Biology subjects

Missiakas, D.

Publications and source records attributed to Missiakas, D..

5 recordsLinked to original sources

bioRxiv2026

Polymer-lipid hybrid nanoparticle enhances mRNA delivery and T cell-mediated immunity

mRNA vaccines have transformed prophylactic immunization against infectious diseases as well as therapeutic interventions for cancer. However, their effectiveness against emerging viral variants and a range of malignancies continues to be hindered by suboptimal induction of T cell-mediated immunity. To overcome this limitation, here we developed a polymer-lipid hybrid nanoparticle (PLNP) platform engineered to improve mRNA delivery to antigen-presenting cells (APCs) and to potentiate T cell responses. Relative to conventional mRNA lipid nanoparticle (LNP) vaccines, mRNA PLNP vaccines demonstrated markedly improved lymph node targeting, APC activation, Th1-biased pro-inflammatory cytokine response, and antigen-specific T cell expansion while retaining robust humoral immunity. Remarkably, mRNA-PLNP vaccines generated approximately 50% more antigen-specific CD8+ T cells than mRNA-LNP vaccines across multiple antigens, including SARS-CoV-2 spike, influenza hemagglutinin, and ovalbumin. In prophylactic applications, mRNA PLNP vaccine provided complete protection against SARS-CoV-2 variants. As a therapeutic approach in a melanoma model, mRNA PLNP vaccination resulted in enhanced tumor control and significantly prolonged survival compared to LNP-based formulations. Collectively, these results establish PLNP as a versatile and broadly applicable platform for augmenting mRNA vaccine efficacy through improved mRNA delivery and T cell priming, offering promising implications for infection prevention and cancer immunotherapy.

immunology↗

bioRxiv2026

Dual-mode ClfA-targeting DARPin biologics protect against diverse methicillin-resistant Staphylococcus aureus strains

Staphylococcus aureus uses the adhesin clumping factor A (ClfA) to bind fibrinogen and promote invasive infection through two distinct interfaces: an exposed, low-afinity site on the N3 head domain and a buried, high-afinity "dock, lock, and latch" (DLL) trench that is exposed only under shear. This dual-interface architecture allows limited antibody penetration, as antibodies typically block only the exposed site. Here, we establish a dual-mode inhibition strategy that overcomes this constraint by combining a high-afinity ClfA-binding designed ankyrin repeat protein (DARPin) with a fibrinogen {gamma}-chain peptide capable of occupying the DLL trench. Using cell-free click display and kinetics-guided afinity maturation, we engineer DARPin-{gamma}-peptide fusion biologics that simultaneously block both fibrinogen-binding interfaces. These molecules inhibit ClfA-fibrinogen interactions, prevent methicillin-resistant S. aureus agglutination in human plasma, neutralize major clinical ClfA variants, and confer Fc-independent protection in a lethal murine bacteremia model. This work provides a strategy for targeting antibody-intractable force-activated staphylococcal adhesins.

molecular biology↗

bioRxiv2025

Type VIIb secretion system recruits a dedicated cell wall hydrolase EssH to enable effector secretion by Staphylococcus aureus

Staphylococcus aureus is a pervasive human pathogen that heavily relies on protein secretion to exert its virulence strategies. S. aureus encodes a specialized type VIIb secretion system (T7SSb) that contributes to virulence and persistence in the host. T7SSb supports secretion of small proteins belonging to a WXG100 family as well as larger LXG polymorphic toxins. Secretion of these proteins is facilitated by the T7SSb complex that assembles in the cell envelope from core components EsaA, EssA, EssB, and the conserved ATPase EssC. T7SSb-mediated secretion also requires the cell wall hydrolase EssH that bears a cystine histidine-dependent amidase/peptidase (CHAP) domain. Hereby, we show that the N-terminal domain of EssH functions together with the CHAP domain to support T7SSb secretion. We find that EssH copurifies with the T7SSb core components and is required for the assembly of EsaA across the cell wall. Finally, secreted EssH is released into the extracellular milieu and degraded by the secreted staphylococcal protease, staphopain A. We propose a model to capture the function of the dedicated cell wall hydrolase EssH for T7SSb in S. aureus. IMPORTANCEStaphylococcus aureus is a leading cause of infections worldwide. S. aureus utilizes a specialized type VIIb secretion system (T7SSb) to persist in the infected host tissues as well as target competitor bacteria to establish its niche. T7SSb assembles into a multiprotein translocation complex and facilitates secretion of a set of small proteins and larger polymorphic toxins across the cytosolic membrane. Beyond the membrane, secreted proteins were thought to diffuse through the thick yet porous cell wall and release into the environment. Here, we demonstrate for the first time that S. aureus T7SSb extends across the cell wall via its EsaA subunit. Furthermore, accommodation of EsaA within the cell wall requires an associated cell wall hydrolase EssH and is essential for protein secretion via T7SSb. Thus, our findings provide a mechanistic insight for a coordinated cell wall processing and T7SSb assembly to support specialized protein secretion in S. aureus.

microbiology↗

bioRxiv2025

Inhibitory activities of monoclonal antibodies against Staphylococcus aureus Clumping factor A

Staphylococcus aureus infection is a frequent cause of sepsis in humans, a disease associated with high mortality and without specific intervention. Clumping factor A (ClfA) displayed on the bacterial surface plays a key role in promoting S. aureus replication during invasive disease. Decades of research have pointed to a wide array of ligands engaged by ClfA. The sum of these interactions supports the unique ability of this pathogen to survive and replicate in the blood stream. One such ligand is fibrin. ClfA acts as the key agglutinating factor of S. aureus by promoting the shielding of bacteria in fibrin cables and their physical escape from phagocytes. Here, we compare a series of monoclonal antibodies elicited against the ligand binding domain of ClfA following immunization of mice. We analyze these antibodies for their ability to neutralize ClfA interactions and to promote the uptake of staphylococci in whole blood. We find that while all the antibodies promoted opsonophagocytic uptake, only those that also inhibited ClfA interactions with ligands, reduced bacterial burdens in animals following blood stream challenge with S. aureus. IMPORTANCEAntibody-based approaches to fight bacterial pathogens have been modeled on toxin-producing or encapsulated pathogens for which correlates of protection can be reduced to measuring antibody neutralization or complement-fixing activities using tissue cultured cells. Such approaches have failed against Staphylococcus aureus raising uncertainty about the value of antibodies. Here, we use a series of mouse monoclonal antibodies directed against ClfA, a surface protein that allows S. aureus to thrive in the blood stream, to query how antibodies may be exploited against a pathogen endowed with a formidable array of virulence factors.

microbiology↗

bioRxiv2023

Reply to Barton et al: signatures of natural selection during the Black Death

Barton et al.1 raise several statistical concerns regarding our original analyses2 that highlight the challenge of inferring natural selection using ancient genomic data. We show here that these concerns have limited impact on our original conclusions. Specifically, we recover the same signature of enrichment for high FST values at the immune loci relative to putatively neutral sites after switching the allele frequency estimation method to a maximum likelihood approach, filtering to only consider known human variants, and down-sampling our data to the same mean coverage across sites. Furthermore, using permutations, we show that the rs2549794 variant near ERAP2 continues to emerge as the strongest candidate for selection (p = 1.2x10-5), falling below the Bonferroni-corrected significance threshold recommended by Barton et al. Importantly, the evidence for selection on ERAP2 is further supported by functional data demonstrating the impact of the ERAP2 genotype on the immune response to Y. pestis and by epidemiological data from an independent group showing that the putatively selected allele during the Black Death protects against severe respiratory infection in contemporary populations.

genomics↗