The forces that govern clonal selection during the genesis and maintenance of specific T cell responses are complex, but amenable to decryption by interrogation of constituent clonotypes within the antigen-experienced T cell pools. Here, we used point-mutated peptide–major histocompatibility complex class I (pMHCI) antigens, unbiased TCRB gene usage analysis, and polychromatic flow cytometry to probe directly ex vivo the clonal architecture of antigen-specific CD8+ T cell populations under conditions of persistent exposure to structurally stable virus-derived epitopes. During chronic infection with cytomegalovirus and Epstein-Barr virus, CD8+ T cell responses to immunodominant viral antigens were oligoclonal, highly skewed, and exhibited diverse clonotypic configurations; TCRB CDR3 sequence analysis indicated positive selection at the protein level. Dominant clonotypes demonstrated high intrinsic antigen avidity, defined strictly as a physical parameter, and were preferentially driven toward terminal differentiation in phenotypically heterogeneous populations. In contrast, subdominant clonotypes were characterized by lower intrinsic avidities and proportionately greater dependency on the pMHCI–CD8 interaction for antigen uptake and functional sensitivity. These findings provide evidence that interclonal competition for antigen operates in human T cell populations, while preferential CD8 coreceptor compensation mitigates this process to maintain clonotypic diversity. Vaccine strategies that reconstruct these biological processes could generate T cell populations that mediate optimal delivery of antiviral effector function.

Background: How does a limited pool of <108 T cell receptors (TCRs) provide immunity to >1015 antigens?Results: A single TCR can respond to >one million different decamer peptides.Conclusion: This unprecedented level of receptor promiscuity explains how the naïve TCR repertoire achieves effective immunity.Significance: TCR degeneracy has enormous potential to be the root cause of autoimmune disease.

T cells have evolved a unique system of ligand recognition involving an antigen T cell receptor (TCR) and a coreceptor that integrate stimuli provided by the engagement of peptide-major histocompatibility complex (pMHC) antigens. Here, we use altered pMHC class I (pMHCI) molecules with impaired CD8 binding (CD8-null) to quantify the contribution of coreceptor extracellular binding to (i) the engagement of soluble tetrameric pMHCI molecules, (ii) the kinetics of TCR/pMHCI interactions on live cytotoxic T lymphocytes (CTLs), and (iii) the activation of CTLs by cell-surface antigenic determinants. Our data indicate that the CD8 coreceptor substantially enhances binding efficiency at suboptimal TCR/pMHCI affinities through effects on both association and dissociation rates. Interestingly, coreceptor requirements for efficient tetramer labeling of CTLs or for CTL activation by determinants displayed on the cell surface operated in different TCR/pMHCI affinity ranges. Wild-type and CD8-null pMHCI tetramers required monomeric affinities for cognate TCRs of K D < ϳ80 M and ϳ35 M, respectively, to label human CTLs at 37°C. In contrast, activation by cellular pMHCI molecules was strictly dependent on CD8 binding only for TCR/pMHCI interactions with K D values >200 M. Altogether, our data provide information on the binding interplay between CD8 and the TCR and support a model of CTL activation in which the extent of coreceptor dependence is inversely correlated to TCR/pMHCI affinity. In addition, the results reported here define the range of TCR/pMHCI affinities required for the detection of antigen-specific CTLs by flow cytometry.In concert with the T cell receptor (TCR), 3 the coreceptors CD4 and CD8 participate in and enhance the process of antigen recognition by T cells through extracellular interactions with peptide-major histocompatibility complex (pMHC) molecules (1-3) and amplification of ensuing signal transduction events (4 -8). CD8 molecules are predominantly expressed as ␣␤ heterodimers on the surface of cytotoxic T lymphocytes (CTLs) (9), but are also found in ␣␣ homodimeric form on intraepithelial ␣␤ T lymphocytes, certain subsets of circulating activated CTLs, and the membranes of distinct cell lineages such as ␥␦ T cells, natural killer T cells, and dendritic cells (reviewed in Ref. 10). CD8␣␣ and CD8␣␤ bind directly to invariant domains of major histocompatibility complex class I (MHCI) molecules (11-13). Although CD8␣␣ and CD8␣␤ bind MHCI molecules with similar affinities (14), it is well established that CD8␣␣ is a much poorer coreceptor for CTLs than is CD8␣␤. Indeed, an emerging concept is that CD8␣␣ acts as an inhibitor of CTL activation (10). More generally, recent experimental evidence has lent credence to the hypothesis that efficient regulation of CTL activity is mediated by modifications of CD8 coreceptor functions in vivo. These modifications include switching to expression of the CD8␣␣ homodimer, post-translational changes of CD8␣␤ following activation (15, 16), and downregulation of CD8 expres...

This pivotal multicenter, double-blind, randomized, sham controlled trial provides level I evidence that percutaneous tibial nerve stimulation therapy is safe and effective in treating overactive bladder symptoms. The compelling efficacy of percutaneous tibial nerve stimulation demonstrated in this trial is consistent with other recently published reports and supports the use of peripheral neuromodulation therapy for overactive bladder.

The off-rate (k off ) of the T cell receptor (TCR)/peptidemajor histocompatibility complex class I (pMHCI) interaction, and hence its half-life, is the principal kinetic feature that determines the biological outcome of TCR ligation. However, it is unclear whether the CD8 coreceptor, which binds pMHCI at a distinct site, influences this parameter. Although biophysical studies with soluble proteins show that TCR and CD8 do not bind cooperatively to pMHCI, accumulating evidence suggests that TCR associates with CD8 on the T cell surface. Here, we titrated and quantified the contribution of CD8 to TCR/ pMHCI dissociation in membrane-constrained interactions using a panel of engineered pMHCI mutants that retain faithful TCR interactions but exhibit a spectrum of affinities for CD8 of >1,000-fold. Data modeling generates a "stabilization factor" that preferentially increases the predicted TCR triggering rate for low affinity pMHCI ligands, thereby suggesting an important role for CD8 in the phenomenon of T cell cross-reactivity.

Analogue peptides with enhanced binding affinity to major histocompatibility class (MHC) I molecules are currently being used in cancer patients to elicit stronger T cell responses. However, it remains unclear as to how alterations of anchor residues may affect T cell receptor (TCR) recognition. We correlate functional, thermodynamic, and structural parameters of TCR–peptide–MHC binding and demonstrate the effect of anchor residue modifications of the human histocompatibility leukocyte antigens (HLA)–A2 tumor epitope NY–ESO-1157–165–SLLMWITQC on TCR recognition. The crystal structure of the wild-type peptide complexed with a specific TCR shows that TCR binding centers on two prominent, sequential, peptide sidechains, methionine–tryptophan. Cysteine-to-valine substitution at peptide position 9, while optimizing peptide binding to the MHC, repositions the peptide main chain and generates subtly enhanced interactions between the analogue peptide and the TCR. Binding analyses confirm tighter binding of the analogue peptide to HLA–A2 and improved soluble TCR binding. Recognition of analogue peptide stimulates faster polarization of lytic granules to the immunological synapse, reduces dependence on CD8 binding, and induces greater numbers of cross-reactive cytotoxic T lymphocyte to SLLMWITQC. These results provide important insights into heightened immunogenicity of analogue peptides and highlight the importance of incorporating structural data into the process of rational optimization of superagonist peptides for clinical trials.

This multicenter, randomized trial demonstrates that percutaneous tibial nerve stimulation is safe with statistically significant improvements in patient assessment of overactive bladder symptoms, and with objective effectiveness comparable to that of pharmacotherapy. Percutaneous tibial nerve stimulation may be considered a clinically significant alternative therapy for overactive bladder.

SummaryThe development of fluorochrome-conjugated peptide-major histocompatibility complex (pMHC) multimers in conjunction with continuing advances in flow cytometry has transformed the study of antigen-specific T cells by enabling their visualization, enumeration, phenotypic characterization and isolation from ex vivo samples. Here, we bring together and discuss some of the 'tricks' that can be used to get the most out of pMHC multimers. These include: (1) simple procedures that can substantially enhance the staining intensity of cognate T cells with pMHC multimers; (2) the use of pMHC multimers to stain T cells with very-low-affinity Tcell receptor (TCR)/pMHC interactions, such as those that typically predominate in tumour-specific responses; and (3) the physical grading and clonotypic dissection of antigen-specific T cells based on the affinity of their cognate TCR using mutant pMHC multimers in conjunction with new approaches to the molecular analysis of TCR gene expression. We also examine how soluble pMHC can be used to examine T-cell activation, manipulate T-cell responses and study allogeneic and superantigen interactions with TCRs. Finally, we discuss the problems that arise with pMHC class II (pMHCII) multimers because of the low affinity of TCR/ pMHCII interactions and lack of 'coreceptor help'.