Cell-mediated immunity wins! A new study highlights the robust nature and kinetics of T-cell priming by SARS-CoV-2 mRNA vaccines. Why does this matter? Long-term antiviral immunity that is likely to ensure lasting protection against SARS-CoV-2 infection!
https://www.biorxiv.org/content/10.1101/2021.04.21.440862v1.full

Firstly, T-cells that specifically respond to SARS-CoV-2 DO get activated by these vaccines! Researchers saw priming of both CD4+ and CD8+ T-cells with mRNA vaccination. CD4+ response wasn’t only rapid, it was universal. All participants responded after their 1st dose regardless

of whether or not they had a previous SARS-CoV-2 infection. CD4+ T-cells are considered "helper" cells because they do not neutralize infections but rather trigger the body's response to infections. CD8+ response developed more gradually. CD8+ T-cells, also known as "killer T-

cells", are cytotoxic- this means that they are able to directly kill virus-infected cells. You want these guys on your side. Researchers saw about 85% of participants who had never COVID had detectable SARS-CoV-2-specific CD8+ T-cells after the 2nd dose. No significant boosting

of CD8+ cells occurred for recovered individuals. Another important point was that researchers saw NO decline in T-cell responses regardless of age! Just because antibody (B-cell) response may not be high for some DOES NOT mean your T-cells won’t be there to protect you!

So now that we know these T-cell responses are present, let’s discuss. If you haven’t read my precious post on immunological memory, please be sure to do so- it’ll help. Researchers realized the T-cell responses initiated by the vaccines appear to indeed have characteristics of

long-lived memory cells (CD45RA- CD27+), falling in central memory and EM1 subsets, which resembles the memory response to SARS-CoV-2 infection. Why does this matter? It matters because it demonstrates your immune system is going to remember how to fight this virus off should it

come into contact with this virus again, and that includes it’s variants. Researchers also observed Th1 and T follicular helper (Tfh) cells by the vaccine, were the same helper cells activated during natural SARS-CoV-2 infection. These guys are a specialized subset of CD4+

T-cell that play a critical role in protective immunity helping B-cells produce antibody against foreign pathogens. These DO matter. Why? Th1 and Tfh cells help the maturation of CD8+ T-cells and B-cells (antibody response), respectively.

Researchers observed Th1 cells primed by the 1st dose strongly correlated with CD8+ responses to the 2nd dose, and the same for Tfh with neutralizing antibodies. This means that CD4+ T-cell responses to the 1st dose play a key part in the developing immune response to the 2nd

dose! Early priming of CD4+ T-cells may be critical to one’s overall immunity generated by vaccination. This is why we express the importance of both doses in naive individuals! Correlation, correlation, correlation, my friends.

Lastly, researchers compiled these reposted into a UMAP to visualize the overall immune responses against SARS-CoV-2. Their analysis revealed a dynamic and coordinated immune response to vaccination and demonstrates the importance of both doses for those who have not had a

previous SARS-CoV-2 infection to achieve optimal immunity, while only a single dose could be necessary for those who have previously recovered from one. TLDR:
•T-cells ARE activated by the vaccines
•Vaccination induced rapid near-maximal antigen-specific CD4+ T-cell responses

after 1st dose
•CD8+ T-cell responses develop gradually after 1st and 2nd dose
•Vaccine-elicited immune response demonstrates key hallmarks of long-term antiviral immunity- which means long lasting protection against SARS-CoV-2!