Rapid Sterilization of Clinical Apheresis Blood Products using Ultra-High Dose Rate Radiation

Abstract

Background and objectives: Apheresis platelets products and plasma are essential for medical interventions, but both still have inherent risks associated with contamination and viral transmission. Platelet products are vulnerable to bacterial contamination due to storage conditions, while plasma requires extensive screening to minimize virus transmission risks. Here we investigate rapid irradiation to sterilizing doses for bacteria and viruses as an innovative pathogen reduction technology.

Materials and methods: We configured a clinical linear accelerator to deliver ultra-high dose rate (6 kGy/min) irradiation to platelet and plasma blood components. Platelet aliquots spiked with 10⁵ CFU of E.coli were irradiated with 0.1-20 kGy, followed by E.coli growth and platelet count assays. COVID Convalescent Plasma (CCP) aliquots were irradiated at a virus-sterilizing dose of 25 kGy and subsequently, RBD-specific antibody binding was assessed.

Results: 1 kGy irradiation of bacteria-spiked platelets reduced E.coli growth by 2.7-log without significant change of platelet count, and 5 kGy or higher produced complete growth suppression. The estimated sterilization (6-log bacterial reduction) dose was 2.3 kGy, corresponding to 31% platelet count reduction. A 25 kGy virus sterilizing dose to CCP produced a 9.2% average drop of RBD-specific IgG binding.

Conclusion: This study shows proof-of-concept of a novel rapid blood sterilization technique using a clinical linear accelerator. Promising platelet counts and CCP antibody binding were maintained at bacteria and virus sterilizing doses, respectively. This represents a potential point-of-care blood product sterilization solution. If additional studies corroborate these findings, this may be a practical method for ensuring blood products safety.

Keywords: Bacteria Spiked Platelets; Blood Products; COVID-19 Convalescent Plasma (CCP); Radiation Based Sterilization; Ultra-High Dose Rate (UHDR).

FIGURE 1

(A-C) Temperature controlled 14-slot blood sample holder for FLASH irradiation and (D-F) beam geometry. (A) CAD design illustrates a 14-slot holder for 2mL cryovial, that allows samples to be immersed in liquid (B), which can be used to control temperature. (C) Demonstrates samples at ~4 °C. (D) Schematic diagram illustrates the geometry of the irradiation, with samples being at 44.1 cm source to surface distance (SSD; surface of the holder from scattering foil). The beam is monitored using an ion chamber (Farmer chamber) that measures the Bremsstrahlung tail of the electron beam. (E) The profiles of the beam were derived using film irradiated with 1 cm build up at 44.8 cm from the source (central depth of the tube) and are relatively flat and comparable in both x and y directions. (F) Dose map of the same films demonstrate relative homogeneity across the 10 × 10 cm² area or interest.

FIGURE 2

(A,B) Dose-response of E.coli bacterial survival and (C-D) platelet count from irradiated apheresis platelet products acquired from five healthy volunteer donors (one aliquot per dose per donor) spiked with approximately 10⁵ CFU of E.coli. (A) Bacterial survival in spiked platelet products post-irradiation per individual donor, and (B) averaged over all donors (dotted line is exponential decay fit). At 1 kGy dose only one sample (1 donor) showed 2-log bacterial reduction with no growth in the rest, while at 5, 10 and 20 kGy there was no bacterial growth in any sample. The extrapolated sterilizing 6-log killing dose is 2.3 ± 0.1 kGy. (C) Platelet counts in the same spiked platelet products post-irradiation per individual donor, and (D) averaged over all donors (dotted curve is one phase decay [exponential decay with plateau] fit). At 1 kGy dose, platelet count reduced minimally to 95% ± 5%. At estimated 6-log killing dose of 2.3 kGy the platelet count is estimated to be 69% ± 1%. Paired t-tests; *P < 0.01; **P < 0.005; ***P < 0.001; all comparisons are against non-irradiated control.

FIGURE 3

Effects of virus sterilizing dose of irradiation on SARS-CoV-2 RBD-specific antibodies in COVID Convalescent Plasma (CCP). 10 CCP donor samples were aliquoted for non-irradiated control and high-dose (25 kGy) irradiation. After irradiation, level of isotype-specific antibody binding was measured by ELISA, with OD405 readout. Each sample aliquot was done in replicate. Values represent average of duplicates ± SD for IgG, IgM, and IgA RBD-binding.