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The triggering receptor expressed on myeloid cells 1 (TREM-1) plays an important role in the innate immune response related to severe infections and sepsis. Modulation of TREM-1–associated activation improves the outcome in rodent models for pneumonia and sepsis. However, the identity and occurrence of the natural TREM-1 ligands are so far unknown, impairing the further understanding of the biology of this receptor. Here, we report the presence of a ligand for TREM-1 on human platelets. Using a recombinant TREM-1 fusion protein, we demonstrate specific binding of TREM-1 to platelets. TREM-1–specific signals are required for the platelet-induced augmentation of polymorphonuclear leukocyte (PMN) effector functions (provoked by LPS). However, TREM-1 interaction with its ligand is not required for platelet/PMN complex formation, which is dependent on integrins and selectins. Taken together, the results indicate that the TREM-1 ligand is expressed by platelets, and the TREM-1/ligand interaction contributes to the amplification of LPS-induced PMN activation. Our results shed new light on our understanding of TREM-1 and its role in the innate inflammatory response in infections and might contribute to the development of future concepts to treat sepsis.

M3258 is an orally bioavailable, potent, selective, reversible inhibitor of the large multifunctional peptidase 7 (LMP7, β5i, PSMB8) proteolytic subunit of the immunoproteasome; a crucial component of the cellular protein degradation machinery, which is highly expressed in malignant hematopoietic cells including multiple myeloma. M3258 was previously shown to deliver strong in vivopreclinical efficacy in multiple myeloma xenograft models, as well as a more benign non-clinical safety profile compared to approved pan-proteasome inhibitors, exemplified by a lack of effects on the central and peripheral nervous systems and cardiac and respiratory organs. Here we describe preclinical PK/PD and PK/efficacy modelling which led to a prediction of the PK profile, and the efficacious and safe dose ranges of M3258 in human which were used to guide the design of the phase I dose-escalation trial of M3258 in >3 line relapsed/refractory multiple myeloma (RRMM) patients.

The triggering receptor expressed on myeloid cells 1 (TREM-1) is an important player in the innate inflammatory response to microbial infections. Activation and expression of TREM-1 by polymorphonuclear neutrophils (PMN) occurs in concert with Toll-like receptors (TLR) such as TLR4 for bacterial lipopolysaccharide. However, it is currently unclear how this is mediated on a molecular level. Using pharmacologic inhibitors and western blot analysis we demonstrate that phosphatidyl inositide 3-kinase, phospholipase C and the mitogen activated kinase p38 are essential for the TREM-1 and TLR4 mediated respiratory burst of human PMN. The down stream phosphorylation of protein kinase B and extracellular signal related kinase show characteristic phosphorylation patterns upon single or co-ligation indicating individual activation pathways of both receptors. TREM-1, but not TLR4 mediated respiratory burst depended on calcium flow via store operated calcium entry channels, while transient receptor potential channels were important for TLR and TREM-1. Taken together, we provide new insights on the mechanisms how TREM-1 and TLR interact creating synergistic activation in PMN. These results shed a new light on our understanding how the innate inflammatory responses are regulated and might contribute to the development of future concepts for the treatment of severe inflammatory conditions such as sepsis.

The triggering receptor expressed on myeloid cells 1 (TREM-1) is constitutively expressed on polymorphonuclear neutrophils (PMN), monocytes and macrophage subsets and has been recently identified as an important player in the innate inflammatory response to microbial infections and sepsis. Expression of TREM-1 and activation of PMN and monocytes is regulated in concert with microbial products via the recognition of Toll-like receptor (TLR) ligands such as bacterial lipopolysaccaride (LPS). However, it is currently unclear how the amplification of the inflammatory responses by TREM-1 and TLR agonists is mediated on an intracellular level. To this end, we were interested to identify signalling events leading to the synergistic activation of PMN upon TREM-1 and TLR ligation. Using pharmacologic inhibitors and western blot analyses we demonstrate that PI3 kinase, PLC-g and p38 MAP kinase are essential for the initiation of the respirator burst as an important and immediate effector mechanism of human PMN. Furthermore, the phosphorylation of PKB/Akt and MAP kinase ERK show a biphasic pattern upon TREM-1/TLR4 coligation indicating distinct activation mechanisms for these receptors. Interestingly, the TLR4, but not TREM-1 mediated respiratory burst was dependent on the activation of ras leading downstream to an augmented calcium flow and subsequently synergistic burst activity. Taken together, we provide a new mechanism how TREM-1 and TLR interact in PMN mediating enhanced activation. These results shed a new light on our understanding how the innate inflammatory responses are regulated and might contribute to the development of future concept for the treatment of a dysregulated immune response in severe inflammatory conditions such as sepsis.