TCRs with Distinct Specificity Profiles Use Different Binding Modes to Engage an Identical Peptide-HLA Complex.

The molecular rules driving TCR cross-reactivity are poorly understood and, consequently, it is unclear the extent to which TCRs targeting the same Ag recognize the same off-target peptides. We determined TCR-peptide-HLA crystal structures and, using a single-chain peptide-HLA phage library, we generated peptide specificity profiles for three newly identified human TCRs specific for the cancer testis Ag NY-ESO-1157-165-HLA-A2. Two TCRs engaged the same central peptide feature, although were more permissive at peripheral peptide positions and, accordingly, possessed partially overlapping peptide specificity profiles. The third TCR engaged a flipped peptide conformation, leading to the recognition of off-target peptides sharing little similarity with the cognate peptide. These data show that TCRs specific for a cognate peptide recognize discrete peptide repertoires and reconciles how an individual's limited TCR repertoire following negative selection in the thymus is able to recognize a vastly larger antigenic pool.

Dependence of T cell antigen recognition on T cell receptor-peptide MHC confinement time.

T cell receptor (TCR) binding to diverse peptide-major histocompatibility complex (pMHC) ligands results in various degrees of T cell activation. Here we analyze which binding properties of the TCR-pMHC interaction are responsible for this variation in pMHC activation potency. We have analyzed activation of the 1G4 cytotoxic T lymphocyte clone by cognate pMHC variants and performed thorough correlation analysis of T cell activation with 1G4 TCR-pMHC binding properties measured in solution. We found that both the on rate (k(on)) and off rate (k(off)) contribute to activation potency. Based on our results, we propose a model in which rapid TCR rebinding to the same pMHC after chemical dissociation increases the effective half-life or "confinement time" of a TCR-pMHC interaction. This confinement time model clarifies the role of k(on) in T cell activation and reconciles apparently contradictory reports on the role of TCR-pMHC binding kinetics and affinity in T cell activation.

Elimination of Latently HIV-infected Cells from Antiretroviral Therapy-suppressed Subjects by Engineered Immune-mobilizing T-cell Receptors.

Persistence of human immunodeficiency virus (HIV) in a latent state in long-lived CD4+ T-cells is a major barrier to eradication. Latency-reversing agents that induce direct or immune-mediated cell death upon reactivation of HIV are a possible solution. However, clearance of reactivated cells may require immunotherapeutic agents that are fine-tuned to detect viral antigens when expressed at low levels. We tested the antiviral efficacy of immune-mobilizing monoclonal T-cell receptors against viruses (ImmTAVs), bispecific molecules that redirect CD8+ T-cells to kill HIV-infected CD4+ T-cells. T-cell receptors specific for an immunodominant Gag epitope, SL9, and its escape variants were engineered to achieve supraphysiological affinity and fused to a humanised CD3-specific single chain antibody fragment. Ex vivo polyclonal CD8+ T-cells were efficiently redirected by immune-mobilising monoclonal T-cell receptors against viruses to eliminate CD4+ T-cells from human histocompatibility leukocyte antigen (HLA)-A*0201-positive antiretroviral therapy-treated patients after reactivation of inducible HIV in vitro. The efficiency of infected cell elimination correlated with HIV Gag expression. Immune-mobilising monoclonal T-cell receptors against viruses have potential as a therapy to facilitate clearance of reactivated HIV reservoir cells.

Different affinity windows for virus and cancer-specific T-cell receptors: implications for therapeutic strategies.

T-cell destiny during thymic selection depends on the affinity of the TCR for autologous peptide ligands presented in the context of MHC molecules. This is a delicately balanced process; robust binding leads to negative selection, yet some affinity for the antigen complex is required for positive selection. All TCRs of the resulting repertoire thus have some intrinsic affinity for an MHC type presenting an assortment of peptides. Generally, TCR affinities of peripheral T cells will be low toward self-derived peptides, as these would have been presented during thymic selection, whereas, by serendipity, binding to pathogen-derived peptides that are encountered de novo could be stronger. A crucial question in assessing immunotherapeutic strategies for cancer is whether natural TCR repertoires have the capacity for efficiently recognizing tumor-associated peptide antigens. Here, we report a comprehensive comparison of TCR affinities to a range of HLA-A2 presented antigens. TCRs that bind viral antigens fall within a strikingly higher affinity range than those that bind cancer-related antigens. This difference may be one of the key explanations for tumor immune escape and for the deficiencies of T-cell vaccines against cancer.

Bi-specific TCR-anti CD3 redirected T-cell targeting of NY-ESO-1- and LAGE-1-positive tumors.

NY-ESO-1 and LAGE-1 are cancer testis antigens with an ideal profile for tumor immunotherapy, combining up-regulation in many cancer types with highly restricted expression in normal tissues and sharing a common HLA-A*0201 epitope, 157-165. Here, we present data to describe the specificity and anti-tumor activity of a bifunctional ImmTAC, comprising a soluble, high-affinity T-cell receptor (TCR) specific for NY-ESO-1157-165 fused to an anti-CD3 scFv. This reagent, ImmTAC-NYE, is shown to kill HLA-A2, antigen-positive tumor cell lines, and freshly isolated HLA-A2- and LAGE-1-positive NSCLC cells. Employing time-domain optical imaging, we demonstrate in vivo targeting of fluorescently labelled high-affinity NYESO-specific TCRs to HLA-A2-, NY-ESO-1157-165-positive tumors in xenografted mice. In vivo ImmTAC-NYE efficacy was tested in a tumor model in which human lymphocytes were stably co-engrafted into NSG mice harboring tumor xenografts; efficacy was observed in both tumor prevention and established tumor models using a GFP fluorescence readout. Quantitative RT-PCR was used to analyze the expression of both NY-ESO-1 and LAGE-1 antigens in 15 normal tissues, 5 cancer cell lines, 10 NSCLC, and 10 ovarian cancer samples. Overall, LAGE-1 RNA was expressed at a greater frequency and at higher levels than NY-ESO-1 in the tumor samples. These data support the clinical utility of ImmTAC-NYE as an immunotherapeutic agent for a variety of cancers.

Kinetics and mechanics of two-dimensional interactions between T cell receptors and different activating ligands.

Adaptive immune responses are driven by interactions between T cell antigen receptors (TCRs) and complexes of peptide antigens (p) bound to Major Histocompatibility Complex proteins (MHC) on the surface of antigen-presenting cells. Many experiments support the hypothesis that T cell response is quantitatively and qualitatively dependent on the so-called strength of TCR/pMHC association. Most available data are correlations between binding parameters measured in solution (three-dimensional) and pMHC activation potency, suggesting that full lymphocyte activation required a minimal lifetime for TCR/pMHC interaction. However, recent reports suggest important discrepancies between the binding properties of ligand-receptor couples measured in solution (three-dimensional) and those measured using surface-bound molecules (two-dimensional). Other reports suggest that bond mechanical strength may be important in addition to kinetic parameters. Here, we used a laminar flow chamber to monitor at the single molecule level the two-dimensional interaction between a recombinant human TCR and eight pMHCs with variable potency. We found that 1), two-dimensional dissociation rates were comparable to three-dimensional parameters previously obtained with the same molecules; 2), no significant correlation was found between association rates and activating potency of pMHCs; 3), bond mechanical strength was partly independent of bond lifetime; and 4), a suitable combination of bond lifetime and bond strength displayed optimal correlation with activation efficiency. These results suggest possible refinements of contemporary models of signal generation by T cell receptors. In conclusion, we reported, for the first time to our knowledge, the two-dimensional binding properties of eight TCR/pMHC couples in a cell-free system with single bond resolution.

Therapeutic high affinity T cell receptor targeting a KRASG12D cancer neoantigen.

Neoantigens derived from somatic mutations are specific to cancer cells and are ideal targets for cancer immunotherapy. KRAS is the most frequently mutated oncogene and drives the pathogenesis of several cancers. Here we show the identification and development of an affinity-enhanced T cell receptor (TCR) that recognizes a peptide derived from the most common KRAS mutant, KRASG12D, presented in the context of HLA-A*11:01. The affinity of the engineered TCR is increased by over one million-fold yet fully able to distinguish KRASG12D over KRASWT. While crystal structures reveal few discernible differences in TCR interactions with KRASWT versus KRASG12D, thermodynamic analysis and molecular dynamics simulations reveal that TCR specificity is driven by differences in indirect electrostatic interactions. The affinity enhanced TCR, fused to a humanized anti-CD3 scFv, enables selective killing of cancer cells expressing KRASG12D. Our work thus reveals a molecular mechanism that drives TCR selectivity and describes a soluble bispecific molecule with therapeutic potential against cancers harboring a common shared neoantigen.

Specificity of bispecific T cell receptors and antibodies targeting peptide-HLA.

Tumor-associated peptide-human leukocyte antigen complexes (pHLAs) represent the largest pool of cell surface-expressed cancer-specific epitopes, making them attractive targets for cancer therapies. Soluble bispecific molecules that incorporate an anti-CD3 effector function are being developed to redirect T cells against these targets using 2 different approaches. The first achieves pHLA recognition via affinity-enhanced versions of natural TCRs (e.g., immune-mobilizing monoclonal T cell receptors against cancer [ImmTAC] molecules), whereas the second harnesses an antibody-based format (TCR-mimic antibodies). For both classes of reagent, target specificity is vital, considering the vast universe of potential pHLA molecules that can be presented on healthy cells. Here, we made use of structural, biochemical, and computational approaches to investigate the molecular rules underpinning the reactivity patterns of pHLA-targeting bispecifics. We demonstrate that affinity-enhanced TCRs engage pHLA using a comparatively broad and balanced energetic footprint, with interactions distributed over several HLA and peptide side chains. As ImmTAC molecules, these TCRs also retained a greater degree of pHLA selectivity, with less off-target activity in cellular assays. Conversely, TCR-mimic antibodies tended to exhibit binding modes focused more toward hot spots on the HLA surface and exhibited a greater degree of crossreactivity. Our findings extend our understanding of the basic principles that underpin pHLA selectivity and exemplify a number of molecular approaches that can be used to probe the specificity of pHLA-targeting molecules, aiding the development of future reagents.

The contribution of major histocompatibility complex contacts to the affinity and kinetics of T cell receptor binding.

The interaction between the T cell antigen receptor (TCR) and antigenic peptide in complex with major histocompatibility complex (MHC) molecules is a crucial step in T cell activation. The relative contributions of TCR:peptide and TCR:MHC contacts to the overall binding energy remain unclear. This has important implications for our understanding of T cell development and function. In this study we used site directed mutagenesis to estimate the contribution of HLA-A2 side-chains to the binding of four TCRs. Our results show that these TCRs have very different energetic 'footprints' on HLA-A2, with no residues contributing to all TCR interactions. The estimated overall contribution of MHC side-chains to the total interaction energy was variable, with lower limits ranging from 11% to 50%. Kinetic analysis suggested a minor and variable contribution of MHC side-chains to the transition state complex, arguing against a two-step mechanism for TCR binding.

C-peptide induces chemotaxis of human CD4-positive cells: involvement of pertussis toxin-sensitive G-proteins and phosphoinositide 3-kinase.

Increased levels of C-peptide, a cleavage product of proinsulin, circulate in patients with insulin resistance and early type 2 diabetes, a high-risk population for the development of a diffuse and extensive pattern of arteriosclerosis. The present study examined the effect of C-peptide on CD4(+) lymphocyte migration, an important process in early atherogenesis. C-peptide stimulated CD4(+) cell chemotaxis in a concentration-dependent manner. This process involves pertussis toxin-sensitive G-proteins as well as activation of phosphoinositide 3-kinase (PI 3-K). Biochemical analysis showed that C-peptide induced recruitment of PI 3-K to the cell membrane as well as PI 3-K activation in human CD4(+) cells. In addition, antidiabetic peroxisome proliferator-activated receptor gamma-activating thiazolidinediones inhibited C-peptide-induced CD4(+) cell chemotaxis as well as PI 3-Kgamma activation. Finally, immunofluorescence staining of thoracic artery specimen of diabetic patients showed intimal CD4(+) cells in areas with C-peptide deposition. Thus, C-peptide might deposit in the arterial intima in diabetic patients during early atherogenesis and subsequently attract CD4(+) cells to migrate into the vessel wall.

C-peptide colocalizes with macrophages in early arteriosclerotic lesions of diabetic subjects and induces monocyte chemotaxis in vitro.

OBJECTIVE: Increased levels of C-peptide, a cleavage product of proinsulin, circulate in patients with insulin resistance and early type 2 diabetes, a high-risk population for the development of a diffuse and extensive pattern of arteriosclerosis. This study tested the hypothesis that C-peptide might participate in atherogenesis in these patients. METHOD AND RESULTS: We demonstrate significantly higher intimal C-peptide deposition in thoracic aorta specimens from young diabetic subjects compared with matched nondiabetic controls as determined by immunohistochemical staining. C-peptide colocalized with monocytes/macrophages in the arterial intima of artery specimen from diabetic subjects. In vitro, C-peptide stimulated monocyte chemotaxis in a concentration-dependent manner with a maximal 2.3+/-0.4-fold increase at 1 nmol/L C-peptide. Pertussis toxin, wortmannin, and LY294002 inhibited C-peptide-induced monocyte chemotaxis, suggesting the involvement of pertussis toxin-sensitive G-proteins as well as a phosphoinositide 3-kinase (PI3K)-dependent mechanism. In addition, C-peptide treatment activated PI3K in human monocytes, as demonstrated by PI3K activity assays. CONCLUSIONS: C-peptide accumulated in the vessel wall in early atherogenesis in diabetic subjects and may promote monocyte migration into developing lesions. These data support the hypothesis that C-peptide may play an active role in atherogenesis in diabetic patients and suggest a new mechanism for accelerated arterial disease in diabetes.

Antigen potency and maximal efficacy reveal a mechanism of efficient T cell activation.

T cell activation, a critical event in adaptive immune responses, depends on productive interactions between T cell receptors (TCRs) and antigens presented as peptide-bound major histocompatibility complexes (pMHCs). Activated T cells lyse infected cells, secrete cytokines, and perform other effector functions with various efficiencies, which depend on the binding parameters of the TCR-pMHC complex. The mechanism through which binding parameters are translated to the efficiency of T cell activation, however, remains controversial. The "affinity model" suggests that the dissociation constant (KD) of the TCR-pMHC complex determines the response, whereas the "productive hit rate model" suggests that the off-rate (koff) is critical. Here, we used mathematical modeling to show that antigen potency, as determined by the EC50 (half-maximal effective concentration), which is used to support KD-based models, could not discriminate between the affinity and the productive hit rate models. Both models predicted a correlation between EC50 and KD, but only the productive hit rate model predicted a correlation between maximal efficacy (Emax), the maximal T cell response induced by pMHC, and koff. We confirmed the predictions made by the productive hit rate model in experiments with cytotoxic T cell clones and a panel of pMHC variants. Thus, we propose that the activity of an antigen is determined by both its potency (EC50) and maximal efficacy (Emax).

Resistin: a newly identified chemokine for human CD4-positive lymphocytes.

AIMS: Increased levels of resistin, a peptide secreted by adipocytes and inflammatory cells, circulate in patients with insulin resistance and early type 2 diabetes, a high-risk population for the development of a diffuse and extensive pattern of arteriosclerosis. Recent data suggest that resistin may activate vascular cells such as smooth muscle cells and endothelial cells, but hitherto nothing is known about the role of resistin in CD4-positive lymphocytes. Therefore, the present study examined the effect of resistin on CD4-positive lymphocyte migration, an important process in early atherogenesis. METHODS AND RESULTS: Resistin stimulated CD4-positive cell chemotaxis in a concentration-dependent manner with a maximal induction of 2.25 +/- 0.54 at 100 ng/mL (P < 0.05, n = 7). This process involves pertussis toxin-sensitive G-proteins as well as activation of Src- and phosphoinositide 3-kinase (PI 3-K). Biochemical analysis showed that resistin induces phosphorylation of Src and PI 3-K activation in human CD4-positive cells. In addition, resistin activates RhoA, Rac-1, and Cdc42 in these cells as shown by affinity precipitation experiments. Finally, resistin-induced phosphorylation of myosin light chain was inhibited by Src short interference RNA transfection, underscoring the importance of the upstream signalling molecule Src in resistin-induced migration. CONCLUSION: These data support an active role of resistin in CD4-positive lymphocyte chemotaxis and elucidate molecular mechanisms in resistin-induced cell migration.