Affinity Thresholds for Naive CD8+ CTL Activation by Peptides and Engineered Influenza A Viruses

Abstract

High-avidity interactions between TCRs and peptide + class I MHC (pMHCI) epitopes drive CTL activation and expansion. Intriguing questions remain concerning the constraints determining optimal TCR/pMHCI binding. The present analysis uses the TCR transgenic OT-I model to assess how varying profiles of TCR/pMHCI avidity influence naive CTL proliferation and the acquisition of effector function following exposure to the cognate H-2Kb/OVA257–264 (SIINFEKL) epitope and to mutants provided as peptide or in engineered influenza A viruses. Stimulating naive OT-I CD8+ T cells in vitro with SIINFEKL induced full CTL proliferation and differentiation that was largely independent of any need for costimulation. By contrast, in vitro activation with the low-affinity EIINFEKL or SIIGFEKL ligands depended on the provision of IL-2 and other costimulatory signals. Importantly, although they did generate potent endogenous responses, infection of mice with influenza A viruses expressing these same OVA257 variants failed to induce the activation of adoptively transferred naive OT-I CTLps, an effect that was only partially overcome by priming with a lipopeptide vaccine. Subsequent structural and biophysical analysis of H2-KbOVA257, H2-KbE1, and H2-KbG4 established that these variations introduce small changes at the pMHCI interface and decrease epitope stability in ways that would likely impact cell surface presentation and recognition. Overall, it seems that there is an activation threshold for naive CTLps, that minimal alterations in peptide sequence can have profound effects, and that the antigenic requirements for the in vitro and in vivo induction of CTL proliferation and effector function differ substantially.

Mini-intronic plasmid vaccination elicits tolerant LAG3+CD8+T cells and inferior antitumor responses

“…Therefore, in order to directly test whether increased TCR stimulation resulted in similar increases in LAG3, we employed previously reported variants of the SIINFEKL peptide, SIIGFEKL, and EIINFEKL, which have been demonstrated to bind H-2k b with similar affinity but have decreased affinity for the OT1 TCR. 42 Consistent with our expectations, stimulation of naive OT1 splenocytes with the epitopte variants led to a decrease in LAG3 on CD8…”

Antigen expression level threshold tunes the fate of CD8 T cells during primary hepatic immune responses

“…By simulating comparable conditions and modes of antigen presentation to Des and OT-I T cells, we confirmed that, regardless of expression levels and frequency of transduction, H-2K b expression did not promote Des T-cell effector function, whereas OVA expression induced OT-I CTL differentiation. Our results suggest that these differing outcomes might be a result of different strengths of TCR:pMHC interactions, a factor known to be critical to the outcome of T-cell responses in the periphery (22,32). Although the relative affinities of the Des and OT-I TCRs for their respective ligands are not known, Des T cells are less efficiently retained and require a longer time before undergoing first division after antigen encounter compared with OT-I cells, suggesting that Des TCR affinity for H-2K b :KVITFIDL is lower than OT-I TCR affinity for H-2K b :SIINFEKL.…”

Antigen-Specific Inhibition of High-Avidity T Cell Target Lysis by Low-Avidity T Cells via Trogocytosis

“…T cell avidity is driven primarily by TCR affinity for its cognate peptide (Corse et al, 2011; Denton et al, 2011; Gourley et al, 2004), and also expression levels of CD3/TCR complex and adhesion molecules. We determined that high and low avidity clones expressed CD3/TCR at similar levels (data not shown).…”