AB1169 IMMUNOMODULATORY EFFECTS OF SARS-CoV-2 VACCINATION: INCREASE OF REGULATORY T CELLS AFTER mRNA VACCINE

BackgroundBesides the ability to induce antigen-specific 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).ObjectivesWe 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 deficiency of Treg cells (2) and in healthy individuals. We also investigated immunologic variables possibly associated with a low immunogenicity of SARS-CoV-2 mRNA vaccine in patients with MCV (3).MethodsWe 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 Pfizer/BioNTech vaccine.ResultsAmong MCV patients we found 15 serological responders and 9 non-responders. All 5 seronegative patients treated recently with rituximab had <5 B cells/µL, 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 significantly increased in seronegative patients.Before receiving the Pfizer/BioNTech vaccine, patients with MCV had a significantly 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 significant increase in the percent and absolute count of Treg among CD4+ T cellsConcerning 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 significantly associated with lack of serological response to vaccine.ConclusionOur findings 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.References[1]Krienke C. et al. A noninflammatory mRNA vaccine for treatment of experimental autoimmune encephalomyelitis. Science. 2021 Jan 8;371(6525):145-153.[2]Boyer O. et al. CD4+CD25+ regulatory T-cell deficiency in patients with hepatitis C-mixed cryoglobulinemia vasculitis. Blood. 2004 May 1;103(9):3428-30.[3]Visentini M. et al. Flares of mixed cryoglobulinaemia vasculitis after vaccination against SARS-CoV-2. Ann Rheum Dis. 2021 Nov 24:annrheumdis-2021-221248.Disclosure of InterestsNone declared