Triggering receptor expressed on myeloid cells-1 (TREM-1) is a potent amplifier of pro-inflammatory innate immune reactions. While TREM-1-amplified responses likely aid an improved detection and elimination of pathogens, excessive production of cytokines and oxygen radicals can also severely harm the host. Studies addressing the pathogenic role of TREM-1 during endotoxin-induced shock or microbial sepsis have so far mostly relied on the administration of TREM-1 fusion proteins or peptides representing part of the extracellular domain of TREM-1. However, binding of these agents to the yet unidentified TREM-1 ligand could also impact signaling through alternative receptors. More importantly, controversial results have been obtained regarding the requirement of TREM-1 for microbial control. To unambiguously investigate the role of TREM-1 in homeostasis and disease, we have generated mice deficient in Trem1. Trem1−/− mice are viable, fertile and show no altered hematopoietic compartment. In CD4+ T cell- and dextran sodium sulfate-induced models of colitis, Trem1−/− mice displayed significantly attenuated disease that was associated with reduced inflammatory infiltrates and diminished expression of pro-inflammatory cytokines. Trem1−/− mice also exhibited reduced neutrophilic infiltration and decreased lesion size upon infection with Leishmania major. Furthermore, reduced morbidity was observed for influenza virus-infected Trem1−/− mice. Importantly, while immune-associated pathologies were significantly reduced, Trem1−/− mice were equally capable of controlling infections with L. major, influenza virus, but also Legionella pneumophila as Trem1+/+ controls. Our results not only demonstrate an unanticipated pathogenic impact of TREM-1 during a viral and parasitic infection, but also indicate that therapeutic blocking of TREM-1 in distinct inflammatory disorders holds considerable promise by blunting excessive inflammation while preserving the capacity for microbial control.

Polysarcosine (pSar) is a polypeptoid based on the endogenous amino acid sarcosine (N-methylated glycine), which has previously shown potent stealth properties. Here, lipid nanoparticles (LNPs) for therapeutic application of messenger RNA were assembled using pSarcosinylated lipids as a tool for particle engineering. Using pSar lipids with different polymeric chain lengths and molar fractions enabled the control of the physicochemical characteristics of the LNPs, such as particle size, morphology, and internal structure. In combination with a suited ionizable lipid, LNPs were assembled, which displayed high RNA transfection potency with an improved safety profile after intravenous injection. Notably, a higher protein secretion with a reduced immunostimulatory response was observed when compared to systems based on polyethylene glycol (PEG) lipids. pSarcosinylated nanocarriers showed a lower proinflammatory cytokine secretion and reduced complement activation compared to PEGylated LNPs. In summary, the described pSar-based LNPs enable safe and potent delivery of mRNA, thus signifying an excellent basis for the development of PEG-free RNA therapeutics.

Intestinal mononuclear phagocytes (iMNP) are critically involved in mucosal immunity and tissue homeostasis.

Polysarcosine (pSar) was one of the first polymers synthesized in a controlled living manner, but it was only recently when it was reconsidered as a promising alternative for poly­(ethylene glycol) (PEG) in biomedical applications. Despite receiving more and more attention, very little is known about the solution properties of pSar, such as coil dimensions and thermodynamic interactions. In this article, we report on these properties of pSar with degrees of polymerization 50 < X n < 400 that were prepared by controlled living ring-opening polymerization. The polymers are characterized by gel permeation chromatography (GPC), MALDI-TOF mass spectrometry, dynamic and static light scattering (SLS), and viscometry. The chain stiffness of pSar in PBS in terms of the Kuhn statistical segment length, l k, was estimated to l k = 1.5 nm by application of the Yamakawa–Fujii wormlike chain theory to the experimentally determined hydrodynamic radii, R h, thus being higher than l k = 1.1 nm for PEG in PBS. Also, the second virial coefficients, A 2, of pSar and PEG in PBS were similar and reflect their good solubility in aqueous solution. While the universal calibration of GPC elution volumes failed for pSar in HFIP utilizing PMMA standards, it worked better in PBS buffer with PEG standards. Alternatively, an R h–M w relation is established in the present work, which enables the determination of molar masses of pSar by simple DLS measurements. In addition, it is demonstrated that pSar independent from its chain length (50 < X n < 400) does not induce any detectable complement activation (C5a) in human serum.

We report on the preparation of the first material for therapeutic delivery of CO. A peptide amphiphile was synthesized with a covalently attached ruthenium tricarbonyl. Self-assembled nanofiber gels containing this peptide spontaneously released CO with prolonged release kinetics compared to soluble CO donors. Oxidatively stressed cardiomyocytes had improved viability when treated with this peptide, demonstrating its potential as a biodegradable gel for localized therapeutic CO delivery.

Background Serological immunoassays that can identify protective immunity against SARS‐CoV‐2 are needed to adapt quarantine measures, assess vaccination responses, and evaluate donor plasma. To date, however, the utility of such immunoassays remains unclear. In a mixed‐design evaluation study, we compared the diagnostic accuracy of serological immunoassays that are based on various SARS‐CoV‐2 proteins and assessed the neutralizing activity of antibodies in patient sera. Methods Consecutive patients admitted with confirmed SARS‐CoV‐2 infection were prospectively followed alongside medical staff and biobank samples from winter 2018/2019. An in‐house enzyme‐linked immunosorbent assay utilizing recombinant receptor‐binding domain (RBD) of the SARS‐CoV‐2 spike protein was developed and compared to three commercially available enzyme‐linked immunosorbent assays (ELISAs) targeting the nucleoprotein (N), the S1 domain of the spike protein (S1) and a lateral flow immunoassay (LFI) based on full‐length spike protein. Neutralization assays with live SARS‐CoV‐2 were performed. Results One‐thousand four‐hundred and seventy‐seven individuals were included comprising 112 SARS‐CoV‐2 positives (defined as a positive real‐time PCR result; prevalence 7.6%). IgG seroconversion occurred between day 0 and day 21. While the ELISAs showed sensitivities of 88.4% for RBD, 89.3% for S1, and 72.9% for N protein, the specificity was above 94% for all tests. Out of 54 SARS‐CoV‐2 positive individuals, 96.3% showed full neutralization of live SARS‐CoV‐2 at serum dilutions ≥1:16, while none of the 6 SARS‐CoV‐2 negative sera revealed neutralizing activity. Conclusions ELISAs targeting RBD and S1 protein of SARS‐CoV‐2 are promising immunoassays which shall be further evaluated in studies verifying diagnostic accuracy and protective immunity against SARS‐CoV‐2.

Controlling the number of monomers in a supramolecular polymer has been a great challenge in programmable self-assembly of organic molecules. One approach has been to make use of frustrated growth of the supramolecular assembly by tuning the balance of attractive and repulsive intermolecular forces. We report here on the use of covalent bond formation among monomers, compensating for intermolecular electrostatic repulsion, as a mechanism to control the length of a supramolecular nanofiber formed by self-assembly of peptide amphiphiles. Circular dichroism spectroscopy in combination with dynamic light scattering, size-exclusion chromatography, and transmittance electron microscope analyses revealed that hydrogen bonds between peptides were reinforced by covalent bond formation, enabling the fiber elongation. To examine these materials for their potential biomedical applications, cytotoxicity of nanofibers against C2C12 premyoblast cells was tested. We demonstrated that cell viability increased with an increase in fiber length, presumably because of the suppressed disruption of cell membranes by the fiber end-caps.

A series of well-defined polypeptide-polypeptoid block copolymers based on the body's own amino acids sarcosine and lysine are prepared by ring opening polymerization of N-carboxyanhydrides. Block lengths were varied between 200-300 for the shielding polysarcosine block and 20-70 for the complexing polylysine block. Dispersity indexes ranged from 1.05 to 1.18. Polylysine is polymerized with benzyloxycarbonyl as well as trifluoroacetyl protecting groups at the ϵ-amine group and optimized deprotection protocols for both groups are reported. The obtained block ionomers are used to complex pDNA resulting in the formation of polyplexes (PeptoPlexes). The PeptoPlexes can be successfully applied in the transfection of HEK 293T cells and are able to transfect up to 50% of cells in vitro (FACS assay), while causing no detectable toxicity in an Annexin V assay. These findings are a first indication that PeptoPlexes may be a suitable alternative to PEG based non-viral transfection systems.