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NEW DELHI : Scientists in India plan to shortly begin clinical trials of a plant-based vaccine against covid-19, which could become one of the world’s first such vaccines against the deadly disease.

A senior official at India’s plant genome research body said scientists are studying the plant Nicotiana benthamiana, a relative of tobacco, to develop a platform to make covid-related antigens to trigger immune response against the SARS-CoV-2 virus that causes covid-19.

Three research groups at the National Institute of Plant Genome Research (NIPGR), New Delhi, under the department of biotechnology, ministry of science and technology, in association with the International Centre for Genetic Engineering and Biotechnology (ICGEB) in New Delhi, are working on the project.

The so-called N-terminal region of SARS-CoV-2 S-glycoprotein consists of a receptor-binding domain (RBD), and studies have shown that antibodies against this region can effectively block RBD ACE2 (host-receptor) interaction, according to scientists. ACE2 receptor is the protein that provides the entry point for the coronavirus to hook on to and infect human cells.

“The leaf extracts of plants expressing the RBD and purified protein will be tested and used for immunization of mice in collaboration with ICGEB, New Delhi, with different doses to trigger a strong immune response against the virus. As plant-based vaccines provide ease of administration and monitoring, developing such a vaccine for SARS CoV-2 would assist in executing mass immunization drives," a spokesperson at NIPGR told Mint.

There are four categories of covid-19 vaccines that are in use currently—whole virus, protein subunit, viral vector and nucleic acid (RNA and DNA).

Inactivated vaccines such as Bharat Biotech’s Covaxin use whole viruses whose genetic material has been destroyed, so they cannot replicate but can still trigger an immune response. Subunit vaccines such as the one from Biological E use pieces of the pathogen—often fragments of protein—to trigger an immune response.

Nucleic acid vaccines use genetic material—either RNA (Pfizer or Moderna) or DNA (Zydus Cadila)—to provide cells with the instructions to make the antigen.

In the case of covid-19, this is usually the viral spike protein. Once this genetic material enters human cells, the vaccine uses cells’ protein factories to make the antigen trigger an immune response.

In viral vector vaccines such as Covishield, the adenovirus virus causing the common cold is used as a vector. Similar to nucleic acid vaccines, the body’s own cellular machinery is hijacked to produce the antigen from those instructions to trigger an immune response.

“This plant-based vaccine against covid-19 is the first in India. It’s an early lead and a very challenging task. Indian scientists are taking up all challenging research while fighting the pandemic. The current development is in a model system and the vaccine will take some time to develop; if successful, India will be among the first countries to have such a vaccine," said Dr. Renu Swarup, secretary, department of biotechnology.

A review published in the journal Vaccines recently said in terms of plant-based vaccines, there have been notable successes, both from a biochemical and a clinical perspective, with several clinical trials showing great promise.

The review noted that the American company, iBio, has announced it is developing a plant-produced subunit vaccine candidate based on segments of Sars CoV-2 spike (S) major surface glycoprotein fused to LickM, a carrier protein derived from Clostridium thermocellum b-1,3-1,4-glucanase, which has previously been used with influenza HA.

Similarly, Kentucky BioProcessing has also announced that it is developing a plant-produced subunit vaccine candidate that is currently being tested in phase 1–2 clinical trials. Scientific data on either of these candidate vaccines have not been made available so far.

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