α-Galactosylceramide-Reactive NKT Cells Increase IgG1 Class Switch against a Clostridioides difficile Polysaccharide Antigen and Enhance Immunity against a Live Pathogen Challenge

B cell-expressed CD1d promotes MPL/TDCM lipid emulsion adjuvant effects in polysaccharide vaccines

T cell-independent type 2 antigens (TI-2 Ags), such as pneumococcal polysaccharides, elicit weak immunoglobulin G (IgG) responses and are refractive to boosting. Overcoming this challenge is critical for improving vaccines. Previously, we demonstrated a lipid-based adjuvant composed of monophosphoryl lipid A, synthetic cord factor, and squalene significantly boosts primary and secondary IgM and IgG production against polysaccharide Ags. Herein, we show beta-2 microglobulin, but not MHC class II, is essential for adjuvant-induced increases in polysaccharide-specific IgG levels. Furthermore, we demonstrate CD1d expression is essential for optimal adjuvant-induced increases in IgG, but is not required for IgG responses to TI-2 Ags administered without adjuvant, with the exception of the bacterial cell wall polysaccharide component, phosphorylcholine. Adoptive transfer of splenic and peritoneal cells from VHB1-8 transgenic mice into CD1d-/- mice revealed adjuvant-induced increases in NP-Ficoll-specific IgG production by CD1d+/+ transgenic B cells, but not recipient B cells, suggesting B cell-expressed CD1d is critical for adjuvant-induced effects on TI-2 antibody responses. Consistent with this, bone marrow chimera mice with selective CD1d deficiency in B cells demonstrated B cell-expressed CD1d was dispensable for iNKT cell development and maintenance but was required for adjuvant-induced increases in protective levels of polysaccharide- and phosphorylcholine-specific IgG. Notably, both iNKT cells and CD1d crosslinking significantly increased IgG production by B cells coactivated with TI-2 Ag and adjuvant, suggesting iNKT-induced CD1d signaling may promote increased IgG production. In summary, our study reveals B cell-dependent CD1d expression is critical for effectiveness of a potent lipid-based adjuvant in augmenting polysaccharide- and phosphorylcholine-specific IgG responses.

Can invariant Natural Killer T cells drive B cell fate? a look at the humoral response

Invariant Natural Killer T (NKT) cells represent a unique subset of innate-like T cells that express both NK cell and T cell receptors. These cells are rapidly activated by glycolipid antigens presented via CD1d molecules on antigen-presenting cells (APCs), including B cells, dendritic cells (DCs), and macrophages, or through cytokine-dependent mechanisms. Their ability to produce a wide range of cytokines and express costimulatory molecules underscores their critical role in bridging innate and adaptive immunity. B cells, traditionally recognized for their role in antibody production, also act as potent APCs due to their high expression of CD1d, enabling direct interactions with iNKT cells. This interaction has significant implications for humoral immunity, influencing B cell activation, class-switch recombination (CSR), germinal center formation, and memory B cell differentiation, thus expanding the conventional paradigm of T cell-B cell interactions. While the influence of iNKT cells on B cell biology and humoral responses is well-supported, many aspects of their interaction remain unresolved. Key questions include the roles of different iNKT cell subsets, the diversity of APCs, the spatiotemporal dynamics of these interactions, especially during early activation, and the potential for distinct glycolipid ligands to modulate immune outcomes. Understanding these factors could provide valuable insights into how iNKT cells regulate B cell-mediated immunity and offer opportunities to harness these interactions in immunotherapeutic applications, such as vaccine development. In this review, we examine these unresolved aspects and propose a novel perspective on the regulatory potential of iNKT cells in humoral immunity, emphasizing their promise as a target for innovative vaccine strategies.

Enhancing COVID-19 Vaccine Efficacy: Dual Adjuvant Strategies with TLR7/8 Agonists and Glycolipids

The controlled release of immunostimulatory agents represents a promising strategy to enhance vaccine efficacy while minimizing side effects. This study aimed to improve the efficacy of the RBD-Fc-based COVID-19 vaccine through combining of an iNKT cell agonist and a TLR7/8 agonist using covalent conjugation and temporal delivery. We hypothesized that these combinations would yield a more balanced Th1/Th2 immune response. For covalent conjugation, we employed an uncleavable linker and a self-immolative disulfide linker to conjugate α-galactosylceramide (αGC) to imidazoquinoline (IMDQ). The αGC-SS-IMDQ-Ac conjugate, designed with a prodrug strategy for controlled TLR7/8 agonist release, elicited a higher IFN-γ/IL-4 T cell response ratio than individual adjuvants or their admixture. In the temporal delivery approach, administering IMDQ followed by αGC after 2 h resulted in the highest IgG2a/IgG1 ratio, significantly surpassing other groups. A 6 h delay between glycolipid and IMDQ injections yielded balanced IgG responses, enhancing IgG, IgG1, and IgG2a levels synergistically.

Bioactivities and Anti-Cancer Activities of NKT-Stimulatory Phenyl-Glycolipid Formulated with a PEGylated Lipid Nanocarrier

Purpose

The glycolipid α-galactosylceramide (α-GalCer), when presented by CD1d, can modulate the immune system through the activation of natural killer T (NKT) cells. Previously, we synthesized over 30 analogs of α-GalCer and identified a compound, C34, which features two phenyl rings on the acyl chain. C34 exhibited the most potent NKT-stimulating activities, characterized by strong Th1-biased cytokines and potent anti-tumor effects in several murine tumor models. Importantly, unlike α-GalCer, C34 did not induce NKT cell anergy. Despite these promising results, the clinical application of C34 is limited by its poor aqueous solubility. PEGylation enhances the solubility of hydrophobic drugs, and numerous PEGylated drugs have received clinical approval. Consequently, we assessed the biological activity of PEGylated C34 in this study.

Methods

Murine NK1.2 cells were cultured with A20-CD1d cells in the presence of either PEGylated lipid nanocarriers encapsulating C34 (PLN-C34) or C34 dissolved in DMSO to determine IL-2 production via ELISA. C57BL/6 mice were i.v. injected with C34 or PLN-C34 to examine cytokine profiles and immune cell populations using luminex and flow cytometry, respectively. The anticancer effects of C34 and PLN-C34 were evaluated in mice bearing TC-1 lung cancer and B16 melanoma tumors. Additionally, human PBMCs were cultured with C34 or PLN-C34 to measure cytokine production through luminex.

Results

PLN-C34 demonstrated a comparable capacity to C34 in activating the NKT cell line in vitro and inducing various cytokines in vivo. Furthermore, treatment with either PLN-C34 or C34 significantly prolonged the survival of TC-1- and B16F10-bearing mice to a similar extent. Additionally, PLN-C34 effectively stimulated cytokine responses in human NKT cells, comparable to those induced by C34.

Conclusion

These findings demonstrate that the newly formulated PLN-C34 retains NKT-stimulatory activity and anti-cancer efficacy of C34, supporting the potential of PLN as a solvent for C34 for further development in cancer therapy.

The screening, identification, design and clinical application of tumor-specific neoantigens for TCR-T cells

Recent advances in neoantigen research have accelerated the development of tumor immunotherapies, including adoptive cell therapies (ACTs), cancer vaccines and antibody-based therapies, particularly for solid tumors. With the development of next-generation sequencing and bioinformatics technology, the rapid identification and prediction of tumor-specific antigens (TSAs) has become possible. Compared with tumor-associated antigens (TAAs), highly immunogenic TSAs provide new targets for personalized tumor immunotherapy and can be used as prospective indicators for predicting tumor patient survival, prognosis, and immune checkpoint blockade response. Here, the identification and characterization of neoantigens and the clinical application of neoantigen-based TCR-T immunotherapy strategies are summarized, and the current status, inherent challenges, and clinical translational potential of these strategies are discussed.

Structure and synthesis of a vaccine and diagnostic target for Enterocloster bolteae, an autism-associated gut pathogen – Part II

Enterocloster bolteae (formerly known as Clostridium bolteae) is a gastro-intestinal pathogenic bacterium often detected in the fecal microbiome of children in the autism spectrum. E. bolteae excretes metabolites that are thought to act as neurotoxins. This study is an update of our first E. bolteae investigation that discovered an immunogenic polysaccharide. Through a combination of chemical derivatizations/degradations, spectrometry and spectroscopy techniques, a polysaccharide composed of disaccharide repeating blocks comprised of 3-linked β-d-ribofuranose and 4-linked α-l-rhamnopyranose, [→3)-β-D-Ribf-(1 → 4)-α-L-Rhap-(1→]_n, was identified. To confirm the structure, and to provide material for subsequent investigations, the chemical synthesis of a corresponding linker-equipped tetrasaccharide, β-D-Ribf-(1 → 4)-α-L-Rhap-(1 → 3)-β-D-Ribf-(1 → 4)-α-L-Rhap-(1→O(CH₂)₈N₃, is also described. Research tools based on this immunogenic glycan structure can form the foundation for serotype classification, diagnostic/vaccine targets and clinical studies into the hypothesized role of E. bolteae in the onset/augmentation of autism related conditions in children.

Serum IgM antibody response to Clostridioides difficile polysaccharide PS-II vaccination in pony foals

OBJECTIVES

Clostridioides difficile (formerly Clostridium difficile) is associated with colitis in foals and mature horses. C. difficile exposes specific phosphorylated polysaccharides (PSs), named PS-I, PS-II and PS-III. These cell-surface PSs are potential vaccine targets, especially the hexasaccharide phosphate PS-II, that has been found in all C. difficile ribotypes examined. Since we previously identified anti-PS-II circulating antibodies in horses, we postulated that vaccinating foals with PS-II may prevent colonization by C. difficile. In this study, we aim to evaluate the IgM antibody responses in foals to PS-II.

METHODS

To evaluate the reactogenicity and immunogenicity of C. difficile PS-II in foals, three-to four-month-old foals were vaccinated intramuscularly three times at intervals of three weeks with 100 μg/dose (3 foals) or 500 μg/dose (3 foals) of purified PS-II antigen with aluminum hydroxide adjuvant, or with a placebo preparation (2 foals) containing adjuvant alone.

RESULTS

No injection site swelling, pain or fever was observed after vaccination. Two of the three foals receiving 100 μg/dose, and three out of three foals receiving 500 μg/dose of PS-II responded with increases in serum IgM antibodies. No control foals that received the placebo had IgM responses to PS-II. There was a trend towards a higher response rate in foals receiving 500  μg PS-II one week after second vaccination when compared to control foals and towards higher concentrations of serum IgM antibodies in foals receiving 500  μg PS-II.

CONCLUSIONS

No adverse reactions were observed following vaccination with PS-II in foals; Serum IgM immune responses were induced by vaccination. A polysaccharide-based vaccine for C. difficile in horses deserves further investigation.

Use of a Clostridioides difficile Murine Immunization and Challenge Model to Evaluate Single and Combination Vaccine Adjuvants Consisting of Alum and NKT Cell-Activating Ligands

Adjuvant combinations may enhance or broaden the expression of immune responses to vaccine antigens. Information on whether established Alum type adjuvants can be combined with experimental CD1d ligand adjuvants is currently lacking. In this study, we used a murine Clostridioides difficile immunization and challenge model to evaluate Alum (Alhydrogel™), α-galactosylceramide (α-GC), and one of its analogs 7DW8-5 singly and in combination as vaccine adjuvants. We observed that the Alum/α-GC combination caused modest enhancement of vaccine antigen-specific IgG1 and IgG2b responses, and a broadening to include IgG2c that did not significantly impact overall protection. Similar observations were made using the Alum/7DW8-5 combination. Examination of the impact of adjuvants on NKT cells revealed expansion of invariant NKT (iNKT) cells with modest expansion of their iNKTfh subset and little effect on diverse NKT (dNKT) cells. Side effects of the adjuvants was determined and revealed transient hepatotoxicity when Alum/α-GC was used in combination but not singly. In summary these results showed that the Alum/α-GC or the Alum/7DW8-5 combination could exert distinct effects on the NKT cell compartment and on isotype switch to produce Th1-driven IgG subclasses in addition to Alum/Th2-driven subclasses. While Alum alone was efficacious in stimulating IgG-mediated protection, and α-GC offered no apparent additional benefit in the C. difficile challenge model, the work herein reveals immune response features that could be optimized and harnessed in other vaccine contexts.