Results of our genetic and pharmacologic studies implicate melanocortinergic signaling in the control of human blood pressure through an insulin-independent mechanism.

T lymphocyte maturation is dependent on interactions between the T cell receptor (TCR) expressed on the developing thymocyte and intrathymic major histocompatibility complex (MHC)-peptide ligands. The relation between the peptide-MHC complex that results in negative or positive selection has not been identified. Here, the requirements for the maturation of thymocytes expressing a defined transgenic TCR specific for a viral peptide are studied in fetal thymic organ culture. Low concentrations of the viral peptide antigen recognized by this transgenic TCR can mediate positive selection, whereas high concentrations result in thymocyte tolerance. These findings support the affinity-avidity model of thymocyte selection.

Throughout much of the last century insulin served a central role in the advancement of peptide chemistry, pharmacology, cell signaling and structural biology. These discoveries have provided a steadily improved quantity and quality of life for those afflicted with diabetes. The collective work serves as a foundation for the development of insulin analogs and mimetics capable of providing more tailored therapy. Advancements in patient care have been paced by breakthroughs in core technologies, such as semisynthesis, high performance chromatography, rDNA-biosynthesis and formulation sciences. How the structural and conformational dynamics of this endocrine hormone elicit its biological response remains a vigorous area of study. Numerous insulin analogs have served to coordinate structural biology and biochemical signaling to provide a first level understanding of insulin action. The introduction of broad chemical diversity to the study of insulin has been limited by the inefficiency in total chemical synthesis, and the inherent limitations in rDNA-biosynthesis and semisynthetic approaches. The goals of continued investigation remain the delivery of insulin therapy where glycemic control is more precise and hypoglycemic liability is minimized. Additional objectives for medicinal chemists are the identification of superagonists and insulins more suitable for non-injectable delivery. The historical advancements in the synthesis of insulin analogs by multiple methods is reviewed with the specific structural elements of critical importance being highlighted. The functional refinement of this hormone as directed to improved patient care with insulin analogs of more precise pharmacology is reported.

Insulin remains indispensable in the treatment of diabetes, but its use is hampered by its narrow therapeutic index. Although advances in peptide chemistry and recombinant DNA-based macromolecule synthesis have enabled the synthesis of structurally optimized insulin analogues, the growing epidemics of obesity and diabetes have emphasized the need for diabetes therapies that are more efficacious, safe and convenient. Accordingly, a broad set of drug candidates, targeting hyperglycaemia plus other disease abnormalities, is now progressing through the clinic. The development of an insulin therapy that is responsive to glucose concentration remains an ultimate goal, with initial prototypes now reaching the proof-of-concept stage. Simultaneously, the first alternatives to injectable delivery have progressed to registration.

SummaryRecent studies have investigated how defined peptides influence T cell development. Using a T cell receptor-transgenic [32-microglobulin--deficient model, we have examined T cell maturation in fetal thymic organ cultures in the presence of various peptides containing single-alanine substitutions of the strong peptide agonist, p33. Cocultivation with the peptide A4Y, which contains an altered T cell contact residue, resulted in efficient positive selection. Several in vitro assays demonstrated that A4Y was a moderate agonist relative to p33. Although A4Y promoted positive selection over a wide concentration range, high doses of this peptide could not induce clonal deletion. Thymocytes maturing in the presence of A4Y were no longer able to respond to A4Y, but could proliferate against p33. These studies demonstrate that (a) peptides that induce eflficient positive selection at high concentrations are not exclusively antagonists; (b) some agonists do not promote clonal deletion; (c) positive selection requires a unique T cell receptor-peptide-major histocompatibility complex interaction; and (d) interactions with selecting peptides during T cell ontogeny may define the functional reactivity of mature T cells. T CRs expressed on maturing thymocytes interact withpeptide-MHC complexes on thymic stromal cells and transmit signals that lead to either positive or negative T cell selection (1-3). Positive selection is an active process that rescues self-MHC-restricted thymocytes from programmed cell death. In contrast, negative selection tolerizes potentially autoreactive T cells, either through clonal deletion or unresponsiveness. Clonal deletion physically removes thymocytes by inducing apoptosis, as compared with unresponsiveness, which modifies developing T cells so that they can no longer respond against the tolerizing antigen. Since positive and negative selection shape the TCR repertoire and define the basis of self-/non-self-antigens, much research has focused on understanding T cell development. Studies have addressed how clonotypic TCRs expressed on CD4+CD8 + double-positive thymocytes can distinguish between these two selection events. Although it has been demonstrated that peptides are involved in positive and negative selection (4, 5), it remains controversial whether the selecting ligand has a qualitative or quantitative role in determining the fate of the developing T cell.Recently, altered peptide ligands have been identified that can inhibit some or all mature T cell effector functions (6-10). Antagonist peptides are defined as ligands that engage TCRs and actively inhibit biological responses. Partial agonists are closely related peptides that stimulate a subset ofT cell effector functions (11). This is in contrast with agonist peptides, which induce a complete range ofT cell responses. Studies by Hogquist et al. (12,13) and Jameson et al. (14) showed a correlation between peptide antagonists and positive selection. These results suggest that a positively selecting peptide is qualitatively diffe...