Opinion Paper

Immunotherapy of COVID-19 with Bacille Calmette – Guerin: Where is the missing red herring?

Hari M. Saxena
Southern African Journal of Infectious Diseases | Vol 36, No 1 | a215 | DOI: https://doi.org/10.4102/sajid.v36i1.215 | © 2021 Hari M. Saxena | This work is licensed under CC Attribution 4.0
Submitted: 08 May 2020 | Published: 05 March 2021

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Hari M. Saxena, Department of Veterinary Microbiology, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana, India

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Coronavirus Disease 2019 (COVID-19) morbidity and mortality was found to be less severe in countries where Bacille Calmette – Guerin (BCG) vaccination of the population is carried out. Conjugating Purified Protein Derivative (PPD) onto tumour cells and injecting into BCG primed mice was found to enhance anti-tumour immune response. We had proposed earlier that in vitro activated autologous anti-tumour T-cells bearing Major Histocompatibility Complex (MHC) II on their surface, if pulsed with PPD and re-infused in a BCG – primed patient, can activate PPD – specific helper T-cells and the focused secretion of lymphokines like the IL-2 can selectively amplify the antitumor T-cell response by their proliferation and activation in a specific manner bypassing the suppression exerted by the anti-idiotypic and suppressor cells. The prime – boost strategy with the BCG–PPD system can also be applied to the immunoprophylaxis and immunotherapy of COVID-19. The autologous anti-Corona virus B and T lymphocytes can be activated in vitro by inactivated virus or mitogens like Concanavalin A to express MHC class II molecules on their surface and pulsed with PPD for carrier targeting in vivo. Such PPD – pulsed activated (MHC-II+ve) anti-viral lymphocytes if transfused back into a patient already vaccinated with BCG during childhood or primed with BCG during adulthood 2 weeks before transfusion, could lead to a high magnitude of selective in vivo amplification of specific anti-viral lymphocytes, which can mount adequate and appropriate immune response to get rid of the virus and cure the patient from COVID-19. Conjugating antigens to PPD and injecting into BCG primed humans may also be helpful for immunoprophylaxis against COVID-19. Thus, PPD may prove to be the red herring in the BCG therapy of COVID-19.


BCG; COVID 19; PPD; SARS CoV2; coronavirus; immunotherapy; vaccine.


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