No abstract

Developing T cells face a series of cell fate choices in the thymus and in the periphery. The role of the individual T cell receptor (TCR) in determining decisions of cell fate remains unresolved. The stochastic/selection model postulates that the initial fate of the cell is independent of TCR specificity, with survival dependent on additional TCR/coreceptor "rescue" signals. The "instructive" model holds that cell fate is initiated by the interaction of the TCR with a cognate peptide-MHC complex. T cells are then segregated on the basis of TCR specificity with the aid of critical coreceptors and signal modulators [Chan S, Correia-Neves M, Benoist C, Mathis (1998) Immunol Rev 165: 195-207]. The former would predict a random representation of individual TCR across divergent T cell lineages whereas the latter would predict minimal overlap between divergent T cell subsets. To address this issue, we have used highthroughput sequencing to evaluate the TCR distribution among key T cell developmental and effector subsets from a single donor. We found numerous examples of individual subsets sharing identical TCR sequence, supporting a model of a stochastic process of cell fate determination coupled with dynamic patterns of clonal expansion of T cells bearing the same TCR sequence among both CD4 + and CD8+ populations.F ollowing production of their T cell receptors (TCRs), T cells experience several developing stages. An encounter with a cognate peptide-MHC complex can induce naïve T (Tn) cells expressing the CD45RA isomer to begin to express CD45RO. Cells expressing both isomers are considered transitional in nature (Tt), thus cells identified on the basis of CD45RA expression alone include Tn and Tt and can thus be referred to as Tn+t. Cells expressing only CD45RO have passed into the memory (Tm) compartment, where they can lay quiescent awaiting repeat stimulation by the same or similar peptide-MHC complexes. Activated T cells (Ta) driven to effector function lose expression of both CD45RA and RO and express CD69. During different developing stages, T cells also face a series of cell fate choices: CD4 + CD8+ cells commit to either the CD4 + helper (Th) or CD8+ cytotoxic (Tc) lineages, a choice closely associated with binding to MHC class II or class I peptide complexes, respectively. Subsequently, CD4 + T cells can develop into regulatory (Tr) CD25+ cells, or into CD25−CD294− Th1 (IFN-γ producing) or CD25−CD294+ Th2 (IL-4 producing) effector subsets. Other choices are also available (1, 2).Although it is generally accepted that the TCR expressed by the developing T lineage cell will determine the response to a specific peptide-MHC complex, the role of the individual TCR in determining decisions of cell fate remains unresolved. To address these issues, we have coupled high-throughput sequencing techniques (3, 4) to high volume antibody covered superparamagnetic polystyrene bead isolation of defined T cell subsets with semiquantitative PCR amplification of the complementarity determining region 3 regions (CDR3) from mR...

Processes that define immunoglobulin repertoires are commonly presumed to be the same for all murine B cells. However, studies here that couple high-dimensional FACS sorting with large-scale quantitative IgH deep-sequencing demonstrate that B-1a IgH repertoire differs dramatically from the follicular and marginal zone B cells repertoires and is defined by distinct mechanisms. We track B-1a cells from their early appearance in neonatal spleen to their long-term residence in adult peritoneum and spleen. We show that de novo B-1a IgH rearrangement mainly occurs during the first few weeks of life, after which their repertoire continues to evolve profoundly, including convergent selection of certain V(D)J rearrangements encoding specific CDR3 peptides in all adults and progressive introduction of hypermutation and class-switching as animals age. This V(D)J selection and AID-mediated diversification operate comparably in germ-free and conventional mice, indicating these unique B-1a repertoire-defining mechanisms are driven by antigens that are not derived from microbiota.DOI: http://dx.doi.org/10.7554/eLife.09083.001

Background Monitoring the adaptive immune responses during the natural course of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection provides useful information for the development of vaccination strategies against this virus and its emerging variants. We thus profiled the serum anti-SARS-CoV-2 antibody levels and specific memory B- and T-cell responses in convalescent coronavirus disease-2019 (COVID-19) patients. Methods Altogether 119 samples from 88 convalescent donors who experienced mild to critical disease were tested for the presence of elevated anti-spike and anti-receptor binding domain antibody levels over a period of eight months. In addition, level of SARS-CoV-2 neutralizing antibodies, specific memory B- and T-cell responses were tested in a subset of samples. Findings Anti-SARS-CoV-2 antibodies were present in 85% of the samples collected within 4 weeks after onset of symptoms in COVID-19 patients. Levels of specific IgM/IgA antibodies declined after 1 month while levels of specific IgG antibodies and plasma neutralizing activities remained relatively stable up to 6 months after diagnosis. Anti-SARS-CoV-2 IgG antibodies were still present, though at a significantly lower level, in 80% of the samples collected at 6-8 months after symptom onset. SARS-CoV-2-specific memory B- and T-cell responses developed with time and were persistent in all patients followed up till 6-8 months. Conclusions Our data suggest that protective adaptive immunity following natural infection of SARS-CoV-2 might persist for at least 6-8 months, regardless of disease severity. Development of medium or long-term protective immunity through vaccination might thus be possible. Funding EU-ATAC consortium, the Italian Ministry of Health and SciLife/KAW.