Pfizer and BioNTech have shared (PDF) phase 1/2 data suggesting their COVID-19 vaccine triggers stronger CD8 T-cell responses than Moderna’s rival candidate. Four-fifths of subjects who received BNT162b1 had vaccine-induced CD8 T-cell responses and researchers classed most of the responses as strong.
Mounting evidence suggests T-cell responses play a role in long-term immunity against the pandemic coronavirus. That evidence has helped expand the focus of evaluations of the promise shown by the frontrunning COVID-19 vaccines beyond antibody responses to include a broader assessment of the ways the prophylactics may induce immunity.
A preprint paper describing data on BioNTech and Pfizer’s mRNA vaccine BNT162b1 released at the start of the month lacked a look at cellular immunity. On Monday, researchers filled that gap in the evidence with a second paper describing the results of the phase 1/2 trial.
The results suggest Pfizer and BioNTech may have an edge over Moderna, which saw “low levels” of CD8 T-cell responses to the S-2P antigen in patients who received two 100-μg doses of mRNA-1273. Pfizer and BioNTech saw stronger CD8 responses in patients who received BNT162b1.
In the view of the researchers, the effect on CD8 cells is part of a “coordinated immune response to counter a viral intrusion” seen in patients who received BNT162b1. Other aspects of the coordinated response include increases in neutralizing antibodies, CD4 T cells and immune-modulatory cytokines. Almost 95% of patients had CD4 T-cell responses.
The immune response appears to be capable of acting against different strains of SARS-CoV-2. Serum taken from subjects effectively neutralized all 17 of the SARS-CoV-2 variants tested in the study. The variants used different receptor binding domains. The ability of sera to neutralize variants that use a different binding domain than the one targeted by BNT162b1 may lessen concerns that the mutation of the coronavirus will render vaccinated patients vulnerable to infection.
BNT162b1 generated the immune responses at low doses. While the antibody response was dose dependent, the researchers found no clear link between the administered dose and strength of the T-cell response. The finding suggests Pfizer and BioNTech may be able to induce immunity using low doses, potentially enabling them to produce more vaccines from the available capacity. BNT162b1 triggered T-cell responses at the 1 µg. Moderna’s data come from a 100 µg dose.
It remains to be seen whether the immune responses seen in the small number of people studied to date translate into protection against the coronavirus. Pfizer and BioNTech plan to assess the efficacy of their vaccine in a 30,000-subject phase 2b/3 trial that is due to start this month.