Co-delivery of autoantigen and dexamethasone in incomplete Freund's adjuvant ameliorates experimental autoimmune encephalomyelitis

Emerging strategies for nanomedicine in autoimmunity

Autoimmune disorders have risen to be among the most prevalent chronic diseases across the globe, affecting approximately 5-7% of the population. As autoimmune diseases steadily rise in prevalence, so do the number of potential therapeutic strategies to combat them. In recent years, fundamental research investigating autoimmune pathologies has led to the emergence of several cellular targets that provide new therapeutic opportunities. However, key challenges persist in terms of accessing and specifically combating the dysregulated, self-reactive cells while avoiding systemic immune suppression and other off-target effects. Fortunately, the continued advancement of nanomedicines may provide strategies to address these challenges and bring innovative autoimmunity therapies to the clinic. Through precise engineering and rational design, nanomedicines can possess a variety of physicochemical properties, surface modifications, and cargoes, allowing for specific targeting of therapeutics to pathological cell and organ types. These advances in nanomedicine have been demonstrated in cancer therapies and have the broad potential to advance applications in autoimmunity therapies as well. In this review, we focus on leveraging the power of nanomedicine for prevalent autoimmune disorders throughout the body. We expand on three key areas for the development of autoimmunity therapies - avoiding systemic immunosuppression, balancing interactions with the immune system, and elevating current platforms for delivering complex cargoes - and emphasize how nanomedicine-based strategies can overcome these barriers and enable the development of next-generation, clinically relevant autoimmunity therapies.

Delivery route considerations for designing antigen-specific biomaterial strategies to combat autoimmunity

Disease modifying drugs and biologics used to treat autoimmune diseases, although promising, are non-curative. As the field moves towards development of new approaches to treat autoimmune disease, antigen-specific therapies immunotherapies (ASITs) have emerged. Despite clinical approval of ASITs for allergies, clinical trials using soluble ASITs for autoimmunity have been largely unsuccessful. A major effort to address this shortcoming is the use of biomaterials to harness the features unique to specific delivery routes. This review focuses on biomaterials being developed for delivery route-specific strategies to induce antigen-specific responses in autoimmune diseases such as multiple sclerosis, type 1 diabetes, rheumatoid arthritis, and celiac disease. We first discuss the delivery strategies used in ongoing and completed clinical trials in autoimmune ASITs. Next, we highlight pre-clinical biomaterial approaches from the most recent 3 years in the context of these same delivery route considerations. Lastly, we provide discussion on the gaps remaining in biomaterials development and comment on the need to consider delivery routes in the process of designing biomaterials for ASITs.

Complete Tolerogenic Adjuvant Stimulates Regulatory T Cell Response to Immunization

We have determined in mice the minimum composition required for forming a vaccine adjuvant that stimulates a regulatory T (Treg) cell response to immunization, and we named the adjuvant "complete tolerogenic adjuvant." This new kind of adjuvant may let us use the well-proven "Ag with adjuvant" form of immunization for inducing Treg cell-mediated Ag-specific immunosuppression. The minimum composition consists of dexamethasone, rapamycin, and monophosphoryl lipid A at a mass ratio of 8:20:3. By dissecting the respective role of each of these components during immunization, we have further shown why immunosuppressive and immunogenic agents are both needed for forming true adjuvants for Treg cells. This finding may guide the design of additional, and potentially more potent, complete tolerogenic adjuvants with which we may form numerous novel vaccines for treating immune diseases.

Development of a TLR7/8 agonist adjuvant formulation to overcome early life hyporesponsiveness to DTaP vaccination

Infection is the most common cause of mortality early in life, yet the broad potential of immunization is not fully realized in this vulnerable population. Most vaccines are administered during infancy and childhood, but in some cases the full benefit of vaccination is not realized in-part. New adjuvants are cardinal to further optimize current immunization approaches for early life. However, only a few classes of adjuvants are presently incorporated in vaccines approved for human use. Recent advances in the discovery and delivery of Toll-like receptor (TLR) agonist adjuvants have provided a new toolbox for vaccinologists. Prominent among these candidate adjuvants are synthetic small molecule TLR7/8 agonists. The development of an effective infant Bordetella pertussis vaccine is urgently required because of the resurgence of pertussis in many countries, contemporaneous to the switch from whole cell to acellular vaccines. In this context, TLR7/8 adjuvant based vaccine formulation strategies may be a promising tool to enhance and accelerate early life immunity by acellular B. pertussis vaccines. In the present study, we optimized (a) the formulation delivery system, (b) structure, and (c) immunologic activity of novel small molecule imidazoquinoline TLR7/8 adjuvants towards human infant leukocytes, including dendritic cells. Upon immunization of neonatal mice, this TLR7/8 adjuvant overcame neonatal hyporesponsiveness to acellular pertussis vaccination by driving a T helper (Th)1/Th17 biased T cell- and IgG2c-skewed humoral response to a licensed acellular vaccine (DTaP). This potent immunization strategy may represent a new paradigm for effective immunization against pertussis and other pathogens in early life.

Synthetic Cationic Autoantigen Mimics Glatiramer Acetate Persistence at the Site of Injection and Is Efficacious Against Experimental Autoimmune Encephalomyelitis

A synthetic peptide, K-PLP, consisting of 11-unit poly-lysine (K11) linked via polyethylene glycol (PEG) to proteolipid protein epitope (PLP) was synthesized, characterized, and evaluated for efficacy in ameliorating experimental autoimmune encephalomyelitis (EAE) induced by PLP. K-PLP was designed to mimic the cationic nature of the relapsing-remitting multiple sclerosis treatment, glatiramer acetate (GA). With a pI of ~10, GA is able to form visible aggregates at the site of injection via electrostatic interactions with the anionic extracellular matrix. Aggregation further facilitates the retention of GA at the site of injection and draining lymph nodes, which may contribute to its mechanism of action. K-PLP with a pI of ~11, was found to form visible aggregates in the presence of glycosaminoglycans and persist at the injection site and draining lymph nodes in vivo, similar to GA. Additionally, EAE mice treated with K-PLP showed significant inhibition of clinical symptoms compared to free poly-lysine and to PLP, which are the components of K-PLP. The ability of the poly-lysine motif to retain PLP at the injection site, which increased the local exposure of PLP to immune cells may be an important factor affecting drug efficacy.

PEGylation enables subcutaneously administered nanoparticles to induce antigen-specific immune tolerance

The development of nanomaterials to induce antigen-specific immune tolerance has shown promise for treating autoimmune diseases. While PEGylation has been widely used to reduce host immune responses to nanomaterials, its tolerogenic potential has not been reported. Here, we report for the first time that a subcutaneous injection of PEGylated poly(lactide-co-glycolide) (PLGA) nanoparticles containing auto-antigen peptide MOG_35-55 without any tolerogenic drugs is sufficient to dramatically ameliorate symptoms after disease onset in an antigen-specific manner in a mouse model of multiple sclerosis. Neither free MOG_35-55 nor particles without PEG exhibit this efficacy. Interestingly, mechanistic studies indicate that PEGylation of nanoparticles does not reduce dendritic cell activation through direct nanoparticle-cell interactions. Instead, PEGylated nanoparticles induce lower complement activation, neutrophil recruitment, and co-stimulatory molecule expression on dendritic cells around the injection sitecompared to non-PEGylated PLGA nanoparticles, creating a more tolerogenic microenvironment in vivo. We further demonstrate that the locally recruited dendritic cells traffic to lymphoid organs to induce T cell tolerance. These results highlight the critical role of surface properties of nanomaterials in inducing immune tolerance via subcutaneous administration.

Antigen-specific immune decoys intercept and exhaust autoimmunity to prevent disease

Relapsing-remitting patterns of many autoimmune diseases such as multiple sclerosis (MS) are perpetuated by a recurring circuit of adaptive immune cells that amplify in secondary lymphoid organs (SLOs) and traffic to compartments where antigen is abundant to elicit damage. Some of the most effective immunotherapies impede the migration of immune cells through this circuit, however, broadly suppressing immune cell migration can introduce life-threatening risks for patients. We developed antigen-specific immune decoys (ASIDs) to mimic tissues targeted in autoimmunity and selectively intercept autoimmune cells to preserve host tissue. Using Experimental Autoimmune Encephalomyelitis (EAE) as a model, we conjugated autoantigen PLP_139-151 to a microporous collagen scaffold. By subcutaneously implanting ASIDs after induction but prior to the onset of symptoms, mice were protected from paralysis. ASID implants were rich with autoimmune cells, however, reactivity to cognate antigen was substantially diminished and apoptosis was prevalent. ASID-implanted mice consistently exhibited engorged spleens when disease normally peaked. In addition, splenocyte antigen-presenting cells were highly activated in response to PLP rechallenge, but CD3⁺ and CD19 ⁺ effector subsets were significantly decreased, suggesting exhaustion. ASID-implanted mice never developed EAE relapse symptoms even though the ASID material had long since degraded, suggesting exhausted autoimmune cells did not recover functionality. Together, data suggested ASIDs were able to sequester and exhaust immune cells in an antigen-specific fashion, thus offering a compelling approach to inhibit the migration circuit underlying autoimmunity.

Acute B-Cell Inhibition by Soluble Antigen Arrays Is Valency-Dependent and Predicts Immunomodulation in Splenocytes

Antigen valency plays a fundamental role in directing the nature of an immune response to be stimulatory or tolerogenic. Soluble antigen arrays (SAgAs) are an antigen-specific immunotherapy that combats autoimmunity through the multivalent display of autoantigen. Although mechanistic studies have shown SAgAs to induce T- and B-cell anergy, the effect of SAgA valency has never been experimentally tested. Here, SAgAs of discrete antigen valencies were synthesized by click chemistry and evaluated for acute B-cell signaling inhibition as well as downstream immunomodulatory effects in splenocytes. Initial studies using the Raji B-cell line demonstrated SAgA valency dictated the extent of calcium flux. Lower valency constructs elicited the largest reductions in B-cell activation. In splenocytes from mice with experimental autoimmune encephalomyelitis, the same valency-dependent effects were evident in the downregulation of the costimulatory marker CD86. The reduction of calcium flux observed in Raji B-cells correlated strongly with downregulation in splenocyte CD86 expression after 72 h. Here, a thorough analysis of SAgA antigenic valency illustrates that low, but not monovalent, presentation of autoantigen was ideal for eliciting the most potent immunomodulatory effects.

Tocopherol Emulsions as Functional Autoantigen Delivery Vehicles Evoke Therapeutic Efficacy in Experimental Autoimmune Encephalomyelitis

Contemporary approaches to treating autoimmune diseases like multiple sclerosis broadly modulate the immune system and leave patients susceptible to severe adverse effects. Antigen-specific immunotherapies (ASIT) offer a unique opportunity to selectively suppress autoreactive cell populations but have suffered from marginal efficacy even when employing traditional adjuvants to improve delivery. The development of immunologically active antigen delivery vehicles could potentially increase the clinical success of antigen-specific immunotherapies. An emulsion of the antioxidant tocopherol delivering an epitope of proteolipid protein autoantigen (PLP139-151) yielded significant efficacy in mice with experimental autoimmune encephalomyelitis (EAE). In vitro studies indicated tocopherol emulsions reduced oxidative stress in antigen-presenting cells. Ex vivo analysis revealed that tocopherol emulsions shifted cytokine responses in EAE splenocytes. In addition, IgG responses against PLP139-151 were increased in mice treated with tocopherol emulsions delivering the antigen, suggesting a possible skew in immunity. Overall, tocopherol emulsions provide a functional delivery vehicle for ASIT capable of ameliorating autoimmunity in a murine model.

Soluble antigen arrays disarm antigen-specific B cells to promote lasting immune tolerance in experimental autoimmune encephalomyelitis

Autoreactive lymphocytes that escape central immune tolerance may be silenced via an endogenous peripheral tolerance mechanism known as anergy. Antigen-specific therapies capable of inducing anergy may restore patients with autoimmune diseases to a healthy phenotype while avoiding deleterious side effects associated with global immunosuppression. Inducing anergy in B cells may be a particularly potent intervention, as B cells can contribute to autoimmune diseases through multiple mechanisms and offer the potential for direct antigen-specific targeting through the B cell receptor (BCR). Our previous results suggested autoreactive B cells may be silenced by multivalent 'soluble antigen arrays' (SAgAs), which are polymer conjugates displaying multiple copies of autoantigen with or without a secondary peptide that blocks intracellular cell-adhesion molecule-1 (ICAM-1). Here, key therapeutic molecular properties of SAgAs were identified and linked to the immunological mechanism through comprehensive cellular and in vivo analyses. We determined non-hydrolyzable 'cSAgAs' displaying multivalent 'click'-conjugated antigen more potently suppressed experimental autoimmune encephalomyelitis (EAE) compared to hydrolyzable SAgAs capable of releasing conjugated antigen. cSAgAs restored a healthy phenotype in disease-specific antigen presenting cells (APCs) by inducing an anergic response in B cells and a subset of B cells called autoimmune-associated B cells (ABCs) that act as potent APCs in autoimmune disease. Accompanied by a cytokine response skewed towards a Th2/regulatory phenotype, this generated an environment of autoantigenic tolerance. By identifying key therapeutic molecular properties and an immunological mechanism that drives SAgA efficacy, this work guides the design of antigen-specific immunotherapies capable of inducing anergy.