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Two types of engineered T cells have been successfully used to treat patients with cancer, one with an antigen recognition domain derived from antibodies [chimeric antigen receptors (CARs)] and the other derived from T cell receptors (TCRs). CARs use high-affinity antigen–binding domains and costimulatory domains to induce T cell activation but can only react against target cells with relatively high amounts of antigen. TCRs have a much lower affinity for their antigens but can react against target cells displaying only a few antigen molecules. Here, we describe a new type of receptor, called a Co-STAR (for costimulatory synthetic TCR and antigen receptor), that combines aspects of both CARs and TCRs. In Co-STARs, the antigen-recognizing components of TCRs are replaced by high-affinity antibody fragments, and costimulation is provided by two modules that drive NF-κB signaling (MyD88 and CD40). Using a TCR-mimic antibody fragment that targets a recurrent p53 neoantigen presented in a common human leukocyte antigen (HLA) allele, we demonstrate that T cells equipped with Co-STARs can kill cancer cells bearing low densities of antigen better than T cells engineered with conventional CARs and patient-derived TCRs in vitro. In mouse models, we show that Co-STARs mediate more robust T cell expansion and more durable tumor regressions than TCRs similarly modified with MyD88 and CD40 costimulation. Our data suggest that Co-STARs may have utility for other peptide-HLA antigens in cancer and other targets where antigen density may limit the efficacy of engineered T cells. Editor's summary: Commonly used T cell therapies such as engineered T cell receptors (TCRs) and chimeric antigen receptors (CARs) have greatly improved outcomes for many patients; however, both still have their associated drawbacks. To overcome some of these limitations, Mog et al. have developed high-affinity antibody–expressing T cells that use a receptor, called a Co-STAR (for costimulatory synthetic TCR and antigen receptor), that combines aspects of both CARs and TCRs. They further show in vivo that these Co-STARs induce T cell expansion and induce long-term regression in mouse models with low densities of antigen, representing a promising strategy that requires further evaluation. —Dorothy Hallberg [ABSTRACT FROM AUTHOR]

[CD4.sup.+] regulatory T cells ([T.sub.regs]) maintain immunological self-tolerance and immune homeostasis by suppressing aberrant or excessive immune responses. The core genetic program of [T.sub.regs] and their ability to suppress pathologic immune responses depends on the transcription factor Foxp3. Despite progress in understanding mechanisms of Foxp3-dependent gene activation, the molecular mechanism of Foxp3-dependent gene repression remains largely unknown. We identified Eos, a zinc-finger transcription factor of the Ikaros family, as a critical mediator of Foxp3-dependent gene silencing in [T.sub.regs]. Eos interacts directly with Foxp3 and induces chromatin modifications that result in gene silencing in Trigs. Silencing of Eos in [T.sub.regs] abrogates their ability to suppress immune responses and endows them with partial effector function, thus demonstrating the critical role that Eos plays in [T.sub.reg] programming.

We used a proteomic approach to identify phosphopeptide-binding modules mediating signal transduction events in the DNA damage response pathway. Using a library of partially degenerate phosphopeptides, we identified tandem BRCT [...]

Specific bispecific antibodies: A major challenge in efforts to develop immunotherapies for T cell cancers is the need to protect healthy T cells while eliminating malignant T cells. Here, Paul et al. developed bispecific antibodies targeting 1 of 30 T cell receptor β chain variable regions, hypothesizing that targeting the β chain expressed by malignant T cells would avoid collateral damage to T cells expressing one of the other 29 β chains. The authors showed that bispecific antibodies recognizing malignant T cell receptor β chains promoted killing of malignant T cells and preservation of healthy T cells in vitro and in mouse models in vivo. These findings support the development of T cell receptor–specific approaches to target T cell cancers. Immunotherapies such as chimeric antigen receptor (CAR) T cells and bispecific antibodies redirect healthy T cells to kill cancer cells expressing the target antigen. The pan-B cell antigen–targeting immunotherapies have been remarkably successful in treating B cell malignancies. Such therapies also result in the near-complete loss of healthy B cells, but this depletion is well tolerated by patients. Although analogous targeting of pan-T cell markers could, in theory, help control T cell cancers, the concomitant healthy T cell depletion would result in severe and unacceptable immunosuppression. Thus, therapies directed against T cell cancers require more selective targeting. Here, we describe an approach to target T cell cancers through T cell receptor (TCR) antigens. Each T cell, normal or malignant, expresses a unique TCR β chain generated from 1 of 30 TCR β chain variable gene families (TRBV1 to TRBV30). We hypothesized that bispecific antibodies targeting a single TRBV family member expressed in malignant T cells could promote killing of these cancer cells, while preserving healthy T cells that express any of the other 29 possible TRBV family members. We addressed this hypothesis by demonstrating that bispecific antibodies targeting TRBV5-5 (α-V5) or TRBV12 (α-V12) specifically lyse relevant malignant T cell lines and patient-derived T cell leukemias in vitro. Treatment with these antibodies also resulted in major tumor regressions in mouse models of human T cell cancers. This approach provides an off-the-shelf, T cell cancer selective targeting approach that preserves enough healthy T cells to maintain cellular immunity. [ABSTRACT FROM AUTHOR]

Diabodies see the unseeable: RAS oncogene mutations are common in various cancers, controlling their growth and survival. Targeting mutant RAS proteins with antibodies has been unsuccessful due to low surface expression, even when targeting mutant RAS peptides presented via HLA on the surface of cancer cells. Douglass et al. used phage display to generate single-chain variable fragments (scFvs) specific for mutant RAS peptide-HLA complexes. The authors tested various bispecific, T cell–engaging antibody formulations, finding that single-chain diabodies (scDbs) combining the aforementioned scFv with an anti-CD3 scFv were able to induce T cell activation and subsequent killing of tumor cells expressing mutant RAS peptide-HLA complexes. This scDb approach opens the door for antibody-based therapies against mutant neoantigens expressed at very low levels on the surface of cancer cells. Mutations in the RAS oncogenes occur in multiple cancers, and ways to target these mutations has been the subject of intense research for decades. Most of these efforts are focused on conventional small-molecule drugs rather than antibody-based therapies because the RAS proteins are intracellular. Peptides derived from recurrent RAS mutations, G12V and Q61H/L/R, are presented on cancer cells in the context of two common human leukocyte antigen (HLA) alleles, HLA-A3 and HLA-A1, respectively. Using phage display, we isolated single-chain variable fragments (scFvs) specific for each of these mutant peptide-HLA complexes. The scFvs did not recognize the peptides derived from the wild-type form of RAS proteins or other related peptides. We then sought to develop an immunotherapeutic agent that was capable of killing cells presenting very low levels of these RAS-derived peptide-HLA complexes. Among many variations of bispecific antibodies tested, one particular format, the single-chain diabody (scDb), exhibited superior reactivity to cells expressing low levels of neoantigens. We converted the scFvs to this scDb format and demonstrated that they were capable of inducing T cell activation and killing of target cancer cells expressing endogenous levels of the mutant RAS proteins and cognate HLA alleles. CRISPR-mediated alterations of the HLA and RAS genes provided strong genetic evidence for the specificity of the scDbs. Thus, this approach could be applied to other common oncogenic mutations that are difficult to target by conventional means, allowing for more specific anticancer therapeutics. [ABSTRACT FROM AUTHOR]

Elucidating the foreign body response: Synthetic materials are the building blocks for medical devices and implants but can induce a foreign body response after implantation, resulting in fibrous scar tissue encompassing the implant. Here, Chung et al. define the role of interleukin 17 (IL17) and cellular senescence in driving the foreign body response. The fibrous capsule from excised breast implants contained IL17-producing T cells and senescent stromal cells. These findings were further validated in a murine model, and the authors found that blocking the IL17 pathway or eliminating senescent cells mitigated local fibrosis around the implant. This study presents new potential therapeutic targets to reduce fibrosis associated with the foreign body response. Medical devices and implants made of synthetic materials can induce an immune-mediated process when implanted in the body called the foreign body response, which results in formation of a fibrous capsule around the implant. To explore the immune and stromal connections underpinning the foreign body response, we analyzed fibrotic capsules surrounding surgically excised human breast implants from 12 individuals. We found increased numbers of interleukin 17 (IL17)–producing γδ+ T cells and CD4+ T helper 17 (TH17) cells as well as senescent stromal cells in the fibrotic capsules. Further analysis in a murine model demonstrated an early innate IL17 response to implanted synthetic material (polycaprolactone) particles that was mediated by innate lymphoid cells and γδ+ T cells. This was followed by a chronic adaptive CD4+ TH17 cell response that was antigen dependent. Synthetic materials with varying chemical and physical properties implanted either in injured muscle or subcutaneously induced similar IL17 responses in mice. Mice deficient in IL17 signaling established that IL17 was required for the fibrotic response to implanted synthetic materials and the development of p16INK4a senescent cells. IL6 produced by senescent cells was sufficient for the induction of IL17 expression in T cells. Treatment with a senolytic agent (navitoclax) that killed senescent cells reduced IL17 expression and fibrosis in the mouse implant model. Discovery of a feed-forward loop between the TH17 immune response and the senescence response to implanted synthetic materials introduces new targets for therapeutic intervention in the foreign body response. [ABSTRACT FROM AUTHOR]

The cobalt complexes HCo(CO)4 and HCo(CO)3(PR3) were the original industrial catalysts used for the hydroformylation of alkenes through reaction with hydrogen and carbon monoxide to produce aldehydes. More recent and expensive rhodium-phosphine catalysts are hundreds of times more active and operate under considerably lower pressures. Cationic cobalt(II) bisphosphine hydrido-carbonyl catalysts that are far more active than traditional neutral cobalt(I) catalysts and approach rhodium catalysts in activity are reported here. These catalysts have low linear-to-branched (L:B) regioselectivity for simple linear alkenes. However, owing to their high alkene isomerization activity and increased steric effects due to the bisphosphine ligand, they have high L:B selectivities for internal alkenes with alkyl branches. These catalysts exhibit long lifetimes and substantial resistance to degradation reactions. [ABSTRACT FROM AUTHOR]

Biomaterials induce an immune response and mobilization of macrophages, yet identification and phenotypic characterization of functional macrophage subsets invivo remain limited. We performed single-cell RNA sequencing analysis on macrophages sorted from either a biologic matrix [urinary bladder matrix (UBM)] or synthetic biomaterial [polycaprolactone (PCL)]. Implantation of UBM promotes tissue repair through generation of a tissue environment characterized by a T helper 2 (TH2)/interleukin (IL)–4 immune profile, whereas PCL induces a standard foreign body response characterized by TH17/IL-17 and fibrosis. Unbiased clustering and pseudotime analysis revealed distinct macrophage subsets responsible for antigen presentation, chemoattraction, and phagocytosis, as well as a small population with expression profiles of both dendritic cells and skeletal muscle after UBM implantation. In the PCL tissue environment, we identified a CD9hi+IL-36γ+ macrophage subset that expressed TH17-associated molecules. These macrophages were virtually absent in mice lacking the IL-17 receptor, suggesting that they might be involved in IL-17–dependent immune and autoimmune responses. Identification and comparison of the unique phenotypical and functional macrophage subsets in mouse and human tissue samples suggest broad relevance of the new classification. These distinct macrophage subsets demonstrate previously unrecognized myeloid phenotypes involved in different tissue responses and provide targets for potential therapeutic modulation in tissue repair and pathology. [ABSTRACT FROM AUTHOR]

Ever since the immune surveillance hypothesis proposed that the immune system could naturally recognize and eliminate tumors, investigators have been seeking cells that could serve such a purpose. Natural killer [...]

Effects of Cyclosporine A on T Cell Development and Clonal Deletion CYCLOSPORINE A (CsA) IS AN IMmunosuppressive drug that inhibits lymphokine production by helper T cells in vitro and has [...]

Characterization of T Cell Receptor Gamma Chain Expression in a Subset of Murine Thymocytes ANTIGEN-SPECIFIC, MHC-RESTRICTED recognition by mature T cells appears to be mediated by the clonotypic heterodimeric receptor [...]

Activation of γδ Cells in the Primary Immune Response to Mycobacterium tuberculosis ALTHOUGH MOST T CELLS EXPRESS the αβ TCR, the γ[deltah TCR is normally expressed on a small percentage [...]

This article presents a study that compared the effects of systemic chemotherapy (SC) and local chemotherapy (LC) on anti-programmed cell death protein 1 (anti-PD-1) efficacy in glioblastoma (GBM). It discusses the characteristics of GBM, the prevalence of severe lymphodepletion caused by the addition of SC to anti-PD-1 treatment, and the enrichment of tumor-infiltrating dendritic cells by LC.

The article looks at a study regarding stimulator of interferon genes (STING) which is a cytosolic receptor that senses both exogenous and endogenous cytosolic cyclic dinucleotides (CDNs). It mentions signal transducer and activator of transcription 6 and signaling pathways to induce robust type I interferon and proinflammatory cytokine responses. It also mentions granulocyte-macrophage colony-stimulating factor for producing cellular cancer vaccines.

We used a proteomic approach to identify phosphopeptide-binding modules mediating signal transduction events in the DMA damage response pathway. Using a library of partially degenerate phosphopeptides, we identified tandem BRCT (BRCA1 carboxyl-terminal) domains in PTIP (Pax transactivation domain-interacting protein) and in BRCA1 as phosphoserine- or phosphothreoninespecific binding modules that recognize substrates phosphorylated by the kinases ATM (ataxia telangiectasia-mutated) and ATR (ataxia telangiectasia- and RAD3-related) in response to γ-irradiation. PTIP tandem BRCT domains are responsible for phosphorylation-dependent protein localization into 53BP1-and phospho-H2AX (γ-H2AX)-containing nuclear foci, a marker of DMA damage. These findings provide a molecular basis for BRCT domain function in the DMA damage response and may help to explain why the BRCA1 BRCT domain mutation Met[sup1775] → Arg, which fails to bind phosphopeptides, predisposes women to breast and ovarian cancer. [ABSTRACT FROM AUTHOR]

Biologic scaffolds synergize with immune checkpoint blockade to inhibit tumor growth in mice in a process requiring T cells and macrophages. Biologic scaffolds: Boon or burden for cancer? Decellularized tissues can serve as scaffolds that promote tissue repair and wound healing—but how do these biologic scaffolds affect tumor formation? Wolf et al. tested the impact of urinary bladder matrix (UBM) on cancer cell growth in mouse models. When implanted with cancer cells, the authors found that UBM altered immune cell recruitment and immune cell phenotypes distinct from tumor-associated immune cell phenotypes. UBM-associated macrophages and T cells were important for inhibiting tumor growth, and UBM improved the efficacy of immune checkpoint inhibition. This study suggests that the prohealing microenvironment induced by UBM could augment anticancer therapies. Biomaterials in regenerative medicine are designed to mimic and modulate tissue environments to promote repair. Biologic scaffolds (derived from decellularized tissue extracellular matrix) promote a wound-healing (proregenerative) immune phenotype and are used clinically to treat tissue loss, including in the context of tumor resection. It is unknown whether a biomaterial microenvironment that encourages tissue formation may also promote tumor development. We implanted a urinary bladder matrix (UBM) scaffold, which is used clinically for wound management, with syngeneic cancer cell lines in mice to study how wound-healing immune responses affect tumor formation and sensitivity to immune checkpoint blockade. The UBM scaffold created an immune microenvironment that inhibited B16-F10 melanoma tumor formation in a CD4+ T cell–dependent and macrophage-dependent manner. In-depth immune characterization revealed an activated type 2–like immune response that was distinct from the classical tumor microenvironment, including activated type 2 T helper T cells, a unique macrophage phenotype, eosinophil infiltration, angiogenic factors, and complement. Tumor growth inhibition by PD-1 and PD-L1 checkpoint blockade was potentiated in the UBM scaffold immune microenvironment. Engineering the local tumor microenvironment to promote a type 2 wound-healing immune signature may serve as a therapeutic target to improve immunotherapy efficacy. [ABSTRACT FROM AUTHOR]

The article discusses the development and formation of the middle ear cavity in mammals, reporting that an article contained in the issue from the researchers Thompson and Tucker indicates that a programmed rupture of the epithelium in mammalian ear development could be associated with the evolution of sound-conducting bones. According to the article, this view could overturn a traditional view of mammalian middle ear development derived from bird lineage tracing studies. The potential roles of ciliated endodermal cells and epithelial cells from mesenchymal cells of neural crest origin in ear development are mentioned.

The article presents a study on roles of induced paracrine factors in kidney organoid development. Topics discussed include multicellular kidney organoids from pluripotent stem cells; complex multicellular differentiation process in a facile manner; and single-cell resolution identification of distinct renal cell types within multilayered kidney organoids.

Immune-mediated tissue regeneration driven by a biomaterial scaffold is emerging as an innovative regenerative strategy to repair damaged tissues. We investigated how biomaterial scaffolds shape the immune microenvironment in traumatic muscle wounds to improve tissue regeneration. The scaffolds induced a pro-regenerative response, characterized by an mTOR/ Rictor-dependent T helper 2 pathway that guides interleukin-4-dependent macrophage polarization, which is critical for functionalmuscle recovery. Manipulating the adaptive immune systemusing biomaterials engineeringmay support the development of therapies that promote both systemic and local pro-regenerative immune responses, ultimately stimulating tissue repair. [ABSTRACT FROM AUTHOR]

CD4+ regulatory T cells (Tregs) maintain immunological self-tolerance and immune homeostasis by suppressing aberrant or excessive immune responses. The core genetic program of Tregs and their ability to suppress pathologic immune responses depends on the transcription factor Foxp3. Despite progress in understanding mechanisms of Foxp3-dependent gene activation, the molecular mechanism of Foxp3-dependent gene repression remains largely unknown. We identified Eos, a zinc-finger transcription factor of the Ikaros family, as a critical mediator of Foxp3-dependent gene silencing in Tregs. EOS interacts directly with Foxp3 and induces chromatin modifications that result in gene silencing in Tregs. Silencing of Eos in Tregs abrogates their ability to suppress immune responses and endows them with partial effector function, thus demonstrating the critical role that Eos plays in Treg programming. [ABSTRACT FROM AUTHOR]

Regulatory T cells (T reg ) are conventionally viewed as suppressors of endogenous and therapy-induced antitumor immunity; however, their role in modulating responses to immune checkpoint blockade (ICB) is unclear. In this study, we integrated single-cell RNA-seq/T cell receptor sequencing (TCRseq) of >73,000 tumor-infiltrating T reg (TIL-T reg ) from anti-PD-1-treated and treatment-naive non-small cell lung cancers (NSCLC) with single-cell analysis of tumor-associated antigen (TAA)-specific T reg derived from a murine tumor model. We identified 10 subsets of human TIL-T reg , most of which have high concordance with murine TIL-T reg subsets. Only one subset selectively expresses high levels of TNFRSF4 (OX40) and TNFRSF18 (GITR), whose engangement by cognate ligand mediated proliferative programs and NF-κB activation, as well as multiple genes involved in T reg suppression, including LAG3 . Functionally, the OX40 hi GITR hi subset is the most highly suppressive ex vivo, and its higher representation among total TIL-T reg correlated with resistance to PD-1 blockade. Unexpectedly, in the murine tumor model, we found that virtually all TIL-T reg -expressing T cell receptors that are specific for TAA fully develop a distinct T H 1-like signature over a 2-week period after entry into the tumor, down-regulating FoxP3 and up-regulating expression of TBX21 ( Tbet) , IFNG , and certain proinflammatory granzymes. Transfer learning of a gene score from the murine TAA-specific T H 1-like T reg subset to the human single-cell dataset revealed a highly analogous subcluster that was enriched in anti-PD-1-responding tumors. These findings demonstrate that TIL-T reg partition into multiple distinct transcriptionally defined subsets with potentially opposing effects on ICB-induced antitumor immunity and suggest that TAA-specific TIL-T reg may positively contribute to antitumor responses.

T cell receptor (TCR) sequencing has been used to characterize the immune response to cancer. However, most analyses have been restricted to quantitative measures such as clonality that do not leverage the complementarity-determining region 3 (CDR3) sequence. We use DeepTCR, a framework of deep learning algorithms, to reveal sequence concepts that are predictive of response to immunotherapy. We demonstrate that DeepTCR can predict response and use the model to infer the antigenic specificities of the predictive signature and their unique dynamics during therapy. The predictive signature of nonresponse is associated with high frequencies of TCRs predicted to recognize tumor-specific antigens, and these tumor-specific TCRs undergo a higher degree of dynamic changes on therapy in nonresponders versus responders. These results are consistent with a biological model where the hallmark of nonresponders is an accumulation of tumor-specific T cells that undergo turnover on therapy, possibly because of the dysfunctional state of these T cells in nonresponders.

Knowledge of the three-dimensional movement patterns of elasmobranchs is vital to understand their ecological roles and exposure to anthropogenic pressures. To date, comparative studies among species at global scales have mostly focused on horizontal movements. Our study addresses the knowledge gap of vertical movements by compiling the first global synthesis of vertical habitat use by elasmobranchs from data obtained by deployment of 989 biotelemetry tags on 38 elasmobranch species. Elasmobranchs displayed high intra- and interspecific variability in vertical movement patterns. Substantial vertical overlap was observed for many epipelagic elasmobranchs, indicating an increased likelihood to display spatial overlap, biologically interact, and share similar risk to anthropogenic threats that vary on a vertical gradient. We highlight the critical next steps toward incorporating vertical movement into global management and monitoring strategies for elasmobranchs, emphasizing the need to address geographic and taxonomic biases in deployments and to concurrently consider both horizontal and vertical movements.

Asymptomatic SARS-CoV-2 infection and delayed implementation of diagnostics have led to poorly defined viral prevalence rates in the United States and elsewhere. To address this, we analyzed seropositivity in 9089 adults in the United States who had not been diagnosed previously with COVID-19. Individuals with characteristics that reflected the U.S. population ( n = 27,716) were selected by quota sampling from 462,949 volunteers. Enrolled participants ( n = 11,382) provided medical, geographic, demographic, and socioeconomic information and dried blood samples. Survey questions coincident with the Behavioral Risk Factor Surveillance System survey, a large probability-based national survey, were used to adjust for selection bias. Most blood samples (88.7%) were collected between 10 May and 31 July 2020 and were processed using ELISA to measure seropositivity (IgG and IgM antibodies against SARS-CoV-2 spike protein and the spike protein receptor binding domain). The overall weighted undiagnosed seropositivity estimate was 4.6% (95% CI, 2.6 to 6.5%), with race, age, sex, ethnicity, and urban/rural subgroup estimates ranging from 1.1% to 14.2%. The highest seropositivity estimates were in African American participants; younger, female, and Hispanic participants; and residents of urban centers. These data indicate that there were 4.8 undiagnosed SARS-CoV-2 infections for every diagnosed case of COVID-19, and an estimated 16.8 million infections were undiagnosed by mid-July 2020 in the United States., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY).)

Next-generation tissue-based biomarkers for immunotherapy will likely include the simultaneous analysis of multiple cell types and their spatial interactions, as well as distinct expression patterns of immunoregulatory molecules. Here, we introduce a comprehensive platform for multispectral imaging and mapping of multiple parameters in tumor tissue sections with high-fidelity single-cell resolution. Image analysis and data handling components were drawn from the field of astronomy. Using this "AstroPath" whole-slide platform and only six markers, we identified key features in pretreatment melanoma specimens that predicted response to anti-programmed cell death-1 (PD-1)-based therapy, including CD163 + PD-L1 - myeloid cells and CD8 + FoxP3 + PD-1 low/mid T cells. These features were combined to stratify long-term survival after anti-PD-1 blockade. This signature was validated in an independent cohort of patients with melanoma from a different institution., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The genomes of cancers deficient in mismatch repair contain exceptionally high numbers of somatic mutations. In a proof-of-concept study, we previously showed that colorectal cancers with mismatch repair deficiency were sensitive to immune checkpoint blockade with antibodies to programmed death receptor-1 (PD-1). We have now expanded this study to evaluate the efficacy of PD-1 blockade in patients with advanced mismatch repair-deficient cancers across 12 different tumor types. Objective radiographic responses were observed in 53% of patients, and complete responses were achieved in 21% of patients. Responses were durable, with median progression-free survival and overall survival still not reached. Functional analysis in a responding patient demonstrated rapid in vivo expansion of neoantigen-specific T cell clones that were reactive to mutant neopeptides found in the tumor. These data support the hypothesis that the large proportion of mutant neoantigens in mismatch repair-deficient cancers make them sensitive to immune checkpoint blockade, regardless of the cancers' tissue of origin., (Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

An artificial receptor has been designed to bind creatinine with a color change (chromogenic response) caused by proton transfer from one end of the receptor to the other. The receptor was synthesized and found to extract creatinine from water into chlorocarbon solvents. The color change in the organic layer is specific for creatinine relative to other organic solutes, and it is selective for creatinine relative to sodium, potassium, and ammonium ions. The chromogenic mechanism is revealed by x-ray crystal structures of creatinine, the free receptor, and the complex, showing "induced fit" binding resulting from electronic complementarity between host and guest.