María de Lourdes Betancourt-Mendiola

Layered double hydroxides (LDH) are promising nanocarriers for vaccine delivery due to their biocompatibility and tunable surface properties. This study evaluated LDH and surface-functionalized derivatives containing amino (LDH–NH₂) and carboxyl (LDH–COOH) groups as delivery platforms for a recombinant Zika virus (ZIKV) antigen (rpZDIII). The nanoparticles were synthesized by coprecipitation/hydrothermal treatment and afterward functionalized via silanization and succinylation. Their physicochemical characterization included hydrodynamic size, ζ potential, point of zero charge, and amine concentration, along with Fourier-transform infrared spectroscopy and thermogravimetric analyses. Protein adsorption was evaluated using bovine serum albumin, α-chymotrypsin, and the recombinant antigen rpZDIII. Cytotoxicity and immunogenicity were evaluated in HEK-293T cells and BALB/c mice, respectively. The functionalization affected the protein adsorption capacity and its retention after washing. The adsorption of rpZDIII was best described by the Freundlich model, with LDH–NH₂ having the highest antigen adsorption and retention. All three formulations maintained high cell viability at lower nanoparticle concentrations (12.5–50 μg/mL). Immunization studies demonstrated that all nanoparticle formulations elicited strong antibody responses against rpZDIII; however, only unmodified LDH-induced antibodies were able to bind the full-length recombinant ZIKV envelope protein. These findings demonstrate that the surface chemistry of LDH influences the adsorption of antigens, their retention, and their further immune recognition, highlighting the importance of preserving antigen accessibility during the design of LDH-based nanovaccines.

Background/Objectives: Nanovaccines have significant potential to enhance immunization strategies by improving efficacy, safety, and cost-effectiveness. In particular, organic nanoparticles hold promise for the generation of low-cost nanovaccines obtained by environmentally friendly methods. In this study, the feasibility of using zein nanoparticles (NPs) as carriers for an antigenic peptide (p30) and the receptor binding domain (RBD) from SARS-CoV-2 spike protein was explored. Methods: A synthesis method for zein NPs was established by combining previously reported techniques, and the resulting NPs were characterized in terms of morphology, particle size, polydispersity index (PDI), surface charge, and colloidal stability using dynamic light scattering (DLS) and transmission electron microscopy (TEM). Tween 20 was employed as a surfactant to enhance particle stability and prevent aggregation. Results: The zein NPs were deemed safe based on an in vitro cytotoxicity assay using Vero cells. Immunogenicity assessments demonstrated that zein NPs:p30 and zein NPs:RBD induced IgG responses in test mice, whose magnitude was comparable to those achieved with alum as an adjuvant. Conclusions: These findings support the use of zein NPs as promising vaccine delivery vehicles with adjuvant effects due to their ease and environmentally friendly synthesis, high stability, and low cost.

Subunit vaccines stand as a leading approach to expanding the current portfolio of vaccines to fight against COVID-19, seeking not only to lower costs but to achieve long-term immunity against variants of concern and have the main attributes that could overcome the limitations of the current vaccines. Herein a chimeric protein targeting S1 and S2 epitopes, called LTp50, was designed as a convenient approach to induce humoral responses against SARS-CoV-2. LTp50 was produced in recombinant Escherichia coli using a conventional pET vector, recovering the expected antigen in the insoluble fraction. LTp50 was purified by chromatography (purity > 90%). The solubilization and refolding stages helped to obtain a stable protein amenable for vaccine formulation. LTp50 was adsorbed onto alum, resulting in a stable formulation whose immunogenic properties were assessed in BALB/c mice. Significant humoral responses against the S protein (BA.5 variant) were detected in mice subjected to three subcutaneous doses (10 µg) of the LTp50/alum formulation. This study opens the path for the vaccine formulation optimization using additional adjuvants to advance in the development of a highly effective anti-COVID-19 vaccine directed against the antigenic regions of the S protein, which are less prone to mutations.

Clay materials and nanoclays have gained recent popularity in the vaccinology field, with biocompatibility, simple functionalization, low toxicity, and low-cost as their main attributes. As elements of nanovaccines, halloysite nanotubes (natural), layered double hydroxides and hectorite (synthetic) are the nanoclays that have advanced into the vaccinology field. Until now, only physisorption has been used to modify the surface of nanoclays with antigens, adjuvants, and/or ligands to create nanovaccines. Protocols to covalently attach these molecules have not been developed with nanoclays, only procedures to develop adsorbents based on nanoclays that could be extended to develop nanovaccine conjugates. In this review, we describe the approaches evaluated on different nanovaccine candidates reported in articles, the immunological results obtained with them and the most advanced approaches in the preclinical field, while describing the nanomaterial itself. In addition, complex systems that use nanoclays were included and described. The safety of nanoclays as carriers is an important key fact to determine their true potential as nanovaccine candidates in humans. Here, we present the evaluations reported in this field. Finally, we point out the perspectives in the development of vaccine prototypes using nanoclays as antigen carriers.

In the last decade, the publications presenting novel physical and chemical aspects of gadolinium-based oxide (Gd₂O₃) and oxysulfide (Gd₂O₂S) particles in the micro- or nano-scale have increased, mainly stimulated by the exciting applications of these materials in the biomedical field. Their optical properties, related to down and upconversion phenomena and the ability to functionalize their surface, make them attractive for developing new probes for selective targeting and emergent bioimaging techniques, either for biomolecule labeling or theranostics. Moreover, recent reports have shown interesting optical behavior of these systems influenced by the synthesis methods, dopant amount and type, particle shape and size, and surface functionality. Hence, this review presents a compilation of the latest works focused on evaluating the optical properties of Gd₂O₃ and Gd₂O₂S particles as a function of their physicochemical and morphological properties; and also on their novel applications as MRI contrast agents and drug delivery nanovehicles, discussed along with their administration routes, biodistribution, cytotoxicity, and clearance mechanisms. Perspectives for this field are also identified and discussed.

MW-irradiation decreases APTES polymerization and enhances the number of NH ₂ attached to porous silicon surfaces.

New fluorescent molecular probes, which can selectively target specific cell surface receptors, are needed for microscopy, in vivo imaging, and image guided surgery. The preparation of multivalent probes using standard synthetic chemistry can be a laborious process due to low reaction yields caused by steric effects. In this study, fluorescent molecular probes were prepared by a programmed non‐covalent pre‐assembly process that used a near‐infrared fluorescent squaraine dye to thread a macrocycle bearing a cyclic arginine‐glycine‐aspartate peptide antagonist (cRGDfK) as a cancer targeting unit. Cell microscopy studies using OVCAR‐4 (ovarian cancer) and A549 (lung cancer) cells that express high levels of the integrin αvβ3 or αvβ5 receptors, respectively, revealed a multivalent cell targeting effect. That is, there was comparatively more cell uptake of a pre‐assembled probe equipped with two copies of the cRGDfK antagonist than a pre‐assembled probe with only one appended cRGDfK antagonist. The remarkably high photostability and low phototoxicity of these near‐infrared probes allowed for acquisition of long‐term fluorescence movies showing endosome trafficking in living cells. In vivo near‐infrared fluorescence imaging experiments compared the biodistribution of a targeted and untargeted probe in a xenograft mouse tumor model. The average tumor‐to‐muscle ratio for the pre‐assembled targeted probe was 3.6 which matches the tumor targeting performance reported for analogous cRGDfK‐based probes that were prepared entirely by covalent synthesis. The capability to excite these pre‐assembled near‐infrared fluorescent probes with blue or deep‐red excitation light makes it possible to determine if a target site is located superficially or buried in tissue, a probe performance feature that is likely to be very helpful for eventual applications such as fluorescence guided surgery.