Biophysical Characterization of Viral and Lipid-Based Vectors for Vaccines and Therapeutics with Light Scattering and Calorimetric Techniques

Scaling laws for nanoparticles - Online shape heterogeneity analysis by size exclusion chromatography coupled with multi-angle light scattering

Nanoparticle-based drug delivery systems are rising technologies to access challenging therapeutic targets. Following commercial success of lipid-based nanoparticles (LBNP), accruing understandings of nanoparticle structures and critical quality attributes through advanced analytics are beneficial to future clinical development and generalization of this delivery platform. The morphological attributes of nanoparticles, such as shape, can affect uptake, cell-interaction, drug release, circulation, and flow. Gaining an understanding of these structure-activity relationships in early-stage formulation development is important because mix morphologies can affect quality and potency but often exist before process control strategies are fully implemented. In this study, we used shape heterogeneous nanoparticle mixtures, containing various populations of liposomes and lipodisks, as a model system and developed an online semi-quantitative method to characterize the nanoparticle shape heterogeneity by size exclusion chromatography (SEC) coupled with multi-angle light scattering (MALS). The liposomes and lipodisks were separated in SEC when their sizes were ∼3 fold different. When the particles of different shapes were in similar sizes, size-based separation was not always feasible. Instead, light scattering data distinguished liposomes and lipodisks by the scaling law linking radius of gyration and molecular weight of the nanoparticles, enabling morphological identification. A semi-quantitative model was built based on the exponential correlation between the scaling law exponents and the ratios of liposomes and lipodisks. The model was applied to test 6 random formulations made with different compositions and manufacturing processes, and the predicted liposome percentage for 5 formulations was within 25 % absolute difference from the percentage determined by cryogenic electron microscopy (cryo-EM). We envision this method being routinely used to characterize liposome and lipodisk shape heterogeneity during formulation screening as well as on stability studies. Potentially, the method can be converted to in-process control method and extended to other categories of nanoparticles beyond liposomes.

Digitally Enabled Generic Analytical Framework Accelerating the Pace of Liquid Chromatography Method Development for Vaccine Adjuvant Formulations

The growing use of adjuvants in the fast-paced formulation of new vaccines has created an unprecedented need for meaningful analytical assays that deliver reliable quantitative data from complex adjuvant and adjuvant-antigen mixtures. Due to their complex chemical and physical properties, method development for the separation of vaccine adjuvants is considered a highly challenging and laborious task. Reversed-phase liquid chromatography (RPLC) is among the most important tests in the (bio)pharmaceutical industry for release and stability indicating measurements including adjuvant content, identity, and purity profile. However, the time constraints of developing "on-demand" robust quantitative methods prior to each change in formulation can easily lead to sample analysis becoming a bottleneck in vaccine development. Herein, a simple and efficient generic analytical framework capable of chromatographically resolving the most commonly used non-aluminum-based adjuvants across academic and industrial sectors is introduced. This was designed to seek a more proactive approach for fast-paced assay development endeavors that evolved from extensive stationary phase screening in conjunction with multifactorial in silico simulations of adjuvant retention time (RT) as a function of gradient time, temperature, organic modifier blending, and buffer concentration. The multifactorial retention models yield 3D resolution maps with excellent baseline separation of all adjuvants in a single run, which was found to be very accurate, with differences between experimental and simulated retention times of less than 1%. The analytical framework described here also includes the introduction of a more versatile approach to method development by introducing a dynamic RT database for adjuvants covering the entire library of adjuvants with broad mechanisms of action across numerous vaccine formulations with excellent linearity, accuracy, precision, and specificity. The power of this framework was also demonstrated with numerous analytical assays that can be generated rapidly from simulations guiding vaccine processes in the development of new adjuvant formulations. Analytical assay in this work covers content, purity profile by LC with diode array detector (DAD) and charged aerosol detector (CAD), and component identification by LC with mass spectrometry (MS) across complex vaccine formulations, including the use of surfactants (e.g., polysorbates) as well as their separation from adjuvant targets.

Characterization of AAV vectors: A review of analytical techniques and critical quality attributes

Standardized evaluation of adeno-associated virus (AAV) vector products for biotherapeutic application is essential to ensure the safety and efficacy of gene therapies. This includes analyzing the critical quality attributes of the product. However, many of the current analytical techniques used to assess these attributes have limitations, including low throughput, large sample requirements, poorly understood measurement variability, and lack of comparability between methods. To address these challenges, it is essential to establish higher-order reference methods that can be used for comparability measurements, optimization of current assays, and development of reference materials. Highly precise methods are necessary for measuring the empty/partial/full capsid ratios and the titer of AAV vectors. Additionally, it is important to develop methods for the measurement of less-established critical quality attributes, including post-translational modifications, capsid stoichiometry, and methylation profiles. By doing so, we can gain a better understanding of the influence of these attributes on the quality of the product. Moreover, quantification of impurities, such as host-cell proteins and DNA contaminants, is crucial for obtaining regulatory approval. The development and application of refined methodologies will be essential to thoroughly characterize AAV vectors by informing process development and facilitating the generation of reference materials for assay validation and calibration.

Construction of a T m-value prediction model and molecular dynamics study of AmNA-containing gapmer antisense oligonucleotide

RNase H-dependent antisense oligonucleotides (gapmer ASOs) represent a class of nucleic acid therapeutics that bind to target RNA to facilitate RNase H-mediated RNA cleavage, thereby regulating the expression of disease-associated proteins. Integrating artificial nucleic acids into gapmer ASOs enhances their therapeutic efficacy. Among these, amido-bridged nucleic acid (AmNA) stands out for its potential to confer high affinity and stability to ASOs. However, a significant challenge in the design of gapmer ASOs incorporating artificial nucleic acids, such as AmNA, is the accurate prediction of their melting temperature (T m ) values. The T m is a critical parameter for designing effective gapmer ASOs to ensure proper functioning. However, predicting accurate T m values for oligonucleotides containing artificial nucleic acids remains problematic. We developed a T m prediction model using a library of AmNA-containing ASOs to address this issue. We measured the T m values of 157 oligonucleotides through differential scanning calorimetry, enabling the construction of an accurate prediction model. Additionally, molecular dynamics simulations were used to elucidate the molecular mechanisms by which AmNA modifications elevate T m , thereby informing the design strategies of gapmer ASOs.

Medical and molecular biophysical techniques as substantial tools in the era of mRNA-based vaccine technology

The COVID-19 pandemic prompted the advancement of vaccine technology using mRNA delivery into the host cells. Consequently, mRNA-based vaccines have emerged as a practical approach against SARS-CoV-2 owing to their inherent properties, such as cost-effectiveness, rapid manufacturing, and preservation. These features are vital, especially in resource-constrained regions. Nevertheless, the design of mRNA-based vaccines is intricately intertwined with the refinement of biophysical technologies, thereby establishing their high potential. The preparation of mRNA-based vaccines involves a sequence of phases combining medical and molecular biophysical technologies. Furthermore, their efficiency depends on the capability to optimize their positive attributes, thus paving the way for their subsequent preclinical and clinical evaluations. Using biophysical techniques, the characterization of nucleic acids extends from their initial formulation to their cellular internalization abilities and encapsulation in biomolecule complexes, such as lipid nanoparticles (LNPs), for designing mRNA-based LNPs. Furthermore, nanoparticles are subjected to a series of careful screening steps to assess their physical and chemical characteristics before achieving an optimum formulation suitable for preclinical and clinical studies. This review provides a comprehensive understanding of the fundamental role of biophysical techniques in the complex development of mRNA-based vaccines and their role in the recent success during the COVID-19 pandemic.

A Physiochemical, In Vitro, and In Vivo Comparative Analysis of Verteporfin-Lipid Conjugate Formulations: Solid Lipid Nanoparticles and Liposomes

VisudyneⓇ, a liposomal formulation of verteporfin (benzoporphyrin derivative; BPD), is the only nanomedicine approved to date for photodynamic therapy (PDT). We have previously demonstrated that BPD conjugated to the lysophospholipid 1-arachidoyl-2-hydroxy-sn-glycero-3-phosphocholine (BPD-PC) exhibits the greatest physical stability in liposomes, while maintaining cancer cell phototoxicity, from a panel of BPD lipid conjugates evaluated. In this study, we prepared 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-based solid lipid nanoparticles (LNPs) that stably entrap BPD-PC, which resemble the composition of the SpikevaxⓇ Moderna COVID-19 vaccine, and compared them to a DPPC based liposomal formulation (Lipo BPD-PC). We evaluated the photochemical, optical, and phototherapeutic properties of both formulations. We also investigated the in vivo distribution and tumor microdistribution of both formulations. Our results demonstrated that Lipo BPD-PC is able to generate 17% more singlet oxygen than LNP BPD-PC, while interestingly, LNP BPD-PC is able to produce 76% more hydroxyl radicals and/or peroxynitrite anion. Importantly, only 28% of BPD-PC leaches out of the LNP BPD-PC formulation during 7 days of incubation in serum at 37 °C, while 100% of BPD-PC leaches out of the Lipo BPD-PC formulation under the same conditions. Despite these differences, there was no significant difference in cellular uptake of BPD-PC or phototoxicity in CT1BA5 murine pancreatic cancer cells (derived from a genetically engineered mouse model). Interestingly, PDT using LNP BPD-PC was more efficient at inducing immunogenic cell death (calreticulin membrane translocation) than Lipo BPD-PC when using IC25 and IC50 PDT doses. In vivo studies revealed that CT1BA5 tumor fluorescence signals from BPD-PC were 2.41-fold higher with Lipo BPD-PC than with LNP BPD-PC; however, no significant difference was observed in tumor tissue selectivity or tumor penetration. As such, we present LNP BPD-PC as a unique and more stable nanoplatform to carry BPD lipid conjugates, such as BPD-PC, with a potential for future photodynamic immune priming studies and multiagent drug delivery.

Electrophoretic Microfluidic Characterization of mRNA- and pDNA-Loaded Lipid Nanoparticles

Lipid nanoparticles (LNPs) are clinically advanced nonviral gene delivery vehicles with a demonstrated ability to address viral, oncological, and genetic diseases. However, the further development of LNP therapies requires rapid analytical techniques to support their development and manufacturing. The method developed and described in this paper presents an approach to rapidly and accurately analyze LNPs for optimized therapeutic loading by utilizing an electrophoresis microfluidic platform to analyze the composition of LNPs with different clinical lipid compositions (Onpattro, Comirnaty, and Spikevax) and nucleic acid (plasmid DNA (pDNA) and messenger RNA (mRNA)) formulations. This method enables the high-throughput screening of LNPs using a 96- or 384-well plate with approximate times of 2-4 min per sample using a total volume of 11 μL. The lipid analysis requires concentrations approximately between 109 and 1010 particles/mL and has an average precision error of 10.4% and a prediction error of 19.1% when compared to using a NanoSight, while the nucleic acid analysis requires low concentrations of 1.17 ng/μL for pDNA and 0.17 ng/μL for mRNA and has an average precision error of 4.8% and a prediction error of 9.4% when compared to using a PicoGreen and RiboGreen assay. In addition, our method quantifies the relative concentration of nucleic acid per LNP. Utilizing this approach, we observed an average of 263 ± 62.2 mRNA per LNP and 126.3 ± 21.2 pDNA per LNP for the LNP formulations used in this study, where the accuracy of these estimations is dependent on reference standards. We foresee the utility of this technique in the high-throughput characterization of LNPs during manufacturing and formulation research and development.

New insights into the potential cardioprotective effects of telmisartan and nanoformulated extract of Spirulina platensis via regulation of oxidative stress, apoptosis, and autophagy in an experimental model

Background

Cardiotoxicity is one of the limiting side effects of the commonly used anticancer agent cyclophosphamide (Cyclo).

Materials and methods

The possible protective effects of telmisartan and nanoformulated Spirulina platensis (Sp) methanolic extract against Cyclo-induced cardiotoxicity were examined in this study. Experimental groups of rats were randomly divided into nine groups as control vehicle, control polymer, telmisartan (TEL, 10 mg/kg), free Sp extract (300 mg/kg), nano Sp extract (100 mg/kg), Cyclo (200 mg/kg), TEL + Cyclo, free Sp + Cyclo, and nano Sp + Cyclo. The groups with Cyclo combinations were treated in the same manner as their corresponding ones without Cyclo, with a single dose of Cyclo on day 18.

Results

The results indicate that Cyclo causes significant cardiotoxicity, manifesting in the form of notable increases of 155.49%, 105.74%, 451.76%, and 826.07% in the serum levels of glutamic oxaloacetic transaminase (SGOT), lactate dehydrogenase (LDH), creatine kinase MB (CK-MB), and cardiac troponin I (cTnI) enzyme activities, respectively, as compared to the control. In addition, the cardiac glutathione (GSH) content and activity of glutathione peroxidase-1 (GPX-1) enzyme decreased by 65.94% and 73.85%, respectively. Treatment with nano Sp extract showed the most prominent restorations of the altered biochemical, histopathological, and immunohistochemical features as compared with those by TEL and free Sp; moreover, reductions of 30.64% and 43.02% in the p-AKT content as well as 60.43% and 75.30% of the endothelial nitric oxide synthase (eNOS) immunoreactivity were detected in the TEL and free Sp treatment groups, respectively. Interestingly, nano Sp boosted the autophagy signal via activation of beclin-1 (36.42% and 153.4%), activation of LC3II (69.13% and 195%), downregulation of p62 expressions (39.68% and 62.45%), and increased gene expressions of paraoxonase-1 (PON-1) (90.3% and 225.9%) compared to the TEL and free Sp treatment groups, respectively.

Conclusion

The findings suggest the protective efficiency of telmisartan and nano Sp extract against cardiotoxicity via activations of the antioxidant, antiapoptotic, and autophagy signaling pathways.

Assessment of Tunable Resistive Pulse Sensing (TRPS) Technology for Particle Size Distribution in Vaccine Formulations - A Comparative Study with Dynamic Light Scattering

PURPOSE

A comparative assessment was performed to evaluate the potential of particle sizing by an ensemble based conventional dynamic light scattering (DLS) technique and an emerging technology based on tunable resistive pulse sensing (TRPS) using particle by particle approach by evaluating three different types of vaccine formulations representing three case studies and showing the limitation of each technique, instrument variability, sensitivity, and the resolution in mixed population.

METHODS

Three types of in-house vaccine formulations- a protein antigen, an outer membrane vesicle and viral particles were simultaneously evaluated by TRPS based Exoid and two DLS instruments-Zetatrac and Zetasizer for particle size distribution, aggregates, and resolution of polydisperse species.

RESULTS

The data from first case study show the risk of possible size overestimation and size averaging in polydisperse samples in DLS measurements which can be addressed by the TRPS analysis. It also shows how TRPS may be utilized only to large size antigens due to its limited size range. The second case study highlights the difference in the sensitivities of two DLS instruments working on the same principle. The third case study show that how TRPS can better resolve the large aggregate species compare to DLS in polydisperse samples.

CONCLUSION

This analysis shows that TRPS can be used as an orthogonal technique in addition to conventional DLS based methods for more precise and in-depth characterization. Both techniques are efficient in size characterization and produce comparable results, however the choice will depend on the type of formulation and size range to be evaluated.

Quality assessment of LNP-RNA therapeutics with orthogonal analytical techniques

The availability of analytical methods for the characterization of lipid nanoparticles (LNPs) for in-vivo intracellular delivery of nucleic acids is critical for the fast development of innovative RNA therapies. In this study, analytical protocols to measure (i) chemical composition, (ii) drug loading, (iii) particle size, concentration, and stability as well as (iv) structure and morphology were evaluated and compared based on a comprehensive characterization strategy linking key physical and chemical properties to in-vitro efficacy and toxicity. Furthermore, the measurement protocols were assessed either by testing the reproducibility and robustness of the same technique in different laboratories, or by a correlative approach, comparing measurement results of the same attribute with orthogonal techniques. The characterization strategy and the analytical measurements described here will have an important role during formulation development and in determining robust quality attributes ultimately supporting the quality assessment of these innovative RNA therapeutics.

Unleashing the Potential: Designing Antibody-Targeted Lipid Nanoparticles for Industrial Applications with CMC Considerations and Clinical Outlook

Antibody-targeted lipid nanoparticles (Ab-LNPs) are rapidly gaining traction as multifaceted platforms in precision medicine, adept at delivering a diverse array of therapeutic agents, including nucleic acids and small molecules. This review provides an incisive overview of the latest developments in the field of Ab-LNP technology, with a special emphasis on pivotal design aspects such as antibody engineering, bioconjugation strategies, and advanced formulation techniques. Furthermore, it addresses critical chemistry, manufacturing, and controls (CMC) considerations and thoroughly examines the in vivo dynamics of Ab-LNPs, underscoring their promising potential for clinical application. By seamlessly blending scientific advancements with practical industrial perspectives, this review casts a spotlight on the burgeoning role of Ab-LNPs as an innovative and potent tool in the realm of targeted drug delivery.

Investigations into mRNA Lipid Nanoparticles Shelf-Life Stability under Nonfrozen Conditions

mRNA LNPs can experience a decline in activity over short periods (ranging from weeks to months). As a result, they require frozen storage and transportation conditions to maintain their full functionality when utilized. Currently approved commercially available mRNA LNP vaccines also necessitate frozen storage and supply chain management. Overcoming this significant inconvenience in the future is crucial to reducing unnecessary costs and challenges associated with storage and transport. In this study, our objective was to illuminate the potential time frame for nonfrozen storage and transportation conditions of mRNA LNPs without compromising their activity. To achieve this goal, we conducted a stability assessment and an in vitro cell culture delivery study involving five mRNA LNPs. These LNPs were constructed by using a standard formulation similar to that employed in the three commercially available LNP formulations. Among these formulations, we selected five structurally diverse ionizable lipids─C12-200, CKK-E12, MC3, SM-102, and lipid 23─from the existing literature. We incorporated these lipids into a standard LNP formulation, keeping all other components identical. The LNPs, carrying mRNA payloads, were synthesized by using microfluidic mixing technology. We evaluated the shelf life stability of these LNPs over a span of 9 weeks at temperatures of 2-8, 25, and 40 °C, utilizing an array of analytical techniques. Our findings indicated minimal impact on the hydrodynamic diameter, zeta potential, encapsulation efficiency, and polydispersity of all LNPs across the various temperatures over the studied period. The RiboGreen assay analysis of LNPs showed consistent mRNA contents over several weeks at various nonfrozen storage temperatures, leading to the incorrect assumption of intact and functional LNPs. This misunderstanding was rectified by the significant differences observed in EGFP protein expression in an in vitro cell culture (using HEK293 cells) across the five LNPs. Specifically, only LNP 1 (C12-200) and LNP 4 (SM-102) exhibited high levels of EGFP expression at the start (T0), with over 90% of HEK293 cells transfected and mean fluorescence intensity (MFI) levels exceeding 1. Interestingly, LNP 1 (C12-200) maintained largely unchanged levels of in vitro activity over 11 weeks when stored at both 2-8 and 25 °C. In contrast, LNP 4 (SM-102) retained its functionality when stored at 2-8 °C over 11 weeks but experienced a gradual decline of in vitro activity when stored at room temperature over the same period. Importantly, we observed distinct LNP architectures for the five formulations through cryo-EM imaging. This highlights the necessity for a deeper comprehension of structure-activity relationships within these complex nanoparticle structures. Enhancing our understanding in this regard is vital for overcoming storage and stability limitations, ultimately facilitating the broader application of this technology beyond vaccines.

Development of Nanofibers with Embedded Liposomes Containing an Immunomodulatory Drug Using Green Electrospinning

Conventional treatments for chronic wounds are often ineffective, thus new therapeutic approaches are needed, such as the delivery of immunomodulatory drugs that can reduce inflammation, restore immune cell function, and facilitate tissue regeneration. A potential drug for such an approach is simvastatin, which has major drawbacks including poor solubility and chemical instability. With the aim of developing a dressing for wound healing, simvastatin and an antioxidant were incorporated into alginate/poly(ethylene oxide) nanofibers by green electrospinning without the use of organic solvents, thanks to their prior encapsulation into liposomes. The composite liposome-nanofiber formulations exhibited fibrillar morphology (160-312 nm) and unprecedentedly high phospholipid and drug content (76%). Transmission electron microscopy revealed dried liposomes as bright ellipsoidal spots homogeneously distributed over the nanofibers. After nanofiber hydration, the liposomes reconstituted in two size populations (~140 and ~435 nm), as revealed by cutting-edge MADLS^® analysis. Lastly, in vitro assays demonstrated that composite liposome-nanofiber formulations are superior to liposomal formulations due to a better safety profile in keratinocytes and peripheral blood mononuclear cells. Furthermore, both formulations exhibited similarly advantageous immunomodulatory effects, measured as decreased inflammation in vitro. A synergistic combination of the two nanodelivery systems shows promise for the development of efficient dressings for chronic wound treatment.

Evaluation and Screening of Biopharmaceuticals using Multi-Angle Dynamic Light Scattering

Biopharmaceuticals are large, complex and labile therapeutic molecules prone to instability due to various factors during manufacturing. To ensure their safety, quality and efficacy, a wide range of critical quality attributes (CQAs) such as product concentration, aggregation, particle size, purity and turbidity have to be met. Size exclusion chromatography (SEC) is the gold standard to measure protein aggregation and degradation. However, other techniques such as dynamic light scattering (DLS) are employed in tandem to measure the particle size distribution (PSD) and polydispersity of biopharmaceutical formulations. In this study, the application of multi-angle dynamic light scattering (MADLS) was evaluated for the determination of particle size, particle concentration and aggregation in 3 different protein modalities, namely bovine serum albumin (BSA) and two biopharmaceuticals including a monoclonal antibody (mAb) and an enzyme. The obtained calibration curve (R² > 0.95) for the particle number concentration of the 3 proteins and the observed correlation between MADLS and SEC (R² = 0.9938) for the analysis of aggregation in the enzyme can be employed as a 3-in-1 approach to assessing particle size, concentration and aggregation for the screening and development of products while also reducing the number of samples and experiments required for analysis prior to other orthogonal tests.

The Storage and In-Use Stability of mRNA Vaccines and Therapeutics: Not A Cold Case

The remarkable impact of mRNA vaccines on mitigating disease and improving public health has been amply demonstrated during the COVID-19 pandemic. Many new mRNA-based vaccine and therapeutic candidates are in development, yet the current reality of their stability limitations requires their frozen storage. Numerous challenges remain to improve formulated mRNA stability and enable refrigerator storage, and this review provides an update on developments to tackle this multi-faceted stability challenge. We describe the chemistry underlying mRNA degradation during storage and highlight how lipid nanoparticle (LNP) formulations are a double-edged sword: while LNPs protect mRNA against enzymatic degradation, interactions with and between LNP excipients introduce additional risks for mRNA degradation. We also discuss strategies to improve mRNA stability both as a drug substance (DS) and a drug product (DP) including the (1) design of the mRNA molecule (nucleotide selection, primary and secondary structures), (2) physical state of the mRNA-LNP complexes, (3) formulation composition and purity of the components, and (4) DS and DP manufacturing processes. Finally, we summarize analytical control strategies to monitor and assure the stability of mRNA-based candidates, and advocate for an integrated analytical and formulation development approach to further improve their storage, transport, and in-use stability profiles.

A thermally robust method of sample sealing for capillary DLS

Capillary Dynamic Light Scattering (DLS), has recently been introduced as a simple and enabling technique that increases the measurement range of traditional DLS analysis with minimized sample volumes (Ruseva et al., 2018). The previously published protocol for the preparation of samples for analysis within a capillary called for sealing of the capillary end using a clay compound (Ruseva et al., 2019). This material is not, however, compatible with organic solvents, nor with elevated sample temperatures. To extend the uses of capillary DLS to more complex assays like thermal aggregation studies, a new sealing method is demonstrated using a UV curing compound. This further motivates the use of capillary DLS to minimize volumes of destroyed precious samples in pharmaceutical development assays to study thermal kinetics.•Use of UV curing compound to seal capillaries used in DLS to preserve low volumes of sample.

Current and next-generation formulation strategies for inactivated polio vaccines to lower costs, increase coverage, and facilitate polio eradication

Implementation of inactivated polio vaccines (IPV) containing Sabin strains (sIPV) will further enable global polio eradication efforts by improving vaccine safety during use and containment during manufacturing. Moreover, sIPV-containing vaccines will lower costs and expand production capacity to facilitate more widespread use in low- and middle-income countries (LMICs). This review focuses on the role of vaccine formulation in these efforts including traditional Salk IPV vaccines and new sIPV-containing dosage forms. The physicochemical properties and stability profiles of poliovirus antigens are described. Formulation approaches to lower costs include developing multidose and combination vaccine formats as well as improving storage stability. Formulation strategies for dose-sparing and enhanced mucosal immunity include employing adjuvants (e.g. aluminum-salt and newer adjuvants) and/or novel delivery systems (e.g. ID administration with microneedle patches). The potential for applying these low-cost formulation development strategies to other vaccines to further improve vaccine access and coverage in LMICs is also discussed.