Human thymopoiesis produces polyspecific CD8 α/β T cells responding to multiple viral antigens.

T-cell receptors (TCRs) are formed by stochastic gene rearrangements, theoretically generating >10 sequences. They are selected during thymopoiesis, which releases a repertoire of about 10 unique TCRs per individual. How evolution shaped a process that produces TCRs that can effectively handle a countless and evolving set of infectious agents is a central question of immunology.

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

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%).

Anti-SARS-CoV-2 vaccines in recipient and/or donor before allotransplant.

The impact of pre-transplant anti-severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) vaccine in 20 recipients of allogeneic hematopoietic stem cell transplantation (Allo-HSCT) and/or their donors is reported here, showing that the persistence of anti-SARS-CoV-2 antibodies can be detected in almost all patients, whatever the type of vaccine used, and up to 9 months post transplant. Also, an anti-SARS-CoV-2 spike glycoprotein CD3+ T-cell response could be detected in six (35%) of 17 evaluable patients. This study provides a rationale to consider anti-SARS-CoV-2 vaccination of both recipients and donors before Allo-HSCT.