Circulating transferrin receptor has been detected in human serum with a sensitive immunoassay. The mean concentrations of the serum transferrin receptor in healthy males and females were 251 +/- 94 (mean +/- SD) ng/ml and 256 +/- 99 ng/ml, respectively. The serum receptor concentration in patients with haematological malignancies, including acute leukaemia, multiple myeloma and malignant lymphoma, varied widely, from normal to 1100 ng/ml. A single band with an approximate molecular weight between 80,000 and 100,000 daltons was obtained by polyacrylamide gel electrophoresis-immunoblotting analysis of serum.

Serum transferrin receptors were measured by a sandwich radioimmunoassay procedure in patients with iron deficiency anemia, autoimmune hemolytic anemia and aplastic anemia. The mean circulating transferrin receptor concentration of normal subjects and patients with iron deficiency anemia, autoimmune hemolytic anemia and aplastic anemia are 253 +/- 82 ng/mL, 730 +/- 391 ng/mL, 1,426 +/- 1,079 ng/mL, and 182 +/- 39 ng/mL, respectively. The values for those with iron deficiency anemia and autoimmune hemolytic anemia were significantly higher than that of normal controls and the values for those with aplastic anemia were lower than that of normal controls. After iron supplementation in iron deficiency anemia, the serum transferrin receptor values increased twofold over those of pretreatment values. This increase parallels an increase in peripheral reticulocytes. Therefore, the number of circulating transferrin receptors in anemic patients may reflect the level of bone marrow erythropoiesis and is a potentially useful new index for red cell production.

A phase I clinical and pharmacokinetic study of recombinant human tumor necrosis factor (rH-TNF) was conducted in a single dose schedule in 33 patients with advanced cancer. rH-TNF was given by i.v. infusion over 30 min with a starting dose of 1 x 10(5) units/m2. The dose was escalated up to 16 x 10(5) units/m2 according to the modified Fibonacci scheme. Toxic effects were similar but not identical to those reported with interferons and interleukin-2, and included fever, rigors, nausea and vomiting and anorexia in a non-dose-dependent manner, and hypotension, leukocytosis, thrombocytopenia and transient elevation of transaminases (SGOT and SGPT) in an approximately dose-dependent manner. DIC syndrome was observed in one patient who had received 16 x 10(5) units/m2. The dose-limiting toxicities were hypotension, thrombocytopenia and hepatotoxicity, and the maximum tolerated dose in a single i.v. infusion of rH-TNF appeared to be 12 x 10(5) units/m2 when thrombocytopenia and elevation of SGOT and SGPT were taken as the dose-limiting toxicities. However, if hypotension was included, the maximum safely tolerated dose appeared to be 5 x 10(5) units/m2.

A mild and efficient procedure for conjugating rabbit Fab' and horseradish peroxidase using a maleimide compound was developed. The enzyme was treated with N-hydroxysuccinimide ester of N-(4-carboxycyclohexylmethyl) maleimide to introduce maleimide groups. Then, the maleimide-enzyme was allowed to react with thiol groups of Fab', and the conjugate formed was separated from unreacted components by gel filtration with Ultrogel AcA 44. In the peak fraction of the separated conjugate, 98% of peroxidase was associated with Fab' and 90% of antibodies was associated with peroxidase. The recoveries in the conjugate of peroxidase and Fab' incubated for conjugation were 65-74%. The conjugate formed appeared to be largely monomeric. Both the enzyme activity and antigen-binding activity of Fab' were fairly well preserved in the conjugate. The cross-link formed was stable at 4 degrees C at least 6 months. Use of the conjugates obtained by this method gave greater sensitivity in sandwich enzyme immunoassay for human ferritin and human thyroid-stimulating hormone than conjugates prepared by the periodate method. The conjugation using N-hydroxysuccinimide ester of m-maleimidobenzoic acid provided a similar monomeric preparation but was less efficient.

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