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Background: Immune responses to seasonal endemic coronaviruses might have a pivotal role in protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Those SARS-CoV-2-crossreactive T cells were recently described in immunocompetent individuals. Still, data on cross-reactive humoral and cellular immunity in kidney transplant recipients is currently lacking. Methods: The pre-existing, cross-reactive antibody B and T cell immune responses against SARS-CoV-2 in unexposed adults with kidney transplantation (Tx, n = 14) and without (non-Tx, n = 12) sampled before the pandemic were compared with 22 convalescent patients with COVID-19 (Cp) applying enzyme-linked immunosorbent assay and flow cytometry. Results: In both unexposed groups, SARS-CoV-2 IgG antibodies were not detectable. Memory B cells binding spike (S) protein SARS-CoV-2 were detected in unexposed individuals (64% among Tx; 50% among non-Tx) and higher frequencies after infection (80% Cp). The numbers of SARS-CoV-2-reactive T cells were comparable between patients who had undergone Tx and those who had not. SARS-CoV-2-reactive follicular T helper cells were present in 61% of the unexposed cohort in both patients who had undergone Tx and those who had not. Conclusions: Cross-reactive memory B and T cells against SARS-CoV-2 exist also in transplanted adults, suggesting a primed adaptive immunity. The effect on the disease course may depend on the concomitant immunosuppressive drugs.

We read with a great interest the article published by Bonelli et al suggesting an inducible cellular immune response in rituximab (Rtx) treated patients.1 The CD20-antibody Rtx is one of the most widespread biologicals worldwide with a broad spectrum of oncological and rheumatological indications. Due to its depleting effect on circulating B cells, the generation of antibodies against novel pathogens is impaired in Rtx-treated patients.2 3 Accordingly, the last EULAR recommendations on vaccination advised that ‘vaccination should be provided at least 6 months after the last administration and 4 weeks before the next course of B cell-depleting therapy’.4 To ensure appropriate SARS-CoV-2 vaccination, the last EULAR advise was to refer to a rheumatologist.5 The American College of Rheumatology (ACR) has recommended to vaccinate Rtx-treated patients not earlier than 5 months after the last administration with the next cycle given not earlier than 2–4 weeks thereafter.6 In any case, the combination of B cell-depleting therapy with vaccination has been quite a challenge for patients and physicians—especially since it became clear that Rtx therapy may be associated with unfavourable outcomes in B cell-depleted patients.7 Fortunately, very recent data by Bonelli et al have now suggested that a cellular response is mounted after SARS-CoV-2 vaccination in Rtx-treated patients despite a failed humoral immune response.1 The authors demonstrated that peripheral blood cells of vaccinated patients do produce Interferon γ (IFNγ) after stimulation with SARS-CoV-2 spike (S) protein-derived overlapping peptides.1 These results increase the scientific interest into a more detailed characterisation of vaccine-reactive T-cell immunity, which has recently been in the focus of our group as well due to a frequent Rtx application in our settings. Applying multiparameter flow cytometry, we explored the …

Background: The ongoing COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, represents a serious worldwide health concern. A deeper understanding of the immune response to SARS-CoV-2 will be required to refine vaccine development and efficacy as well as to evaluate long-term immunity in convalescent patients. With this in mind, we investigated the formation of SARS-CoV-2 specific BMEMORY cells from patient blood samples. Methods: A standard flow cytometry-based protocol for the detection of SARS-CoV-2 specific B cells was applied using fluorochrome-coupled SARS-CoV-2 spike (S) full-length protein. Cohorts of 26 central European convalescent mild/moderate COVID-19 patients and 14 healthy donors were assessed for the levels of SARS-CoV-2 S- specific BMEMORY cells. Results: Overall B cell composition was not affected by SARS-CoV-2 infection in convalescent patients. Our analysis of SARS-CoV-2 specific BMEMORY cells in samples collected at different time points revealed that S-protein specific B cells remain in peripheral blood at least up to 6 months after COVID-19 diagnosis. Conclusions: Detection of SARS-CoV-2 specific BMEMORY cells may improve our understanding of the long-term adaptive immunity in response to SARS-CoV-2, allowing for an improved public health response and vaccine development during the COVID-19 pandemic. Further validation of the study in larger and more diverse populations and a more extended observation period will be required.

Background Recent data demonstrate potentially protective pre-existing T cells reactive against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in samples of healthy blood donors, collected before the SARS-CoV-2 pandemic. Whether pre-existing immunity is also detectable in immunosuppressed patients is currently not known. Methods Fifty-seven patients were included in this case–control study. We compared the frequency of SARS-CoV-2-reactive T cells in the samples of 20 renal transplant (RTx) patients to 20 age/gender matched non-immunosuppressed/immune competent healthy individuals collected before the onset of the SARS-CoV-2 pandemic. Seventeen coronavirus disease 2019 (COVID-19) patients were used as positive controls. T cell reactivity against Spike-, Nucleocapsid-, and Membrane- SARS-CoV-2 proteins were analyzed by multi-parameter flow cytometry. Antibodies were analyzed by neutralization assay. Results Pre-existing SARS-CoV-2-reactive T cells were detected in the majority of unexposed patients and healthy individuals. In RTx patients, 13/20 showed CD4+ T cells reactive against at least one SARS-CoV-2 protein. CD8+ T cells reactive against at least one SARS-CoV-2 protein were demonstrated in 12/20 of RTx patients. The frequency and Th1 cytokine expression pattern of pre-formed SARS-CoV-2 reactive T cells did not differ between RTx and non-immunosuppressed healthy individuals. Conclusions This study shows that the magnitude and functionality of pre-existing SARS-CoV-2 reactive T cell in transplant patients is non-inferior compared to the immune competent cohort. Although several pro-inflammatory cytokines were produced by the detected T cells, further studies are required to prove their antiviral protection. Graphic abstract

BackgroundThe efficacy of the humoral and cellular immunity determines the outcome of viral infections. An appropriate immune response mediates protection, whereas an overwhelming immune response has been associated with immune-mediated pathogenesis in viral infections. The current study explored the general and SARS-CoV-2 specific cellular and humoral immune status in patients with different COVID-19 severities.MethodsIn this prospective study, we included 53 patients with moderate, severe, and critical COVID-19 manifestations comparing their quantitative, phenotypic, and functional characteristics of circulating immune cells, SARS-CoV-2 antigen specific T-cells, and humoral immunity.ResultsSignificantly diminished frequencies of CD8+T-cells, CD4+ and CD8+T-cell subsets with activated differentiated memory/effector phenotype and migratory capacity were found in circulation in patients with severe and/or critical COVID-19 as compared to patients with moderate disease. Importantly, the improvement of the clinical courses from severe to moderate was accompanied by an improvement in the T-cell subset alterations. Furthermore, we surprisingly observed a detectable SARS-CoV-2-reactive T-cell response in all three groups after stimulation with SARS-CoV-2 S-protein overlapping peptide pool already at the first visit. Of note, patients with a critical COVID-19 demonstrated a stronger response of SARS-CoV-2-reactive T-cells producing Th1 associated inflammatory cytokines. Furthermore, clear correlation between antibody titers and SARS-CoV-2-reactive CD4+ frequencies underscore the role of specific immunity in disease progression.ConclusionOur data demonstrate that depletion of activated memory phenotype circulating T-cells and a strong SARS-CoV-2-specific cellular and humoral immunity are associated with COVID-19 disease severity. This counter-intuitive finding may have important implications for diagnostic, therapeutic and prophylactic COVID-19 management.

Preventing the progression to acute respiratory distress syndrome (ARDS) in COVID-19 is an unsolved challenge. The involvement of T cell immunity in this exacerbation remains unclear. To identify predictive markers of COVID-19 progress and outcome, we analyzed peripheral blood of 10 COVID-19-associated ARDS patients and 35 mild/moderate COVID-19 patients, not requiring intensive care. Using multi-parametric flow cytometry, we compared quantitative, phenotypic and functional characteristics of circulating bulk immune cells, and SARS-CoV-2 S-protein reactive T cell between the two groups. ARDS patients demonstrated significantly higher S-protein reactive CD4+ and CD8+ T cells compared to non-ARDS patients. Of interest, comparison of circulating bulk T cells in ARDS patients to non-ARDS patients demonstrated decreased frequencies of CD4+ and CD8+ T cell subsets with activated memory/effector T cells expressing tissue migration molecule CD11a++. Importantly, survival from ARDS (4/10) was accompanied by a recovery of the CD11a++ T cell subsets in peripheral blood. Conclusively, data on S-protein reactive polyfunctional T cells indicate the ability of ARDS patients to generate antiviral protection. Furthermore, decreased frequencies of activated memory/effector T cells expressing tissue migratory molecule CD11a++ observed in circulation of ARDS patients might suggest their involvement in ARDS development and propose CD11a-based immune signature as a possible prognostic marker., Graphical Abstract, This study shows a strong SARS-CoV-2 S-protein T-cell response and decreased frequencies of activated memory/effector T-cells expressing migratory molecule CD11a++ in ARDS patients. The data suggest the involvement of the analyzed T-cell subsets in ARDS development and propose CD11a-based immune signature as a possible prognostic marker for COVID-19 progression.