ALBERT

Description: Securing communications in wireless sensor networks is increasingly important as the diversity of applications increases. However, even today, it is equally important for the measures employed to be energy efficient. For this reason, this publication analyzes the suitability of various cryptographic primitives for use in WSNs according to various criteria and, finally, describes a modular, PKI-based framework for confidential, authenticated, secure communications in which most suitable primitives can be employed. Due to the limited capabilities of common WSN motes, criteria for the selection of primitives are security, power efficiency and memory requirements. The implementation of the framework and the singular components have been tested and benchmarked in our testbed of IRISmotes.

Description: The use of dendritic cells (DCs) in therapeutic cancer vaccination requires their loading with tumor-specific antigen(s). DEC-205, a phagocytosis receptor mediating antigen uptake, is associated with CD8+ T-cell responses in mice. Here we fused an anti–DEC-205scFv to an HLA-DP4–restricted epitope from the tumor antigen MAGE-A3, and examined the suitability and efficacy of DEC-205 to deliver a helper epitope to human monocyte-derived DCs (moDCs). The construct specifically bound DEC-205 on human moDCs without negative impact on DC phenotype and function. We measured antigen presentation with specific autologous CD4+ T cells, generated by TCR-RNA transfection. DEC-205 targeting resulted in significant major histocompatibility complex class II–restricted antigen presentation, and was superior to loading DCs by electroporation of mRNA encoding endosome-targeted MAGE-A3-DCLAMP or by direct peptide pulsing. Anti–DEC-205scFv-MAGE-A3 was presented 100 times more efficiently than the control constructs. DC maturation before or during incubation with anti–DEC-205scFv-MAGE-A3 reduced the interleukin-10/interleukin-2 ratio. Moreover, we successfully applied the DEC-205 targeting strategy to moDCs from malignant melanoma patients. Again, DEC-205–targeted mature DCs (mDCs) presented the antigen more efficiently than peptide-pulsed DCs and maintained their stimulatory capacity after cryoconservation. Thus, DEC-205 targeting represents a feasible and effective method to deliver helper epitopes to DCs in anticancer vaccine strategies, which may also be suitable for DC targeting in vivo.

Description: Abstract 2843 Natural killer group 2 member D (NKG2D) is an important activating receptor controlling cytotoxicity of natural killer (NK) cells and T cells and plays an important role in immune surveillance against tumors. For redirecting NK cells to B-lymphoid tumor cells two recombinant bifunctional antibody-based fusion proteins were designed in order to coat malignant cells with ligands for NKG2D and attract NK cells. Therefore, a human CD20-directed single-chain fragment variable (scFv) was fused to NKG2D-specific ligands, either MHC class I chain-related protein A (MICA) or unique long 16-binding protein 2 (ULBP2). These two fully human fusion proteins, designated MICA:CD20 and ULBP2:CD20, respectively, were expressed in eukaryotic cells and purified to homogeneity. Size exclusion chromatography revealed that both purified proteins predominantly formed monomers. MICA:CD20 and ULBP2:CD20 specifically and simultaneously bound to CD20 and NKG2D and efficiently mediated lysis of lymphoma cell lines with mononuclear cells from healthy donors as effector cells. Analysis of the activation status of NKG2D-positive T cells and NK cells revealed that MICA:CD20 and ULBP2:CD20 activated resting NK cells, but not T cells, indicating that NK cells were the relevant effector cell population for the two molecules. In cytotoxicity assays using human NK cells from healthy donors, both agents sensitized lymphoma cell lines as well as fresh tumor cells for NK cell-mediated lysis. MICA:CD20 and ULBP2:CD20 induced lysis at low nanomolar concentrations with half maximum effective concentrations between 1 and 4 nM depending on target cells. Interestingly, ULBP2:CD20 exhibited a higher cytolytic potential than MICA:CD20 in terms of maximum lysis. Importantly, MICA:CD20 and ULBP2:CD20 induced lysis of 13/13 tested primary tumor cell samples from patients with different B cell malignancies including chronic lymphocytic leukemia, mantle cell lymphoma and marginal zone lymphoma. Interestingly, cell surface expression of endogenous MICA and ULBP2 was low or not detectable on fresh tumor cells. In addition, ULBP2:CD20 was also capable of inducing lysis of tumor cells in cytotoxicity experiments using autologous patient-derived NK cells as effector cells, indicating that the triggering signal was sufficient to overcome inhibition by interactions between killer cell immunoglobulin-like receptors and MHC class I molecules. Moreover, both MICA:CD20 and ULBP2:CD20 synergistically enhanced antibody-dependent cellular cytotoxicity (ADCC) by the monoclonal antibody daratumumab directed against CD38 which is co-expressed together with CD20 on certain B cell lymphomas. This approach of simultaneously triggering ADCC and natural cytotoxicity by these bifunctional fusion proteins may represent a promising strategy to achieve stronger NK cell-mediated antitumor responses. Disclosures: de Weers: Genmab : Employment. van De Winkel:Genmab: Employment. Parren:Genmab: Employment.

Description: Abstract 2846 Although the CD20 antibody rituximab considerably improved the treatment of B-cell neoplasias, novel optimized CD20-targeting strategies may still offer therapeutic gains. Analysis of Fc receptor (FcR) polymorphisms of rituximab-treated patients and animal studies demonstrated the crucial role for activating FcRs and effector cell recruitment. In the current study a novel CD20-directed bispecific antibody (bsab) [(CD20)2×CD16] in the tribody format was evaluated to enhance antibody dependent cellular cytotoxicity (ADCC). The heterodimeric molecule forms a CD16-directed F(ab) fragment with a CD20-directed scFv c-terminally fused to both peptide chains. [(CD20)2×CD16] was expressed in HEK-293T cells and purified using affinity chromatography. Specific binding to CD20- or FcγRIIIa- (CD16a) positive cells was demonstrated by flow cytometry. No significant difference in binding to both CD16a alloforms (CD16a-F158 and CD16a-V158) was observed. In chromium release assays [(CD20)2×CD16] mediated specific lysis of different burkitt's lymphoma cell lines in a dose-dependent manner even at low picomolar concentrations. Potency of target cell lysis was improved compared to rituximab (10-fold) irrespective of the effector cell donors' CD16a V/F-polymorphism status. In addition, the bsab triggered lysis of primary tumor cells from 12/12 lymphoma patients (CLL; MCL; MZL). [(CD20)2×CD16] triggered significantly stronger target cell lysis than rituximab or the parental CD20 antibody. Importantly, specific lysis of primary tumor cells was also observed using autologous NK cells as effector cells, suggesting that [(CD20)2×CD16] is capable in triggering tumor cell lysis in the presence of a strong MHC I inhibitory signal. Interestingly, when B-cell depletion was analyzed in whole blood, significantly higher depletion rates were obtained with the bsab compared to rituximab (75% vs 25%). Depletion of B cells was accompanied by activation of NK cells, as evidenced by CD69 expression on NK cells. Finally, NOD-SCID mice were transplanted with CD34-positive cord blood cells to reconstitute a humanized hematopoietic system. Distribution and numbers of engrafted human B cells and human CD16-positive effector cells were analyzed by flow cytometry. CD16 was expressed on splenic monocytes and NK cells. After daily injection of [(CD20)2×CD16] for three days a significant reduction of B cells was observed. Thus, the CD16-directed bispecific antibody [(CD20)2×CD16] may extend the therapeutic range and represents a promising candidate for further clinical development. Disclosures: Parren: Genmab: Employment. van De Winkel:Genmab: Employment.

Description: Although the mortality of autologous stem cell transplantation in contrast to allogeneic is low, in AML patients the lack of immune surveillance as well as contamination of the transplant with residual leukemic stem cells (LSC) limits its use. Therefore, elimination of LSC by targeted therapy may represent a promising therapeutic approach. Recently, CD96 was identified as marker antigen on AML-LSC (Hosen et al., PNAS 104: 11008, 2007). Here, by addressing CD96 with magnetic cell sorting (MACS) or using antibody dependent cellular cytotoxicity (ADCC), new strategies for engineering autologous stem cell grafts or for in vivo targeting of residual AML stem cells are presented. To evaluate the efficacy of depletion of LSC by MACS technology, grafts containing hematopoietic stem cells were spiked with CD96 positive AML cells. Using biotinylated CD96 antibody TH111 raised in our laboratory in combination with anti-biotin-micro beads (Miltenyi Biotech, Bergisch Gladbach, Germany) up to a 1000-fold depletion of targeted cells was achieved. The viability, cell count and the potential of hematopoietic progenitor cells (HPC) to proliferate and differentiate were not affected by this procedure as documented by flow cytometry and colony forming assays. As residual LSC residing within the patient may also account for AML relapse after high-dose chemotherapy and subsequent SCT, eradication of AML stem cells in vivo is desirable. To target CD96+ AML-LSC by ADCC, chimeric antibodies containing wild type or affinity maturated variable regions in combination with an optimized human IgG1Fc were generated by recombinant DNA technologies. Both recombinant antibodies were expressed in Hek 293 cells enriched to homogeneity by affinity chromatography and analyzed for their functional properties. As shown by flow cytometry, the antigen binding affinity of the maturated antibody was enhanced (EC50 0.6 μg/ml vs. 2 μg/ml). Moreover, as analyzed in standard ADCC assays, NK cell mediated lytic properties against CD96-positive target cells were elevated (maximum lysis: 52%) using the affinity maturated chimeric CD96 antibody (EC50: 0.02 μg/ml vs. 0.15 μg/ml). Thus, this CD96 purging strategy avoids unwanted transplantation of AML-LSC and may help to revitalize autologous stem cell transplantation in this indication. Although, specific side effects by CD96 application will have to be considered, this may allow for an additional therapeutic avenue to eliminate in vivo residual AML-LSC in autologous as well as in allogeneic situations. Disclosures: No relevant conflicts of interest to declare.

Description: Introduction: Three unconjugated CD20 antibodies have been approved for the treatment of lymphoma patients. All three are of human IgG1 isotype, but nevertheless they differ in their modes of action: type I antibodies (e.g. rituximab and ofatumumab) trigger effective complement-dependent cytotoxicity (CDC), whereas type II antibodies (e.g. obinutuzumab) are potent inducers of direct cell death, while both type I and II antibodies can induce antibody-dependent cellular cytotoxicity (ADCC). Studies in syngeneic mouse models suggest that myeloid cells are the predominant effector cell type for CD20 antibodies (Uchida et al. J Exp Med 199:1659, 2004). However, human myeloid cells, particularly PMN, are activated more effectively by human IgA than by IgG1 antibodies (Dechant et al. Blood 100:4574, 2002) - especially when the latter are engineered for enhanced FcγRIII affinity (Peipp et al. Blood 112:2390, 2008). Antibodies of IgA isotype constitute an integral part of the mucosal immune system, and differ from IgG antibodies in their pharmacokinetic properties and immune effector mechanisms (Boross et al. EMBO Mol Med 5:1213, 2013, Lohse et al. Cancer Res 76:403, 2016). Here, we compared the efficiency of IgG1 and IgA2 isotype variants of the type I CD20 antibody 1F5 in killing lymphoma cells in vitro and in vivo. Methods: Recombinant antibodies against human CD20 were produced by co-transfecting BHK cells with vectors encoding the 1F5 variable, Igα2 or Igγ1 heavy, and κ light chain constant regions, respectively. The resulting isotype variants were compared for their biochemical characteristics as well as Fab- and Fc- mediated effector functions using human lymphoma cell lines as targets. NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (NSG) mice xenotransplanted with human RAJI lymphoma cells were employed to investigate the therapeutic efficacy of human CD20 antibodies. Additionally, in vivo depletion of human CD20 transgenic B cells was evaluated in a syngeneic B cell depletion model using wildtype, human FcαRI transgenic and C3 knock-out mice. Results and Discussion: In vivo studies with xenotransplanted RAJI cells in NSG mice, which lack functional T and NK cells, demonstrated significantly prolonged survival of treated as compared to non-treated mice, indicating that myeloid effector cells may contribute to the therapeutic efficacy of CD20 antibodies against human lymphoma cells. In vitro, neither IgG1 nor IgA2 variants of 1F5 showed efficient Fab-mediated effects such as direct cell death induction and homotypic aggregation compared to type II antibodies. However, human IgA2 but not IgG1 antibody variants against CD20 effectively triggered ADCC by human PMN, the most numerous myeloid effector cell population. Although IgA does not bind C1q, CD20 IgA antibodies also triggered CDC against several lymphoma cell lines. CDC was predominantly mediated by the alternative pathway, as evidenced by the kinetics of lysis, the requirement for higher serum concentrations and inhibition by the C3 inhibitor compstatin. Further in vivo experiments demonstrated that 1F5-IgA2 effectively depleted B cells in a syngeneic human CD20 transgenic B cell depletion model. However, studies in human FcαRI transgenic or C3 knock-out mice indicated that B cell depletion was not mediated by FcαRI or complement - suggesting that other currently undefined mechanisms contribute to the in vivo efficacy of IgA antibodies against CD20. Conclusions: Together, the presented results suggest that CD20 antibodies of human IgA isotype constitute promising immunotherapeutic reagents with unique effector functions. Additional studies are required to further elucidate their effector mechanisms in vitro and in vivo. Disclosures Cragg: Roche: Consultancy, Research Funding; Gilead Sciences: Research Funding; Baxalta: Consultancy; Bioinvent International: Consultancy, Research Funding; GSK: Research Funding.

Description: Background: Monoclonal antibodies directed against various target antigens have proven efficacy in cancer therapy including hematological malignancies. Recently, daratumumab and elotuzumab became the first antibodies approved for the treatment of multiple myeloma (MM). Due to the substantial number of patients still in need for long-term disease control, the investigation of additional target structures and potent molecule formats for antibody-based therapy of MM remains important. Methods: Human synthetic single-chain fragment variable (scFv) phage display libraries were subjected to a cellular screening approach. The MSH-TP15 clone was selected based on its binding to various MM cell lines and patient-derived CD138-positive malignant plasma cells. Intercellular adhesion molecule-1 (ICAM-1/CD54), known to be important for the interaction of malignant plasma cells with the bone marrow microenvironment, was identified as target antigen. Based on the scFv sequence, fully human IgG1 antibody variants with selected mutations in the Fc domain were constructed to generate wild-type, antibody-dependent cell-mediated cytotoxicity (ADCC)-optimized and Fc-knockout variants. First, these variants were analyzed for their capacity to kill MM cells in vitro. Apoptosis induction and growth inhibition were tested by flow cytometry and in MTS proliferation assays. ADCC and complement-dependent cytotoxicity were investigated in chromium-release assays using human serum, peripheral blood mononuclear cells or purified NK cells of healthy donors. In vivoefficacy of an ADCC-optimized variant was analyzed in the INA-6 myeloma xenograft model. Results: The MSH-TP15 antibodies target an epitope on the N-terminal part of the extracellular domain of human ICAM-1/CD54. The antibody variants showed no anti-proliferative effects on patient-derived bone marrow stromal cells, nor directly induced apoptosis or inhibited proliferation of myeloma cells. While complement-dependent cytotoxic activity was generally absent, the Fc-engineered antibody variant MSH-TP15e significantly triggered ADCC against various MM cell lines and freshly isolated patient myeloma cells. The recruitment of human NK cells was crucial for the cytotoxic effects observed in vitro. Importantly, an ADCC-optimized variant completely prevented tumor engraftment in the INA-6 xenograft model. Conclusions: The novel ADCC-optimized fully human antibody MSH-TP15e directed against ICAM-1/CD54 exerts potent anti-myeloma activity in vitro and in vivo. Therefore, it has promising characteristics and will be further evaluated for MM immunotherapy. Disclosures Guenther: Novartis: Consultancy, Honoraria; Celgene: Honoraria; Takeda: Consultancy, Honoraria.

Description: Abstract 1838 Despite new treatment modalities, the clinical outcome of at least a subgroup of patients with multiple myeloma still needs improvement. Recently antibody-based targeted therapies with a toxic payload have documented impressing activity. HM1.24 (CD317), a surface molecule overexpressed on malignant plasma cells, is efficiently internalized and may represent a promising target for the development of myeloma-directed immunoconstructs. Here, the generation and characterization of a novel single-chain immunotoxin, HM1.24-ETA′, is described. HM1.24-ETA′ was generated by genetic fusion of a CD317-specific single-chain Fv antibody and a truncated variant of Pseudomonas aeruginosa exotoxin A (ETA′). The immunotoxin was expressed in E. coli and the protein was purified to homogeneity by affinity chromatography. HM1.24-ETA′ efficiently inhibited growth of myeloma cell lines (INA-6, RPMI8226, U266) analyzed in MTT assays. Half maximal growth inhibition was observed at low nanomolar concentrations. Target cell killing occurred via induction of apoptosis as indicated by annexin V / propidium iodide staining and analysis of PARP cleavage. The delivery of HM1.24-ETA′ to target cells is antigen-specific, because excess of unconjugated parental antibody completely blocked the cytotoxic effect. The proliferation of IL-6 dependent INA-6 was efficiently reduced by HM1.24-ETA′ even in co-culture experiments with bone marrow stromal cells that otherwise strongly support tumor cell growth. Importantly, HM1.24-ETA′ strongly triggered apoptosis (up to 80% annexin V-positive cells) of freshly isolated tumor cells from 5 of 5 myeloma patients. In a xenograft SCID mouse model, establishment of INA-6 plasma cell tumors was efficiently abrogated by treatment with HM1.24-ETA′ immunotoxin (p 〈 0.04). Thus, HM1.24-ETA′ immunotoxin in vitro and in the preclinical xenograft model in vivo demonstrates that the CD317 antigen may represent a promising target structure for immunotherapy of multiple myeloma using immunoconjugates with toxic payloads. Disclosures: No relevant conflicts of interest to declare.