Early drop of circulating T cells negatively correlates with the protective immune response to Yellow Fever vaccination

Persistence of spike-specific immune responses in BNT162b2-vaccinated donors and generation of rapid ex-vivo T cells expansion protocol for adoptive immunotherapy: A pilot study

Introduction

The BNT162b2 mRNA-based vaccine has shown high efficacy in preventing COVID-19 infection but there are limited data on the types and persistence of the humoral and T cell responses to such a vaccine.

Methods

Here, we dissect the vaccine-induced humoral and cellular responses in a cohort of six healthy recipients of two doses of this vaccine.

Results and discussion

Overall, there was heterogeneity in the spike-specific humoral and cellular responses among vaccinated individuals. Interestingly, we demonstrated that anti-spike antibody levels detected by a novel simple automated assay (Jess) were strongly correlated (r=0.863, P<0.0001) with neutralizing activity; thus, providing a potential surrogate for neutralizing cell-based assays. The spike-specific T cell response was measured with a newly modified T-spot assay in which the high-homology peptide-sequences cross-reactive with other coronaviruses were removed. This response was induced in 4/6 participants after the first dose, and all six participants after the second dose, and remained detectable in 4/6 participants five months post-vaccination. We have also shown for the first time, that BNT162b2 vaccine enhanced T cell responses also against known human common viruses. In addition, we demonstrated the efficacy of a rapid ex-vivo T cell expansion protocol for spike-specific T cell expansion to be potentially used for adoptive-cell therapy in severe COVID-19, immunocompromised individuals, and other high-risk groups. There was a 9 to 13.7-fold increase in the number of expanded T cells with a significant increase of anti-spike specific response showing higher frequencies of both activation and cytotoxic markers. Interestingly, effector memory T cells were dominant in all four participants' CD8+ expanded memory T cells; CD4+ T cells were dominated by effector memory in 2/4 participants and by central memory in the remaining two participants. Moreover, we found that high frequencies of CD4+ terminally differentiated memory T cells were associated with a greater reduction of spike-specific activated CD4+ T cells. Finally, we showed that participants who had a CD4+ central memory T cell dominance expressed a high CD69 activation marker in the CD4+ activated T cells.

Yellow fever virus vaccination: an emblematic model to elucidate robust human immune responses

By preventing infectious diseases, vaccines contribute substantially to public health. Besides, they offer great opportunities to investigate human immune responses. This is particularly true for live-attenuated virus vaccines which cause resolving acute infections and induce robust immunity. The fact that one can precisely schedule the time-point of vaccination enables complete characterization of the immune response over time, short-term and over many years. The live-attenuated Yellow Fever virus vaccine strain YF-17D was developed in the 1930's and gave rise to the 17D-204 and 17DD vaccine sub-strains, administered to over 600 million individuals worldwide. YF vaccination causes a systemic viral infection, which induces neutralizing antibodies that last for a lifetime. It also induces a strong T cell response resembling the ones of acute infections, in contrast to most other vaccines. In spite of its use since 1937, learning how YF vaccination stimulates such strong and persistent immune responses has gained substantial knowledge only in the last decades. Here we summarize the current state of knowledge on the immune response to YF vaccination, and discuss its contribution as a human model to address complex questions on optimal immune responses.