Query: elispot  SARS-CoV-2

title: Robust SARS CoV 2 specific T cell immunity is maintained at 6 months following primary infection
abstract: The immune response to SARS CoV 2 is critical in both controlling primary infection and preventing re infection. However, there is concern that immune responses following natural infection may not be sustained and that this may predispose to recurrent infection. We analysed the magnitude and phenotype of the SARS CoV 2 cellular immune response in 100 donors at six months following primary infection and related this to the profile of antibody level against spike, nucleoprotein and RBD over the previous six months. T cell immune responses to SARS CoV 2 were present by ELISPOT and/or ICS analysis in all donors and are characterised by predominant CD4+ T cell responses with strong IL 2 cytokine expression. Median T cell responses were 50% higher in donors who had experienced an initial symptomatic infection indicating that the severity of primary infection establishes a 'setpoint' for cellular immunity that lasts for at least 6 months. The T cell responses to both spike and nucleoprotein/membrane proteins were strongly correlated with the peak antibody level against each protein. The rate of decline in antibody level varied between individuals and higher levels of nucleoprotein specific T cells were associated with preservation of NP specific antibody level although no such correlation was observed in relation to spike specific responses. In conclusion, our data are reassuring that functional SARS CoV 2 specific T cell responses are retained at six months following infection although the magnitude of this response is related to the clinical features of primary infection.

title: Highly functional virus specific cellular immune response in asymptomatic SARS CoV 2 infection
abstract: The efficacy of virus specific T cells in clearing pathogens involves a fine balance between their antiviral and inflammatory features. SARS CoV 2 specific T cells in individuals who clear SARS CoV 2 infection without symptoms or disease could reveal non pathological yet protective characteristics. We therefore compared the quantity and function of SARS CoV 2 specific T cells in a cohort of asymptomatic individuals (n=85) with that of symptomatic COVID 19 patients (n=76) at different time points after antibody seroconversion. We quantified T cells reactive to structural proteins (M, NP and Spike) using ELISpot assays, and measured the magnitude of cytokine secretion (IL 2, IFN g, IL 4, IL 6, IL 1b, TNF a and IL 10) in whole blood following T cell activation with SARS CoV 2 peptide pools as a functional readout. Frequencies of T cells specific for the different SARS CoV 2 proteins in the early phases of recovery were similar between asymptomatic and symptomatic individuals. However, we detected an increased IFN g and IL 2 production in asymptomatic compared to symptomatic individuals after activation of SARS CoV 2 specific T cells in blood. This was associated with a proportional secretion of IL 10 and pro inflammatory cytokines (IL 6, TNF a and IL 1b) only in asymptomatic infection, while a disproportionate secretion of inflammatory cytokines was triggered by SARS CoV 2 specific T cell activation in symptomatic individuals. Thus, asymptomatic SARS CoV 2 infected individuals are not characterized by a weak antiviral immunity; on the contrary, they mount a robust and highly functional virus specific cellular immune response. Their ability to induce a proportionate production of IL 10 might help to reduce inflammatory events during viral clearance.

title: Healthy donor T cell responses to common cold coronaviruses and SARS CoV 2.
abstract: The T cell responses to the common cold coronaviruses have not been well characterized. Pre existing T cell immunity to SARS CoV 2 has been reported, and a recent study suggested that this was due to cross recognition of the novel coronavirus by T cells specific for the common cold coronaviruses.  We used the ELISpot assay to characterize the T cell responses against peptide pools derived from the spike protein of three common cold coronaviruses (HCoV 229E, HCoV NL63, and HCoV OC43) and SARS CoV 2 in 21 healthy donors who were seronegative for SARS CoV 2 and had no known exposure to the virus. An in vitro expansion culture assay was also used to analyze memory T cell responses.  We found responses to the spike protein of the three common cold coronaviruses in many donors. We then focused on HCoV NL63 and demonstrated broad T cell responses to the spike protein and identified 22 targeted peptides. Interestingly, only one subject had a significant response to SARS CoV 2 spike or nucleocapsid protein in the ELISpot assay. In vitro expansion studies suggested that T cells specific for the HCoV NL63 spike protein in this subject could also recognize SARS CoV 2 spike protein peptide pools.  Healthy donors have circulating T cells specific for the spike proteins of HCoV NL63, HCoV 229E, and HCoV OC43. T cell responses to SARS CoV 2 spike and nucleocapsid proteins were present in only one subject and were potentially the result of cross recognition by T cells specific for the common cold coronaviruses. Further studies are needed to determine whether this influences COVID 19 outcomes.

title: SARS CoV 2 specific T cell immunity in COVID 19 convalescent patients and unexposed controls measured by ex vivo ELISpot assay
abstract: SARS CoV 2 T cell response characterization represents a crucial issue for defining the role of immune protection against COVID 19. The aim of the study was to assess the SARS CoV 2 T cell response in a cohort of COVID 19 convalescent patients' and in a group of unexposed subjects.  SARS CoV 2 T cell response was quantified from peripheral blood mononuclear cells (PBMC) of 87 COVID19 convalescent subjects (range 7 239 days after symptoms' onset) and 33 unexposed donors by ex vivo ELISpot assay. Follow up of SARS CoV 2 T cell response was performed in 10 subjects up to 12 months after symptoms' onset. The role of SARS CoV 2 specific CD4 and CD8 T cells was characterized in a group of COVID 19 convalescent subjects. Moreover, neutralizing antibodies were determined in serum samples.  In 14/33 (42.4% unexposed donors and 85/87 (97.7% COVID 19 convalescent subjects a positive result for at least one SARS CoV 2 antigen was observed. A positive response was observed up to 12 months after COVID 19 infection (median 246 days after symptoms' onset; range 118 362 days) Of note, SARS CoV 2 T cell response seems to be mainly mediated by CD4 T cells. A weak positive correlation was observed between Spike specific T cell response and neutralizing antibody titre (p=0.0028; r2=0.2891) and positive SARS CoV 2 T cell response was observed in 8/9 (88.9% COVID 19 convalescent subjects with undetectable SARS CoV 2 neutralizing antibodies.  Cross reactive SARS CoV 2 T cell response in uninfected patients may be due to previous infections with other common coronaviruses. Our data suggest that long term SARS CoV 2 T cell response might accompany a waning humoral response.

title: Cellular Immunity in COVID 19 Convalescents with PCR Confirmed Infection but with Undetectable SARS CoV 2 Specific IgG.
abstract: We investigated immune responses against severe acute respiratory syndrome coronavirus 2 (SARS CoV 2) among a group of convalescent, potential blood donors in Germany who had PCR confirmed SARS CoV 2 infection. Sixty days after onset of symptoms, 13/78 (17% study participants had borderline or negative results to an ELISA detecting IgG against the S1 protein of SARS CoV 2. We analyzed participants with PCR confirmed infection who had strong antibody responses (ratio >3) as positive controls and participants without symptoms of SARS CoV 2 infection and without household contact with infected patients as negative controls. Using interferon g ELISpot, we observed that 78% of PCR positive volunteers with undetectable antibodies showed T cell immunity against SARS CoV 2. We observed a similar frequency (80% of T cell immunity in convalescent donors with strong antibody responses but did not detect immunity in negative controls. We concluded that, in convalescent patients with undetectable SARS CoV 2 IgG, immunity may be mediated through T cells.

title: T cell assays differentiate clinical and subclinical SARS CoV 2 infections from cross reactive antiviral responses
abstract: A major issue in identification of protective T cell responses against SARS CoV 2 lies in distinguishing people infected with SARS CoV 2 from those with cross reactive immunity generated by exposure to other coronaviruses. We characterised SARS CoV 2 T cell immune responses in 168 PCR confirmed SARS CoV 2 infected subjects and 118 seronegative subjects without known SARS CoV 2 exposure using a range of T cell assays that differentially capture immune cell function. Strong ex vivo ELISpot and proliferation responses to multiple antigens (including M, NP and ORF3) were found in those who had been infected by SARS CoV 2 but were rare in pre pandemic and unexposed seronegative subjects. However, seronegative doctors with high occupational exposure and recent COVID 19 compatible illness showed patterns of T cell responses characteristic of infection, indicating that these readouts are highly sensitive. By contrast, over 90% of convalescent or unexposed people showed proliferation and cellular lactate responses to spike subunits S1/S2, indicating pre existing cross reactive T cell populations. The detection of T cell responses to SARS CoV 2 is therefore critically dependent on the choice of assay and antigen. Memory responses to specific non spike proteins provides a method to distinguish recent infection from pre existing immunity in exposed populations.

title: COVID 19 patients display distinct SARS CoV 2 specific T cell responses according to disease severity
abstract: Adaptive Immune responses generated by SARS CoV 2 virus in convalescent patients according to disease severity remain poorly characterized. To this end, we designed a prospective study (NCT04365322) that included 60 COVID 19 convalescent patients (1 month post infection) in two cohorts respectively entitled mild illness and severe pneumonia. The monitoring of peripheral immune responses was performed using IFNg ELISpot assay. The serology index of each patient was investigated at the same time. Patients with severe pneumonia were older and had more comorbidities than patients with mild illness. T cell responses in term of frequency and intensity were clearly distinct between mild illness and severe pneumonia patients. Furthermore, our results demonstrated that recent history of COVID 19 did not hamper viral memory T cell pool against common viruses (Cytomegalovirus, Epstein Barr virus and Flu virus) The presence of potent adaptive immunity even in patients who underwent severe pneumonia sustain the rationale for the development of protective therapeutics against SARS CoV 2.

title: Robust SARS CoV 2 specific T cell immunity is maintained at 6 months following primary infection
abstract: The immune response to SARS CoV 2 is critical in both controlling primary infection and preventing re infection. However, there is concern that immune responses following natural infection may not be sustained and that this may predispose to recurrent infection. We analysed the magnitude and phenotype of the SARS CoV 2 cellular immune response in 100 donors at six months following primary infection and related this to the profile of antibody level against spike, nucleoprotein and RBD over the previous six months. T cell immune responses to SARS CoV 2 were present by ELISPOT or ICS analysis in all donors and are characterised by predominant CD4+ T cell responses with strong IL 2 cytokine expression. Median T cell responses were 50% higher in donors who had experienced an initial symptomatic infection indicating that the severity of primary infection establishes a set point for cellular immunity that lasts for at least 6 months. The T cell responses to both spike and nucleoprotein/membrane proteins were strongly correlated with the peak antibody level against each protein. The rate of decline in antibody level varied between individuals and higher levels of nucleoprotein specific T cells were associated with preservation of NP specific antibody level although no such correlation was observed in relation to spike specific responses. In conclusion, our data are reassuring that functional SARS CoV 2 specific T cell responses are retained at six months following infection although the magnitude of this response is related to the clinical features of primary infection.

title: Elevated nucleoprotein induced interferon g release in COVID 19 patients detected in a SARS CoV 2 enzyme linked immunosorbent spot assay
abstract: COVID 19; ELISpot; Interferon Gamma release assay; SARS CoV 2; Tcell response.

title: Severe SARS CoV 2 patients develop a higher specific T cell response
abstract: Assessment of the adaptive immune response against severe acute respiratory syndrome coronavirus 2 (SARS CoV 2) is crucial for studying long term immunity and vaccine strategies. We quantified IFNg secreting T cells reactive against the main viral SARS CoV 2 antigens using a standardised enzyme linked immunospot assay (ELISpot)