How different COVID-19 vaccines work

In a recent study published in bioRxiv*Preprint server Researchers at the University of Tübingen and Imperial College London evaluated the humoral and cellular immune responses generated by the recombinant adenovirus vector (rAdVV) – and mRNA-based coronavirus 2019 (COVID-19) vaccines.

Studies have reported that COVID-19 vaccines confer immune protection against SARS-CoV-2 infection by stimulating antibody (AB) and T lymphocyte-based cellular immune responses. However, a comprehensive examination of the mechanisms that underlie COVID-19 vaccines has not been conducted.

Stady: Multi-OMICS Single-Cell Comparative Atlas of Five COVID-19 Vaccines (rAdVV and mRNA) describes unique and distinct mechanisms of action. Image Credit: Orpheus FX / Shutterstock

about studying

In the current longitudinal study, researchers investigated the immunogenicity and mechanisms of action of five different COVID-19 vaccines based on rAdVV. [Ad26.CoV2.S by Johnson & Johnson or Janssen (JJ), ChAdOx1 nCoV-19 by AstraZeneca (AZ)] the mRNA Pfizer/BioNTech (PB) BNT162b1 (PB), mRNA-1273 from Moderna (MD); CureVac (CV) CVnCV vaccination pads.

OMICS multiplex transcriptional analysis was performed, and humoral Ab counters and markers of the cellular immune response were evaluated. AZ or mixed AZ, PB, JJ, PB, MD and CV were given to four, three, fifteen, three, and three participants, respectively. Participants vaccinated with JJ received only one vaccination.

Serum samples were obtained before vaccination (PrV1, n = 23), seven to 10 days after the first vaccination (PoV1), and after the second, third and fourth vaccinations. Individuals were given the second vaccination (PoV2) one to three months after PoV1. The third vaccination (PoV3) was given six months after PoV2, and the fourth vaccination (PoV4) four to six months after PoV3.

The study group was divided into two groups. The first group included 28 unvaccinated and vaccinated people. Peripheral blood mononuclear lymphocytes (PBMCs) were isolated from serum samples and subjected to scRNA-seq (single-cell RNA sequencing) and FC analysis (flow cytometry). In addition, CITE-seq (Cellular Indexing Transcripts and Loops Sequencing) analysis was performed to detect the surface protein.

The second group consisted of 82 individuals who received two vaccines with mRNA, rAdVV, or both (rAdVV/mRNA) vaccines, and their samples were obtained three to 12 months after PoV2. 34 subjects, eight, three, two, and 34 subjects received PB, MD, CV, and JJ, or combined AZ and PB/MD vaccines, respectively. Forty-nine and 11 individuals were administered a PB and MD mRNA vaccine as PoV3, respectively.

The team excluded individuals previously exposed to SARS-CoV-2 which was identified by the presence of serum anti-SARS-CoV-2 nucleocapsid (N) Abs. Ab/cytokine assessments and immunophenotyping analyzes were performed on the placebo group samples. Immunoglobulin G (IgG) titer was determined against protein subunit 1 (S1), N, and receptor-binding domain (RBD) of SARS-CoV-2 spike (S).

consequences

In all, the sample population consisted of 110 individuals, of whom 36 and 74 individuals were male and female, respectively. Vaccine platforms (rAdVV and mRNA) contain distinct and unique immune mechanisms of T lymphocyte activation and antigen presentation by monocytes and dendritic lymphocytes (DCs) that can alter the outcome of vaccine efficacy.

In particular, rAdVV vaccines negatively regulated activation of the four differentiation group positive (CD4+) T lymphocytes, leukocyte chemotaxis, interleukin-18 (IL-18) signaling, and monocyte antigen presentation. Conversely, mRNA vaccines positively regulate natural killer (NKT) lymphocyte activation, chemokine-mediated immune pathways, and platelet activation. In addition, antigen-specific cellular immune responses were elicited after PoV1 but not increased by the second homologous vaccination and depended on the type of vaccine used.

Uniform branched approximation and projection (UMAP) analysis of PrV1 and PoV1 subjects mainly showed cell populations of CD4+, CD8+ T, NKT, monocytes, CD4+ FOXP3+ (forkhead box P3 positive) regulatory T lymphocytes (Tregs) and T-cells. B. lymphocytes Significant changes are observed in the CD8 +, CD4 + and NK cell compartments.

An elevated Ab titer (5-500ug/ml) was observed three to six months after PoV2 in vaccinated subjects, regardless of vaccine platform (AZ, PB and MD) compared to PrvV1 and PoV1 but diminished after six months. sc-RNA-seq analysis showed 27 populations of 32,920 lymphocytes from PMBC, mostly CD4+ T-naive, central memory (TCM), and effector memory (TEM) CD4+ T lymphocytes. The results of the differential cell abundance assay analysis indicated that monocytes, T lymphocytes, and NK cells could be important markers for the detection of vaccine-induced immune fingerprinting.

Comparisons of PrV1 and PoV2 showed that most of the genes in the p-monocytes (promonocytes) of rAdVV and mRNA vaccines were upregulated. Furthermore, downregulation of the major histocompatibility complex II (MHC II), CD83, CXC and chemokine receptor 4 (CXCR4) genes was observed following rAdVV (but not mRNA) immunizations.

T-cell receptor (TCR) genes were upregulated after vaccination against rAdVV, whereas recombinant human perforin-1 (PRF1), T-box transcription factor (TBX21), CD69, CX3C chemokine receptor 1 (CX3CR1), and KLRG1 ( Co-inhibitory receptor killer- G1 cell-like receptor genes were upregulated by mRNA vaccine. Platelets were activated after rAdVV (but not mRNA) vaccinations.

PoV3 enhanced humoral responses, with increased Tregs and CD4+ T lymphocytes and decreased CD8+ T lymphocytes. After PB and MD vaccinations, the number of SARS-CoV-2 S-specific T lymphocytes increased. After PoV4, CD8+ T lymphocytes increased , and TEMRA (terminally differentiated responsive memory cells) lymphocytes were decreased. MCP1 (monocyte chemoattractant protein), IL-10RA, and CXCL-10 cytokines were found to be essential markers of vaccine efficacy.

Overall, the study results showed that SARS-CoV-2 vaccines induce robust but differentiated immune responses at the cellular, protein and RNA levels.

*Important note

bioRxiv It publishes preliminary scientific reports that have not been peer-reviewed and therefore should not be considered conclusive, guide clinical practice/health-related behaviour, or be treated as established information.