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DISC-0974 is a humanized monoclonal anti-HJV antibody with high binding affinity for human, rat and cynomolgus monkey HJV (100 pM, 240 pM and 110 pM Kd, respectively) [Kovac 2016]. DISC-0974 inhibits the interaction between HJV and the key hepcidin regulatory ligands, bone morphogenetic proteins (BMPs), leading to decreased SMAD phosphorylation (SMAD-P) and reduced hepcidin expression [Kovak 2016]. Elevated hepcidin is a hallmark of and plays a critical role in the pathogenesis of anemia of inflammation (and other forms of anemia) by reducing transferrin saturation and erythroid iron availability, leading to failure of erythropoiesis and decreased hemoglobin synthesis. DISC-0974 is being developed to reduce hepcidin synthesis and treat anemia in these patients. A critical early signal of therapeutic effect is the effect of DISC-0974 on transferrin saturation (TSAT). TSAT has therefore been used as the primary pharmacodynamic marker in a series of non-clinical studies to determine the relationship between drug exposure and pharmacological activity. In non-human primates (NHP) DISC-0974 elicits a dose-dependent reduction in hepcidin levels leading to increases in serum iron and consequently TSAT. PK/PD responses were examined over 60 days for a single 6 mg/kg intravenous dose of DISC-0974 in three male NHPs and in repeat dose studies occurring at 14 day intervals administered 3 times (vehicle, 0.6 and 3 mg/kg) or two times (60 mg/kg). In these studies, the serum iron response saturated in an exposure-dependent manner over the 0.6-60 mg/kg dose range. The onset of iron elevation lagged compared to the DISC-0974 maximal plasma concentrations by 1- 4 days post dose and persisted beyond what could be predicted by DISC-0974 plasma concentration alone. The observed PD responses were well-described by a delayed response PK/PD model of serum iron which was fit globally to all studies. We will present single and multiple dose simulations showing that low monthly doses of DISC-0974 are sufficient to elicit a biologically significant and controlled PD modulation (serum iron, TSAT, hepcidin) over a sustained period-of-time (Figure 1). DISC-0974 is under development for the treatment of anemia of inflammation associated with high hepcidin. Disclosures Blaustein: Disc Medicine:Current Employment, Current equity holder in private company.King:Disc Medicine:Current Employment, Current equity holder in private company.Nguyen:Disc Medicine:Current Employment, Current equity holder in private company.Savage:Disc Medicine:Current Employment, Current equity holder in private company.Beconi:Disc Medicine:Current Employment, Current equity holder in private company.

In diseases characterized by chronic inflammation, hepcidin levels are often elevated causing reduced transferrin-bound iron, reduced erythroid iron availability, diminished erythropoiesis and anemia despite the presence of adequate iron stores. Hemojuvelin (HJV) is a key selective regulator of hepcidin production in humans; patients with homozygous loss-of-function in the gene coding for HJV exhibit dramatically reduced hepcidin levels and a severe iron overload syndrome, juvenile hemochromatosis Type 2A. DISC-0974 is a humanized monoclonal anti-HJV antibody with high binding affinity for human, rat and cynomolgus monkey HJV (100 pM, 240 pM and 110 pM Kd, respectively) [Kovac 2016]. DISC-0974 inhibits the interaction between HJV and the key hepcidin regulatory ligands, bone morphogenetic proteins (BMPs), leading to decreased SMAD phosphorylation (SMAD-P) and reduced hepcidin expression [Kovak 2016]. The multiple-dose pharmacokinetics and pharmacodynamics (PK/PD) of DISC-0974 was first evaluated in healthy NHPs in which regulation of iron metabolism is primarily controlled by BMP/SMAD regulation of hepcidin synthesis. Dose levels were selected to modulate the pharmacodynamic response (transferrin saturation [TSAT]) but to be either below saturation (0.6 mg/kg), or to saturate the TSAT response (3 and 60 mg/kg). As expected from the mechanism of action, hepcidin concentrations decreased following DISC-0974 administration with return to baseline that was exposure dependent. The decrease in hepcidin was associated with increased TSAT, which DISC-0974 modulated in a dose-dependent manner. At 0.6 mg/kg, the TSAT response was maintained below saturation (~65%) after the first dose; saturation increased following subsequent doses, consistent with higher DISC-0974 serum concentrations. At the 3.0 and 60 mg/kg doses TSAT saturation (>85%) was achieved within 5 days post first dose and remained elevated through the end of the study, also consistent with the serum concentrations of DISC-0974. In vivo efficacy of DISC-0974 was evaluated in an NHP model of inflammation-induced (IL-6) high-hepcidin to establish whether inhibition of BMP/SMAD signaling could effectively control hepcidin increases generated by inflammatory signals. In this study, monkeys were challenged with 6×104 IU IL-6/kg on Day 1 and on Day 4. Groups of N=3 received 0 (vehicle), 0.6 or 6 mg/kg DISC-0974. On Day 11 all groups received a second challenge of 6×104 IU IL-6/kg. TSAT, hepcidin-25 and DISC-0974 concentrations were determined. DISC-0974 was effective in preventing IL-6-induced hepcidin increase in a dose-dependent manner in this model (Figure 1). In summary, in healthy NHPs, administration of DISC-0974 causes reduction in hepcidin levels leading to release of stored iron from macrophages of the reticuloendothelial system, making iron available for erythropoiesis as demonstrated by the dose-dependent modulation of TSAT. DISC-0974 is also effective in preventing hepcidin increases caused by IL-6, which is generally regarded at the classical cytokine stimulator of hepcidin synthesis. Given the similarity of the mechanism of hepcidin regulation between NHPs and humans, DISC-0974 is anticipated to provide a similar effect in the treatment of anemia of inflammation in humans by lowering cytokine-induced increases in hepcidin and improving iron availability for erythropoiesis. Figure Disclosures MacDonald: Disc Medicine: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees. Blaustein:Disc Medicine: Current Employment, Current equity holder in private company. Nguyen:Disc Medicine: Current Employment, Current equity holder in private company. King:Disc Medicine: Current Employment, Current equity holder in private company. Hong:Disc Medicine: Current Employment, Current equity holder in private company. Savage:Disc Medicine: Current Employment, Current equity holder in private company. Venkatraman:Disc Medicine: Current Employment, Current equity holder in private company. Beconi:Disc Medicine: Current Employment, Current equity holder in private company.

Delayed T-cell recovery is an important complication of allogeneic bone marrow transplantation (BMT). We demonstrate in murine models that donor BM-derived T cells display increased apoptosis in recipients of allogeneic BMT with or without GVHD. Although this apoptosis was associated with a loss of Bcl-2 and Bcl-XL expression, allogeneic recipients of donor BM deficient in Fas-, tumor necrosis factor–related apoptosis-inducing ligand (TRAIL)- or Bax-, or BM-overexpressing Bcl-2 or Akt showed no decrease in apoptosis of peripheral donor-derived T cells. CD44 expression was associated with an increased percentage of BM-derived apoptotic CD4+ and CD8+ T cells. Transplantation of RAG-2-eGFP–transgenic BM revealed that proliferating eGFPloCD44hi donor BM-derived mature T cells were more likely to undergo to apoptosis than nondivided eGFPhiCD44lo recent thymic emigrants in the periphery. Finally, experiments using carboxyfluorescein succinimidyl ester–labeled T cells adoptively transferred into irradiated syngeneic hosts revealed that rapid spontaneous proliferation (as opposed to slow homeostatic proliferation) and acquisition of a CD44hi phenotype was associated with increased apoptosis in T cells. We conclude that apoptosis of newly generated donor-derived peripheral T cells after an allogeneic BMT contributes to delayed T-cell reconstitution and is associated with CD44 expression and rapid spontaneous proliferation by donor BM-derived T cells.

Graft-versus-host disease (GVHD) is a serious complication of allogeneic bone marrow transplantation, and donor T cells are indispensable for GVHD. Current therapies have limited efficacy, selectivity, and high toxicities. We used a novel flow cytometry technique for the analysis of intracellular phosphorylation events in single cells in murine BMT models to identify and validate novel GVHD drug targets.1-7 This method circumvents the requirement for large numbers of purified cells, unlike western blots. We defined a signaling profile for alloactivated T cells in vivo and identified the phosphorylation of ERK1/2 and STAT-3 as important events during T-cell (allo)activation in GVHD. We establish that interference with STAT-3 phosphorylation can inhibit T-cell activation and proliferation in vitro and GVHD in vivo. This suggests that phospho-specific flow cytometry is useful for the identification of promising drug targets, and ERK1/2 and STAT-3 phosphorylation in alloactivated T cells may be important for GVHD.

234 Thymic GVHD (tGVHD) after allogeneic bone marrow transplantation (allo-BMT) is associated with prolonged immunodeficiency. We have previously shown that thymic output after allo-BMT is directly related to thymus size, and inversely related to donor T cell dose and GVHD severity. Additionally, radiation-containing preparative regimens upregulate the death receptors Fas and DR5 on thymic stroma (especially epithelium) while decreasing expression of the anti-apoptotic protein cFLIP, thereby sensitizing the thymus to GVHD. Moreover, small numbers of donor alloreactive T cells are sufficient to cause tGVHD, and they utilize the Fas/Fas ligand (FasL) and TRAIL/DR5 pathways to mediate damage thymic stroma, architecture and function. We performed experiments in both MHC-mismatched and MHC-matched minor antigen-disparate model systems, and demonstrated the exquisite sensitivity of the thymus to as few as 1–2.5×10 5 donor T cells, which mediated tGVHD without evidence of overt clinical disease or significant weight loss. Additionally, tGVHD is partially reversible in our model systems (contingent on a low T cell dose), such that mice with tGVHD exhibit a transient but partially reversible decrease in thymic cellularity when measured at days 28 vs. 60 post-transplant (Figure 1). To further study the role of TRAIL in tGVHD, we asked whether (1) alloreactive T cells and (2) the inflammation associated with conditioning and acute GVHD, were strictly required for TRAIL/DR5-mediated thymic damage. We treated recipients of T cell-depleted allo-BMT with the amDR5-1 agonistic antibody (0.2 mg i.p. per dose) either in the ‘early‘ peri-transplant period, or ‘late,‘ in the second week post-transplant. Allo-BMT recipients treated ‘early‘ with amDR5-1 had significantly decreased thymic cellularity and splenic BM-derived T cells as compared with controls. Furthermore, we observed similar BM cellularity and BM-derived lineage − sca-1 + ckit + (LSK), all in the absence of donor alloreactive T cells and GVHD (Figure 2). We observed similar results with mice treated ‘late‘ amDR5-1 using the later schedule, which indicates that the thymus has continued sensitivity to TRAIL throughout the post-transplant period, and that GVHD and/or conditioning-associated cytokines are not required to enable TRAIL-mediated damage to the thymus. We further assessed the expression of DR5 on donor BM-derived thymocytes to determine whether amDR5-1 acted directly on thymocytes. We observed that on day 28 after T cell-depleted allo-BMT, only 1-2% of donor thymocytes expressed DR5, suggesting that amDR5-1 (and potentially TRAIL) mediate their effects on thymic cellularity and function primarily via an indirect mechanism (Figure 3). These data suggest to us that significant damage to the thymus and thymopoiesis during allo-BMT: can be mediated by soluble TRAIL agonists, even without the presence of whole donor alloreactive T cells can occur, via the TRAIL pathway, without a full complement of the inflammatory processes typically associated with GVHD pathophysiology, including the cytokine storm, and can occur early and late post-transplant, and that early exposure of the thymus to TRAIL/DR5 signals are sufficient to cause a durable loss in thymic cellularity, donor CD4 + CD8 + thymocytes counts, and numbers of donor BM T cells exported to the periphery. ccurs via the TRAIL pathway, without significant direct damage (via TRAIL/DR5 interactions) to the bone marrow compartment, and thus by implication, thymic-seeding precursors derived from the BM. Together, our data in clinically-relevant mouse allo-BMT models suggests that the thymus is highly sensitive to GVHD and endures severe damage at relatively low levels of systemic GVHD. Moreover, post-transplant thymic atrophy is a partially-reversible process which depends on the T cell dose, and which occurs via the TRAIL pathway. Finally, we provide significant mechanistic insight which shows that TRAIL-mediated thymic damage can occur (1) throughout the early post-transplant period, and (2) does not strictly require alloreactive T cells, or the inflammatory processes associated with conditioning and GVHD. Disclosures: No relevant conflicts of interest to declare.

T cell deficiencies can occur in many settings, including aging, autoimmune and genetic disorders, hematological malignancies, infectious diseases, and exposure to cytotoxic/cytostatics agents. Notch-based culture systems can be utilized for ex vivo generation of large numbers of T lineage committed lymphoid precursor cells, and we recently reported that the adoptive transfer of T cell precursors significantly enhances T cell reconstitution and function after allogeneic T cell depleted HSCT. The aim of this study was to evaluate if allogeneic T cell precursors are safe and effective when used for adoptive transfer across MHC barriers in the absence of allogeneic HSCs to overcome radiation injury, enhance T cell function and improve anti-tumor activity in immunosuppressed recipients. We found that positive selection of adoptively transferred allogeneic (C57BL/6) precursor cells ± syngeneic (BALB/c) HSCs in irradiated hosts (BALB/c) is dependent on MHC molecules on non-hematopoietic host cells, resulting in the in vivo development of host-MHC restricted allogeneic T cells. We demonstrate that negative selection of these cells is mediated by donor-derived antigen presenting cells (APCs), resulting in host-tolerance. Adoptively transferred allogeneic T cell precursors significantly improved survival of BALB/c mice after irradiation (675 cGy) and enhanced anti-tumor activity against liquid (A20 lymphoma) and solid (renal cell carcinoma) tumors in syngeneic HSCT recipients. Furthermore, we demonstrate the feasibility of genetic engineering of antigen-specific T cell precursors, by transducing them to express a chimeric antigen receptor (CAR) targeting human CD19. Transduction efficiencies were routinely in the range of 50%–70%. Adoptive transfer of CAR-expressing T cell precursors resulted in the in vivo generation of high numbers of appropriately selected CAR-expressing T cells with significantly enhanced anti-tumor activity (compared with CAR-negative T cell precursors) against a CAR-sensitive tumor, but without any undesirable auto/alloreactivity. We conclude that adoptively transferred allogeneic T cell precursors develop into host-MHC restricted and host-tolerant T cells characterized by selection of a functional TCR repertoire even in a fully mismatched thymic epithelial MHC environment. This strategy overcomes important limitations of conventional adoptive T cell therapies: rejection, alloreactivity and impaired antigen recognition due to restriction to MHC disparate from the one expressed on APCs. The use of allogeneic instead of autologous cells eliminates the risk of contamination with residual malignant patient cells and allows the generation and storage of virtually unlimited quantities of precursor cells for ‘off-the-shelf’ immunotherapy. This procedure has not only substantial logistic advantages, but it facilitates ex vivo manipulation, in particular genetic engineering, to generate antigen-specific or otherwise enhanced designer cells. Adoptive transfer of MHC mismatched and genetically enhanced T cell precursors therefore represents a promising novel strategy for targeted ‘off-the-shelf’ immunotherapy in immunosuppressed patients.

Carcinoembryonic antigen associated cell adhesion molecule 1 (CEACAM-1) belongs to a family of carcinoembryonic antigen-associated glycoproteins. It is expressed on leukocytes, endothelium, and epithelium. Microarray analysis showed that CEACAM-1 mRNA is increased in the small bowel during gut graft-versus-host-disease (GVHD) after allogeneic bone marrow transplantation (allo-BMT). Using CEACAM-1−/− mice as recipients or sources of donor bone marrow or T cells caused significantly worse GVHD mortality (p

Graft-versus-host-disease (GVHD) is a serious complication of allogeneic bone marrow transplantation (allo-BMT). The physiology of GVHD is dominated by alloactivated donor T cells, yet current treatments are often nonspecific and offer limited efficacy with relatively high toxicities. We screened for novel drug targets in alloactivated T cells in a murine allo-BMT model using a flow cytometric technique for the in vivo analysis of intracellular signaling. We defined the signaling profile of normal T cells and alloreactive T cells during GVHD, focusing on pathways involved in T cell receptor (TCR), costimulatory, and cytokine signaling. This analysis revealed that although proteins in multiple pathways (MAP kinases, PI3K, Jak/STAT signaling) were all heavily phosphorylated in alloactivated T cells, phosphorylation of STAT-3 and ERK1/2 were particularly prominently increased in donor alloactivated CD4 T cells. We further analyzed the importance of STAT-3 and ERK1/2 signaling in alloactivated T cells via the use of small-molecule inhibitors of STAT-3 (curcurbitacin E/I) and ERK1/2 phosphorylation (SL327). Treatment with these inhibitors attenuated T cell proliferation in response to anti-CD3+CD28 stimulation and in mixed leukocyte reactions in vitro in a dose-dependent fashion (figure 1). Figure 1 Figure 1. Pre-incubation of donor splenocytes with cucurbitacin E significanly reduced T cell activation (CD25, CD69) at 24 hours in adoptive transfer experiments in vivo (p Figure 2 Figure 2. We conclude that flow cytometric analysis of signaling pathways in single cells represents a novel methodology to assess the in vivo signaling profiles of specific cell populations in order to select drug targets for further study. STAT-3 and ERK1/2 phosphorylation may also represent potential targets to selectively inhibit donor T cell alloactivation and proliferation in GVHD.