New Therapeutic Approaches for Allergy: A Review of Cell Therapy and Bio- or Nano-Material-Based Strategies

Subnanomolar MAS-related G protein-coupled receptor-X2/B2 antagonists with efficacy in human mast cells and disease models

The MAS-related G protein-coupled receptor-X2 (MRGPRX2), an orphan receptor expressed on mast cells (MCs), is upregulated upon inflammation and induces hypersensitivity and inflammatory diseases. In contrast to the large number of MRGPRX2 agonists, only a few antagonists have been described, and no optimization has been reported to improve potency, selectivity, and drug-like properties. Antagonists with ancillary inhibition of the putative mouse ortholog MRGPRB2 have not been described. Here, we present a multi-disciplinary approach involving chemistry, biology, and computational science, resulting in the development of a small-molecule MRGPRX2 antagonist (PSB-172656, 3-ethyl-7,8-difluoro-2-isopropylbenzo[4,5]imidazo [1,2-a] pyrimidin-4(1H)-one) based on a fragment screening hit. The compound exhibits metabolic stability, low cytotoxicity, and competitive blockade of MRGPRX2 activation induced by a diverse range of agonists. It displays subnanomolar potency in Ca2+ mobilization assays (Ki value 0.142 nM) and was found to block MRGPRX2-mediated Gαq and Gαi1 dissociation, in addition to β-arrestin-2 recruitment. PSB-172656 is selective for MRGPRX2 versus all other MRGPRX subtypes. Its effect on MCs was confirmed in cell lines, including rat basophilic leukemia cells (RBL-2H3) recombinantly expressing human MRGPRX2, human Laboratory of Allergic Diseases 2 (LAD2) MCs, and native human skin MCs. PSB-172656 was found to additionally block the putative mouse ortholog of MRGPRX2, MRGPRB2, as determined in Ca2+ mobilization assays (Ki 0.302 nM), and to prevent mouse tracheal contractions, local allergic reactions, and systemic anaphylactic symptoms. PSB-172656 constitutes a unique pharmacological tool and has the potential to be developed as a drug for mast cell-mediated hypersensitivity reactions and chronic inflammatory diseases, addressing a huge unmet medical need.

Allergy Treatment: A Comprehensive Review of Nanoparticle-based Allergen Immunotherapy

Allergic disorders rising in prevalence globally, affecting a substantial proportion of individuals in industrialized nations. The imbalance in the immune system, characterized by elevated allergen-specific T helper 2 (Th2) cells and immunoglobulin E (IgE) antibodies, is a key factor in allergy development. Allergen-specific immunotherapy (AIT) is the only treatment capable of alleviating allergic symptoms, preventing new sensitizations, and reducing asthma risk in allergic rhinitis patients. Traditional AIT, however, faces challenges such as frequent administration, adverse effects, and inconsistent patient outcomes. Nanoparticle-based approaches have emerged as a promising strategy to enhance AIT. This review explores the utilization of nanoparticles in AIT, highlighting their ability to interact with the immune system and improve therapeutic outcomes. Various types of nanoparticles, including polyesters, polysaccharide polymers, liposomes, protamine-based nanoparticles (NPs), and polyanhydrides, have been employed as adjuvants or carriers to enhance AIT's efficacy and safety. Nanoparticles offer advantages such as allergen protection, improved immune response modulation, targeted cell delivery, and reduced side effects. This review provides an overview of the current landscape of nanoparticle-based allergen immunotherapy, discussing its potential to revolutionize allergy treatment compared to traditional immunotherapy.

Engineering nanoparticle therapeutics for food allergy

Food allergy is a growing public health issue among children and adults that can lead to life-threatening anaphylaxis following allergen exposure. The criterion standard for disease management includes food avoidance and emergency epinephrine administration because current allergen-specific immunotherapy treatments are limited by adverse events and unsustained desensitization. A promising approach to remedy these shortcomings is the use of nanoparticle-based therapies that disrupt disease-driving immune mechanisms and induce more sustained tolerogenic immune pathways. The pathophysiology of food allergy includes multifaceted interactions between effector immune cells, including lymphocytes, antigen-presenting cells, mast cells, and basophils, mainly characterized by a TH2 cell response. Regulatory T cells, TH1 cell responses, and suppression of other major allergic effector cells have been found to be major drivers of beneficial outcomes in these nanoparticle therapies. Engineered nanoparticle formulations that have shown efficacy at reducing allergic responses and revealed new mechanisms of tolerance include polymeric-, lipid-, and emulsion-based nanotherapeutics. This review highlights the recent engineering design of these nanoparticles, the mechanisms induced by them, and their future potential therapeutic targets.

Nanomaterials for antigen-specific immune tolerance therapy

Impairment of immune tolerance might cause autologous tissue damage or overactive immune response against non-pathogenic molecules. Although autoimmune disease and allergy have complicated pathologies, the current strategies have mainly focused on symptom amelioration or systemic immunosuppression which can lead to fatal adverse events. The induction of antigen-specific immune tolerance may provide therapeutic benefits to autoimmune disease and allergic response, while reducing nonspecific immune adverse responses. Diverse nanomaterials have been studied to induce antigen-specific immune tolerance therapy. This review will cover the immunological background of antigen-specific tolerance, clinical importance of antigen-specific immune tolerance, and nanomaterials designed for autoimmune and allergic diseases. As nanomaterials for modulating immune tolerances, lipid-based nanoparticles, polymeric nanoparticles, and biological carriers have been covered. Strategies to provide antigen-specific immune tolerance have been addressed. Finally, current challenges and perspectives of nanomaterials for antigen-specific immune tolerance therapy will be discussed.

Microneedle array patches for allergen-specific immunotherapy

The incidence of allergies has been steadily increasing in recent years. Allergen-specific immunotherapy (AIT) represents the only approach capable of inducing long-term immune tolerance toward allergens. However, the clinical success of AIT is limited by efficacy or safety concerns related to the administration route. Therapeutic delivery in the skin appears promising, given the presence of immune cells in the skin and the relatively low level of systemic distribution that occurs with this delivery method. However, the stratum corneum greatly limits this route. In this regard, the use of microneedles has been proposed to improve the delivery of therapeutics into the skin. In this review, we discuss recent developments in the use of microneedles for AIT, highlighting avenues for future research.

Short-Chain Fatty Acids Augment Differentiation and Function of Human Induced Regulatory T Cells

Regulatory T cells (Tregs) control immune system activity and inhibit inflammation. While, in mice, short-chain fatty acids (SCFAs) are known to be essential regulators of naturally occurring and in vitro induced Tregs (iTregs), data on their contribution to the development of human iTregs are sparse, with no reports of the successful SCFAs-augmented in vitro generation of fully functional human iTregs. Likewise, markers undoubtedly defining human iTregs are missing. Here, we aimed to generate fully functional human iTregs in vitro using protocols involving SCFAs and to characterize the underlying mechanism. Our target was to identify the potential phenotypic markers best characterizing human iTregs. Naïve non-Treg CD4⁺ cells were isolated from the peripheral blood of 13 healthy adults and cord blood of 12 healthy term newborns. Cells were subjected to differentiation toward iTregs using a transforming growth factor β (TGF-β)-based protocol, with or without SCFAs (acetate, butyrate, or propionate). Thereafter, they were subjected to flow cytometric phenotyping or a suppression assay. During differentiation, cells were collected for chromatin-immunoprecipitation (ChIP)-based analysis of histone acetylation. The enrichment of the TGF-β-based protocol with butyrate or propionate potentiated the in vitro differentiation of human naïve CD4⁺ non-Tregs towards iTregs and augmented the suppressive capacity of the latter. These seemed to be at least partly underlain by the effects of SCFAs on the histone acetylation levels in differentiating cells. GITR, ICOS, CD39, PD-1, and PD-L1 were proven to be potential markers of human iTregs. Our results might boost the further development of Treg-based therapies against autoimmune, allergic and other chronic inflammatory disorders.