Hemoglobin Utilization in Asplenic and Non-Splenectomized Transfusion Dependent Thalassemia Patients Supported with Pathogen Reduced Red Blood Cell Concentrates in a Phase 3 Study (SPARC)

Introduction: Transfusion dependent thalassemia (TDT) requires regular transfusion of red cell concentrates (RBCC) to prevent the complications of anemia and excessive erythroid expansion. Despite donor testing, long-term transfusion has a substantial cumulative risk of transfusion-transmitted infection (TTI) due to undetected viruses, bacteria, and protozoa. Splenectomized (-S) TDT patients may have greater TTI morbidity than patients with spleens (+S); but may benefit from reduced use of red blood cell concentrates (RBCC) and reduced transfusion iron (Fe) loading. Pathogen reduction (PR) of RBCC with amustaline-glutathione (A-GSH) offers potential to reduce the risk of TTI.

Objectives: To determine, the impact of PR-RBCC on hemoglobin (Hb) use, transfused Fe burden, incidence of RBC antibodies, and safety in -S and +S TDT patients.

Methods: TDT patients at 3 sites, not stratified by spleen status, were prospectively enrolled in a two- period cross-over study randomized by sequence for RBCC preparation. Leukocyte reduced PR-RBCC (Test) were treated with 0.2mM amustaline and 20 mM GSH, re-suspended in saline-adenine-glucose mannitol (SAGM), and stored up to 35 days at 4°C. Leukocyte reduced conventional RBCC (Control) were suspended in SAGM and stored for up to 35 days at 4°C. Patients received 6 transfusions in each treatment sequence of Test or Control RBCC over ~ 5 months. Clinicians, blinded to RBCC Hb content and treatment sequence, ordered RBCC to maintain targeted pre-transfusion Hb thresholds of ~ 9-10 g/dL. Transfusion intervals or number of RBCC transfused were adjusted for clinical management. The primary efficacy outcome was assessed by non-inferiority (NI) analysis for Hb use (expressed as g/kg body weight/ day) using a pre-specified NI margin (≤ 15% of the observed Control mean).

Results: Overall, mean (SD) Hb content (g) of 1024 Test RBCC = 54.6±5.9 (range: 39-73) and of 1008 Control RBCC = 55.6 ± 5.9 (range: 35-74) and varied widely. By intent-to-treat (ITT), 80 patients (40 +S and 40 -S) were transfused. For ITT patients (Table), the baseline Hb level (BL-Hb, g/dL) at first transfusion of Control periods was significantly lower than at Test periods; but the mean number of RBCC transfused, RBCC storage days, total Hb dose (g), and transfusion intervals were not significantly different for Test and Control. ITT analysis for all transfusion episodes showed Hb use for Test RBCC (0.110 g/kg/d) was not different from Control RBCC (0.112 g/kg/day). Non-inferiority was demonstrated (T-C = - 0.002 g/kg/d: 95% CI: -0.005, 0.001). ITT Test patients received a slightly lower mean total Hb dose (- 14g), and mean pre-transfusion Hb levels declined after 6 transfusions (9.4 to 8.8 g/dL).

-S patients had lower BL-Hb levels (g/dL) than S+ patients in Test (9.2 vs 9.7) and Control (8.8 vs 9.2) periods (Table). -S patients received a lower mean total Hb dose of Test than Control RBCC (p=0.019); and had a decline in mean pre-transfusion Hb levels during Test periods (from 9.2 to 8.7 g/dL). Transfusion intervals were significantly longer for -S patients than +S patients with both Test and Control RBCC (p< 0.001 by 2-sample t test, respectively); and -S patients had lower Hb use than +S patients. However, Hb use of Test and Control RBCC was comparable within -S and + S cohorts (Table). Transfused Fe was less for -S patients for Test and Control RBCC. During 6 Test and 3 Control treatment periods, 8 patients (6 -S, 2 +S) had worsening anemia with pre-transfusion Hb levels (6.0-7.8 g/dL) substantially below the targeted transfusion threshold, but without evidence of hemolysis. Each of these patients received one or more Hb doses below the average RBCC transfusion episode dose (Test: 114.5 g) or (Control: 116.7 g); and 3 patients had concurrent infections. None of 80 patients had evidence of increased RBC clearance, developed antibodies to PR-RBCC, or had treatment emergent RBC alloantibodies in either treatment period. There were no differences in the overall safety profiles for Test and Control RBCC.

Conclusions: Amustaline-GSH PR treatment of RBCCs offers the potential to reduce TTI risk without impacting Hb use or Fe burden in TDT. However, Hb content of Test and Control RBCC varies widely and may contribute to unexpected changes in pre-transfusion Hb levels. Spleen status affected Hb use comparably for PR-RBCC and Control RBCC, and remains an important factor in assessing transfusion requirements and Fe loading.

Table.

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