The linker molecule LAT is a substrate of the tyrosine kinases activated following TCR engagement. Phosphorylated LAT binds many critical signaling molecules. The central role of this molecule in TCR-mediated signaling has been demonstrated by experiments in a LAT-deficient cell line. To probe the role of LAT in T cell development, the LAT gene was disrupted by targeting. LAT-deficient mice appeared healthy. Flow cytometric analysis revealed normal B cell populations but the absence of any mature peripheral T cells. Intrathymic development was blocked within the CD4- CD8- stage. No gross abnormality of NK or platelet function was observed. LAT is thus critical to both T cell activation and development.

An animal model of gram-positive septicemia was developed to evaluate the effects of antithrombin (AT) concentrates on morbidity, mortality, and laboratory consequences of disseminated intravascular coagulation (DIC). DIC was induced in guinea pigs by infusing Staphylococcus aureus (SA) isolated from blood cultures of patients with DIC (DIC-SA) or without DIC (non–DIC-SA). The non–DIC-SA animals and animals infused with sterile saline served as controls. Varying doses of AT were administered either 30 minutes or 24 hours after infusion of SA. DIC was confirmed within 4 hours by changes in prothrombin time, activated partial thromboplastin time, fibrinogen, fibrinogen-fibrin degradation products, and AT activity. Clinical bleeding was also evident. Mortality of untreated DIC-SA animals was 36% within 24 hours and up to 75% by 72 hours. Intervention with any dose of AT between 125 and 1,000 IU/kg 30 minutes after DIC-SA infusion was associated with 100% survival (P ≤ .05 in the 250 IU/kg group) and sustained increases in AT activity and fibrinogen concentrations (P ≤ .05). When AT was administered in combination with low molecular weight heparin (LMWH) or if LMWH was adminstered alone, mortality from DIC-SA was slightly, but not significantly reduced compared with untreated DIC-SA. Gross hemorrhage was observed premortem and at autopsy in all of the DIC-SA animals but in substantially fewer animals that received AT (P ≤ .001 in the 250, 500, and 1,000 IU/kg groups). In contrast, groups treated with LMWH, alone or with AT, experienced hemorrhage and appeared to develop pathologic DIC. Fibrin formation in end-organs was detected in all guinea pigs in the untreated DIC-SA group and in the groups treated with 125 IU/kg AT and LMWH alone. AT doses between 250 and 1,000 IU/kg administered 30 minutes after DIC-SA infusion prevented fibrin formation in end-organs (P ≤ .001 in the 250 and 1,000 IU/kg groups). AT administered 24 hours after DIC-SA could not reverse pre-existing histopathologic evidence of DIC but favorably affected survival, which reached statistical significance in the 1,000 IU/kg AT group (P ≤ .025). In summary, suprapharmacologic doses of AT concentrate significantly decreased morbidity and mortality and ameliorated adverse changes in laboratory measures induced by DIC-SA in this guinea pig model and were not associated with untoward hemorrhagic complications. These findings provide justification for studying the use of AT therapy in patients with DIC-SA.

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This is the first human clinical study with TAC-101, a RAR-alpha selective retinoid. Musculoskeletal toxicity and hypertriglyceridemia were observed characteristics of previously studied retinoids. The recommended phase II dose is 24 mg/m(2) with this treatment schedule. Alternative treatment schedules and prospective evaluation of thrombotic risk will be investigated in subsequent studies.