Preservation of naive-phenotype CD4+ T cells after vaccination contributes to durable immunity.

Memory T cells are conventionally associated with durable recall responses. In our longitudinal analyses of CD4+ T cell responses to the yellow fever virus (YFV) vaccine by peptide-MHC tetramers, we unexpectedly found CD45RO-CCR7+ virus-specific CD4+ T cells that expanded shortly after vaccination and persisted months to years after immunization. Further phenotypic analyses revealed the presence of stem cell-like memory T cells within this subset.

Differentiation marker-negative CD4 T cells persist after yellow fever virus vaccination and contribute to durable memory.

Factors that contribute to durable immunological memory remain incompletely understood. In our longitudinal analyses of CD4 T cell responses to the yellow fever virus (YFV) vaccine by peptide-MHC tetramers, we unexpectedly found naïve phenotype virus-specific CD4 T cells that persisted months to years after immunization. These Marker negative T cells (T) lacked CD95, CXCR3, CD11a, and CD49d surface protein expression, distinguishing them from previously discovered stem-cell memory T cells.

SARS-CoV-2-specific T cells in unexposed adults display broad trafficking potential and cross-react with commensal antigens.

The baseline composition of T cells directly affects later response to pathogens, but the complexity of precursor states remains poorly defined. Here, we examined the baseline state of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T cells in unexposed individuals. SARS-CoV-2-specific CD4 T cells were identified in prepandemic blood samples by major histocompatibility complex (MHC) class II tetramer staining and enrichment.

SARS-CoV-2-specific T cells in unexposed adults display broad trafficking potential and cross-react with commensal antigens.

Unlabelled: The baseline composition of T cells directly impacts later response to a pathogen, but the complexity of precursor states remains poorly defined. Here we examined the baseline state of SARS-CoV-2 specific T cells in unexposed individuals. SARS-CoV-2 specific CD4 T cells were identified in pre-pandemic blood samples by class II peptide-MHC tetramer staining and enrichment.