SARS-CoV-2 T-Cell Responses in Allogeneic Hematopoietic Stem Cell Recipients following Two Doses of BNT162b2 mRNA Vaccine

Abstract

Background: At variance to humoral responses, cellular immunity after anti-SARS-CoV-2 vaccines has been poorly explored in recipients of allogeneic hematopoietic stem-cell transplantation (Allo-HSCT), especially within the first post-transplant years where immunosuppression is more profound and harmful.

Methods: SARS-CoV-2 Spike protein-specific T-cell responses were explored after two doses of BNT162b2 mRNA vaccine in 45 Allo-HSCT recipients with a median time from transplant of less than 2 years by using INF-γ ELISPOT assay and flow-cytometry enumeration of CD4⁺ and CD8⁺ T lymphocytes with intracellular cytokine production of IFN-γ and TNF-α.

Results: A strong TNF-α⁺ response from SARS-CoV-2-specific CD4⁺ T-cells was detected in a majority of humoral responders (89%) as well as in a consistent population of non-humoral responders (40%).

Conclusions: T-cells are likely to participate in protection against COVID-19 viral infection, even in the absence of detectable antibody response, especially in the first years post-transplant in Allo-HSCT recipients.

Keywords: BNT162b2; CD4+ T cells; CD8+ T cells; COVID 19; IFNγ; SARS-CoV-2 mRNA; TNFα; allogeneic hematopoietic stem cell transplantation; cellular immunity; humoral immunity; vaccine.

Figure 1

Anti-SARS-CoV-2 Spike T-cells analysis in 45 Allo-HSCT recipients (AML n = 26, MDS n = 19) with humoral (HRP n = 35) or no humoral (NHRP n = 10) response and healthy controls (n = 16) after two injections of the BNT162b2 mRNA vaccine. Panel (A) shows the number of IFNγ spots per 100 CD3⁺ T cells after stimulation of PBMC stimulated with Spike or EBV-consensus peptide; (B) PBMC phenotype analysis used for the ELISpot assay. Results show population frequencies among viable CD45⁺ cells. Horizontal lines indicate median values.

Figure 2

Features of specific CD3⁺, CD4⁺ and CD8⁺ T-cell responses against SARS-CoV-2 Spike and EBV peptides according to INFγ and TNFα production in Allo-HSCT recipients (n = 17: 2 NHRP, 15 HRP and 12 healthy donors (HD)) after two injections of BNT162b2 mRNA vaccine. PBMC were stimulated with Spike, EBV peptides, Cytostim (positive control) or not stimulated (NS). (A) Gating strategy and representative flow cytometry plots for one patient. (B) Dot plots representing the frequencies of CD3⁺, CD4⁺, and CD8⁺ T-cells producing IFN-γ, TNF-α, or both. Each dot represents one subject. For this group of patients, the magnitude of the INFγ⁺ CD3⁺ T-cell response correlated with that obtained by the INF-γ ELISPOT assay (data not shown). (C) Bar graphs showing the expression of INFγ and TNFα among SARS-CoV-2 Spike- and EBV-specific CD3⁺, CD4⁺ and CD8⁺ T cells in Allo-HSCT recipients (n = 19 [P] and 12 healthy donors [HD]). Data are shown as means of the percentage of T-cell responders.

Figure 3

Anti-Spike T-cell response according to the time interval between transplantation and vaccination. (A) Anti-Spike T-cell responses according to the time interval between transplantation and vaccination for non-humoral responder patients (NHRP, n = 10) and humoral responder patients (HRP, n = 35). (B) Anti-Spike T-cell responses according to the time interval between transplantation and vaccination for patients under immunosuppressive therapy (IS, n = 9) or not (n = 36, 80%) at the time of vaccination. Patients were under treatment including 5 for active chronic GVHD (cyclosporine n = 2, cyclosporine + corticosteroids n = 3), while one patient was under corticosteroids for a chronic rheumatic disease and another one received 5′ azacytidine for relapse prevention. Two early patients were on their way to stop cyclosporine. None of the patients had acute graft-versus-host disease (GVHD) at the time of analysis.