Assessing compatibility of antimicrobial violet-blue light for pathogen reduction of red blood cell concentrates

Transfusion-related sepsis is the most frequent infectious complication of blood transfusion. With millions of units transfused per year, product safety is key to public health but currently relies upon donor deferral and product testing. Pathogen reduction technologies can also be used, with several systems CE marked or FDA approved for platelet and plasma use, but only one CE marked for whole blood. 405 nm violet-blue light has recently demonstrated potential for in situ bacterial reduction of ex vivo stored plasma and platelet products, along with preliminary antiviral potential in plasma. This study assesses the potential compatibility of 405 nm antimicrobial light with red blood cell (RBC) components.

Sheep RBC were analysed, showing light transmissibility and absorption characteristics over wavelengths of 220-1100 nm using neat–1000X dilutions. Irradiances of 10-100 mW/cm2 405 nm light were then applied to red cell samples with ∼1.3 & 7.8 mm depths over 10-60 minutes, giving doses of 9-360 J/cm2. Treatment effects on cell integrity were demonstrated by microscopy and photometric detection of leaked haemoglobin using the Harboe method.

RBC transmission analysis highlighted the high opacity of RBC suspension at 18% haematocrit with 1 cm depths, with peak absorption found to be at 417 nm. Results suggested the requirement of sample depths <1 cm to provide potential for penetration. Photometric analysis demonstrated RBC damage was influenced by the irradiance levels and exposure times used. Haemolysis increased by 0.37 & 1.26% over 15-60 minutes with 20 & 50 mW/cm2 irradiances respectively. A greater increase of 5.06% was observed by 100 mW/cm2 exposures over 15-30 minutes. Haemolysis rose sharply during 100 mW/cm2 exposures and was supported by a visual decrease in stained viable cells. Low treatment doses ≤90 J/cm2 with irradiances ≤50 mW/cm2, showed potential compatibility, producing haemolysis below the 0.8% European limit.

Future work will build on these findings and investigate the potential for antimicrobial efficacy of a 405 nm light treatment system at levels compatible with RBC physiology.