Booster Dose of SARS-CoV-2 mRNA Vaccine in Kidney Transplanted Patients Induces Wuhan-Hu-1 Specific Neutralizing Antibodies and T Cell Activation but Lower Response against Omicron Variant

Abstract

Kidney transplanted recipients (KTR) are at high risk of severe SARS-CoV-2 infection due to immunosuppressive therapy. Although several studies reported antibody production in KTR after vaccination, data related to immunity to the Omicron (B.1.1.529) variant are sparse. Herein, we analyzed anti-SARS-CoV-2 immune response in seven KTR and eight healthy controls after the second and third dose of the mRNA vaccine (BNT162b2). A significant increase in neutralizing antibody (nAb) titers were detected against pseudoviruses expressing the Wuhan-Hu-1 spike (S) protein after the third dose in both groups, although nAbs in KTR were lower than controls. nAbs against pseudoviruses expressing the Omicron S protein were low in both groups, with no increase after the 3rd dose in KTR. Reactivity of CD4⁺ T cells after boosting was observed when cells were challenged with Wuhan-Hu-1 S peptides, while Omicron S peptides were less effective in both groups. IFN-γ production was detected in KTR in response to ancestral S peptides, confirming antigen-specific T cell activation. Our study demonstrates that the 3rd mRNA dose induces T cell response against Wuhan-Hu-1 spike peptides in KTR, and an increment in the humoral immunity. Instead, humoral and cellular immunity to Omicron variant immunogenic peptides were low in both KTR and healthy vaccinated subjects.

Keywords: COVID-19; Omicron variant; SARS-CoV-2; T cells; immunity; kidney transplanted patients; mRNA vaccine; neutralizing antibodies; transplantation.

Figure 1

Study design. (A) Flow chart of the study population; n: number of samples. (B) Time points schematic representation.

Figure 2

Spike antibody response. Measurement of total Ig and neutralizing anti-spike antibody titers in healthy subjects (H) and kidney transplanted patients (KTR) after the 2nd and 3rd vaccine dose (T2 and T3 time points). Statistical analysis was performed by paired Wilcoxon test (* p ≤ 0.05). (A) Total anti-Spike/RBD Ig quantitative detection in sera collected at T2 and T3 time points, measured by Elecsys^® Anti-SARS-CoV-2 S assay. BAU/mL: Binding Antibody Units. (B,C) Neutralization of Wu and O variant spike-expressing pseudotyped lentiviral particles by antibodies in sera of KTR and H donors at T2 and T3 time points. The graphs show the geometric means (GMT) +/− 95% confidence intervals. (D) Correlation between the anti-Wu spike neutralizing and total antibodies in H (squares, N = 6) and KTR (circles, N = 7) vaccinated volunteers at T3 is shown. Correlation was assessed using the non-parametric Spearman rank correlation coefficient. Mann–Whitney test was used to compare data in panels (B,C), with a p value < 0.05 considered statistically significant (* p < 0.05; ** p < 0.005). All statistical analyses were performed with GraphPad Prism 8.0.

Figure 3

Wuhan-Hu-1 and Omicron spike-specific CD4⁺ and CD8⁺ T cell response by AIM assay. (A) Spike-specific CD4⁺ T cells were evaluated in KTR and healthy controls by AIM assay after the 2nd and 3rd vaccine dose (T2 and T3 time points). The percentage of OX40⁺CD137⁺CD4⁺ T cells were measured in PBMCs after stimulation with spike protein overlapping peptides derived from ancestral Wuhan-Hu-1 strain (Wu) and Omicron variant of concern (O) by flow cytometry. Percentage of OX40⁺CD137⁺CD4⁺ T cells detected in healthy subjects (H, N = 7) and kidney transplanted patients (KTR, N = 7). Data are plotted as NET value, subtracted of DMSO background values (mean value 0.06%, range 0–0.16). (B). Spike-specific CD8⁺ T cells were evaluated in KTR and healthy controls by AIM assay after the 2nd and 3rd vaccine dose (T2 and T3 time points). The percentage of CD69⁺CD137⁺CD8⁺ T cells were measured in PBMCs after stimulation with spike protein overlapping peptides derived from ancestral Wuhan-Hu-1 strain (Wu) and Omicron variant of concern (O) by flow cytometry. Percentages of CD69⁺CD137⁺CD8⁺ T cells detected in healthy subjects (H, N = 7) and kidney transplanted patients (KTR, N = 7). Data are plotted as NET value, subtracted of DMSO background values (mean value 0.23%, range 0.027–1.26). Paired Wilcoxon test was used to assess statistical significance, with a p value < 0.05 considered significant (* p < 0.05). All statistical analyses were performed using GraphPad Prism 8.0.

Figure 4

IFN-γ cytokine production and correlation between adaptive cellular and humoral responses. Spike protein-induced IFN-γ production was assessed after 2nd and 3rd vaccine dose (at T2 and T3 time points) in healthy volunteers (H) and kidney transplanted patients (KTR). (A) IFN-γ was detected in the cell supernatants by enzyme-linked immunosorbent assay (ELISA) after 24 h stimulation of PBMCs with overlapping peptides derived from ancestral Wuhan-Hu-1 strain (Wu) and Omicron variant of concern (O). IFN-γ data were subtracted of background DMSO values. Each bar indicates the mean of value and standard deviation. (B) Profile of immune responsiveness to ancestral Wuhan-Hu-1 strain after the vaccine booster dose (T3). Immune response against SARS-CoV-2 ancestral Wuhan-Hu-1 strain, assessed as either an AIM test and/or IFN-γ production, was considered positive when it was at least two-fold greater than the baseline (DMSO control) values. The cut-off for positive nAb response was a neutralization titer ≥ 10. Correlation between IFN-γ production and total anti-RBD antibody titers (C) and between IFN-γ production and anti-Wuhan-Hu-1 nAb antibody titers (D) in 5 H (squares) and 7 KTR (circles) and 7 H (squares) and 7 KTR (circles) subjects, respectively. Correlations were performed using the non-parametric Spearman rank correlation coefficient to compare the magnitudes of total and neutralizing antibodies against Wuhan-Hu-1 strain after the 3rd vaccination. All statistical analyses were performed by GraphPad Prism 8.0, and a p value < 0.05 was considered statistically significant.