ALBERT

Description: Background: The immune response is probably important for the long-term outcome of patients with tumours, including leukemias. However, its efficiency is often modulated by various immunosuppressive mechanisms, such as the expression of inhibitory receptors on the surface of the immune cells and of their ligands on tumor cells. The introduction of blocking antibodies against these receptors and ligands has gained considerable interest in the past several years and renewed the relevance of the stimulation of anti-tumor immune responses in the treatment of cancers. The significance of PD-1/PD-L1 expression in leukemias is not yet well established, although monoclonal antibodies targeting either PD-1 or PD-L1 are currently in clinical trials also for hematologic malignancies. Aim and methods: We have recently shown that the surface expression of PD-L1 protein correlates with the ratio of two PD-L1 transcript variants (v1/v2) in hematopoietic cells (Brodská et al., submitted to Cancer Immunotherapy Research). This finding has enabled a retrospective examination of PD-L1 expression in frozen cDNA samples obtained from the peripheral blood of AML patients at diagnosis. A total of 55 patients with high leukocyte counts were selected for this analysis as their samples were presumed to be predominantly composed of leukemic cells. As our previous findings suggested the existence of anti-nucleophosmin immune response in vivo, the patients were divided into two groups according to the nucleophosmin mutation status. Results: The majority of the tested samples were PD-L1-positive (Fig. 1). The positivity was of 65% in patients with nucleophosmin mutations (NPM1mut, N = 31) and of 88% in patients with wild-type nucleophosmin (NPM1wt, N = 24). A better overall survival for PD-L1-low patients was observed in NPM1mut patient group, although the difference was not statistically significant (p = 0.21, Fig.2). The cutoff value for v1/v2 transcript levels was of 8.25. Conclusions: Although PD-L1 expression in AML patients at diagnosis is usually low, we found very high incidence of PD-L1 positivity among patients with leukocytosis. Therefore, a high diagnostic leukocyte count may be associated with immune response failure in AML. Acknowledgment: The work was supported by the Ministry of Health of the Czech Republic (grant No 16-30268A and the project for conceptual development of the research organization No 00023736). Figure 1 PD-L1 expression in AML patients with high leukocyte counts at diagnosis. The surface expression of the protein was assessed through the ratio of the transcript levels for variants 1 and 2. Figure 1. PD-L1 expression in AML patients with high leukocyte counts at diagnosis. The surface expression of the protein was assessed through the ratio of the transcript levels for variants 1 and 2. Figure 2 Overall survival curves for AML patient groups according to PD-L1 expresssion and NPM1 status Figure 2. Overall survival curves for AML patient groups according to PD-L1 expresssion and NPM1 status Disclosures No relevant conflicts of interest to declare.

Description: Background We have recently identified a skewed distribution of class I human leukocyte antigens (HLA) among patients with AML and mutated nucleophosmin gene (NPMc+ AML). A lower frequency of several HLA allelic groups in the NPMc+ AML patient cohort was in good correlation with the results of theoretical predictions for high-affinity immunopeptides derived from NPM1, suggesting that an anti-NPM1 immune response could prevent leukemia development in patients with a suitable HLA class I type. Aim We here present more detailed analysis of HLA-specific features, in a much larger cohort (N = 357) of AML patients with NPM1 mutation (type A/D) from several centers in the Czech Republic, Germany and Poland. Results Most importantly, we confirmed the lower incidence of B´40 and C´07 allelic groups in NPMc+ AML compared to the normal values. The moderate decrease of A´02 allelic group frequency became statistically significant in this larger patient cohort (see Table). On the other hand, no difference in HLA class II frequencies was found compared to the normal distribution. Furthemore, patients with B´07 allelic group had a significantly better prognosis, but only in the absence of Flt-3-ITD mutations (p = 0.049, see Figure). HLA typing was performed by molecular methods in a subgroup of patients (N = 73), allowing for discrimination between C´07 alleles. In this subgroup, C*07:01, but not C*07:02/04 expression was associated with better overall survival (p = 0.036), in agreement with theoretical predictions. Conclusion Our results support the hypothesis that anti-NPM1 immune response reduces AML development and contributes to a better outcome of NPMc+ AML patients with suitable HLA class I type (including at least A´02, B´07, B´40 and C*07:01). Furthermore, NPMc+ immunogenicity is caused rather by its aberrant localization than by the generation of a unique aminoacid sequence. Figure Figure. Disclosures Schetelig: Sanofi: Honoraria. Thiede:AgenDix: Employment, Other: Ownership.

Description: Introduction Thrombosis is a common pathology underlying ischemic heart disease, stroke, and venous thromboembolism. D-dimer is a global indicator of blood coagulation activation and fibrinolysis and, therefore, an indirect marker of thrombotic activity. D-dimers half-life is 48 hours. D-dimer determination is the standard procedure in the treatment of thrombosis. Serine protease thrombin plays pivotal roles in thrombosis and hemostasis, blood coagulation and platelet activation. Thrombin has a short half-life and naturally occurring inhibitors, such as antithrombin, rapidly bind thrombin, which makes the direct measurements of in vivo active thrombin difficult. Thrombin binds to fibrin where it is quite efficiently protected from inhibition by heparin-antithrombin but susceptible to inactivation by different antithrombin-independent inhibitors. There are two low affinity non-substrate thrombin binding sites, one in each half of the dimeric fibrinogen E region, and one high affinity thrombin non-substrate binding site on fibrinogen gamma' chains inside the D region (Meh DA, Siebenlist KR, Mosesson MW, J Biol Chem. 1996, 23121-5). We have shown that thrombin bound to fibrin promotes further fibrin growth in the presence of fibrinogen and absence of free thrombin in solution (Riedel T, Brynda E, Dyr JE, Houska, M, J. Biomed. Mater. Res. Part A 2009, 437-447). The aim of this project was to look for any thrombin activity on isolated D-dimers using several commercial D-dimer kits in groups of patients with elevated D-dimers. Methods Three D-dimers kits were used (ELISA kits CEA506Hu, USCN and D-Dimer (D2D), BioAssay™; and immunoturbidimetric assay D-Dimer KAI-090, K-ASSAY). To detect thrombin activity on captured D-dimers one chromogenic (S-2238, Chromogenix) and two fluorogenic (SN-59, Haematologic Technologies, Inc.; (p-tosyl-Gly-Pro-Arg)2-R110, Thermo Fisher Scientific, Inc.) specific substrates and specific inhibitors (hirudine and PPACK) were used. Independently, bound proteins were removed from immobilized antibodies in 8 M urea and after treatment with trypsin analyzed by mass spectrometry (TripleTOF 5600, Sciex). 34 patients with high, moderate, and low levels of D-dimers and with different diagnosis were analyzed. Results Out of 18 patients with main diagnosis linked with thrombosis 61 % exhibited active thrombin on D-dimers. In these patients we found active thrombin bound to D-dimers captured by antibodies in all applied D-dimer kits. Using mass spectrometry thrombin bound to isolated D-dimers was detected. Specificity of thrombin activity related to D-dimers was determined by combination of several specific thrombin substrates and inhibitors. The activity of bound thrombin was remarkably stable over the period of more than 24 hours. It showed that precise measurement of even very low activity of thrombin was possible. In the group of 16 non-thrombotic patients with elevated D-dimers only 19 % exhibited thrombin activity. Interestingly, differences in values of thrombin activity were up to five orders of magnitude and differences in the activities related to the value of captured D-dimers were even greater. Conclusion This, to our knowledge, is the first report showing the presence of active thrombin bound to circulating D-dimers. Although the group of patients we were so far able to evaluate is too small to being statistically tested, the results are highly encouraging. The amount of bound active thrombin on fibrin degradation products reflects the way of thrombus formation and its degradation (times, durations and rates of relevant reactions and especially the rate of thrombin generation). The thrombin concentration present at the time of fibrin gelation plays an important role in formation of fibrin clot structure, including its mechanical and fibrinolytic stability. It remains to be seen in further studies with much larger cohorts of patients if the presence of active thrombin has any impact on pathophysiology of thrombosis and if its determination may be of importance for the improvement of diagnosis of thrombotic events. Supported by the project of the Ministry of Health of the Czech Republic for conceptual development of the research organization 00023736, by Grant from the Academy of Sciences, Czech Republic (P205/12/G118), and by ERDF OPPK CZ.2.1.16/3.1.00/28007. Disclosures No relevant conflicts of interest to declare.

Description: In our recent work, we described changes in HLA class I frequencies in AML patients with nucleophosmin (NPM) mutations. Several allelic groups were found to be depleted in patients with C-terminal NPM mutations (NPMc+), but not in patients with wild-type NPM, and these differences corresponded well to in silico prediction of NPM-derived peptides binding to HLA class I. Moreover, patients with "favorable" HLA type (i.e., expressing HLA alleles suitable for presentation of NPM-derived peptides) were found to have significantly better overall survival than those without suitable HLA alleles. Altogether, our results suggested that spontaneous anti-NPM immune response may prevent AML development and helps achieve durable cure. In this contribution, an extended patient cohort (N = 71 patients with all available data) was divided into four groups according to HLA type (favorable/unfavorable) and Flt3-ITD status. Patients expressing suitable HLA alleles and not having internal tandem duplications in Flt3 gene (HLA+/Flt3-) had the best overall survival (Figure 1). The impact of unfavorable HLA type alone was comparable to that of Flt3-ITD positivity while the combination of both adverse factors was associated with particularly poor outcome (p = 0.0066 for trend). On the basis of these results, we believe that NPMc+ AML patients with favorable HLA type (about 65% of all NPMc+ AML patients) could benefit from an immunomodulatory therapy. Besides inhibitory receptors (such as PD-1, CTLA-4, TIM-3), regulatory T-cells or decreased HLA expression, reduced antigen presentation by leukemic cells belongs to possible mechanisms of immune escape. Insufficiency of molecular complexes such as the proteasome or the transport-associated protein (TAP) can result in increased presentation of Class II-associated invariant chain peptide (CLIP). Indeed, increased CLIP expression on residual leukemic blasts has recently been reported to correlate with increased relapse risk in AML. Interestingly, valproic acid used in combination with standard chemotherapy has been described to significantly decrease the relapse rate in elderly AML patients with mutated NPM (but not in other AML subgroups). This could be associated with restored antigen presentation following treatment with histonedeacetylase inhibitors. In our experiments, we observed marked reduction of CLIP expression on primary NPMc+ AML blasts following in vitro treatment with suberoylanilide hydroxamic acid (SAHA, Figure 2). Both the fraction of CLIP-positive cells (open circles) and CLIP surface density on positive cells (closed circles) were reduced. HLA class I expression was normal and was not affected by SAHA treatment. Importantly, the effect on CLIP expression occurred even at subtoxic (0.5 µM) drug concentration. Figure 1. Figure 1. Figure 2. Figure 2. Disclosures No relevant conflicts of interest to declare.

Description: Hepcidin is a major regulator of iron metabolism. Hepcidin-based therapeutics/diagnostics could play roles in hematology in the future, and thus, hepcidin transport is crucial to understand. In this study, we identify α2-macroglobulin (α2-M) as the specific hepcidin-binding molecule in blood. Interaction of 125I-hepcidin with α2-M was identified using fractionation of plasma proteins followed by native gradient polyacrylamide gel electrophoresis and mass spectrometry. Hepcidin binding to nonactivated α2-M displays high affinity (Kd 177 ± 27 nM), whereas hepcidin binding to albumin was nonspecific and displayed nonsaturable kinetics. Surprisingly, the interaction of hepcidin with activated α2-M exhibited a classical sigmoidal binding curve demonstrating cooperative binding of 4 high-affinity (Kd 0.3 μM) hepcidin-binding sites. This property probably enables efficient sequestration of hepcidin and its subsequent release or inactivation that may be important for its effector functions. Because α2-M rapidly targets ligands to cells via receptor-mediated endocytosis, the binding of hepcidin to α2-M may influence its functions. In fact, the α2-M–hepcidin complex decreased ferroportin expression in J774 cells more effectively than hepcidin alone. The demonstration that α2-M is the hepcidin transporter could lead to better understanding of hepcidin physiology, methods for its sensitive measurement and the development of novel drugs for the treatment of iron-related diseases.

Description: Compared to solid tumors, the role of PD-L1 in hematological malignancies is less explored, and the knowledge in this area is mostly limited to lymphomas. However, several studies indicated that PD-L1 is also overexpressed in myeloid malignancies. Successful treatment of the acute myeloid leukemia (AML) is likely associated with elimination of the residual disease by the immune system, and possible involvement of PD-L1 in this process remains to be elucidated. We analyzed PD-L1 expression on AML primary cells by flow cytometry and, in parallel, transcript levels were determined for the transcription variants v1 and v2. The ratio of v1/v2 cDNA correlated with the surface protein amount, and high v1/v2 levels were associated with worse overall survival (p = 0.0045). The prognostic impact of PD-L1 was limited to AML with mutated nucleophosmin and concomitant internal tandem duplications in the FLT3 gene (p less than 0.0001 for this particular AML subgroup).