ALBERT

Description: Key Points IRF4 deletion in Tcl-1 tg mice and IRF4low CLL patients enhances disease progression due to increased tumor immune evasion. This is caused by a downregulation of the antigen processing and presentation machinery and reduced T-cell costimulation.

Description: Abstract 1773 T cell exhaustion is a state of T cell dysfunction in response to chronic antigen exposure, marked by impaired effector function and the continued expression of inhibitory receptors such as Programmed Death 1 (PD-1) (Wherry EJ. Nat Immunol. 2011 Jun;12(6):492–9.). Because tumour growth in chronic lymphocytic leukaemia (CLL) occurs over a long period of time, we hypothesized that the continued exposure of T cells to a CLL-derived antigen could also lead to a state of T cell exhaustion. We therefore investigated whether T cell exhaustion is induced in CLL by using the Eμ-TCL1 transgenic (tcl1tg) tumour transfer mouse model for this disease (Hofbauer JP, et al. Leukemia. 2011 Sep;25(9):1452-8) and by analyzing primary samples from CLL patients. We found that the number of PD-1+ T cells was increased in both CD4+ and CD8+ populations and in all lymphoid compartments examined of the Eμ-TCL1 transgenic (tcl1tg) tumour recipient mice, but not in recipient mice receiving wildtype (WT) splenocytes showing that leukemic mice have an increased number of T cells displaying an exhausted phenotype that is induced by the presence of CLL cells. We next assessed the expression of the ligands for PD-1 on the surface of murine CLL cells. Peripheral CLL tumour cells showed only a modest increase in PD-L1 expression as compared to WT B cells. However, lymph node and spleen residing tumour cells showed a marked increase in PD-L1 expression, which suggests a microenvironment-induced upregulation of PD-L1 on tumour cells, e.g. by their close contact to accessory cells. To validate our results on primary human CLL samples, we collected peripheral blood from 89 unselected CLL patients and 18 healthy donors and observed an increase in surface expression of PD-1 on the CD4+ and CD8+ T cell populations. While the percentage of PD-1+ CD4+ T cells in chemonaive patients was comparable to healthy donors, chemotherapy drastically increased the number of PD-1-expressing CD4+ T cells (63.81% ±19.75 vs 35.70% ±19.22; p

Description: Introduction: Chronic Lymphocytic Leukemia (CLL) is characterized by an accumulation of CD19+ CD5+ CLL cells in the peripheral blood and the lymphoid compartments. The disease is still incurable despite recent advances in the development of novel therapy concepts (e.g. inhibitors of BCR signaling). Although it is not entirely clear how CLL develops, proliferation centers located in the lymph node and the bone marrow are thought to be the crucial niche that provides the surrounding in which CLL cells originate and re-establish the clone after therapy, leading to relapse in almost 100% of CLL patients. In analogous normal lymphoproliferative environments the transcription factor IRF4 plays an important role in controlling B cell maturation, differentiation, proliferation and survival. A SNP in the human IRF4 3’UTR was linked to CLL susceptibility (DiBernardo Nat.Gen. 2008) and in the mouse model germline deletion of IRF4 in all lineages contributed to CLL development in the New Zealand Black and in the VH11 mouse model (Shukla Blood 2013, Ma J.Biol.Chem. 2013). Methods: CLL samples were collected from the peripheral blood of CLL patients according to the Declaration of Helsinki and with written informed consent. IRF4 mRNA expression analyses were performed in purified CD19+ CLL cells using TaqMan Real Time PCR. In vitro studies were performed in soloculture without stimulation or in coculture systems mimicking the lymph node microenvironment, as previously described (Asslaber Br.J.Haematol. 2013). IRF4 knockdown was performed using lipofection and IRF4 specific siRNAs or non-targeting control siRNAs. IRF4 protein expression was measured by intracellular flow cytometry. Proliferation was detected by Ki-67 intracellular staining. All intracellular stainings were performed after gating on viable CD19+ CD5+ CLL cells. Cell death was assessed by Annexin V / 7AAD staining or using a fixable viability dye. Results: Overall, IRF4 mRNA expression was decreased in CLL patients (N=101) when compared to healthy donors (N=8, P=0.04). In the CLL cohort low IRF4 mRNA expression (cut-off determined by ROC analysis and Youden Index calculation) was significantly correlated with earlier time to treatment (median treatment-free survival: 40 month in the IRF4LOW and 69 month in the IRF4HIGH CLL patient group (P

Description: Introduction. Ibrutinib, a small molecule inhibitor of Bruton's tyrosine kinase (BTK), has proven to be an efficient treatment for chronic lymphocytic leukemia (CLL). A distinct characteristic of ibrutinib therapy is transient lymphocytosis. Recently, we have demonstrated that CLL patients with high levels of CD49d show reduced lymphocytosis and inferior nodal response under ibrutinib due to residual activity of BCR-induced inside-out activation of the CD49d/CD29 integrin VLA-4 (Tissino E et al. J Exp Med. 2018;215(2):681-697). Here, we used Tcl1 transgenic (tg) mice as a model to further validate the observation of VLA-4 activation under ibrutinib and to study involved signaling pathways and the effect of VLA-4 inhibition in vivo. Methods. Surface receptor expression analysis of various receptors was performed by flow cytometry. The phosphorylation of signaling molecules was measured by phosflow and western blotting. VLA-4 affinity state was determined by a real-time kinetic assay described in Chigaev A et al. J Biol Chem. 2001;276(52):48670-8. To analyze the distribution of individual VLA-4 molecules on the cell surface, immunofluorescence approaches and superresolution microscopy (STORM, Abbelight) were employed. Mouse treatment studies were performed upon transplantation of TCL1-tg splenocytes to wild-type C57BL/6J mice using the small molecule VLA-4 inhibitor firategrast in drinking water. Tumor infiltration of different organs was measured by flow cytometry. Results. Analyzing the surface expression of CD49d and other homing receptors, we found that TCL1-tg mice correspond with the CD49d-high CLL cohort. We found that both CLL cells from TCL1-tg mice and human CD49d-high CLL show similar CD49d expression levels as the corresponding healthy B cells (human: N = 116 CD49d-high CLL and 32 healthy donor, P = 0.8717; mouse: N = 12 per group, P = 0.6845). Next, we analyzed the impact of BCR pathway inhibitors on the phosphorylation of signaling molecules involved in the BCR pathway after activation by anti-IgM (aIgM) in TCL1-tg leukemic cells. Ibrutinib and idelalisib showed specific patterns of inhibition of BTK and PI3K, respectively. The combination of ibrutinib and idelalisib proved to be the most efficient in reducing the phosphorylation of BTK, SYK, ERK1/2 and Akt upon IgM activation, compared to the phosphorylation of stimulated cells without inhibition (N = 6, P = 0.0003, 0.0305, 0.0039, 0.0019, respectively). IgM stimulation induced VLA-4 high affinity as well as a reorganization of VLA-4 molecules on the cell surface, forming areas of high VLA-4 density. BCR-induced inside-out activation of VLA-4 remained functional upon treatment with ibrutinib (N = 5, cnt vs aIgM P = 0.0017, cnt vs ibrutinib+aIgM P = 0.0499), while idelalisib reduced VLA-4 activation more effectively (N = 5, cnt vs aIgM P = 0.0014, cnt vs idelalisib+aIgM P = 0.0803), suggesting a pivotal role of PI3K in the transmission of the exogenous antigen signal to the integrin. Finally, to analyze the potential of VLA-4 blockage in a tumor setting similar to VLA-4-high CLL patients, we treated wild-type C57BL/6J mice (N = 6 mice per group), which were transplanted with TCL1-tg splenocytes, with the CD49d inhibitor firategrast. This treatment reduced the tumor load in spleen and bone marrow. Conclusion. We found that the TCL1-tg mouse model is adequate to study the activity of the BCR-VLA-4 axis in CLL. Using this model, we show that a) BCR stimulation induces both, an increase in VLA-4 affinity as well as avidity (clustering), b) that PI3K is an essential transmitter between BCR and VLA-4, and c) that VLA-4 inhibition alters tumor infiltration patterns in vivo. Synergies of VLA-4 blockage with established therapy options as a possible way of reducing microenvironment-induced resistance development are currently been investigated. Disclosures Egle: Celgene: Honoraria, Other: Advisory board and Travel support. Greil:Eisai: Honoraria; Daiichi Sankyo: Consultancy, Honoraria; Sandoz: Honoraria; Genentech: Honoraria, Research Funding; Cephalon: Consultancy, Honoraria, Research Funding; Sanofi Aventis: Honoraria; Janssen-Cilag: Honoraria; AstraZeneca: Consultancy, Honoraria, Other: Travel/accomodation expenses, Research Funding; GSK: Research Funding; Boehringer Ingelheim: Honoraria; AbbVie: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Other: Travel/accomodation expenses, Research Funding; Pfizer: Honoraria, Research Funding; Bristol-Myers-Squibb: Consultancy, Honoraria, Other: Travel/accomodation expenses, Research Funding; Merck: Consultancy, Honoraria, Research Funding; Mundipharma: Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Other: Travel/accomodation expenses, Research Funding; Celgene: Consultancy, Honoraria, Other: Travel/accomodation expenses, Research Funding; Novartis: Consultancy, Honoraria, Other: Travel/accomodation expenses, Research Funding; MSD: Consultancy, Honoraria, Other: Travel/accomodation expenses, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Ratiopharm: Research Funding; Gilead: Consultancy, Honoraria, Other: Travel/accomodation expenses, Research Funding.

Description: The therapeutic concept of unleashing a pre-existing immune response against the tumor by the application of immune-checkpoint inhibitors (ICI) has resulted in long-term survival in advanced cancer patient subgroups. However, the majority of patients do not benefit from single-agent ICI and therefore new combination strategies are eagerly necessitated. In addition to conventional chemotherapy, kinase inhibitors as well as tumor-specific vaccinations are extensively investigated in combination with ICI to augment therapy responses. An unprecedented clinical outcome with chimeric antigen receptor (CAR-)T cell therapy has led to the approval for relapsed/refractory diffuse large B cell lymphoma and B cell acute lymphoblastic leukemia whereas response rates in solid tumors are unsatisfactory. Immune-checkpoints negatively impact CAR-T cell therapy in hematologic and solid malignancies and as a consequence provide a therapeutic target to overcome resistance. Established biomarkers such as programmed death ligand 1 (PD-L1) and tumor mutational burden (TMB) help to select patients who will benefit most from ICI, however, biomarker negativity does not exclude responses. Investigating alterations in the antigen presenting pathway as well as radiomics have the potential to determine tumor immunogenicity and response to ICI. Within this review we summarize the literature about specific combination partners for ICI and the applicability of artificial intelligence to predict ICI therapy responses.

Description: Chronic lymphocytic leukemia (CLL) is a malignancy of mature B cells that is characterized by apoptosis resistance and dysfunctional immune system. The chronic nature and slow development of the disease indicates a contribution of CLL-induced inflammation in the disease course. Previous reports suggested a potential role of myeloid cells in mediating these defects. However, the composition and function of CLL-associated myeloid cells have not been thoroughly investigated in an in vivo system. Here, we used the well-established CLL mouse model, Eµ-TCL1 mice (TCL1), to characterize changes within myeloid cell populations along with CLL development and the influence of their depletion on disease progression and immune dysfunction. We have recently shown that CLL development in TCL1 mice is associated with massive changes within myeloid cell populations. In the peritoneal cavity (PC) of leukemic mice we observed an infiltration of monocytes and an M2-like skewing of macrophages according to phenotypical and signaling signatures. Along this line, monocytes infiltrated the spleens of leukemic animals, both in primary CLL and adoptive transfer models, which is most likely due to high CCL2 serum levels. These monocytes lost the inflammatory Ly6Chi subset and were severely skewed towards Ly6Clow patrolling monocytes, accompanied by high expression of adhesion and angiogenic molecules like ICAM1, PECAM1 and MMP14. Gene expression profiling of splenic myeloid cells from TCL1 mice revealed an enrichment of various genes involved in dendritic cell (DC) maturation and MHC-II-mediated antigen presentation. However, the numbers of MHC-IIhi mature DCs and macrophages were significantly decreased, suggesting a monocyte differentiation arrest leading to impaired anti-tumor immune response. The observed transcriptional upregulation of multiple inflammatory cytokines like TNF-α, CXCL9, CXCL10 and CXCL16 in monocytes was confirmed by serum cytokine arrays, and is likely due to the overexpression of the pro-inflammatory regulator TREM-1. In addition, TCL1 monocytes upregulated the expression of several inhibitory molecules like PD-L1, IL-10, IL1ra and IL4i1 suggesting an impaired immune function. While CLL-induced immune dysfunction is a well-established phenomenon, the contribution of myeloid cells in this context was not clear. We therefore sought to determine the in vivo effects of myeloid cell depletion on CLL development and its associated immune defects. For that purpose we used liposomal clodronate to selectively ablate macrophages and monocytes from young wild-type mice adoptively transferred with murine CLL. Our data clearly show control of CLL development in clodronate-treated mice relative to control liposomes as demonstrated by decreased spleen weight (1.09 vs. 0.54 g, p 〈 0.0001) and a significant drop in tumor load, defined as CD5+CD19+ cells, in spleen (60.58% vs. 42.25%), peripheral blood (43% vs 11.8%), PC (66.2% vs 3.1%), lymph nodes (4.9% vs 1.2%) and bone marrow (1.9% vs 0.8%). In addition, we observed changes in immune effector cells in response to myeloid cell depletion suggesting better immune status in treated mice. Interestingly, the loss of macrophages/monocytes was compensated by increased splenic monocyte proliferation as shown by EdU incorporation in vivo. In contrast to control mice, the repopulating monocytes upon clodronate treatment were largely inflammatory Ly6Chi monocytes. In summary, our data show that skewing of myeloid cells actively contributes to CLL development via; 1) enhancing the survival of leukemic cells, and 2) suppressing anti-tumor immune functions. In the absence of monocytes and macrophages, disease development is delayed in mice adoptively transferred with murine CLL. Therefore, we suggest that targeting non-malignant myeloid cells in CLL might serve as a novel strategy for CLL immunotherapy. Disclosures No relevant conflicts of interest to declare.

Description: Abstract 803 Introduction: The development of B cell chronic lymphocytic leukaemia (CLL) involves antigenic selection of the B cell clone, as evidenced by a skewed BCR repertoire found in CLL cells, as well as continuing BCR signaling detected in subgroups of CLL. T cell involvement in the maintenance of the malignant clone is also suggested by a number of evidential lines, such as the severe skewing of T cell subsets in CLL and the presence of relevant numbers of CD4 cells in the so-called “proliferation centers” in lymph nodes. However, neither clonal nor immunologic identities of these T cells have been sufficiently determined. Recently, we have shown in Tcl1 transgenic mice that CLL clones were able to directly drive changes in the T cell repertoire, resulting in relatively fast skewing in subset distribution (similar to that observed in human CLL) as well as a clonal selection of T cells, both in spontaneously developing CLL in the model, as well as in immunocompetent congenic recipient mice in experiments transplanting established murine CLL. Methods: To establish evidence for similar interactions in human CLL, we collected a descriptive database determining patterns of T cell diversity in CLL patient blood. We analyzed T cells from 53 previously-untreated CLL patients established TCR V beta clonality and frequency based on CDR3 length polymorphism in sorted CD4 cells and, in a confirmatory subset, based on TCR V gene-specific flow cytometry. CLL samples were also investigated regarding the BCR VH gene usage, mutation status and clinical and prognostic parameters. Results: BCR analysis confirmed antigenic selection in our patient set with 6 IgVH genes accounting for 〉 50% of the cases. Stereotyped CDR3 regions were common and one third of the patients showed unmutatetd IgVH gene sequence. Analysing 20 TCR genes by PCR spectratyping, the TCR CDR3 size distribution pattern revealed a relevant frequency of oligoclonal/monoclonal CD4 T cells in CLL samples. While a number of patients showed completely polyclonal patterns in all their TCR CDR3 regions, others showed either single or multiple clonal TCR families. In corresponding flow cytometric analyses clonal T cells could make up to 48% of total CD4 cells in a given patient. In patients with longitudinal samples we found relevant stability of these TCR patterns over time. By comparing the data from the TCR clonality database with our BCR dataset we established that these clonal patterns significantly, but not exclusively, clustered in unmutated patient samples. Overall we found no strong association with any specific IgVH gene, but intriguingly, in some patients a specific clonal TCR corresponded to a stereotyped BCR receptor. In fact in two patient pairs with identical IgVH rearrangements we found corresponding TCR clones that showed sequence identity between the CD4 T cell clones derived from the other patient. In addition in both pairs we found a shared HLA DR and DQ haplotype. These data strongly suggests that there may be an important link between the antigenic selection on the B-CLL clone and the selection of certain TCR clones, thus for the first time postulating an antigentic identity of the CLL-associated T cells. This proposed identity, however, currently remains unclear. Finally, we tested for an influence of T cell clonality on clinical behaviour of CLL disease in the patients. We could intentify the presence of more than one clonal TCR family as a significant predictor of a short treatment-free interval (p=0.03). This was true for both, patients with mutated and unmutated IgVH receptors, although it remained a trend in the latter. Conclusion: Our results imply that a restricted CD4 T cell diversity may be important for CLL progression and that an as of yet still undefined antigenic drive for T cells may be important for this. This may help to define specific monoclonal CD4 T cells as a promising novel target for future therapeutic intervention. Disclosures: No relevant conflicts of interest to declare.

Description: Abstract 563 Introduction The molecular characterization of chronic lymphocytic leukemia (CLL) with whole genome sequencing has recently begun to foster a novel understanding of the disease, identifying pathways of importance in CLL biology. One of the target genes that was identified by this approach was BIRC3 (Rossi et. al. Blood 2012). BIRC3 (cIAP2) and its close homolog BIRC2 (cIAP1), are members of the IAP (inhibitior of apoptosis) protein family, that unlike other IAPs, do not directly interfere with apoptosis but are key components of the canonical and non-canonical NFKB signalling pathways. As such they play an important role in B-cell differentiation, survival and proliferation. In the murine system BIRC2 and BIRC3 were shown to be redundant (Gardam et. al. Blood 2011). Their combined loss rendered murine B-cells independent of some survival factors and led to uncontrolled B-cell accumulation. In CLL, Rossi et. al. reported recurrent mutations in BIRC3 that were rare at diagnosis (