Written By: Longjam Dineshwori | Published : June 29, 2020 9:12 AM IST
Production of SARS-CoV-2-specific T cells in patients increases over time, say researchers.
The COVID-19 pandemic has literally united the world as a nation with many countries coming together in their attempt to find a cure for the deadly disease. According to the World Health Organisation's draft landscape of COVID19 vaccines, around 13 experimental vaccines are undergoing clinical trials and another 129 are in the preclinical evaluation stage. One of the most promising vaccine candidates is the one jointly developed by the University of Oxford and AstraZeneca Plc. The ChAdOx1 nCoV-19 vaccine, also known as AZD1222, is already in the final stages of clinical trials and is expected to be in the market by October. This vaccine has shown very good results in animal trails suggesting that a two-dose approach may be more effective in getting protection against COVID-19. In what could lead to better strategies for vaccine design, a team of scientists has provided new clues about immune cells that are involved in protection against COVID-19.
They revealed that patients suffering from severe respiratory symptoms due to SARS-CoV-2 infection can rapidly generate virus-attacking T cells and that this production increases over time. For the study, the researchers including those from the University of California in the US assessed T cells from 10 COVID-19 patients under intensive care treatment.
They also found that healthy individuals without prior exposure to the virus also harbored SARS-CoV-2-reactive T cells. This suggests that the said T cells can cross-react to the novel coronavirus due to past infection with related coronaviruses that cause common cold symptoms.
Based on their findings, the researchers were able to confirm that SARS-CoV-2-specific T cell responses vary in patients over time depending on disease severity and that patients with more severe symptoms can also generate protective virus-specific T cells.
In addition, the study provided new clues regarding the cells responsible for excessive immune responses, including life-threatening "cytokine storms," which may be of great help in vaccine design.
For the study, Daniela Weiskopf from the La Jolla Institute for Immunology in the US and his team extracted blood cells from 10 patients at weekly intervals starting soon after they were admitted to the ICU for COVID-19. These cells were then exposed to "megapools" of known SARS-CoV-2 epitopes - a technique meant to capture a large fraction of total viral-reactive T cells.
The researchers found that SARS-CoV-2-specific CD4+ helper T cells in all 10 patients and CD8+ "killer" T cells in 8 out of 10 patients. They could also gather more information about the cells' production of specific inflammation-triggering cytokines.
As per their observation, the strongest T cell responses were directed to the virus' spike (S) surface glycoprotein. This supports previous studies that had pointed to the S protein as a promising target to induce virus-specific T cells.
After screening all patients at 0, 7, and 14 days, the researchers found that SARS-CoV-2-specific T cells were present relatively early during the course of infection and their production increased in these patients over time.
The researchers then used the same T cell stimulation technique in age-matched healthy individuals. Surprisingly, they found SARS-CoV-2-reactive T cells in 2 out of the 10 individuals. These findings, according to the authors, lead to promising areas for future work. They noted that further investigation may help understand how preexisting SARS-CoV-2-specific T cells in healthy controls correlate to protection against COVID-19 disease, as well as identify the T cell types responsible for cytokine storms. The findings of this study appeared in the journal Science Immunology.
