contain two apparently novel activities that mature normal monocytes to M2-like macrophages. The first acts directly by an action that is apparently independent of IL-4 and associates with 13q14 Δ or 17p13 Δ abnormalities. The second acts indirectly through IFNg and leads to macrophages with a hybrid M2/M1 phenotype (CD23+CD64+), suggestive of a new type of macrophage. Disclosures No relevant conflicts of interest to declare.

Description: Abstract 288 BACKGROUND. Chronic lymphocytic leukemia (CLL) patients with mutated IGHV genes (M-CLL) have better outcomes than patients with unmutated IGHV genes (U-CLL). It has been proposed that this difference reflects the fact that IGHV mutations alter the structure of the B-cell antigen receptor (BCR) such that it no longer binds stimulatory (auto) antigens and therefore cannot deliver trophic signals to the leukemic cells. For this theory to be correct, only replacement (R) mutations and in particular non-conservative R mutations that would more likely alter amino structure of the IGHV/D/J rearrangements would have relevance. Silent (S) mutations by definition do not change amino acid structure and could not alter antigen binding. We sought to investigate this hypothesis by analyzing the types (S, conservative R, non-conservative R) and distribution of mutations that occur in IGHVs of M-CLL clones and then comparing the time to first therapy (TTFT) in patients with different IGHV features. This analysis expanded an initial study of 1569 CLL cases in the US to include 1858 patients from Europe for a total of 3427 cases. METHODS. Using IGMT software and tools, we analyzed the rearranged IGHV sequences of 3427 cases and characterized their mutations in several respects: first, if IGHV mutations altered amino acid structure (S vs. R); second, if mutations occurred in CDRs (antigen binding domains) or FRs (scaffolds of the BCR); third, if R mutations were conservative or non-conservative as determined by charge, hydropathy, and size. TTFT for patients was examined with various combinations of the above parameters. Differences in TTFT were estimated by the method of Kaplan and Meier and assessed using the log rank test. RESULTS. First, TTFT was compared for 4 groups of patients with the following mutation profiles: no mutations; only S mutations (median 1 per sample); only R mutations (median 1 per sample); and mixed S and R mutations (median 16 per sample). These 4 categories were significantly different (P

Description: Chronic lymphocytic leukemia (CLL) cells actively participate in the formation of the tumor microenvironment (TME). The interplay of CLL cells and leukemia-supporting cells such as Th2 cells and regulatory T cells (Tregs) promotes a leukemia-supportive, immune-tolerant TME. In these supportive/tolerogenic niches of lymph nodes (LN) and bone marrow (BM), CLL cells slowly proliferate, and the rate of proliferation correlates with disease progression. However, how these dividing/recently-divided cells and other intraclonal CLL fractions interact with non-neoplastic cells to shape the TME to support growth and accelerate disease is unclear. To address these questions, matched LN and PB samples collected at day 13 after 2H2O ingestion from treatment-naïve patients (7 with stable disease and 7 with active disease) were sorted to determine in vivo growth rates of CLL cells within the proliferative fraction (PF, CXCR4DimCD5Bright), resting fraction (RF, CXCR4BrightCD5Dim) and intermediate fraction (IF, CXCR4IntCD5Int). In LN, PF cells had the highest 2H-DNA levels, and only the growth rate of PF but not IF or RF cells correlated with disease aggressiveness. In the PB, PF cells also had the highest growth rate; however, all 3 fractions (PF, IF, RF) had 2H-DNA levels that correlated with disease aggressiveness. Thus, PF cells from patients with aggressive clinical course undergo quicker transitions to the IF and then to the RF which might promote faster tissue homing and disease progression. Indeed, more PF cells from active than stable disease patients were found in the spleen (SP) and BM and less remained in PB, 18 hours post-injection into NSG mice. Gene expression profiling (GEP) was then performed on RF, IF, and PF from 7 paired PB and LN samples. GEP signatures of the PF from PB and LN were similar, consistent with 2H2O data that the PF are recent emigrants from TME. These GEP also inferred enhanced cell proliferation (CCND2, CDK2AP1), adhesion and motility (FERMT3, CD49d, CD11a, CD21), antigen presentation (CD1C), and promotion of T-cell trafficking (CCL3, CCL4) in LN CLL cells within the PF but not the IF or RF. Thus, CLL cells within the three intraclonal fractions might promote distinct biologic functions. To test this, we studied T cell responses stimulated by the CXCR4/CD5 fractions in vitro and in vivo. In an antigen-driven allo-MLR, the whole clone of CLL cells triggered the division of normal T cells, but PF induced the highest level of T-cell division that is ≥ 3 times more than any other fraction. Similarly, in an autologous polyclonal CD4 T cell response stimulated by anti-CD3/28 Dynabeads and IL-2, T-cell division was suppressed by unseparated CLL cells and each fraction. However, the least suppression was seen in T cells co-cultured with PF cells compared to those cultured alone or with IF or RF. In both settings, PF cells induced significantly more IL-4+ T cells, and RF cells triggered more Tregs. Similar numbers of Th1 cells were seen in all cultures. The RF and IF, but not the PF, produced the immunosuppressive cytokine IL-10. Finally, when dividing cases based on disease aggressiveness, significantly more T-cell division was triggered by PF and RF from active patients than stable patients; the percentages of Th1 and Th2 cells however were similar. These results were confirmed in vivo; in NSG mice injected with autologous T cells together with the PF, IF or RF sorted from 2 sets of active versus stable disease patients, PF from all 4 cases induced the highest levels of CLL B and T cell expansion in SP and BM, and RF from active but not stable disease patients triggered the growth of CLL T and B cells. In summary, CLL disease progression correlates with the rate of CLL cell division, and the rapidity that CLL cells home to the TME. The intraclonal fractions of CLL clones exhibit distinct biologic properties that can be further differentiated based on disease aggressiveness. This appears especially relevant for the development of a leukemia-supportive, immune-tolerant TME contributed by all 3 CXCR4/CD5 fractions, albeit by different mechanisms. The PF creates this by superior antigen presentation capacity and skewing T cell function to an immunosuppressive Th2 phenotype. For the IF and RF, this is done by inducing IL-10 secretion and amplifying Tregs. Together, these findings suggest the possibility of targeting specific subpopulations in CLL clones with distinct immunoregulatory modalities as a novel form of therapy. Disclosures Chen: Beigene: Research Funding; Pharmacyclics: Research Funding; Verastem: Research Funding. Wiestner:Pharmacyclics LLC, an AbbVie Company: Research Funding. Rai:Cellectis: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Roche/Genentech: Membership on an entity's Board of Directors or advisory committees. Chiorazzi:Janssen, Inc: Consultancy; AR Pharma: Equity Ownership.

Description: In chronic lymphocytic leukemia (CLL), bidirectional interactions of leukemic B cells with components of a complex, yet incompletely defined tumor microenvironment (TME) are critical for leukemic cell survival and proliferation. Ibrutinib, a Bruton's tyrosine kinase (BTK) inhibitor, blocks signals that are crucial for survival of CLL cells which are delivered by the B cell receptor (BCR) and certain other receptors. However since BTK and its family members are expressed by other cell types, ibrutinib can also affect non-leukemic cells, thereby altering their function. Here, we focused on understanding how myeloid-derived suppressor cells (MDSCs), a non-leukemic cell type within the TME, and their main target, T cells, are affected by ibrutinib therapy. Using blood cells from a set of 20 previously untreated patients receiving ibrutinib, we analyzed circulating MDSCs and their subsets 15 days before and 1, 2 and 3 months after treatment initiation. As anticipated, at the first month time point the absolute CLL B-cell count increased significantly (P=0.024), followed by a progressive reduction at consecutive time points (P