Recent works have allowed a greater advancement in our understanding of the mechanism regulating immune response at the molecular level. This, in turn, has led to improved modulation of the immunological parameters to develop an intervention strategy to counter difficult-to-treat disorders. A case in point concerns the delineation of the regulatory mechanism that inhibits the activation of immune response (dubbed ‘immune checkpoint’) by J. Allison of Univ. of Texas M. D. Anderson Cancer Center (Nobel prize, 2018), whose blocking led to the suppression of cancer in a subset of melanoma patients. Though the reason why only a subset of melanoma patients has responded is not clear, its therapeutic efficacy has been partly attributed to the presence of ‘professional antigen presenting cells’ (ex. dendritic cells) in the skin (Akinleye et al., 2019).
Vaccination to counter infectious diseases caused by virus has become an integral part of modern medicine. Amongst the notable achievements was the successful development of vaccine against poliovirus in the 1950s. Poliovirus is a nonenveloped virus containing single-stranded positive-sense RNA genome. Though most healthy individuals develop minor symptoms following the infection, in approximately 0.1-0.5% of infected cases, it causes poliomyelitis, resulting in paralysis due to weakened muscles. The development of inactivated polio vaccine by J. Salk and the oral attenuated polio vaccine by A. Sabin was instrumental in suppressing a number of cases (Baicus, 2012). According to WHO (World Health Organization), polio has been largely eradicated globally due to these two vaccines.
Consequently, on the immunological front, a high level of optimism lies in developing vaccines that could neutralize COVID-19 coronavirus. Recently, an experimental support for this view was gained by the investigators at the University of Washington (United States), who showed that antibodies directed against SARS coronavirus could recognize COVID-19 coronavirus. Consistently, treating COVID-19 with the plasma containing antibodies (from mice immunized with SARS coronavirus) blocked the virus from entering VeroE6 cells (derived from kidney epithelial cells of African green monkey) in the laboratory (Walls et al., 2020). Nonetheless, FDA has yet to approve a vaccine for human coronaviruses including SARS.
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The attempt to develop anti-COVID-19 vaccine is being pursued at multiple universities, research institutes and pharmaceutical industries. Notable among the current approaches is the initiative to inoculate (using electric current) DNA plasmids encoding the suspected epitopes of COVID-19 protein to stimulate immune response. Previously, a similar strategy was used to transfer DNA (via gene gun) encoding tumor specific antigens (that are mutated or overexpressed in cancer) into the skin (Norell et al., 2010). Upon expression, the antigen is proteolytically cleaved into peptides, some of which are presented by MHC (major histocompatibility complex) molecules of target cells to circulating T cells for recognition and immune stimulation. One hurdle with the above approach has been an inadequate expression of the antigen by the injected cells.
Similarly, injecting mRNA (encoding spike protein) for vaccination is being attempted as it is safer than using infectious agents—though this approach had difficulty advancing to phase III clinical trial in the past. Continuing on this theme, the possibility of transferring mRNA enclosed in a lipid nanoparticle is also being explored as a potential COVID-19 vaccine (Johns Hopkins, 2020).
Previously, various viral vectors have been used to express foreign genes in vivo for gene therapy, ex. blood clotting factor VIII for haemophilia A patients, Rb or p53 gene for cancer patients (Rangarajan et al., 2017; Zhang & Roth., 1997). Consequently, one strategy is to utilize recombinant adenovirus Ad26 to express a suspected immunogenic protein of COVID-19 coronavirus. Aside from non-replicating viruses, replicating types such as weakened measles virus are being considered as alternative viral vectors to express COVID-19 immunogens.
Protein-based approaches for vaccination include the direct injection of protein(s) derived from COVID-19 coronavirus (with or without adjuvants). Alternatively, introducing the COVID-19 virus shell devoid of the genetic material (to avoid infectivity) is being considered (Callaway, 2020). Another approach is to use live attenuated influenza virus to express the antigenic regions of SARS coronavirus to induce cross-reactive immunity against COVID-19 (Johns Hopkins, 2020).
The key to preventing epidemic is the ability to diagnose the infected early to preempt further propagation. For this, Bio-Synthesis, Inc. provides primers and probes (as well as synthetic RNA control) for COVID-19 diagnosis via RT-PCR assay. Antibody purification, characterization/quantification, modification and labeling are also offered. It specializes in oligonucleotide modification and provides an extensive array of chemically modified nucleoside analogues (over ~200) including bridged nucleic acid (BNA). A number of options are available to label oligonucleotides (DNA or RNA) with fluorophores either terminally or internally as well as conjugate to peptides. It recently acquired a license from BNA Inc. of Osaka, Japan, for the manufacturing and distribution of BNANC, a third generation of BNA oligonucleotides. To meet the demands of therapeutic application, its oligonucleotide products are approaching GMP grade. Bio-Synthesis, Inc. has recently entered into collaborative agreement with Bind Therapeutics, Inc. to synthesize miR-21 blocker using BNA for triple negative breast cancer. The BNA technology provides superior, unequalled advantages in base stacking, binding affinity, aqueous solubility and nuclease resistance. It also improves the formation of duplexes and triplexes by reducing the repulsion between the negatively charged phosphates of the oligonucleotide backbone. Its single-mismatch discriminating power is especially useful for diagnosis (ex. FISH using DNA probe). For clinical application, BNA oligonucleotide exhibits lesser toxicity than other modified nucleotides.
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References
Akinleye A, Rasool Z. Immune checkpoint inhibitors of PD-L1 as cancer therapeutics. J Hematol Oncol. 12:92 (2019). PMID: 31488176 doi: 10.1186/s13045-019-0779-5.
Baicus A. History of polio vaccination. World J Virol 1:108-14 (2012). PMID: 24175215 doi: 10.5501/wjv.v1.i4.108.
Callaway E. The race for coronavirus vaccines: a graphical guide. Nature 580:576-577 (2020). PMID: 32346146 doi: 10.1038/d41586-020-01221-y
Johns Hopkins Center for Health Security, Vaccines in Development to Target COVID-19 Disease. April 20, 2020. [centerforhealthsecurity.org]
Norell H, Poschke I, Charo J, Wei WZ, Erskine C, Piechocki MP, et al. Vaccination with a plasmid DNA encoding HER-2/neu together with low doses of GM-CSF and IL-2 in patients with metastatic breast carcinoma: a pilot clinical trial. J Transl Med 8:53 (2010). PMID: 20529245 doi: 10.1186/1479-5876-8-53.
Rangarajan S, Walsh L, Lester W, Perry D, Madan B, Laffan M, et al. AAV5-Factor VIII Gene Transfer in Severe Hemophilia A. N Engl J Med 377:2519-2530 (2017). PMID: 29224506 doi: 10.1056/NEJMoa1708483
Walls AC, Park YJ, Tortorici MA, Wall A, McGuire AT, Veesler D. Structure, Function, and Antigenicity of the SARS-CoV-2 Spike Glycoprotein. Cell 181:281-292.e6 (2020). PMID: 32155444 doi: 10.1016/j.cell.2020.02.058
Zhang WW, Roth JA. Methods for cancer gene therapy using tumor suppressor genes. Methods Mol Med. 7:403-18 (1997). PMID: 24493444 doi: 10.1385/0-89603-484-4:403