IMMUNOMODULATORY EFFECTS of SARS-COV-2 VACCINATION: INCREASE of REGULATORY T CELLS after MRNA VACCINE

ABSTRACT

Background: Besides the ability to induce antigen-specifc responses, vaccines can be endowed with immunomodulatory properties including the capacity to induce or downregulate regulatory T cells (Treg) that suppress adaptative and autoreactive immune responses (1). Objectives: We asked if an anti-SARS-CoV-2 mRNA vaccine could also induce an accumulation of Treg cells in patients with mixed cryoglobulinemia vasculitis (MCV), who have a defciency of Treg cells (2) and in healthy individuals. We also investigated immunologic variables possibly associated with a low immunogenic-ity of SARS-CoV-2 mRNA vaccine in patients with MCV (3). Methods: We analyzed peripheral blood lymphocyte subpopulations and anti-SARS-CoV-2 serological response in 24 patients with MCV and 9 Healthy donors (HD) before and after 2 weeks after the second dose of the Pfzer/BioNTech vaccine. Results: Among MCV patients we found 15 serological responders and 9 non-responders. All 5 seronegative patients treated recently with rituximab had <5 B cells/μ L, whereas the absolute B cell count was increased in 2 of 4 untreated patients due to monoclonal B cell lymphocytosis, with monoclonal cells representing more than 90% of B cells, associated with non-Hodgkin lymphoma. The percentage of pathologic CD21low B cells was signifcantly increased in seronegative patients. Before receiving the Pfzer/BioNTech vaccine, patients with MCV had a signifcantly reduced frequency of Treg cells among CD4+ T cells compared to HD. After the second dose of the vaccine, there was in MCV patients a signifcant increase in the percent and absolute count of Treg among CD4+ T cells Concerning the pre-vaccination distribution of T cells subpopulations, including the percentages and absolute counts of total CD3+, CD4+, CD8+, HLA-DR+ activated, Treg or CD56+ natural killer T cells, we could not reveal any pattern signifcantly associated with lack of serological response to vaccine. Conclusion: Our fndings show that lack of immunoreactivity in patients with MCV may be associated with expansion of pathologic B cells and that anti-SARS-CoV2 mRNA vaccine may induce an increase of Treg cells.