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The SARS-CoV-2 pandemic has changed our world in just half a year: a large number of people have died from the virus-induced pneumonia COVID-19, and the global economy is at an unprecedented low with unknown near- and long-term consequences.
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The coronavirus pandemic needs a two-pronged approach: a short-term solution to find a drug to treat the massive number of seriously ill patients, and long-term development of preventive and curative drugs for future corona outbreaks.
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De novo drug discovery takes years to move from idea and/or pre-clinic to market release and is not a short-term solution for the current SARS-CoV-2 pandemic. Drug repurposing is perhaps the only short-term solution, and vaccination is a middle-term solution.
Summary
SARS-CoV-2 (previously 2019-nCoV or Wuhan coronavirus) caused an unprecedented fast-spreading worldwide pandemic. Although currently with a rather low mortality rate, the virus spread rapidly over the world using the modern world’s traffic highways. The coronavirus (CoV) family members were responsible for several deadly outbreaks and epidemics during the last decade. Not only governments but also the scientific community reacted promptly to the outbreak, and information is shared quickly. For example, the genetic fingerprint was shared, and the 3D structure of key proteins was rapidly solved, which can be used for the discovery of potential treatments. An overview is given on the current knowledge of the spread, disease course, and molecular biology of SARS-CoV-2. We discuss potential treatment developments in the context of recent outbreaks, drug repurposing, and development timelines.
In December 2019, an outbreak of pneumonia of an unknown cause was reported in Wuhan, in Hubei province, China. It was speculated that the first patient caught the infection from a seafood market that also traded wild animals. The causing agent was quickly identified as a novel coronavirus (CoV). The CoV responsible for the outbreak is now called SARS-CoV-2. The respiratory illness caused by SARS-CoV-2 is called COVID-19. The symptoms of the SARS-CoV-2 infection range from asymptomatic to mild to severe to death.
It soon became clear that person-to-person transmission was also occurring, as was the case with the previous human CoV. In an unprecedented documented speed, the SARS-CoV-2 travels around the globe, and as of May 15th led to >4.5 million infections and 300,000 fatalities. Based on the previous experience with the SARS-CoV outbreak at the beginning of this century, very stringent measures were taken by the Chinese government, and several multimillion-inhabitant cities were isolated and put under quarantine in order to slow the pandemic spread. Different hosts of the SARS-CoV-2 are proposed, including snails, bats, and pangolins.
CoVs are a large family of zoonotic viruses and their outbreaks are common to humans, although major outbreaks have been experienced in animals, especially in cattle. Under the electron microscope, they exhibit formations that are reminiscent of the solar corona. The common cold is often caused by human CoVs. They are single-stranded enveloped positive RNA viruses and stand out because of their rather large genome. As with viruses in general, the structure is rather simple. SARS-CoV-2 is generally less pathogenic than SARS-CoV, much less pathogenic than the Middle East respiratory syndrome MERS-CoV, but more pathogenic than practically harmless HCoV-OC43, HCoV-HKU1, HCoV-229E, and HCoV-NL63. The reported case-fatality rate of COVID-19 is ≤3% and is thus rather low as compared with SARS (30%, Table 1). However, the transmission rate (TR) (number of newly infected people per infected person) of 2.5 to 3 is high and accounts for the danger of the current pandemic. For comparison, the TR of the yearly common cold is less than 1.4.
Table 1Some Data to the New and Previous Epi- and Pandemics
What are the issues and chances for a rapid approval of a new medicine to treat COVID-19? In principle, there are several potential strategies to pharmacologically fight COVID-19: vaccines, monoclonal antibodies, oligonucleotide-based therapies, peptides, interferon therapies, small-molecule drugs, or natural medicines (e.g., traditional Chinese medicine [TCM]). The timelines for de novo development of a small-molecule drug are historically >6–7 years, and in the best case less than 2 years. Vaccines can be developed much faster, but rapid development in the range of 1–2 years is very challenging. Antibodies to support the body’s immune system are also a strategy to combat viral diseases. Again, the typical development timelines are several years. Therefore, is there a hope for a drug to come rapidly to the market? A strategy that is promising in the current situation is drug repurposing. Drug repurposing aims to discover novel indication areas for already approved drugs.
The overwhelming advantage of drug repurposing is the potential for much faster market approval because of the already extensive knowledge of the drug’s behavior in humans.
An expert opinion on the potential for repurposing existing antiviral agents to treat COVID-19, some of which are already clinically evaluated, was recently given.
Here, we discuss molecular targets of the SARS-CoV-2, some of the known small molecules, and the potential for repurposing existing drugs.
Molecular Biology and Targets
Despite the rather large size of the RNA virus genome of ~30,000 bases, the SARS-CoV-2 genome encodes for few proteins (Figure 1): the structural spike (S) protein, nucleocapsid (N) protein, membrane (M) protein, and the envelope (E) protein, which are needed to produce a structurally complete viral particle. Additionally, the SARS-CoV-2 genome encodes 16–17 non-structural proteins (ns1 to ns17), such as 3-chymotrypsin-like protease (3CLpro), papain-like protease (PLpro), helicase, and RNA-dependent RNA polymerase (RdRp).
Figure 1Scheme of SARS-CoV-2 and Some of Its Molecular Protein Targets
Both the virus-encoded proteases 3CLpro and PLpro are involved in the processing of the two viral polyproteins in a coordinated manner, and thus comprise important drug targets. The structure, function, and inhibition of CoV 3CLpro (also called Mpro) has been recently comprehensively reviewed.
The 3CLpro is a cysteine protease that cleaves and processes the viral polyproteins.
SARS-CoV-2 and SARS-CoV share 96% sequence identity in their 3CLpro. On the basis of the rapidly published virus sequence data, a homology model was created.
Because of the high sequence similarity of different CoV 3CLpros, a lot of previously described inhibitors can be considered to be of great use in the current SARS-CoV-2. A majority of inhibitors of the 3CLpro are covalent in nature, binding to the active-site cysteine (Scheme 1). Different electrophilic warheads are known, including α-halocarbonyl, acrylamides, sulfonyl chlorides, aldehydes (2),
Many of the molecules are rather large and are based on extensive amide chemistry, mimicking part of the peptide substrate of the protease. Moreover, their selectivity toward other potential targets in the human body has not been established.
Interestingly, some compounds binding to the active site of the 3CLpro—using a noncovalent mechanism—have been established. A high-throughput screening (HTS) identified pyrazolidinone (5), which displayed 1,3,5-triaryl substitution patterns, as SARS-CoV 3CLpro inhibitors.
α-aminoacylamides were identified by an HTS, and a strong stereochemical effect was noted. The simple one-pot accessible scaffold by an Ugi-four component condensation was the key to rapidly generate structure activity relationship (SAR) for the putative P2-P1 and P1 subgroups. An optimized version ML188 (7) was designated as the probe status (Figure 3). A P3 truncated version of 8 allowing for significant molecular weight (MW) reduction without diminishing potency was developed as a second probe ML300 (9) with potent enzyme inhibition and cellular activity. These compounds comprise rare examples of a noncovalent SARS-CoV 3CLpro inhibitor of moderate MW with good enzyme and antiviral inhibitory activity. However, these molecules suffer from extensive metabolism and rapid clearance. Nonetheless, they are a promising starting point for further drug development.
Even if such compounds cannot be rapidly developed to cope with the current situation, their development is highly warranted to be prepared for likely future CoV outbreaks. It is noteworthy that different computational approaches, including machine learning, have been published to propose approved drugs potentially binding to 3CLpro (drug repurposing).
Ten different commercial medicines were proposed that might form hydrogen bonds to key residues within the binding pocket of SARS-CoV-2 3CLpro, which might have higher mutation tolerance than lopinavir or ritonavir.
Flavonoids (10–14) are plant-derived natural products with diverse reported biological activities, and they have been shown to be also able to inhibit the 3CLpro (Figure 4).
The broad-spectrum and established use of plant-based medicines to combat infectious diseases in TCM is the basis of several currently ongoing clinical trials in China. One of the largest among them assesses shuanghuanglian, a Chinese herbal medicine that contains extracts from the dried fruit lianqiao (Forsythiae fructus), which is purported to have been used for treating infections for more than 2,000 years.
Figure 4Flavonoids Inhibiting 3CLPro as They Occur in Liang Quiao, the Seeds of the Forsythiae fructus Plant Used in the TCM Shuanghuanglian
They were hypothesized to inhibit the SARS-CoV 3Clpro: HIV protease is a Asp protease and differs considerably from the Cys protease 3Clpro, but it also shares some common elements, such as a tetrahedral transition state and receptor pockets to recognize the amino acid side chains of the substrates. Given that SARS-CoV-2 and SARS-CoV share very high identical sequence in their 3CLpro, these HIV protease inhibitors are currently again repurposed for the treatment of COVID-19 (Chinese Clinical Trial Registry: ChiCTR2000029539).
The coronaviral PLpro is another attractive antiviral drug target because it is essential for CoV replication. The structure, function, and inhibition of the SARS-CoV PLpro has been extensively reviewed.
Although the primary function of PLpro and 3CLpro is to process the viral polyprotein in a coordinated manner, PLpro has the additional function of stripping ubiquitin and ISG15 from host-cell proteins to help CoV to evade the host innate immune responses. Therefore, it was recently argued that targeting PLpro with antiviral drugs might have an advantage in not only inhibiting viral replication but also inhibiting the dysregulation of signaling cascades in infected cells that might lead to cell death in surrounding, uninfected cells.
Different compounds forming a covalent bond to the active-site Cys112 have been described, including epoxyketones, α-halo-ketones, alkynes, aldehydes, trifluoromethyl ketones, α,β-unsaturated ketone, activated esters, or vinyl sulfones.
Disulfiram (19), an approved drug for the treatment of chronic alcohol dependence, has a great potential for drug repurposing because it has been shown to inhibit PLpro of MERS-CoV and SARS-CoV.
Potent naphthyl methylamine hits (e.g., 22) which have been structurally characterized and have been subsequently optimized toward better metabolic stability were identified from an HTS campaign,
The envelope-anchored S protein mediates CoV entry into host cells by first binding to a host receptor and then fusing viral and host membranes. The SARS-CoV-2 S protein was solved by cryoelectron microscopy and just released;
knowing the Å-resolution structure of the SARS-CoV-2 spike will allow for additional protein engineering efforts that could improve antigenicity and protein expression for vaccine development. Moreover, the Å-resolution detail will enable the design and screening of small molecules with fusion-inhibiting potential.
It is the affinity between the viral receptor-binding domain (RBD) and the host receptor in the initial viral attachment step that primarily determines which host is susceptible to SARS-CoV infection. The SARS-CoV-2 entry through receptor binding was elucidated independently by several groups.
On the basis of the rich knowledge about SARS-CoV and the sequence homology, it was suggested that SARS-CoV-2 uses angiotensin-converting enzyme 2 (ACE2) as its receptor (Figure 6). It uses the SARS-CoV receptor ACE2 and the cellular protease TMPRSS2 for entry into target cells.
The interplay of the ACE receptor in cardiovascular diseases (with the well-known drug class of ACE inhibitors) and as the docking point for SARS-CoV-2 cellular infection is a current point of intense debate and research.
It was found that several critical residues in SARS-CoV-2 RBM (particularly Gln493) provide favorable interactions with human ACE2, consistent with SARS-CoV-2’s capacity for human cell infection.
On the basis of the extensive modeling of the virus-human receptor interactions, it was also predicted that a single N501T mutation might significantly enhance the binding affinity between SARS-CoV-2 RBD and human ACE2 and thus potentially lead to much more virulent bodies.
Mutations in the S protein are the ones causing the zoonosis, and as a result, not all of them will lead to their binding to ACE2. Therefore, drugs targeting the S protein-ACE2 interaction might not apply to some of the future CoVs. On the other hand, the spike-shaped protein on the surface of the viruses causing SARS, MERS, and COVID-19 provides a tantalizing target for antibodies or other compounds, which could prevent CoVs from invading human cells.
The virus’ S protein seems to emerge as the consensus target antigen.
RdRp
The RdRp enzyme allows the viral genome to be transcribed into new RNA copies by using the host cell’s machinery. RdRp inhibitors are emerging as a new strategy to fight viral infections.
RdRp proteins of SARS-CoV-2 and SARS-CoV share 96% sequence identity. Favipiravir (24) is an approved RNA polymerase inhibitor for the treatment of the influenza pandemic. It has been shown not only to be active in influenza but also active against other RNA viruses (Figure 7).
Favipiravir is a prodrug, which is metabolized in cells into the active purine-mimicking nucleotide favipiravir-ribofuranosyl-5-triphosphate that inhibits the RNA replication and thus the viral progression.
Interestingly, it does not inhibit host DNA and RNA synthesis and inosine 5′-monophosphate dehydrogenase (IMPDH) activity. Favipiravir reportedly demonstrated efficacy with minor side effects in an ongoing 70-patient clinical trial in Shenzhen, Guangdong province.
Remdesivir (25) reduced SARS-CoV-2 infection of monkey kidney cells with an EC50 of 0.77 μM. The compound is in late-stage clinical development and has been recently described to inhibit multiple RNA viruses on a cellular level, including Ebola and SARS. The presumed mode of action of the adenosine analog prodrug remdesivir is pre-mature RNA synthesis termination by incorporation into nascent viral RNA chains.
Galidesivir (26) is another antiviral drug under clinical development with potential in COVID-19 treatment (Figure 7). It is an adenosine analog and is currently developed for Ebola virus disease and Marburg virus disease. It also shows broad-spectrum antiviral activity against RNA virus families including CoVs.
Its mode of action is unclear. However, chloroquine inhibits endosomal acidification and thus could stop the release of viral DNA into the cytoplasm. It is under assessment in more than 100 patients at over ten hospitals in Beijing and Guangdong province. Plans for an additional study in Hunan province are underway.
Other Viral Proteins
The role of the other SARS-CoV-2 N proteins as drug-discovery targets is less clear. For the assembly of the replication and/or transcription complexes, there is a vast interaction network described between the non-structural proteins. Similarly, viral particle assembly requires orchestrated interaction between N, S, M, and E proteins. All these interactions can be potential targets, but the structural information is currently minimal. Resolution of the protein and complex structures will provide new unique drug targets. For example, the crystal structure of SARS-CoV-2 N protein RNA-binding domain was just published and will give structural insight as a potential drug target.
It is rapidly detected by antibodies in serum, plasma, and peripheral blood, and might therefore serve to develop specific diagnostics.
Host Targets
Using methods of machine learning-enabled scientific literature analysis, the biotech company BenevolentAI proposed the AP2-associated protein kinase 1 (AAK1) as a host target to fight SARS-CoV-2. AAK1 is the key enzyme of receptor-mediated endocytosis, which is the major mechanism of most viruses to enter their host cells. Thus, they predict the approved (for rheumatoid arthritis) kinase inhibitor baricitinib 29 to reduce the ability of the virus to infect lung cells (Figure 8).
The recent emergence of the Wuhan CoV (SARS-CoV-2) has put the world on alert. The rapid worldwide spread and the high human-to-human transmissibility, combined with the inability to contain the pandemic, is causing an increasing death toll and also considerable paralysis of the world economy. The COVID-19 could decrease and disappear or could be established worldwide in the human population and reoccur seasonally in future mutations through zoonosis from one of the animal reservoirs. However, it is very likely that in the upcoming years, we will see more outbreaks from CoV and other viruses. The basic, translational, and public health research communities have to prepare for this much better. The outbreak has emphasized the urgent need for renewed efforts to develop broad-spectrum antiviral agents to combat CoVs. On the positive side, much new information of the virus biology and the spread was immediately shared, whereas, on the negative side, many past opportunities to develop antivirals against CoVs were not taken, despite a large number of promising approaches and compounds.
The past decade has shown that CoV outbreaks are regularly reoccurring with more or less health effect on human and livestock. It remains to be hoped that the current pandemic will slow down and end as predicted in summer. Furthermore, it turns out that containment measures are not effective to avoid more severe spread. It remains to be seen whether efficient and long-lasting immunity will develop in the infected population with regard to future outbreaks and whether pharmacological measures can be rapidly developed to be able to treat severely sick people.
Acknowledgments
Research in the Dömling laboratory is sponsored through ITN “Accelerated Early stage drug dIScovery” ( AEGIS , grant agreement 675555 ), the National Institute of Health (NIH) ( 2R01GM097082-05 ), the European Lead Factory (IMI) (grant agreement 115489 ), the Qatar National Research Foundation ( NPRP6-065-3-012 ), Cofunds Alert (grant agreement 665250 ), Prominent (grant agreement 754425 ), and KWF Kankerbestrijding grant (grant agreement 10504 ). L.G. is grateful for a CSC stipendship. Both authors are grateful to Micky Tortorella (GBH) for helpful discussions.
Author Contributions
A.D. and L.G. wrote the manuscript.
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Hallis Mailin is a suffering war veteran who has bad legs and needs his computer. He is having problems with Microsoft.
Dear Hallis Mailin
Firefox and flash are Microsoft competitors. Microsoft will allow them to sit on your desk-top and also in your download files but will absolutely not allow them to take over the operating system. Microsoft controls the operating system and they will make you pay to use Windows.
You are not alone in your misery. I began using computers in 1972 and at the time we used PC plus to keep our files in order. We used Borland disks and Doss and CPlus and a few more programs and we used Bell telephone lines. For a long time Bell did not know we existed and we lived in Nerd heaven with our programs until Microsoft began buying them up and incorporating them into their programs. It was then Windows came along with Win3.1 and Win3.11 and today I continue to have problems with their Windows 10. I remember Windows 95 which was a great system where everything worked fine and everybody made copies on their computer drives until Microsoft got fed up and gave us the program, free! But then they upgraded to a Windows 98 which proved to be garbage and so I bought a Windows XP computer which proved to be very good. So good that some genius, somewhere decided to change from 32 to 64 and that effectively blocked my XP. Now I use a cheap H.P. computer with a Windows 10 but Microsoft can’t find my account and so they decided to give me temporary access where nothing I write will remain on my computer…or so they think. For example, nothing is stopping me from using their executive computer to write these words. I am older than Bill Gates and Steve Jobs is dead. I have millions of contacts around the world and creating change for the better is something I like to do and so here is a tip for you. I saved an old computer which still runs Windows 98 and still reads the hundreds of CD’s filled with programs I have saved over the years. I use UBUNTU to improve its efficiency and today you can access the internet free from your local library. From there I suggest you go to Google and download Ubuntu and store it on a small flash drive key. They are expensive but flash drive keys are possible mini computers and they run on older computers and that includes library computers. Many older ‘puters’ still have USB ports. Today, the cloud dominates the internet but it is still possible to find cheap older computers or even free older computers. Some people are actually throwing then away! What a waste!
Before he died, Steve Jobs decided to miniaturize his computers and so we now all have pocket computers that connect by satellites and also work as telephones but who in hell can write on those things and they are way too expensive to operate. I miss Ma Bell and her Twenty Dollar a month basic telephone. If you want to do something besides play games, how about using your computer to understand how SARS-COv-2 works. Visit human4us2.blogspot.com and study the complicated science until you understand the jargon. Then contribute what you can. That is what I am doing today. You can write me at human4usbillions@gmail.com but identify yourself as you are not alone. Buy for now!
Signed: Nelson J. Raglione
Please correct me if I am wrong! Here is what I understand so far about Covid-19. 1. The SARS-CoV-2 enters the body by the nose, mouth and eyes. 2. It travels down the esophagus and into the lungs. 3. It quietly enters into the lung cells without alarming the immune system. 4. The job of lung cells is to transfer oxygen from the air we breath into the blood stream. 5. Infected lung cells are not aware they are infected because the virus blocks the lung cells from using an immune system alarm called interferon. Interferon triggers B and T proteins. T proteins rush to arrive to destroy the infection. 6. B and T cells are part of the immune system and they attack germ and virus infections when they are warned early enough. 7. Without an immune response, the virus enters the blood stream and then slowly stops the process of breathing. It quietly spreads itself via the blood stream everywhere in the body and it creates blood clots. 8. As a last resort for a sick patient, doctors intubate by pushing an oxygen tube into the lungs. Unfortunately, however, this protocol is proving wrong because by the late stage of the SARS-C0V-2 infection, the lungs are incapable of processing oxygen and intubating hinders rather than helps. The protocol is questioned?
9. Doctors are wondering how and why dangerous blood clots are created in Covid patients. One theory needing verification is that the virus in the blood stream connects with other virus to create blood clots.
10. Laboratories around the world are creating vaccines to help the body recognize the SARS-CoV-2. Some large pharmaceutical companies are balking at spending millions to create a non-profit vaccine thus slowing the process of discovery.
11. The Houston medical hospital is reporting good results with a plasma injection that uses the blood plasma of recovered patients to alleviate the symptoms of sick patients. 12. "Most convalescent plasma obtained from individuals who recover from COVID-19 do not contain high levels of neutralizing activity. Nevertheless, rare but recurring RBD-specific antibodies with potent antiviral activity were found in all individuals tested, suggesting that a vaccine designed to elicit such antibodies could be broadly effective.
Davide F. Robbiani
Present address: Institute for Research in Biomedicine, Università della Svizzera italiana, Bellinzona, Switzerland
12. The virus is air born and for self protection and the protection of others, wear a mask and remain more than three meters from other people unless you are a professional care giver. 13 Wash your hands constantly. 14, Remain isolated as long as possible and have yourself tested for the virus because you may not have early warning signs.
Keep safe and good luck! Signed: Nelson Joseph Raglione Dir: The World Friendly Peace and Ecology Movement. P.S. For science based information visit human4us2.blogspot
Science’s COVID-19 reporting is supported by the Pulitzer Center.
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The coronavirus that for weeks had been crippling hospitals in her hometown of Seattle changed Jennifer Haller’s life on 16 March—but not because she caught it. Haller, an operations manager at a tech company in the city, became the first person outside of China to receive an experimental vaccine against the pandemic virus, and in the days since, she has been flooded by an outpouring of gratitude. “There’s been overwhelming positivity, love, and prayers coming at me from strangers around the world,” Haller says. “We all just feel so helpless, right? This was one of the few things happening that people could latch on to and say, ‘OK, we’ve got a vaccine coming.’ Disregard that it’s going to take at least 18 months, but it’s just one bright light in some really devastating news across the world.”
The vaccine Haller volunteered to test is made by Moderna, a well-financed biotech that has yet to bring a product to market. Moderna and China’s CanSino Biologics are the first to launch small clinical trials of vaccines against coronavirus disease 2019 (COVID-19) to see whether they are safe and can trigger immune responses. (The CanSino vaccine trial also began on 16 March, according to researchers from the Chinese military’s Institute of Biotechnology, which is collaborating on it.) An ever-growing table put together by the World Health Organization now lists 52 other vaccine candidates that could soon follow. “This is a wonderful response from the biomedical community to an epidemic,” says Lawrence Corey, a virologist at the Fred Hutchinson Cancer Research Center who has run vaccine trials against a dozen diseases but is not involved with a COVID-19 effort. “It’s both gratifying and problematic in the sense of how do you winnow all this down?”
Broadly speaking, these vaccines group into eight different “platforms”—among them old standbys such as inactivated or weakened whole viruses, genetically engineered proteins, and the newer messenger RNA (mRNA) technology that is the backbone of the Moderna vaccine—and their makers include biotechs, academia, military researchers, and a few major pharmaceutical companies. On 30 March, Johnson & Johnson (J&J) announced what it said could be a $1 billion COVID-19 vaccine project, with about half the money coming from the U.S. Biomedical Advanced Research and Development Authority if milestones are met.
Many viruses, including HIV and hepatitis C, have thwarted vaccine developers. But the new coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), doesn’t appear to be a particularly formidable target. It changes slowly, which means it’s not very good at dodging the immune system, and vaccines against the related coronaviruses that cause SARS and Middle East respiratory syndrome (MERS) have worked in animal models. Corey heads the United States’s HIV Vaccine Trials Network, which has seen one candidate vaccine after another crash and burn, is optimistic about a SARS-CoV-2 vaccine. “I don’t think this is going to be that tough.”
One concern is whether people develop durable immunity to SARS-CoV-2, which is crucial given that vaccines try to mimic a natural infection. Infections with the four human coronaviruses that typically cause minor colds don’t trigger long-lasting immunity. Then again, researchers have found long-lasting immune responses to the viruses causing SARS and MERS, and genetically they are far more like SARS-CoV-2. And unlike cold-causing viruses, which stay in the nose and throat, the new coronavirus targets the lower respiratory tract, where the immune response to a pathogen can be stronger, says Mark Slifka, an immunologist who studies vaccines at the Oregon National Primate Research Center. “When you get an infection in the lungs, you actually get high levels of antibodies and other immune cells from your bloodstream into that space.”
Even with this all-out effort, Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases (NIAID), predicts getting a vaccine to the public “is going to take a year, a year and a half, at least.” And Fauci adds “at least” because side effects, dosing issues, and manufacturing problems can all cause delays. Already some are calling for an ethically fraught shortcut to speed up clinical trials: giving people candidate vaccines and then intentionally attempting to infect them to see whether they’re protected.
A new vaccine might also be made available to health care workers and others at high risk even before phase III efficacy trials are completed. And Stanley Perlman, a veteran coronavirus researcher at the University of Iowa, suggests a vaccine that only offers limited protection and durability could be good enough—at first. “In this kind of epidemic setting, as long as you have something that tides us along and prevents a lot of deaths, that may be adequate,” he says.
A better spike
On 13 January, 3 days after Chinese researchers first made public the full RNA sequence of SARS-CoV-2, NIAID immunologist Barney Graham sent Moderna an optimized version of a gene that would become the backbone of its vaccine. Sixty-three days later, the first dose of the vaccine went into Haller and other volunteers participating in the small trial at the Kaiser Permanente Washington Health Research Institute. In 2016, Graham had made a Zika virus vaccine that went from lab bench to the first volunteer in what he then thought was a lightning-fast 190 days. “We beat that record by nearly 130 days,” he says.
The effort benefited from lessons Graham learned from his past vaccine efforts, including his work on respiratory syncytial virus (RSV). The search for an RSV vaccine has a checkered past: in 1966, a trial of a candidate vaccine was linked to the death of two children. Later studies identified the problem as vaccine-triggered antibodies that bound to the surface protein of the virus but did not neutralize its ability to infect cells. This antibody-viral complex, in turn, sometimes led to haywire immune responses.
Best shot
The World Health Organization has tallied dozens of vaccine candidates, based on a variety of technologies. Two have started human safety trials (*).
Platform
Candidates
Protein subunit
18
RNA
8*
DNA
3
Nonreplicating vector
8*
Replicating vector
5
Inactivated virus
2
Attenuated virus
2
Viruslike particle
1
Studying the 3D structures of the RSV surface protein, Graham discovered that the dynamic molecule had different orientations before and after fusing with the cell. Only the pre-fusion state, it turned out, triggered high levels of neutralizing antibodies, so in 2013 he engineered a stable form of the molecule in that configuration. “It was so clear at that point that if you didn’t have structure, you didn’t really know what you were doing,” Graham says. An RSV vaccine that built on this concept has worked well in early trials.
The experience came in handy in 2015, when a member of Graham’s lab made a pilgrimage to Mecca, Saudi Arabia, and came back ill. Worried that it might be MERS, which is endemic in Saudi Arabian camels and repeatedly jumps into humans there, Graham’s team checked for the virus and instead pulled out a common cold coronavirus. It was relatively easy to determine the structure of its spike, which then allowed the team to make stable forms of the spikes for the SARS and MERS viruses, and, in January, for SARS-CoV-2’s. That’s the basis of the Moderna COVID-19 vaccine, which contains mRNA that directs a person’s cells to produce this optimized spike protein.
Still a new strategy, no mRNA vaccine has yet reached a phase III clinical trial, let alone been approved for use. But producing huge numbers of vaccine doses may be easier for mRNA vaccines than for traditional ones, says Mariola Fotin-Mleczek of the German company CureVac, which is also working on mRNA vaccine for the new coronavirus. CureVac’s experimental rabies vaccine showed a strong immune response with a single microgram of mRNA. That means 1 gram could be used to vaccinate 1 million people. “Ideally, what you have to do is produce maybe hundreds of grams. And that would be enough,” Fotin-Mleczek says.
Many companies are relying on time-tested techniques. Sinovac Biotech is making a SARS-CoV-2 vaccine by chemically inactivating whole virus particles and adding an immune booster called alum. Sinovac used the same strategy for a SARS vaccine it developed and tested in a phase I clinical trial 16 years ago, says Meng Weining, a vice president at Sinovac. “We immediately just restarted the approach we already know.” The company’s SARS vaccine worked in monkeys and although there were concerns that an inactivated coronavirus vaccine might trigger the sort of antibody enhancement disease that occurred with the RSV vaccine, Meng stresses that no such problems surfaced in their animal studies.
Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai, says inactivated virus vaccines have the advantage of being a tried-and-true technology that can be scaled up in many countries. “Those manufacturing plants are out there, and they can be used,” says Krammer, who co-authored a status report about COVID-19 vaccines that appears online in Immunity.
CanSino is now testing another approach. Its vaccine uses a nonreplicating version of adenovirus-5 (Ad5), which also causes the common cold, as a “vector” to carry in the gene for the coronavirus spike protein. Other vaccine researchers worry that because many people have immunity to Ad5, they could mount an immune response against the vector, preventing it from delivering the spike protein gene into human cells—or it might even cause harm, as seemed to happen in a trial of an Ad5-based HIV vaccine made by Merck that was stopped early in 2007. But the same Chinese collaboration produced an Ebola vaccine, which Chinese regulators approved in 2017, and a company press release claimed its new candidate generated “strong immune responses in animal models” and has “a good safety profile.” “I think pre-existing Ad5 immunity and HIV vaccine risk are not a problem,” Hou Lihua, a scientist working on the project at the Institute of Biotechnology, wrote in an email to Science, noting that the Ebola vaccine trial results adds to their confidence that these will not be issues.
Disregard that [a vaccine is] going to take at least 18 months, but it’s just one bright light in some really devastating news across the world.
Other COVID-19 vaccine platforms include a laboratory-weakened version of SARS-CoV-2, a replicating but harmless measles vaccine virus that serves as the vector for the spike gene, genetically engineered protein subunits of the virus, a loop of DNA known as a plasmid that carries a gene from the virus, and SARS-CoV-2 proteins that self-assemble into “viruslike particles.” J&J is using another adenovirus, Ad26, which does not commonly infect humans, as its vector. These different approaches can stimulate different arms of the immune system, and researchers are already “challenging” vaccinated animals with SARS-CoV-2 to see which responses best correlate with protection.
Many researchers assume protection will largely come from neutralizing antibodies, which primarily prevent viruses from entering cells. Yet Joseph Kim, CEO of Inovio Pharmaceuticals, which is making a DNA COVID-19 vaccine, says a response by T cells—which clear infected cells—proved a better correlate of immunity in monkey studies of the company’s MERS vaccine, which is now in phase II trials. “I think having a balance of antibody and T cell responses probably is the best approach.”
Kim and others applaud the variety of strategies. “At this early stage, I think it makes sense to try anything plausible,” he says. As Stéphane Bancel, CEO of Moderna, says, “Nobody knows which vaccines are going to work.”
Final products
Spurring many of the efforts in the nascent COVID-19 field has been the Coalition for Epidemic Preparedness Innovations (CEPI), a nonprofit set up to coordinate R&D for vaccines against emerging infectious diseases. So far, CEPI has invested nearly $30 million in vaccine development at Moderna, Inovio, and six other groups. “We have gone through a selective process to pick the ones that we think have the greatest likelihood of meeting our goals—which we think ought to be the world’s goals—of speed, scale, and access,” says CEPI CEO Richard Hatchett. But he is rooting for other candidates as well. “We don’t want to be in a situation where we have [one] successful vaccine and we have a contamination event [during manufacturing] and suddenly we don’t have any vaccine supply.”
CEPI invests in manufacturing facilities at the same time it puts money into staging clinical trials. “By doing things in parallel rather than in serial fashion, we hope to compress the overall timelines,” Hatchett says. After reviewing phase I data and animal model data, CEPI plans to move six of the eight products into larger safety studies to arrive at three that are worthy of full-scale efficacy trials that enroll perhaps 5000 participants.
CEPI has less than $300 million in its coffers for the effort, and Hatchett estimates the price tag at $2 billion. He says CEPI hopes to raise this money from governments, private philanthropies, industry, and the United Nations Foundation.
Seth Berkley, who heads Gavi, the Vaccine Alliance, argued in an editorial in the 27 March issue of Science that the world needs to come together even more to streamline the search for a COVID-19 vaccine. “If ever there was a case for a coordinated global vaccine development effort using a ‘big science’ approach, it is now,” Berkley wrote, stressing that there must be extraordinary sharing of data, coordination of clinical trials, and funding. “You can’t move 100 vaccines forward,” he says.
Moderna and J&J both say that if everything goes perfectly, they could launch an efficacy trial with about 5000 people by late November and determine by January 2021 or so whether the vaccine works. Meng says that, depending on approval from Chinese regulatory agencies, Sinovac could move its vaccine through small phase I and II tests by June. But, because of China’s success at controlling its epidemic, the company may have to find another country that has high transmission of SARS-CoV-2 to stage an efficacy trial quickly.
Haller has had no serious side effects from the mRNA injected into her arm but realizes that the phase I study will not determine whether the vaccine is effective. “The chances of the one that I got being really anything? I don’t know,” Haller says. “This is just the first of many, many vaccines, and it’s just stupid luck that I was the first one.”
With reporting by Kai Kupferschmidt.
*Correction, 1 April, 11 a.m.: A World Health Organization table inaccurately described Sinovac’s inactivation process as using formaldehyde. The company does chemically inactivate the virus but does not want to disclose specifics.
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