SARS-CoV-2-reactive IFN-γ-producing CD4+ and CD8+ T cells in blood do not correlate with clinical severity in unvaccinated critically ill COVID-19 patients.

We examined the relationship between peripheral blood levels of SARS-CoV-2 S (Spike protein)1/M (Membrane protein)-reactive IFN-γ-producing CD4+ and CD8+ T cells, serum levels of biomarkers of clinical severity, and mortality in critically ill COVID-19 patients. The potential association between SARS-CoV-2-S-Receptor Binding Domain (RBD)-specific IgG levels in sera and mortality was also investigated. SARS-CoV-2 T cells and anti-RBD IgG levels were monitored in 71 non-consecutive patients (49 male and 22 female; median age, 65 years) by whole-blood flow cytometry and Enzyme-linked immunosorbent assay (ELISA), respectively (326 specimens). SARS-CoV-2 RNA loads in paired tracheal aspirates [TA] (n = 147) were available from 54 patients. Serum levels of interleukin-6, ferritin, D-Dimer, lactose dehydrogenase and C-reactive protein in paired sera were known. SARS-CoV-2 T cells (either CD4+, CD8+ or both) were detectable in 70 patients. SARS-CoV-2 IFN-γ CD4+ T-cell responses were documented more frequently than their CD8+ counterparts (62 vs. 56 patients) and were of greater magnitude overall. Detectable SARS-CoV-2 S1/M-reactive CD8+ and CD4+ T-cell responses were associated with higher SARS-CoV-2 RNA loads in TA. SARS-CoV-2 RNA load in TA decreased over time, irrespective of the dynamics of SARS-CoV-2-reactive CD8+ and CD4+ T cells. No correlation was found between SARS-CoV-2 IFN-γ T-cell counts, anti-RBD IgG concentrations and biomarker serum levels (Rho ≤ 0.3). The kinetics of both T cell subsets was comparable between those who died or survived, whereas anti-RBD IgG levels were higher across different time points in deceased patients than in survivors. Enumeration of peripheral blood levels of SARS-CoV-2-S1/M-reactive IFN-γ CD4+ and CD8+ T cells does not predict viral clearance from the lower respiratory tract or poor clinical outcomes in critically ill COVID-19 patients. In contrast, anti-RBD IgG levels were directly associated with increased mortality.

Adaptive immune responses to SARS-CoV-2 in recovered severe COVID-19 patients.

BACKGROUND: There is an imperative need to determine the durability of adaptive immunity to SARS-CoV-2. We enumerated SARS-CoV-2-reactive CD4+ and CD8+ T cells targeting S1 and M proteins and measured RBD-specific serum IgG over a period of 2-6 months after symptoms onset in a cohort of subjects who had recovered from severe clinical forms of COVID-19. PATIENTS AND METHODS: We recruited 58 patients (38 males and 20 females; median age, 62.5 years), who had been hospitalized with bilateral pneumonia, 60% with one or more comorbidities. IgG antibodies binding to SARS-CoV-2 RBD were measured by ELISA. SARS-CoV-2-reactive CD69+-expressing-IFNγ-producing-CD4+ and CD8+ T cells were enumerated in heparinized whole blood by flow cytometry for ICS. RESULTS: Detectable SARS-CoV-2-S1/M-reactive CD69+-IFN-γ CD4+ and CD8+ T cells were displayed in 17 (29.3%) and 6 (10.3%) subjects respectively, at a median of 84 days after onset of symptoms (range, 58-191 days). Concurrent comorbidities increased the risk (OR, 3.15; 95% CI, 1.03-9.61; P = 0.04) of undetectable T-cell responses in models adjusted for age, sex and hospitalization ward. Twenty-one out of the 35 patients (60%) had detectable RBD-specific serum IgGs at a median of 118 days (range, 60-145 days) after symptoms onset. SARS-CoV-2 RBD-specific IgG serum levels were found to drop significantly over time. CONCLUSION: A relatively limited number of subjects who developed severe forms of COVID-19 had detectable SARS-CoV-2-S1/M IFNγ CD4+ and CD8+ T cells at midterm after clinical diagnosis. Our data also indicated that serum levels of RBD-specific IgGs decline over time, becoming undetectable in some patients.

B- and T-cell immune responses elicited by the Comirnaty® COVID-19 vaccine in nursing-home residents.

OBJECTIVES: The immunogenicity of the Comirnaty® vaccine against coronavirus disease 2019 (COVID-19) has not been adequately studied in elderly people with comorbidities. We assessed antibody and T-cell responses targeted to the S protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) following full vaccination in nursing-home residents. METHODS: Sixty nursing-home residents (44 female, age 53-100 years), of whom ten had previously been diagnosed with COVID-19, and 18 healthy controls (15 female, age 27-54 years) were recruited. Pre- and post-vaccination blood specimens were available for quantification of total antibodies binding the SARS-CoV-2 S protein and for enumeration of SARS-CoV-2 S-reactive IFN-γ CD4+ and CD8+ T cells by flow cytometry. RESULTS: The seroconversion rate in (presumably) SARS-CoV-2-naïve nursing-home residents (41/43, 95.3%) was similar to that in controls (17/18, 94.4%). A booster effect was documented in post-vaccination samples of nursing-home residents with prior COVID-19. Plasma antibody levels were higher (p < 0.01) in recovered nursing-home residents (all 2500 IU/mL) than in individuals across the other two groups (median 1120 IU/mL in naïve nursing-home residents and 2211 IU/ml in controls). A large percentage of nursing-home residents had SARS-CoV-2 S-reactive IFN-γ CD8+ (naïve 31/49, 63.2%; recovered 8/10, 80%) or CD4+ T cells (naïve 35/49, 71.4%; recovered 7/10, 70%) at baseline, in contrast to healthy controls (3/17, 17.6% and 5/17, 29%, respectively). SARS-CoV-2 IFN-γ CD8+ and CD4+ T-cell responses were documented in 88% (15/17) and all control subjects after vaccination, respectively, but only in 65.5% (38/58) and 22.4% (13/58) of nursing-home residents. Overall, the median frequency of SARS-CoV-2 IFN-γ CD8+ and CD4+ T cells in nursing-home residents decreased in post-vaccination specimens, whereas it increased in controls. CONCLUSION: The Comirnaty COVID-19 vaccine elicits robust SARS-CoV-2 S antibody responses in nursing-home residents. Nevertheless, the rate and frequency of detectable SARS-CoV-2 IFN-γ T-cell responses after vaccination was lower in nursing-home residents than in controls.

T cell-mediated response to SARS-CoV-2 in liver transplant recipients with prior COVID-19.

Whether immunosuppression impairs severe acute respiratory syndrome coronavirus 2-specific T cell-mediated immunity (SARS-CoV-2-CMI) after liver transplantation (LT) remains unknown. We included 31 LT recipients in whom SARS-CoV-2-CMI was assessed by intracellular cytokine staining (ICS) and interferon (IFN)-γ FluoroSpot assay after a median of 103 days from COVID-19 diagnosis. Serum SARS-CoV-2 IgG antibodies were measured by ELISA. A control group of nontransplant immunocompetent patients were matched (1:1 ratio) by age and time from diagnosis. Post-transplant SARS-CoV-2-CMI was detected by ICS in 90.3% (28/31) of recipients, with higher proportions for IFN-γ-producing CD4+ than CD8+ responses (93.5% versus 83.9%). Positive spike-specific and nucleoprotein-specific responses were found by FluoroSpot in 86.7% (26/30) of recipients each, whereas membrane protein-specific response was present in 83.3% (25/30). An inverse correlation was observed between the number of spike-specific IFN-γ-producing SFUs and time from diagnosis (Spearman's rho: -0.418; p value = .024). Two recipients (6.5%) failed to mount either T cell-mediated or IgG responses. There were no significant differences between LT recipients and nontransplant patients in the magnitude of responses by FluoroSpot to any of the antigens. Most LT recipients mount detectable-but declining over time-SARS-CoV-2-CMI after a median of 3 months from COVID-19, with no meaningful differences with immunocompetent patients.

SARS-CoV-2-specific Cell-mediated Immunity in Kidney Transplant Recipients Recovered From COVID-19.

BACKGROUND: The magnitude and kinetics of severe acute respiratory syndrome coronavirus 2-specific cell-mediated immunity (SARS-CoV-2-CMI) in kidney transplant (KT) recipients remain largely unknown. METHODS: We enumerated SARS-CoV-2-specific interferon-γ-producing CD69+ CD4+ and CD8+ T cells at months 4 and 6 from the diagnosis of coronavirus disease 2019 (COVID-19) in 21 KT recipients by intracellular cytokine staining. Overlapping peptides encompassing the SARS-CoV-2 spike (S) glycoprotein N-terminal 1- to 643-amino acid sequence and the membrane protein were used as stimulus. SARS-CoV-2 IgG antibodies targeting the S1 protein were assessed by ELISA at month 6. RESULTS: Detectable (≥0.1%) SARS-CoV-2-specific CD4+ T-cell response was found in 57.1% and 47.4% of patients at months 4 and 6. Corresponding rates for CD8+ T cells were 19.0% and 42.1%, respectively. Absolute SARS-CoV-2-specific T-cell counts increased from month 4 to month 6 in CD8+ (P = 0.086) but not CD4+ subsets (P = 0.349). Four of 10 patients with any detectable response at month 4 had lost SARS-CoV-2-CMI by month 6, whereas 5 of 9 patients mounted SARS-CoV-2-CMI within this period. All but 2 patients (89.5%) tested positive for SARS-CoV-2 IgG. Patients lacking detectable SARS-CoV-2-specific CD4+ response by month 6 were more likely to be under tacrolimus (100.0% versus 66.7%; P = 0.087) and to have received tocilizumab for the previous COVID-19 episode (40.0% versus 0.0%; P = 0.087). CONCLUSIONS: Although still exploratory and limited by small sample size, the present study suggests that a substantial proportion of KT recipients exhibited detectable SARS-CoV-2-CMI after 6 months from COVID-19 diagnosis.

SARS-CoV-2-reactive interferon-γ-producing CD8+ T cells in patients hospitalized with coronavirus disease 2019.

There is limited information on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) T-cell immune responses in patients with coronavirus disease 2019 (COVID-19). Both CD4+ and CD8+ T cells may be instrumental in resolution of and protection from SARS-CoV-2 infection. Here, we tested 25 hospitalized patients either with microbiologically documented COVID-19 (n = 19) or highly suspected of having the disease (n = 6) for presence of SARS-CoV-2-reactive CD69+ expressing interferon-γ (IFN-γ) producing CD8+ T cells using flow-cytometry for intracellular cytokine staining assay. Two sets of overlapping peptides encompassing the SARS-CoV-2 Spike glycoprotein N-terminal 1 to 643 amino acid sequence and the entire sequence of SARS-CoV-2 M protein were used simultaneously as antigenic stimulus. Ten patients (40%) had detectable responses, displaying frequencies ranging from 0.15 to 2.7% (median of 0.57 cells/µL; range, 0.43-9.98 cells/µL). The detection rate of SARS-CoV-2-reactive IFN-γ CD8+ T cells in patients admitted to intensive care was comparable (P = .28) to the rate in patients hospitalized in other medical wards. No correlation was found between SARS-CoV-2-reactive IFN-γ CD8+ T-cell counts and SARS-CoV-2 S-specific antibody levels. Likewise, no correlation was observed between either SARS-CoV-2-reactive IFN-γ CD8+ T cells or S-specific immunoglobulin G-antibody titers and blood cell count or levels of inflammatory biomarkers. In summary, in this descriptive, preliminary study we showed that SARS-CoV-2-reactive IFN-γ CD8+ T cells can be detected in a non-negligible percentage of patients with moderate to severe forms of COVID-19. Further studies are warranted to determine whether quantitation of these T-cell subsets may provide prognostic information on the clinical course of COVID-19.