Reproducible selection of high avidity CD8 ⁺ T-cell clones following secondary acute virus infection

Abstract

The recall of memory CD8 + cytotoxic T lymphocytes (CTLs), elicited by prior virus infection or vaccination, is critical for immune protection. The extent to which this arises as a consequence of stochastic clonal expansion vs. active selection of particular clones remains unclear. Using a parallel adoptive transfer protocol in combination with single cell analysis to define the complementarity determining region (CDR) 3α and CDR3β regions of individual Tcell receptor (TCR) heterodimers, we characterized the antigendriven recall of the same memory CTL population in three individual recipients. This high-resolution analysis showed reproducible enrichment (or diminution) of particular TCR clonotypes across all challenged animals. These changes in clonal composition were TCRα− and β chain-dependent and were directly related to the avidity of the TCR for the virus-derived peptide (p) + major histocompatibility complex class I molecule. Despite this shift in clonotype representation indicative of differential selection, there was no evidence of overall repertoire narrowing, suggesting a strategy to optimize CTL responses while safeguarding TCR diversity.+ cytotoxic T lymphocytes (CTLs) are key for effective pathogen clearance. To exert their antiviral effects, naïve CD8 + CTL precursors (CTLps) must first be activated through the specific recognition of virus-derived peptides (p) in the context of major histocompatibility complex class I molecules (MHCI) expressed on the surface of dendritic cells. Ligation of these pMHCI epitopes is mediated via specific T-cell receptor (TCR) αβ heterodimers, leading to the recruitment, proliferation, and activation of antigen-specific CTLs. Subsequent to virus clearance, CTL populations contract to form a stable pool of resting memory cells, typically at around 5-10% of their acute phase numbers (1, 2). On secondary virus encounter, this memory pool of CD8 + T cells is able to expand rapidly, providing potent immune protection (2).An understanding of CD8 + T-cell recruitment/expansion into the recall response has significant implications for effective vaccine strategies. If recruitment and expansion occur stochastically, a memory population in which highly effective clones predominate is desirable. Alternatively, if selection is deterministic, the basic requirement would be the presence of highquality clones in the memory population for selective expansion by antigen-driven mechanisms. Moreover, different mechanisms of memory recruitment have different long-term implications for the clonal diversity of epitope-specific populations, especially with repeated virus exposure. Repeated selection of particular clones inherent in deterministic clonal selection has the potential consequence of narrowing the CTL repertoire, whereas stochastic recruitment/expansion seems more likely to maintain CTL diversity, shown to be beneficial for virus control (3-7). Despite the implications, there remains conjecture about how epitope-specific CD8 + T cells are recruited from the memory pool. Studies h...

Reversed T Cell Receptor Docking on a Major Histocompatibility Class I Complex Limits Involvement in the Immune Response

“…Moreover, the observation that the fold expansion of each Rg T cell population (TRBV13-1 + or TRBV17 + ) was reproducible, irrespective of whether they were transferred separately or together, or in the presence or absence of an endogenous IAV-specific CD8 + T cell response, indicates that the poor responsiveness of the TRBV17 + T cell population is intrinsic and unrelated to competition with other responding T cell populations. The reduced capacity of the TRBV17 + TCRs to contribute to the IAV-specific immune response is possibly due to the relative low avidity of the TRBV17 + T cells towards H-2D b -NP 366 compared to that of the TRBV13-1 + T cell population (Busch and Pamer, 1999;Cukalac et al, 2014;McHeyzer-Williams et al, 1999;Price et al, 2005). Mutational analyses demonstrated that the relative impact of disrupting TCR-pMHC-I affinity, correlated with the extent of impact on T cell signaling.…”

“…Combined with our previous observation that the naïve H-2D b -NP 366 -specific CTL precursor pool is comprehensively recruited into the response (La Gruta et al, 2010), these data suggest that the paucity of TRBV17 + H-2D b -NP 366 -specific T cells in the immune response is due to a failure to undergo extensive proliferation once recruited. Accordingly, (Cukalac et al, 2014;Cukalac et al, 2015). For a given amount of surface TCR expression ( Fig.…”

Sizing up the key determinants of the CD8+ T cell response

“…The notion of selective clonal recruitment and expansion leads to a discussion of the impact of TCR affinity as a determinant of primary CTL response magnitude. Analyses of both CD4 + T helper cell and CTL responses have indicated that clonal prevalence within epitope-specific CTL responses may be reflective of TCR affinity for pMHC [49][50][51][52] . Affinitymediated repertoire selection could be an indirect consequence of the fact that precursors with exceptionally low affinity for antigen are not recruited 35 , or it may reflect the continued expansion of high-affinity clones in pathogen-specific responses 33 .…”

Structural Basis for Clonal Diversity of the Public T Cell Response to a Dominant Human Cytomegalovirus Epitope

“…Together, high-throughput sequencing and single-cell analysis have greatly improved our understanding of the breadth of virus-specific T cell responses and the degree of overlap of TCR repertoires among individuals. Thus, studies of CD8 ϩ T cell responses to infection with CMV and influenza virus have revealed highly diverse TCR repertoires directed against immunodominant epitopes, such as the CMV NLV peptide, accompanied by antigen-driven selection of high avidity T cell clones that presumably eliminate infected cells more rapidly (12,13,16,17). However, clonal focusing does not appear to result in overall repertoire narrowing, suggesting a strategy to optimize CTL responses while safeguarding TCR structural diversity (18).…”