Page 191 - Haematologica Vol. 110 - January 2025

LETTER TO THE EDITOR
Safety and efficacy of human apotransferrin infusion in patients with β-thalassemia intermedia: the AIM study
β-thalassemia intermedia comprises a diverse group of pa- tients with various mutations.1,2 These patients mostly suffer from transfusion or non-transfusion-dependent anemia and iron overload, an important factor in morbidity related to complications of β-thalassemia.1 Circulatory iron-levels in thalassemia intermedia exceed transferrin iron binding capacity resulting in elevated levels of free circulating non-transferrin bound iron (NTBI), responsible for oxidative stress.3,4 In a mouse model of β-thalassemia intermedia, homozygous for a deletion of the gene encoding β–ma- jor globin (Hbbth1/th1), induction of supranormal transferrin levels by repeated human apotransferrin administration normalized NTBI levels, and reduced hemolysis, increased hemoglobin (Hb) levels and reduction of splenomegaly.5 These results were also demonstrated in another mouse model (Hbbth3/+) with heterozygous β1/β2 globin gene dele- tion.6 However, apotransferrin administration has not been studied in patients with β-thalassemia intermedia. The aim of our study was to investigate the safety and efficacy of repeated human apotransferrin administration on mark- ers of erythropoiesis, iron metabolism and spleen size in patients with non-transfusion-dependent β-thalassemia intermedia (NTDTI) and transfusion-dependent β-thalas- semia intermedia (TDTI). In the current study, an effect of repeated human apotransferrin infusions on markers of erythropoiesis or iron metabolism was not observed, except for a temporary decrease in NTBI levels.
The AIM-study is a phase II, single-centre, open-label, feasibility trial conducted in a teaching hospital in Amster- dam, the Netherlands. Patients aged ≥18 years with NTDTI and TDTI were included. NTDTI is defined as ≤5 red blood cell (RBC) units during the 24-week period and no RBC transfusions within weeks prior to the start of the study. TDTI is defined as 6 to 20 RBC units transfused during a 24-week period and a transfusion-free period of ≤6-week before start of the study. Other inclusion criteria were: nor- mal renal function, normal hepatic function, World Health Organization performance score <3, and written informed consent. Exclusion criteria were: a history of allergic re- action on human plasma (products), a concurrent severe or uncontrolled medical condition, cardiac dysfunction (myocardial infarction <6 months of study entry, unstable angina or arrhythmias), pregnant or lactating females or known IgA deficiency. Human apotransferrin (Prothya Bioso- lutions B.V., Amsterdam, the Netherlands) was initially given at an intravenous dose of 170 mg/kg every 2 weeks after a loading dose of 170 mg/kg at day -1, based on simulation of the single-dose PK profile of transferrin in adults who received hematopoietic stem cell transplantation.7 Due to
insufficient increases (<2 g/L) in plasma transferrin concen- tration in the first three patients, the dose was increased to 340 mg/kg every 2 weeks without a loading dose, based on simulation data of the first three patients. Treatment duration was 14 weeks in NTDTI patients and 18 weeks in TDTI patients. Apotransferrin was administered in TDTI patients directly pre-transfusion during transfusion days. The primary outcomes were defined as change from baseline of Hb level in NTDTI and change from baseline of number of RBC units transfused per week in TDTI patients. Secondary outcomes were defined as: number of patients with an increase of >1.5 g/dL in Hb levels for both NTDTI and TDTI patients (before transfusion) as compared to baseline, as well as a reduction in transfusion dependency (number of RBC units/week) by at least 50% compared to baseline for TDTI patients. Baseline transfusion dependency was defined as the number of RBC units transfused in the 20 weeks prior to inclusion. Reduction in iron overload was reflected by changes in levels of serum iron, transferrin, transferrin saturation, ferritin, NTBI levels, hepcidin-25, and soluble transferrin receptor (sTfR). The effect on erythropoiesis was determined by measuring pre-dose Hb levels, reticulocyte count, red cell indices (in the TDTI group only prior to RBC transfusion), pre-transfusion Hb levels (in the TDTI patients only) and spleen size. Serum hepcidin was measured us- ing the enzyme immunoabsorbant assay kit (Hepcidin 25 (bioactive), EIA-5782, DRG Diagnostics, Marburg, Germany). NTBI was measured using a nitrolotriacetic chelation ul- trafiltration detection approach. Iron was measured using a colorimetric assay and transferrin by immunochemical turbidimetry. Iron was released from transferrin by acid- ifying the serum, reduced from Fe3+ to Fe2+, complexed with a chromogen. For calculation of transferrin saturation (%) from the measured transferrin (g/L) and iron (umol/L) levels a conversion factor of 25.2 was used. Levels of sTfR (Ramco Laboratories, TX, USA) and ferritin (Cobas, Roche diagnostics B.V., Almere, the Netherlands) were measured using immunochemical assays. Blood samples were ana- lysed after collection or stored at -80°C. Spleen size was measured by ultrasound in patients receiving 170 mg/kg dose and by magnetic resonance imaging (MRI) in patients receiving the 340 mg/kg dose. Pharmacokinetic parameters were evaluated during steady state after blood sampling in week 4 or 6. Samples were taken before infusion of apotransferrin, and 5 minutes, 2 hours, 1 day, 7 days and 14 days thereafter to determine the elimination half-life (T1/2 term), pre-dose serum transferrin concentration, the average steady state concentration, the maximal observed concentration (Cmax), time to reach the maximal observed
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