Estimating Glycemia From HbA1c and CGM: Analysis of Accuracy and Sources of Discrepancy

OBJECTIVE

To examine the accuracy of different periods of continuous glucose monitoring (CGM), hemoglobin A1c (HbA1c), and their combination for estimating mean glycemia over 90 days (AG90).

RESEARCH DESIGN AND METHODS

We retrospectively studied 985 CGM periods of 90 days with <10% missing data from 315 adults (86% of whom had type 1 diabetes) with paired HbA1c measurements. The impact of mean red blood cell age as a proxy for nonglycemic effects on HbA1c was estimated using published theoretical models and in comparison with empirical data. Given the lack of a gold standard measurement for AG90, we applied correction methods to generate a reference (eAG90) that we used to assess accuracy for HbA1c and CGM.

RESULTS

Using 14 days of CGM at the end of the 90-day period resulted in a mean absolute error (95th percentile) of 14 (34) mg/dL when compared with eAG90. Nonglycemic effects on HbA1c led to a mean absolute error for average glucose calculated from HbA1c of 12 (29) mg/dL. Combining 14 days of CGM with HbA1c reduced the error to 10 (26) mg/dL. Mismatches between CGM and HbA1c >40 mg/dL occurred more than 5% of the time.

CONCLUSIONS

The accuracy of estimates of eAG90 from limited periods of CGM can be improved by averaging with an HbA1c-based estimate or extending the monitoring period beyond ∼26 days. Large mismatches between eAG90 estimated from CGM and HbA1c are not unusual and may persist due to stable nonglycemic factors.

Hematologic setpoints are a stable and patient-specific deep phenotype

The complete blood count is an important screening tool for healthy adults and is the most commonly ordered test at periodic physical exams. However, results are usually interpreted relative to one-size-fits-all reference intervals, undermining the goal of precision medicine to tailor medical care to the needs of individual patients based on their unique characteristics. Here we show that standard complete blood count indices in healthy adults have robust homeostatic setpoints that are patient-specific and stable, with the typical healthy adult's set of 9 blood count setpoints distinguishable from 98% of others, and with these differences persisting for decades. These setpoints reflect a deep physiologic phenotype, enabling improved detection of both acquired and genetic determinants of hematologic regulation, including discovery of multiple novel loci via GWAS analyses. Patient-specific reference intervals derived from setpoints enable more accurate personalized risk assessment, and the setpoints themselves are significantly correlated with mortality risk, providing new opportunities to enhance patient-specific screening and early intervention. This study shows complete blood count setpoints are sufficiently stable and patient-specific to help realize the promise of precision medicine for healthy adults.

Computer vision quantitation of erythrocyte shape abnormalities provides diagnostic, prognostic, and mechanistic insight

Examination of red blood cell (RBC) morphology in peripheral blood smears can help diagnose hematologic diseases, even in resource-limited settings, but this analysis remains subjective and semiquantitative with low throughput. Prior attempts to develop automated tools have been hampered by their poor reproducibility and limited clinical validation. Here, we present a novel, open-source machine-learning approach (denoted as RBC-diff) to quantify abnormal RBCs in peripheral smear images and generate an RBC morphology differential. RBC-diff cell counts showed high accuracy for single-cell classification (mean AUC, 0.93) and quantitation across smears (mean R2, 0.76 compared with experts, interexperts R2, 0.75). RBC-diff counts were concordant with the clinical morphology grading for 300 000+ images and recovered the expected pathophysiologic signals in diverse clinical cohorts. Criteria using RBC-diff counts distinguished thrombotic thrombocytopenic purpura and hemolytic uremic syndrome from other thrombotic microangiopathies, providing greater specificity than clinical morphology grading (72% vs 41%; P < .001) while maintaining high sensitivity (94% to 100%). Elevated RBC-diff schistocyte counts were associated with increased 6-month all-cause mortality in a cohort of 58 950 inpatients (9.5% mortality for schist. >1%, vs 4.7% for schist; <0.5%; P < .001) after controlling for comorbidities, demographics, clinical morphology grading, and blood count indices. RBC-diff also enabled the estimation of single-cell volume-morphology distributions, providing insight into the influence of morphology on routine blood count measures. Our codebase and expert-annotated images are included here to spur further advancement. These results illustrate that computer vision can enable rapid and accurate quantitation of RBC morphology, which may provide value in both clinical and research contexts.

Correlation of extent of ALK FISH positivity and crizotinib efficacy in three prospective studies of ALK-positive patients with non-small-cell lung cancer

Background

In clinical trials of patients with anaplastic lymphoma kinase (ALK)-positive non-small-cell lung cancer (NSCLC) treated with crizotinib, evaluation of the relationship between the percentage of ALK-positive cells by fluorescence in situ hybridization (FISH)-particularly near the cut-off defining positive status-and clinical outcomes have been limited by small sample sizes.

Patients and methods

Data were pooled from three large prospective trials (one single-arm and two randomized versus chemotherapy) of crizotinib in patients with ALK-positive NSCLC determined by Vysis ALK Break Apart FISH using a cut-off of ≥15% ALK-positive cells. Logistic regression and proportional hazards regression analyses were used to explore the association of percent ALK-positive cells with objective response and progression-free survival (PFS), respectively.

Results

Of 11 081 screened patients, 1958 (18%) were ALK positive, 7512 (68%) were ALK negative, and 1540 (14%) were uninformative. Median percentage of ALK-positive cells was 58% in ALK-positive patients and 2% in ALK-negative patients. Of ALK-positive patients, 5% had 15%-19% ALK-positive cells; of ALK-negative patients, 2% had 10%-14% ALK-positive cells. Objective response rate for ALK-positive, crizotinib-treated patients with ≥20% ALK-positive cells was 56% (n = 700/1246), 55% (n = 725/1312) for those with ≥15% ALK-positive cells, and 38% for those with 15%-19% ALK-positive cells (n = 25/66). As a continuous variable, higher percentages of ALK-positive cells were estimated to be associated with larger differences in objective response and PFS between crizotinib and chemotherapy; however, tests for interaction between treatment and percentage of ALK-positive cells were not significant (objective response, P = 0.054; PFS, P = 0.17).

Conclusions

Patients with ALK-positive NSCLC benefit from treatment with crizotinib across the full range of percentage of ALK-positive cells, supporting the clinical utility of the 15% cut-off. The small number of patients with scores near the cut-off warrant additional study given the potential for misclassification of ALK status due to technical or biologic reasons.

The NFAT-related protein NFATL1 (TonEBP/NFAT5) is induced upon T cell activation in a calcineurin-dependent manner

NFAT DNA binding complexes regulate programs of cellular activation and differentiation by translating receptor-dependent signaling events into specific transcriptional responses. NFAT proteins, originally defined as calcium/calcineurin-dependent regulators of cytokine gene transcription in T lymphocytes, are expressed in many different cell types and represent critical signaling intermediates that mediate an increasingly wide spectrum of biologic responses. Recent studies have identified a novel protein containing a region of similarity to the NFAT DNA binding domain. Here we demonstrate that this protein, designated NFATL1 (also known as tonicity enhancer binding protein and NFAT5) is expressed at high levels in the thymus but is undetectable in mature lymphocytes. However, NFATL1 can be induced in both primary quiescent T lymphocytes and differentiated Th1 and Th2 cell populations upon mitogen- or Ag receptor-dependent activation. The induction of NFATL1 protein, as well as NFATL1-dependent transcription, is inhibited by cyclosporin A and FK506, and expression of constitutively active calcineurin induces NFATL1-dependent transcription. Overexpression of NFATc1 and inhibition of NFATc activity through the use of a dominant negative NFATc1 protein have no affect on NFATL1-dependent transcription, indicating that NFATc proteins do not play a role in the calcineurin-dependent induction of NFATL1. Interestingly, induction of NFATL1 by a hyperosmotic stimulus is not blocked by the inhibition of calcineurin. Moreover, osmotic stress response genes such as aldose reductase are not induced upon T cell activation. Thus inducible expression of NFATL1 represents a mechanism by which receptor-dependent signals as well as osmotic stress signals are translated into transcriptional responses that regulate cell function.

Redundant expression but selective utilization of nuclear factor of activated T cells family members

Nuclear factor of activated T cells (NF-AT) complexes regulate the induction of many early T cell activation molecules. Four related proteins can function as the cytoplasmic subunit of NF-AT, and their overlapping expression patterns and the mild phenotype of the NF-ATp null mice suggest that they may be functionally redundant. We characterized the distribution and activation of cytoplasmic NF-AT proteins in mature lymphocytes and found that NF-ATc, NF-ATp, and NF-AT4/x/c3 are co-expressed and co-regulated in mature T and B cells. Each protein forms independent DNA binding complexes, and at physiologic concentrations, NF-ATc and NF-ATp complexes out-compete NF-AT4/x/c3 for occupancy of NF-AT sites from the IL-2, IL-3/granulocyte-macrophage CSF, IL-4, and CD40 ligand genes. This predicts heavily redundant immune regulatory functions of NF-ATp and NF-ATc, but distinct activities for NF-AT4/x/c3. Additionally, Ab interaction with NF-ATp induces high affinity NF-kappaB site interaction, suggesting that nuclear partners may dramatically vary the specificity of the NF-AT family.

Redundant expression but selective utilization of nuclear factor of activated T cells family members

Nuclear factor of activated T cells (NF-AT) complexes regulate the induction of many early T cell activation molecules. Four related proteins can function as the cytoplasmic subunit of NF-AT, and their overlapping expression patterns and the mild phenotype of the NF-ATp null mice suggest that they may be functionally redundant. We characterized the distribution and activation of cytoplasmic NF-AT proteins in mature lymphocytes and found that NF-ATc, NF-ATp, and NF-AT4/x/c3 are co-expressed and co-regulated in mature T and B cells. Each protein forms independent DNA binding complexes, and at physiologic concentrations, NF-ATc and NF-ATp complexes out-compete NF-AT4/x/c3 for occupancy of NF-AT sites from the IL-2, IL-3/granulocyte-macrophage CSF, IL-4, and CD40 ligand genes. This predicts heavily redundant immune regulatory functions of NF-ATp and NF-ATc, but distinct activities for NF-AT4/x/c3. Additionally, Ab interaction with NF-ATp induces high affinity NF-kappaB site interaction, suggesting that nuclear partners may dramatically vary the specificity of the NF-AT family.

Transcriptional control in keratinocytes and fibroblasts using synthetic ligands

The skin is an attractive tissue for regulated target gene expression by virtue of its accessibility to topical regulating stimuli. We have used synthetic ligand-driven intracellular oligomerization to accomplish specific target gene regulation in human skin keratinocytes and fibroblasts. GAL4 DNA binding domains and VP16 transactivation domains, each linked to the FK506 binding protein, were expressed in normal human skin keratinocytes and fibroblasts. These hybrid proteins underwent heterodimerization via the novel intracellular dimerizing agent FK1012 to generate a heterodimeric activator of target gene expression in vitro. Dimeric FK1012, but not monomeric FK506M induced target gene expression in a dose-dependent fashion. FK1012 exerted no detectable nonspecific effects on expression of cutaneous genes and did not alter cellular proliferation kinetics. Controlled oligomerization of hybrid transcription activators offers a potential approach to target gene regulation in cells of normal human skin.

Nuclear localization of NF-ATc by a calcineurin-dependent, cyclosporin-sensitive intramolecular interaction

The NF-AT family of transcription factors participates in the regulation of early immune response genes such as IL-2, IL-4, CD40 ligand, and Fas ligand in response to Ca2+/calcineurin signals initiated at the antigen receptor. Calcineurin activation leads to the rapid translocation of NF-AT family members from cytoplasm to nucleus, an event that is blocked by the immunosuppressive drugs cyclosporin A and FK506. We show that translocation requires two redundant nuclear localization sequences and that one sequence is in an intramolecular association with phosphorserines in a conserved motif located at the amino terminus of each NF-AT protein. Mutation of serines in this motif in NF-ATc both disrupts this intramolecular interaction and leads to nuclear localization, suggesting a model of NF-AT nuclear import in which dephosphorylation by calcineurin causes exposure of two nuclear localization sequences.

Unusual Rel-like architecture in the DNA-binding domain of the transcription factor NFATc

Transcription factors of the NFAT family regulate the production of effector proteins that coordinate the immune response. The immunosuppressive drugs FK506 and cyclosporin A (CsA) act by blocking a Ca2+-mediated signalling pathway leading to NFAT. Although FK506 and CsA have enabled human organs to be transplanted routinely, the toxic side-effects of these drugs limit their usage. This toxicity might be absent in antagonists that target NFAT directly. As a first step in the structure-based search for NFAT antagonists, we now report the identification and solution structure of a 20K domain of NFATc (NFATc-DBD) that is both necessary and sufficient to bind DNA and activate transcription cooperatively. Although the overall fold of the NFATc DNA-binding domain is related to that of NF-kappaB p50 (refs 2, 3), the two proteins use significantly different strategies for DNA recognition. On the basis of these results, we present a model for the cooperative complex formed between NFAT and the mitogenic transcription factor AP-1 on the interleukin-2 enhancer.

Rapid shuttling of NF-AT in discrimination of Ca2+ signals and immunosuppression

Cells need to distinguish between transient Ca2+ signals that induce events such as muscle contraction, secretion, adhesion and synaptic transmission, and sustained Ca2+ signals that are involved in cell proliferation and differentiation. The latter class of events is blocked in lymphocytes by the immunosuppressive drugs cyclosporin A and FK506, which inhibit calcineurin, a Ca2+-activated serine/threonine phosphatase necessary for the nuclear import of NF-AT transcription factors. Here we report that sustained high concentrations of Ca2+, but not transient pulses, are required to maintain NF-AT transcription factors in the nucleus, where they participate in Ca2+-dependent induction of genes required for lymphocyte activation and proliferation. Furthermore, overexpression and constitutive nuclear localization of NF-AT, but not Jun, Fos, NF-kappaB, Oct or Ets family members, renders the interleukin-2 enhancer in Jurkat T lymphocytes resistant to FK506 and cyclosporin A. Thus a primary effect of these immunosuppressive reagents is to control the subcellular localization of the NF-AT family of transcription factors.

Dimeric ligands define a role for transcriptional activation domains in reinitiation

Eukaryotic transcriptional activators mediate transcriptional induction through stabilization of the preinitiation complex, probably through direct interactions with basal transcription factors. In vitro studies on the role of an activator in the maintenance of on-going transcription (reinitiation) have been contradictory, suggesting that, after formation of a preinitiation complex, an activator may or may not be necessary for transcription to be maintained. We have developed a means of regulating transcription in living cells through the use of both homodimeric and heterodimerizing synthetic ligands that allow the ligand-dependent association and disassociation of a transcriptional activation domain with a promoter. Here we report that maintaining the transcription of endogenous genes in vivo, in both yeast and human cells, requires the continuous presence of the activation domain. The use of synthetic ligands as a transcriptional on-off switch represents a powerful means of controlling the transcription in vitro and in vivo for both experimental and therapeutic purposes.

Functional analysis of Fas signaling in vivo using synthetic inducers of dimerization

BACKGROUND

Genetic abnormalities in the Fas receptor or its trimeric ligand, FasL, result in massive T-cell proliferation and a lupus-like autoimmune syndrome, which was initially attributed to excessive lymphoproliferation but is now ascribed to the absence of Fas-mediated cell death. Although Fas is normally expressed on most thymocytes, negative selection seems to be unperturbed in Fas-deficient (lpr) mice. This suggests that Fas has an important function in peripheral, but not thymic, T cells.

RESULTS

To explore the Fas-mediated cell death pathway both in vitro and in vivo, we used conditional alleles of the Fas receptor that can be triggered by an intracellularly active chemical inducer of dimerization known as FK1012. We found that membrane attachment is important for Fas function and, unlike previous results with anti-Fas monoclonal antibodies, we show that dimerization is sufficient to trigger apoptosis. Finally, the administration of FK1012 in vivo to transgenic animals expressing the conditional FAS receptor in thymocytes demonstrates that sensitivity to FAS-mediated apoptosis is restricted to CD4+CD8+ thymocytes.

CONCLUSIONS

Here, we describe the first in vivo application of non-toxic, cell-permeable synthetic ligands to regulate signal transduction in transgenic mice expressing a conditional receptor. Using this system, we show that the Fas pathway is restricted to double-positive thymocytes in vivo, consistent with recent in vitro findings with thymocytes. This method promises to be more useful not only for developmental studies involving cell ablation, but also for studies involving the regulation of a wide variety of signaling molecules.

Controlling protein association and subcellular localization with a synthetic ligand that induces heterodimerization of proteins

Extracellular growth and differentiation factors induce changes in gene expression in the nucleus by initiating a series of protein associations that alter the subcellular localization of intracellular signaling proteins. Initial events involve receptor homo- or heterodimerization and subsequent recruitment of cytosolic signaling proteins to the inner leaflet of the plasma membrane. Intermediate events involve the translocation of proteins into the nucleus. Late events involve the recruitment of transcriptional activators to the vicinity of specific genes in the nucleus, resulting in increased gene transcription. The ability to induce signals at each of these three phases of signaling pathways is illustrated by the use of a heterodimeric chemical inducer of dimerization that causes a proximal relationship between two different target proteins.

NFATc3, a lymphoid-specific NFATc family member that is calcium-regulated and exhibits distinct DNA binding specificity

Signals transduced by the T cell antigen receptor (TCR) regulate developmental transitions in the thymus and also mediate the immunologic activation of mature, peripheral T cells. In both cases TCR stimulation leads to the assembly of the NFAT transcription complex as a result of the calcium-dependent nuclear translocation of cytosolic subunits, NFATc, and the Ras/protein kinase C-dependent induction of a nuclear subunit, NFATn. To further understand the diverse roles of antigen receptor signaling throughout T cell development, we have identified a new NFATc family member, NFATc3, that is expressed at highest levels in the thymus. NFATc3 is the product of a gene on murine chromosome 8 that is not linked to the other NFATc genes. NFATc3, like other NFATc family members, contains a conserved rel similarity domain, and also defines a region conserved among NFATc family members, the SP repeat region, characterized by the repeated motif SPxxSPxxSPrxsxx (D/E)(D/E)swl. NFATc3 activates NFAT site-dependent transcription when overexpressed, yet exhibits a pattern of DNA site specificity distinct from other NFATc proteins. Additionally, thymic NFATc3 undergoes modifications in response to agents that mimic T cell receptor signaling, including a decrease in apparent molecular mass upon elevation of intracellular calcium that is inhibited by the immunosuppressant FK506. Given the preferential expression of NFATc3 in the thymus, NFATc family members may regulate distinct subsets of genes during T cell development.

Cloning and chromosomal localization of the human and murine genes for the T-cell transcription factors NFATc and NFATp

The nuclear factor of activated T cells (NFAT) is a transcription factor complex involved in the activation of cytokines and cell surface molecules associated with coordinating the actions of different cells required for an immune response. Two different genes have recently been cloned that encode proteins capable of functioning as the pre-existing (p) and cytosolic (c) component of the NFAT transcription complex, NFATc of human and NFATp of murine origin (Northrop et al., 1994; McCaffrey et al., 1993b). We report here the partial cDNA cloning of the murine homolog of NFATc and the human homolog of NFATp, and the chromosomal localization of both genes in both species to conserved syntenic regions. Through the use of mapping panels of human x Chinese hamster and mouse x rodent cells hybrids, the NFATc genes were mapped to human and mouse chromosomes 18. By analyzing a chromosome 18 radiation hybrid panel, the human NFATc gene was localized to the q terminus, closely linked to STS marker D18S497. The murine Nfatc gene was sublocalized to chromosome band 18E4 by FISH. The NFATp genes were mapped by somatic cell hybrid analysis to human chromosome 20 and mouse chromosome 2. Human NFATp was assigned to chromosome region 20q13.2-->q13.3 by FISH. Based on the conserved syntenic region on human chromosome 20 and mouse chromosome 2, murine Nfatp is predicted to reside in the vicinity of a mutant locus wasted. Homozygous wst/wst mice display a phenotype reminiscent of severe combined immune deficiency or ataxia telangiectasia, disorders that could therefore be considered candidates for NFATp mutations.

Three-dimensional structure in solution of griseoviridin, a group A antibiotic

The solution conformation of griseoviridin, a broad spectrum antibiotic, has been determined by 1H-NMR in deuterated dimethylsulfoxide. The structural determination is based on experimental data of NOE constraints Five structures were obtained from restrained molecular dynamics calculations, by imposing (the condition for) a minimum violation of distance constraints. These structures satisfy well the experimental restraints, with small values of NOE violation and total energies. On comparison with its crystal structure, a good agreement is noted with a backbone root-mean-square deviation value of 0.084 nm. However, a small variation between the structures is observed at the aminodecanoic acid part of the molecule.

Specific inhibition of formation of transcription complexes by a calicheamicin oligosaccharide: a paradigm for the development of transcriptional antagonists

Sequence-specific DNA ligands that antagonize DNA-protein interactions represent a potentially powerful means of modulating gene expression. Calicheamicin gamma 1I, a member of the DNA-cleaving enediyne class of anticancer antibiotics, binds to specific DNA sequences through an aryltetrasaccharide domain. To take advantage of this unique sequence-specific recognition capability, the methyl glycoside of the aryltetrasaccharide of calicheamicin gamma 1I (CLM-MG) was used to investigate the ability of glycoconjugate DNA ligands to inhibit DNA-protein interactions. CLM-MG inhibits the formation of DNA-protein complexes at micromolar concentrations in a sequence-specific manner and rapidly dissociates preformed complexes. CLM-MG also inhibits transcription in vivo with similar sequence specificity. These results suggest a strategy for the development of a class of novel biological probes and therapeutic agents.

Solution conformation of enopeptin A, a depsipeptide antibiotic, using 2D NMR and restrained molecular dynamics studies

Studies on the solution conformation of the cyclic depsipeptide antibiotic enopeptin A have been carried out using 2D NMR and molecular modelling techniques. The proton resonances of the antibiotic in DMSO-d6 have been assigned by the use of TOCSY and ROESY experiments. The interproton distance information obtained from the ROESY experiments have been used as the basis for elucidating the probable structures in solution. The restrained molecular dynamics technique was applied to calculate the structures in solution, and six resultant structures with fewer distance constraint violations were obtained that satisfy the experimental restraints very well. The conformation of the cyclic moiety of the molecules is well defined whereas the aliphatic chain segment is disordered.

NF-AT components define a family of transcription factors targeted in T-cell activation

The NF-AT transcription complex is required for the expression of a group of proteins that collectively coordinate the immune response. Here we purify two proteins encoded by separate genes that represent the pre-existing (p) and cytosolic (c) components of NF-AT. Expression of the full-length complementary DNA encoding NF-ATc activates the interleukin (IL-2) promoter in non-T lymphocytes, whereas a dominant negative of NF-ATc specifically blocks activation of the IL-2 promoter in T lymphocytes, indicating that NF-ATc is required for IL-2 gene expression. NF-ATc RNA expression is largely restricted to lymphoid tissues and is induced upon T-cell activation. The other protein, NF-ATp, is highly homologous to NF-ATc over a limited domain which shows similarity to the Dorsal/Rel family, but has a wider tissue distribution. Agents that increase intracellular Ca2+ or activate protein kinase C independently modify NF-ATc, indicating that distinct signalling pathways converge on NF-ATc to regulate its function.

FL-120A-D', new products related to kinamycin from Streptomyces chattanoogensis subsp. taitungensis subsp. nov. II. Isolation and structure determination

Six new kinamycin antibiotics have been isolated from the culture filtrate of Streptomyces chattanoogensis. The structures of six related components were determined employing 1D and 2D NMR spectroscopy and mass spectrometry. These structures represent the first reported epoxide kinamycin (2, 3) and propionyl derivative of kinamycin (5), and new isobutyryl derivatives of kinamycin (1, 4, 6).

Gene splicing by overlap extension: tailor-made genes using the polymerase chain reaction

Gene Splicing by Overlap Extension or "gene SOEing" is a PCR-based method of recombining DNA sequences without reliance on restriction sites and of directly generating mutated DNA fragments in vitro. By modifying the sequences incorporated into the 5'-ends of the primers, any pair of polymerase chain reaction products can be made to share a common sequence at one end. Under polymerase chain reaction conditions, the common sequence allows strands from two different fragments to hybridize to one another, forming an overlap. Extension of this overlap by DNA polymerase yields a recombinant molecule. This powerful and technically simple approach offers many advantages over conventional approaches for manipulating gene sequences.

Regulatory effects of transforming growth factor-beta on IL-2- and IL-4-dependent T cell-cycle progression

Previous studies suggested that the potent immunosuppressive activities of transforming growth factor-beta (TGF-beta) were mediated in part through the inhibition of IL-2-dependent S-phase progression and mitosis of activated T cells. To further investigate the mechanism of T cell growth inhibition by TGF-beta, two constitutively activated murine T cell clones were employed as defined model systems for the growth factor-dependent phase of T cell proliferation. The Th cell line, HT-2, proliferated in response to either IL-2 or IL-4, whereas the cytotoxic T cell line, CT6, exhibited strict dependence on IL-2 for growth stimulation. In both cell lines, picomolar concentrations of TGF-beta inhibited S-phase progression stimulated by IL-2 or IL-4. TGF-beta pretreatment decreased the expression of high affinity IL-2R on HT-2 cells, but not on CT6 cells. In contrast, IL-2-stimulated transferrin receptor expression was markedly inhibited by TGF-beta in both T cell lines. Analyses of growth factor-dependent specific mRNA accumulation revealed that TGF-beta exerted selective inhibitory effects on gene expression in HT-2 and CT6 cells. TGF-beta significantly reduced early (1 to 2 h) increases in c-myc mRNA levels stimulated by IL-2 or IL-4 in both cell lines. In HT-2 cells, TGF-beta pretreatment also inhibited the early increase in granulocyte-macrophage CSF mRNA stimulated by IL-2 or IL-4. The inhibition of c-myc and granulocyte-macrophage cyte-macrophage CSF gene expression by TGF-beta was explained, at least in part, by suppression of the growth factor-dependent transcriptional activation of these genes. These studies suggest that inhibition of c-myc gene transcription may play a fundamental role in the antiproliferative effect of TGF-beta on IL-2- or IL-4-stimulated T cells.

Regulatory effects of transforming growth factor-beta on IL-2- and IL-4-dependent T cell-cycle progression

Previous studies suggested that the potent immunosuppressive activities of transforming growth factor-beta (TGF-beta) were mediated in part through the inhibition of IL-2-dependent S-phase progression and mitosis of activated T cells. To further investigate the mechanism of T cell growth inhibition by TGF-beta, two constitutively activated murine T cell clones were employed as defined model systems for the growth factor-dependent phase of T cell proliferation. The Th cell line, HT-2, proliferated in response to either IL-2 or IL-4, whereas the cytotoxic T cell line, CT6, exhibited strict dependence on IL-2 for growth stimulation. In both cell lines, picomolar concentrations of TGF-beta inhibited S-phase progression stimulated by IL-2 or IL-4. TGF-beta pretreatment decreased the expression of high affinity IL-2R on HT-2 cells, but not on CT6 cells. In contrast, IL-2-stimulated transferrin receptor expression was markedly inhibited by TGF-beta in both T cell lines. Analyses of growth factor-dependent specific mRNA accumulation revealed that TGF-beta exerted selective inhibitory effects on gene expression in HT-2 and CT6 cells. TGF-beta significantly reduced early (1 to 2 h) increases in c-myc mRNA levels stimulated by IL-2 or IL-4 in both cell lines. In HT-2 cells, TGF-beta pretreatment also inhibited the early increase in granulocyte-macrophage CSF mRNA stimulated by IL-2 or IL-4. The inhibition of c-myc and granulocyte-macrophage cyte-macrophage CSF gene expression by TGF-beta was explained, at least in part, by suppression of the growth factor-dependent transcriptional activation of these genes. These studies suggest that inhibition of c-myc gene transcription may play a fundamental role in the antiproliferative effect of TGF-beta on IL-2- or IL-4-stimulated T cells.

Engineering hybrid genes without the use of restriction enzymes: gene splicing by overlap extension

Gene splicing by overlap extension is a new approach for recombining DNA molecules at precise junctions irrespective of nucleotide sequences at the recombination site and without the use of restriction endonucleases or ligase. Fragments from the genes that are to be recombined are generated in separate polymerase chain reactions (PCRs). The primers are designed so that the ends of the products contain complementary sequences. When these PCR products are mixed, denatured, and reannealed, the strands having the matching sequences at their 3' ends overlap and act as primers for each other. Extension of this overlap by DNA polymerase produces a molecule in which the original sequences are 'spliced' together. This technique is used to construct a gene encoding a mosaic fusion protein comprised of parts of two different class-I major histocompatibility genes. This simple and widely applicable approach has significant advantages over standard recombinant DNA techniques.

Site-directed mutagenesis by overlap extension using the polymerase chain reaction

Overlap extension represents a new approach to genetic engineering. Complementary oligodeoxyribonucleotide (oligo) primers and the polymerase chain reaction are used to generate two DNA fragments having overlapping ends. These fragments are combined in a subsequent 'fusion' reaction in which the overlapping ends anneal, allowing the 3' overlap of each strand to serve as a primer for the 3' extension of the complementary strand. The resulting fusion product is amplified further by PCR. Specific alterations in the nucleotide (nt) sequence can be introduced by incorporating nucleotide changes into the overlapping oligo primers. Using this technique of site-directed mutagenesis, three variants of a mouse major histocompatibility complex class-I gene have been generated, cloned and analyzed. Screening of mutant clones revealed at least a 98% efficiency of mutagenesis. All clones sequenced contained the desired mutations, and a low frequency of random substitution estimated to occur at approx. 1 in 4000 nt was detected. This method represents a significant improvement over standard methods of site-directed mutagenesis because it is much faster, simpler and approaches 100% efficiency in the generation of mutant product.

Increased specificity of PCR-amplified products by size-fractionation of restriction enzyme-digested template genomic DNA

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Interleukin 1-mediated activation of interleukin 4 (IL 4)-producing T lymphocytes. Proliferation by IL 4-dependent and IL 4-independent mechanisms

The role of IL 1 in the activation of IL 4-producing murine T cell clones was investigated by using a calcium ionophore (ionomycin) or a phorbol ester (12-O-tetradecanoylphorbol 13-acetate; TPA) as T cell receptor-independent costimuli. The use of these pharmacologic agents to investigate IL 1-mediated T cell activation revealed two distinct mechanisms of activation. IL 1 in combination with ionomycin (iono/rIL 1) stimulated a proliferative response that was associated with the production of IL 4 as measured by lymphokine bioassay and mRNA studies. Furthermore, inhibition of this proliferative response with an anti-IL 4 monoclonal antibody or cyclosporine indicated that IL 4 functions as an autocrine growth factor. In contrast, IL 1 synergized with TPA (TPA/rIL 1) to induce proliferation in the absence of either IL 4 or IL 2 gene transcription or lymphokine secretion. The IL 4-independence of this activation mechanism was further supported by the failure of both anti-IL 4 antibodies and cyclosporine to inhibit the response. In addition, activation by TPA/rIL 1 caused no detectable alteration in cytoplasmic calcium levels. Both IL 4-dependent and IL 4-independent activation responses were associated with the expression of functional receptors for IL 2 as well as IL 4. Characterization of these activation responses suggests that the synergistic activity of IL 1 during T cell activation is multipotential. The nature of an IL 1-dependent T cell growth response, therefore, may vary depending on the balance of intracellular signals generated concurrently through the T cell receptor complex and other regulatory surface molecules.

Interleukin 1-mediated activation of interleukin 4 (IL 4)-producing T lymphocytes. Proliferation by IL 4-dependent and IL 4-independent mechanisms

The role of IL 1 in the activation of IL 4-producing murine T cell clones was investigated by using a calcium ionophore (ionomycin) or a phorbol ester (12-O-tetradecanoylphorbol 13-acetate; TPA) as T cell receptor-independent costimuli. The use of these pharmacologic agents to investigate IL 1-mediated T cell activation revealed two distinct mechanisms of activation. IL 1 in combination with ionomycin (iono/rIL 1) stimulated a proliferative response that was associated with the production of IL 4 as measured by lymphokine bioassay and mRNA studies. Furthermore, inhibition of this proliferative response with an anti-IL 4 monoclonal antibody or cyclosporine indicated that IL 4 functions as an autocrine growth factor. In contrast, IL 1 synergized with TPA (TPA/rIL 1) to induce proliferation in the absence of either IL 4 or IL 2 gene transcription or lymphokine secretion. The IL 4-independence of this activation mechanism was further supported by the failure of both anti-IL 4 antibodies and cyclosporine to inhibit the response. In addition, activation by TPA/rIL 1 caused no detectable alteration in cytoplasmic calcium levels. Both IL 4-dependent and IL 4-independent activation responses were associated with the expression of functional receptors for IL 2 as well as IL 4. Characterization of these activation responses suggests that the synergistic activity of IL 1 during T cell activation is multipotential. The nature of an IL 1-dependent T cell growth response, therefore, may vary depending on the balance of intracellular signals generated concurrently through the T cell receptor complex and other regulatory surface molecules.

Differential bioassay of interleukin 2 and interleukin 4

The T cell-derived lymphokines interleukin 2 (IL-2) and interleukin 4 (IL-4, originally BSF-1) both exhibit T cell growth-promoting activity. Recent observations that T cell lines commonly used as indicator cells in IL-2 bioassays also proliferate in response to IL-4 demonstrate the lack of specificity of these bioassays for IL-2. In this report we describe a bioassay method to differentiate IL-2 and IL-4 through the parallel use of two T cell lines with defined lymphokine specificity. The IL-2-responsive CT6 cell line, when used in conjunction with the IL-2- and IL-4-responsive HT-2 cell line, allows for the differentiation of IL-2 and IL-4 in conditioned media.

Transmembrane signaling during interleukin 1-dependent T cell activation. Interactions of signal 1- and signal 2-type mediators with the phosphoinositide-dependent signal transduction mechanism

The murine T lymphoma line, LBRM-33 1A5, requires synergistic signals delivered by phytohemagglutinin (PHA) and interleukin 1 (IL1) for activation to high level interleukin 2 production. The activation signals provided by PHA and IL1 were replaced by the Ca2+ ionophore, ionomycin, and the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate (TPA), respectively. These observations supported a two-signal model for T cell activation involving increases in intracellular Ca2+ concentration ([Ca2+]i) (signal 1) and activation of protein kinase C (signal 2) as necessary and sufficient events. However, biochemical analyses revealed that additional signals were involved in the activation of LBRM-33 cells by both receptor-dependent and -independent mediators. Both signal 1-type mediators, PHA and ionomycin, exerted pleiotropic effects at the concentrations required for synergy with signal 2-type mediators (IL1, TPA). Within 1-2 min of addition, PHA stimulated phospholipid turnover, including hydrolysis of phosphatidylinositol 4,5-bisphosphate, Ca2+ mobilization, and protein kinase C activation. The [Ca2+]i increase induced by PHA was due to influx from both intracellular and extracellular Ca2+ pools. Similarly, ionomycin increased phospholipid turnover, [Ca2+]i, and directly affected protein kinase C activity in LBRM-33 cells. In contrast, the signal 2-type mediators, TPA and IL1, appeared to act by distinct intracellular mechanisms. TPA induced a protracted association of cellular protein kinase C with the plasma membrane, consistent with the two-signal activation model. Furthermore, acute TPA treatment inhibited PHA-stimulated inositol phosphate release and Ca2+ mobilization, suggesting that this mediator partially antagonized signal 1 delivery. IL1, in contrast, neither activated protein kinase C directly nor did it positively modulate the coupling of signal 1-type mediators to [Ca2+]i or protein kinase C via the phosphoinositide pathway. The intracellular signal delivered by IL1 is, therefore, generated through a mechanism distinct from or distal to the activation of protein kinase C. These studies indicate that the two-signal hypothesis, in its simplest form, is inadequate to explain the signals required for the initiation of IL1-dependent T cell activation.