Enhanced potency of a fucose-free monoclonal antibody being developed as an Ebola virus immunoprotectant

Exploring the potential of monoclonal antibody therapeutics for HIV-1 eradication

The HIV field has seen an increased interest in novel cure strategies. In particular, new latency reversal agents are in development to reverse latency to flush the virus out of its hiding place. Combining these efforts with immunotherapeutic approaches may not only drive the virus out of latency, but allow for the rapid elimination of these infected cells in a "shock and kill" approach. Beyond cell-based approaches, growing interest lies in the potential use of functionally enhanced "killer" monoclonal therapeutics to purge the reservoir. Here we discuss prospects for a monoclonal therapeutic-based "shock and kill" strategy that may lead to the permanent elimination of replication-competent virus, making a functional cure a reality for all patients afflicted with HIV worldwide.

Structures of protective antibodies reveal sites of vulnerability on Ebola virus

Ebola virus (EBOV) and related filoviruses cause severe hemorrhagic fever, with up to 90% lethality, and no treatments are approved for human use. Multiple recent outbreaks of EBOV and the likelihood of future human exposure highlight the need for pre- and postexposure treatments. Monoclonal antibody (mAb) cocktails are particularly attractive candidates due to their proven postexposure efficacy in nonhuman primate models of EBOV infection. Two candidate cocktails, MB-003 and ZMAb, have been extensively evaluated in both in vitro and in vivo studies. Recently, these two therapeutics have been combined into a new cocktail named ZMapp, which showed increased efficacy and has been given compassionately to some human patients. Epitope information and mechanism of action are currently unknown for most of the component mAbs. Here we provide single-particle EM reconstructions of every mAb in the ZMapp cocktail, as well as additional antibodies from MB-003 and ZMAb. Our results illuminate key and recurring sites of vulnerability on the EBOV glycoprotein and provide a structural rationale for the efficacy of ZMapp. Interestingly, two of its components recognize overlapping epitopes and compete with each other for binding. Going forward, this work now provides a basis for strategic selection of next-generation antibody cocktails against Ebola and related viruses and a model for predicting the impact of ZMapp on potential escape mutations in ongoing or future Ebola outbreaks.

Structural and functional characterization of an anti-West Nile virus monoclonal antibody and its single-chain variant produced in glycoengineered plants

Previously, our group engineered a plant-derived monoclonal antibody (MAb pE16) that efficiently treated West Nile virus (WNV) infection in mice. In this study, we developed a pE16 variant consisting of a single-chain variable fragment (scFv) fused to the heavy chain constant domains (CH) of human IgG (pE16scFv-CH). pE16 and pE16scFv-CH were expressed and assembled efficiently in Nicotiana benthamiana ∆XF plants, a glycosylation mutant lacking plant-specific N-glycan residues. Glycan analysis revealed that ∆XF plant-derived pE16scFv-CH (∆XFpE16scFv-CH) and pE16 (∆XFpE16) both displayed a mammalian glycosylation profile. ∆XFpE16 and ∆XFpE16scFv-CH demonstrated equivalent antigen-binding affinity and kinetics, and slightly enhanced neutralization of WNV in vitro compared with the parent mammalian cell-produced E16 (mE16). A single dose of ∆XFpE16 or ∆XFpE16scFv-CH protected mice against WNV-induced mortality even 4 days after infection at equivalent rates as mE16. This study provides a detailed tandem comparison of the expression, structure and function of a therapeutic MAb and its single-chain variant produced in glycoengineered plants. Moreover, it demonstrates the development of anti-WNV MAb therapeutic variants that are equivalent in efficacy to pE16, simpler to produce, and likely safer to use as therapeutics due to their mammalian N-glycosylation. This platform may lead to a more robust and cost-effective production of antibody-based therapeutics against WNV infection and other infectious, inflammatory or neoplastic diseases.

Reversion of advanced Ebola virus disease in nonhuman primates with ZMapp

Without an approved vaccine or treatments, Ebola outbreak management has been limited to palliative care and barrier methods to prevent transmission. These approaches, however, have yet to end the 2014 outbreak of Ebola after its prolonged presence in West Africa. Here we show that a combination of monoclonal antibodies (ZMapp), optimized from two previous antibody cocktails, is able to rescue 100% of rhesus macaques when treatment is initiated up to 5 days post-challenge. High fever, viraemia and abnormalities in blood count and blood chemistry were evident in many animals before ZMapp intervention. Advanced disease, as indicated by elevated liver enzymes, mucosal haemorrhages and generalized petechia could be reversed, leading to full recovery. ELISA and neutralizing antibody assays indicate that ZMapp is cross-reactive with the Guinean variant of Ebola. ZMapp exceeds the efficacy of any other therapeutics described so far, and results warrant further development of this cocktail for clinical use.

Controlled glycosylation of plant-produced recombinant proteins

Despite their recognized importance for therapeutic proteins, the production of structurally defined glycans is still a challenging issue. However, an increased understanding of glycosylation pathways, recent advances in analytical tools, and emerging technologies for subcellular targeting using chimeric glycosyltransferases are facilitating the rational design of new glycan biosynthetic pathways. Plants are particularly amenable to glyco-engineering approaches and thus they are increasingly being used for the production of recombinant proteins. Here we summarize the main achievements in the field of in planta glyco-engineering for the production of therapeutically relevant proteins.

Emerging antibody-based products

Antibody-based products are not widely available to address many global health challenges due to high costs, limited manufacturing capacity, and long manufacturing lead times. There are now tremendous opportunities to address these industrialization challenges as a result of revolutionary advances in plant virus-based transient expression. This review focuses on some antibody-based products that are in preclinical and clinical development, and have scaled up manufacturing and purification (mg of purified mAb/kg of biomass). Plant virus-based antibody products provide lower upfront cost, shorter time to clinical and market supply, and lower cost of goods (COGs). Further, some plant virus-based mAbs may provide improvements in pharmacokinetics, safety and efficacy.

An update on the use of antibodies against the filoviruses

Multiple recent, independent studies have confirmed that passively administered antibodies can provide effective postexposure therapy in nonhuman primates after exposure to an otherwise lethal dose of Ebola virus or Marburg virus. In this article, we review composition and performance of the antibody cocktails tested thus far, what is known about antibody epitopes on the viral glycoprotein target and ongoing research questions in further development of such cocktails for pre-exposure or emergency postexposure use.

Manufacturing economics of plant-made biologics: case studies in therapeutic and industrial enzymes

Production of recombinant biologics in plants has received considerable attention as an alternative platform to traditional microbial and animal cell culture. Industrially relevant features of plant systems include proper eukaryotic protein processing, inherent safety due to lack of adventitious agents, more facile scalability, faster production (transient systems), and potentially lower costs. Lower manufacturing cost has been widely claimed as an intuitive feature of the platform by the plant-made biologics community, even though cost information resides within a few private companies and studies accurately documenting such an advantage have been lacking. We present two technoeconomic case studies representing plant-made enzymes for diverse applications: human butyrylcholinesterase produced indoors for use as a medical countermeasure and cellulases produced in the field for the conversion of cellulosic biomass into ethanol as a fuel extender. Production economics were modeled based on results reported with the latest-generation expression technologies on Nicotiana host plants. We evaluated process unit operations and calculated bulk active and per-dose or per-unit costs using SuperPro Designer modeling software. Our analyses indicate that substantial cost advantages over alternative platforms can be achieved with plant systems, but these advantages are molecule/product-specific and depend on the relative cost-efficiencies of alternative sources of the same product.

Vaccinating captive chimpanzees to save wild chimpanzees

Infectious disease has only recently been recognized as a major threat to the survival of Endangered chimpanzees and Critically Endangered gorillas in the wild. One potentially powerful tool, vaccination, has not been deployed in fighting this disease threat, in good part because of fears about vaccine safety. Here we report on what is, to our knowledge, the first trial in which captive chimpanzees were used to test a vaccine intended for use on wild apes rather than humans. We tested a virus-like particle vaccine against Ebola virus, a leading source of death in wild gorillas and chimpanzees. The vaccine was safe and immunogenic. Captive trials of other vaccines and of methods for vaccine delivery hold great potential as weapons in the fight against wild ape extinction.

Post-exposure therapy of filovirus infections

Filovirus infections cause fatal hemorrhagic fever characterized by the initial onset of general symptoms before rapid progression to severe disease; the most virulent species can cause death to susceptible hosts within 10 days after the appearance of symptoms. Before the advent of monoclonal antibody (mAb) therapy, infection of nonhuman primates (NHPs) with the most virulent filovirus species was fatal if interventions were not administered within minutes. A novel nucleoside analogue, BCX4430, has since been shown to also demonstrate protective efficacy with a delayed treatment start. This review summarizes and evaluates the potential of current experimental candidates for treating filovirus disease with regard to their feasibility and use in the clinic, and assesses the most promising strategies towards the future development of a pan-filovirus medical countermeasure.

Glycan variants of a respiratory syncytial virus antibody with enhanced effector function and in vivo efficacy

Respiratory syncytial virus (RSV) can cause devastating lower respiratory tract infections in preterm infants or when other serious health problems are present. Immunoprophylaxis with palivizumab (Synagis), a humanized IgG1 mAb, is the current standard of care for preventing RSV infection in at-risk neonates. We have explored the contribution of effector function to palivizumab efficacy using a plant-based expression system to produce palivizumab N-glycan structure variants with high homogeneity on different antibody isotypes. We compared these isotype and N-glycoform variants with commercially available palivizumab with respect to both in vitro receptor and C1q binding and in vivo efficacy. Whereas the affinity for antigen and neutralization activity of each variant were indistinguishable from those of palivizumab, their Fcγ receptor binding profiles were very different, which was reflected in either a reduced or enhanced ability to influence the RSV lung titer in challenged cotton rats. Enhanced Fcγ receptor binding was associated with reduced viral lung titers compared with palivizumab, whereas abrogation of receptor binding led to a drastic reduction in efficacy. The results support the hypotheses that classic antibody neutralization is a minor component of efficacy by palivizumab in the cotton rat and that antibody-dependent cell-mediated cytotoxicity activity can significantly enhance the efficacy of this antiviral mAb.

Therapeutic intervention of Ebola virus infection in rhesus macaques with the MB-003 monoclonal antibody cocktail

Ebola virus (EBOV) remains one of the most lethal transmissible infections and is responsible for high fatality rates and substantial morbidity during sporadic outbreaks. With increasing human incursions into endemic regions and the reported possibility of airborne transmission, EBOV is a high-priority public health threat for which no preventive or therapeutic options are currently available. Recent studies have demonstrated that cocktails of monoclonal antibodies are effective at preventing morbidity and mortality in nonhuman primates (NHPs) when administered as a post-exposure prophylactic within 1 or 2 days of challenge. To test whether one of these cocktails (MB-003) demonstrates efficacy as a therapeutic (after the onset of symptoms), we challenged NHPs with EBOV and initiated treatment upon confirmation of infection according to a diagnostic protocol for U.S. Food and Drug Administration Emergency Use Authorization and observation of a documented fever. Of the treated animals, 43% survived challenge, whereas both the controls and all historical controls with the same challenge stock succumbed to infection. These results represent successful therapy of EBOV infection in NHPs.

Generation and analysis of novel plant-derived antibody-based therapeutic molecules against West Nile virus

Previously, our group engineered a plant-derived monoclonal antibody (MAb) (pHu-E16) that efficiently treated West Nile virus (WNV) infection in mice. In this study, we developed several pHu-E16 variants to improve its efficacy. These variants included a single-chain variable fragment (scFv) of pHu-E16 fused to the heavy chain (HC) constant domains (CH(1-3)) of human IgG (pHu-E16scFv-CH(1-3)) and a tetravalent molecule (Tetra pHu-E16) assembled from pHu-E16scFv-CH(1-3) with a second pHu-E16scFv fused to the light chain (LC) constant region. pHu-E16scFv-CH(1-3) and Tetra pHu-E16 were efficiently expressed and assembled in plants. To assess the impact of differences in N-linked glycosylation on pHu-E16 variant assembly and function, we expressed additional pHu-E16 variants with various combinations of HC and LC components. Our study revealed that proper pairing of HC and LC was essential for the complete N-glycan processing of antibodies in both plant and animal cells. Associated with their distinct N-glycoforms, pHu-E16, pHu-E16scFv-CH(1-3) and Tetra pHu-E16 exhibited differential binding to C1q and specific Fcγ receptors (FcγR). Notably, none of the plant-derived Hu-E16 variants showed antibody-dependent enhancement (ADE) activity in CD32A+ human cells, suggesting the potential of plant-produced antibodies to minimize the adverse effect of ADE. Importantly, all plant-derived MAb variants exhibited at least equivalent in vitro neutralization and in vivo protection in mice compared to mammalian cell-produced Hu-E16. This study demonstrates the capacity of plants to express and assemble a large, complex and functional IgG-like tetravalent mAb variant and also provides insight into the relationship between MAb N-glycosylation, FcγR and C1q binding, and ADE. These new insights may allow the development of safer and cost effective MAb-based therapeutics for flaviviruses, and possibly other pathogens.

Plant glyco-biotechnology on the way to synthetic biology

Plants are increasingly being used for the production of recombinant proteins. One reason is that plants are highly amenable to glycan engineering processes and allow the production of therapeutic proteins with increased efficacies due to optimized glycosylation profiles. Removal and insertion of glycosylation reactions by knock-out/knock-down approaches and introduction of glycosylation enzymes have paved the way for the humanization of the plant glycosylation pathway. The insertion of heterologous enzymes at exactly the right stage of the existing glycosylation pathway has turned out to be of utmost importance. To enable such precise targeting chimeric enzymes have been constructed. In this short review we will exemplify the importance of correct targeting of glycosyltransferases, we will give an overview of the targeting mechanism of glycosyltransferases, describe chimeric enzymes used in plant N-glycosylation engineering and illustrate how plant glycoengineering builds on the tools offered by synthetic biology to construct such chimeric enzymes.

Enrichment strategies in glycomics-based lung cancer biomarker development

PURPOSE

There is a need to identify better glycan biomarkers for diagnosis, early detection, and treatment monitoring in lung cancer using biofluids such as blood. Biofluids are complex mixtures of proteins dominated by a few high abundance proteins that may not have specificity for lung cancer. Therefore, two methods for protein enrichment were evaluated; affinity capturing of IgG and enrichment of medium abundance proteins, thus allowing us to determine which method yields the best candidate glycan biomarkers for lung cancer.

EXPERIMENTAL DESIGN

N-glycans isolated from plasma samples from 20 cases of lung adenocarcinoma and 20 matched controls were analyzed using nLC-PGC-chip-TOF-MS (where PGC is porous-graphitized carbon). N-glycan profiles were obtained for five different fractions: total plasma, isolated IgG, IgG-depleted plasma, and the bound and flow-through fractions of protein enrichment.

RESULTS

Four glycans differed significantly (false discovery rate, FDR < 0.05) between cases and controls in whole unfractionated plasma, while four other glycans differed significantly by cancer status in the IgG fraction. No significant glycan differences were observed in the other fractions.

CONCLUSIONS AND CLINICAL RELEVANCE

These results confirm that the N-glycan profile in plasma of lung cancer patients is different from healthy controls and appears to be dominated by alterations in relatively abundant proteins.

Efficient single tobamoviral vector-based bioproduction of broadly neutralizing anti-HIV-1 monoclonal antibody VRC01 in Nicotiana benthamiana plants and utility of VRC01 in combination microbicides

Broadly neutralizing monoclonal antibodies (bnMAbs) may offer powerful tools for HIV-1 preexposure prophylaxis, such as topical microbicides. However, this option is hampered due to expensive MAb biomanufacturing based on mammalian cell culture. To address this issue, we developed a new production system for bnMAb VRC01 in Nicotiana benthamiana plants using a tobamovirus replicon vector. Unlike conventional two-vector-based expression, this system was designed to overexpress full-length IgG1 from a single polypeptide by means of kex2p-like enzyme recognition sites introduced between the heavy and light chains. An enzyme-linked immunosorbent assay (ELISA) revealed that gp120-binding VRC01 IgG1 was maximally accumulated on 5 to 7 days following vector inoculation, yielding ~150 mg of the bnMAb per kg of fresh leaf material. The plant-made VRC01 (VRC01p) was efficiently purified by protein A affinity followed by hydrophobic-interaction chromatography. ELISA, surface plasmon resonance, and an HIV-1 neutralization assay demonstrated that VRC01p has gp120-binding affinity and HIV-1-neutralization capacity virtually identical to the human-cell-produced counterpart. To advance VRC01p's use in topical microbicides, we analyzed combinations of the bnMAb with other microbicide candidates holding distinct antiviral mechanisms in an HIV-1 neutralization assay. VRC01p exhibited clear synergy with the antiviral lectin griffithsin, the CCR5 antagonist maraviroc, and the reverse transcriptase inhibitor tenofovir in multiple CCR5-tropic HIV-1 strains from clades A, B, and C. In summary, VRC01p is amenable to robust, rapid, and large-scale production and may be developed as an active component in combination microbicides with other anti-HIV agents such as antiviral lectins, CCR5 antagonists, and reverse transcriptase inhibitors.

Prophylactic and therapeutic testing of Nicotiana-derived RSV-neutralizing human monoclonal antibodies in the cotton rat model

Severe lower respiratory tract infection in infants and small children is commonly caused by respiratory syncytial virus (RSV). Palivizumab (Synagis(®)), a humanized IgG1 monoclonal antibody (mAb) approved for RSV immunoprophylaxis in at-risk neonates, is highly effective, but pharmacoeconomic analyses suggest its use may not be cost-effective. Previously described potent RSV neutralizers (human Fab R19 and F2-5; human IgG RF-1 and RF-2) were produced in IgG format in a rapid and inexpensive Nicotiana-based manufacturing system for comparison with palivizumab. Both plant-derived (palivizumab-N) and commercial palivizumab, which is produced in a mouse myeloma cell line, showed protection in prophylactic (p < 0.001 for both mAbs) and therapeutic protocols (p < 0.001 and p < 0.05 respectively). The additional plant-derived human mAbs directed against alternative epitopes displayed neutralizing activity, but conferred less protection in vivo than palivizumab-N or palivizumab. Palivizumab remains one of the most efficacious RSV mAbs described to date. Production in plants may reduce manufacturing costs and improve the pharmacoeconomics of RSV immunoprophylaxis and therapy.

Utility of the P19 suppressor of gene-silencing protein for production of therapeutic antibodies in Nicotiana expression hosts

To study how the P19 suppressor of gene-silencing protein can be used effectively for the production of therapeutic glycoproteins, the following factors were examined: the genetic elements used for expressing recombinant proteins; the effect of different P19 concentrations; compatibility of P19 with various Nicotiana tabacum cultivars for transgenic expression; the glycan profile of a recombinant therapeutic glycoprotein co-expressed with P19 in an RNAi-based glycomodified Nicotiana benthamiana expression host. The coding sequences for the heavy and light chains of trastuzumab were cloned into five plant expression vectors (102-106) containing different 5' and 3' UTRs, designated as vector sets 102-106 mAb. The P19 protein of Tomato bushy stunt virus (TBSV) was also cloned into vector 103, which contained the Cauliflower mosaic virus (CaMV) 35S promoter and 5'UTR together with the terminator region of the nopaline synthase gene of Agrobacterium. Transient expression of the antibody vectors resulted in different levels of trastuzumab accumulation, the highest being 105 and 106 mAb at about 1% of TSP. P19 increased the concentration of trastuzumab approximately 15-fold (to about 2.3% of TSP) when co-expressed with 103 mAb but did not affect antibody levels with vectors 102 and 106 mAb. When 103 mAb was expressed together with P19 in different N. tabacum cultivars, all except Little Crittenden showed a marked discolouring of the infiltrated areas of the leaf and decreased antibody expression. Co-expression of P19 also abolished antibody accumulation in crosses between N. tabacum cv. I-64 and Little Crittenden, indicating a dominant mode of inheritance for the observed P19-induced responses.

Discovery and early development of AVI-7537 and AVI-7288 for the treatment of Ebola virus and Marburg virus infections

There are no currently approved treatments for filovirus infections. In this study we report the discovery process which led to the development of antisense Phosphorodiamidate Morpholino Oligomers (PMOs) AVI-6002 (composed of AVI-7357 and AVI-7539) and AVI-6003 (composed of AVI-7287 and AVI-7288) targeting Ebola virus and Marburg virus respectively. The discovery process involved identification of optimal transcript binding sites for PMO based RNA-therapeutics followed by screening for effective viral gene target in mouse and guinea pig models utilizing adapted viral isolates. An evolution of chemical modifications were tested, beginning with simple Phosphorodiamidate Morpholino Oligomers (PMO) transitioning to cell penetrating peptide conjugated PMOs (PPMO) and ending with PMOplus containing a limited number of positively charged linkages in the PMO structure. The initial lead compounds were combinations of two agents targeting separate genes. In the final analysis, a single agent for treatment of each virus was selected, AVI-7537 targeting the VP24 gene of Ebola virus and AVI-7288 targeting NP of Marburg virus, and are now progressing into late stage clinical development as the optimal therapeutic candidates.

Delayed treatment of Ebola virus infection with plant-derived monoclonal antibodies provides protection in rhesus macaques

Filovirus infections can cause a severe and often fatal disease in humans and nonhuman primates, including great apes. Here, three anti-Ebola virus mouse/human chimeric mAbs (c13C6, h-13F6, and c6D8) were produced in Chinese hamster ovary and in whole plant (Nicotiana benthamiana) cells. In pilot experiments testing a mixture of the three mAbs (MB-003), we found that MB-003 produced in both manufacturing systems protected rhesus macaques from lethal challenge when administered 1 h postinfection. In a pivotal follow-up experiment, we found significant protection (P < 0.05) when MB-003 treatment began 24 or 48 h postinfection (four of six survived vs. zero of two controls). In all experiments, surviving animals that received MB-003 experienced little to no viremia and had few, if any, of the clinical symptoms observed in the controls. The results represent successful postexposure in vivo efficacy by a mAb mixture and suggest that this immunoprotectant should be further pursued as a postexposure and potential therapeutic for Ebola virus exposure.

Potential vaccines and post-exposure treatments for filovirus infections

Viruses of the family Filoviridae represent significant health risks as emerging infectious diseases as well as potentially engineered biothreats. While many research efforts have been published offering possibilities toward the mitigation of filoviral infection, there remain no sanctioned therapeutic or vaccine strategies. Current progress in the development of filovirus therapeutics and vaccines is outlined herein with respect to their current level of testing, evaluation, and proximity toward human implementation, specifically with regard to human clinical trials, nonhuman primate studies, small animal studies, and in vitro development. Contemporary methods of supportive care and previous treatment approaches for human patients are also discussed.

Glyco-engineering in plants to produce human-like N-glycan structures

It is now possible to produce complex human proteins, largely correctly folded and N-glycosylated, in plants. Much effort has been invested in engineering expression technologies to develop products with superior characteristics. The results have begun to show success in controlling important posttranslational modifications such as N-glycosylation. With the emerging data increasingly indicating the significance of proper N-glycosylation for the efficacy of a drug, glyco-engineering has become an important issue not only for academia but also for the biopharmaceutical industry. Plants have demonstrated a high degree of tolerance to changes in the N-glycosylation pathway, allowing recombinant proteins to be modified into human-like structures in a specific and controlled manner. Frequently the results are a largely homogeneously glycosylated product, currently unrivalled by that of any other expression platforms. This review provides a comprehensive analysis of recent advances in plant N-glyco-engineering in the context of the expression of therapeutically relevant proteins, highlighting both the challenges and successes in the application of such powerful technologies.

A nonreplicating subunit vaccine protects mice against lethal Ebola virus challenge

Ebola hemorrhagic fever is an acute and often deadly disease caused by Ebola virus (EBOV). The possible intentional use of this virus against human populations has led to design of vaccines that could be incorporated into a national stockpile for biological threat reduction. We have evaluated the immunogenicity and efficacy of an EBOV vaccine candidate in which the viral surface glycoprotein is biomanufactured as a fusion to a monoclonal antibody that recognizes an epitope in glycoprotein, resulting in the production of Ebola immune complexes (EICs). Although antigen-antibody immune complexes are known to be efficiently processed and presented to immune effector cells, we found that codelivery of the EIC with Toll-like receptor agonists elicited a more robust antibody response in mice than did EIC alone. Among the compounds tested, polyinosinic:polycytidylic acid (PIC, a Toll-like receptor 3 agonist) was highly effective as an adjuvant agent. After vaccinating mice with EIC plus PIC, 80% of the animals were protected against a lethal challenge with live EBOV (30,000 LD(50) of mouse adapted virus). Surviving animals showed a mixed Th1/Th2 response to the antigen, suggesting this may be important for protection. Survival after vaccination with EIC plus PIC was statistically equivalent to that achieved with an alternative viral vector vaccine candidate reported in the literature. Because nonreplicating subunit vaccines offer the possibility of formulation for cost-effective, long-term storage in biothreat reduction repositories, EIC is an attractive option for public health defense measures.