Pathogen inactivation techniques

Abstract

The desire to rid the blood supply of pathogens of all types has led to the development of many technologies aimed at the same goal--eradication of the pathogen(s) without harming the blood cells or generating toxic chemical agents. This is a very ambitious goal, and one that has yet to be achieved. One approach is to shun the 'one size fits all' concept and to target pathogen-reduction agents at the Individual component types. This permits the development of technologies that might be compatible with, for example, plasma products but that would be cytocidal and thus incompatible with platelet concentrates or red blood cell units. The technologies to be discussed include solvent detergent and methylene blue treatments--designed to inactivate plasma components and derivatives; psoralens (S-59--amotosalen) designed to pathogen-reduce units of platelets; and two products aimed at red blood cells, S-303 (a Frale--frangible anchor-linker effector compound) and Inactine (a binary ethyleneimine). A final pathogen-reduction material that might actually allow one material to inactivate all three blood components--riboflavin (vitamin B2)--is also under development. The sites of action of the amotosalen (S-59), the S-303 Frale, Inactine, and riboflavin are all localized in the nucleic acid part of the pathogen. Solvent detergent materials act by dissolving the plasma envelope, thus compromising the integrity of the pathogen membrane and rendering it non-infectious. By disrupting the pathogen's ability to replicate or survive, its infectivity is removed. The degree to which bacteria and viruses are affected by a particular pathogen-reducing technology relates to its Gram-positive or Gram-negative status, to the sporulation characteristics for bacteria, and the presence of lipid or protein envelopes for viruses. Concerns related to photoproducts and other breakdown products of these technologies remain, and the toxicology of pathogen-reduction treatments is a major ongoing area of investigation. Clearly, regulatory agencies have a major role to play in the evaluation of these new technologies. This chapter will cover the several types of pathogen-reduction systems, mechanisms of action, the inactivation efficacy for specific types of pathogens, toxicology of the various systems and the published research and clinical trial data supporting their potential usefulness. Due to the nature of the field, pathogen reduction is a work in progress and this review should be considered as a snapshot in time rather than a clear picture of what the future will bring.

Figure 1

Molecular structure of tri-(n-butyl)-phosphate (TNBP). From Delipidation treatments for large scale protein purification process (from ref. 22).

Figure 2

Partial molecular structure of Triton X-100 (from ref. 22).

Figure 3

Molecular structure methylene blue (MB) (from refs 53, 56, 66).

Figure 4

Generic molecular structure of the leukobase form of phenothiazinium dyes (from ref. 56).

Figure 5

Mechanism of action of pathogen inactivation (PI). Amotosalen (S-59) is a synthetic psoralen that inhibits nucleic acid replication through UVA-light-mediated covalent addition to nucleic acids. Left: the molecule penetrates cells, viruses, bacteria, or other pathogens and seeks out DNA or RNA. 2nd left: amotosalen intercalates between the base pairs. 2nd right: once illuminated by UVA light, amotosalen forms monoadducts between pyrimidine bases. Right: another photon of light enables the molecule to form cross-links (diadducts) between DNA or RNA strands (from ref. 73).

Figure 6

The INTERCEPT Blood System for plasma. Collected plasma is mixed with amotosalen and the mixture is placed in an ultraviolet A (UVA) illumination device. The contents are then passed through a Compound Adsorption Device (CAD) for reduction of amotosalen and free photoproducts. After CAD treatment, the plasma is placed in a final storage container until transfusion (from ref. 72).

Figure 7

PEN110 kinetics of viral reduction of four enveloped viruses in CPD/AS-1, CP2D/AS-3 or CPD/AS-5 red blood cell concentrate (RBCC) units at 22±2 °C for up to 22±2 h. ♦, CPD/AS-1; ▪, CP2D/AS-3; ▴, CPD/AS-5; ●, limit of detection. (a) Inactivation kinetics of sindbis (SIN) virus; (b) inactivation kinetics of vesicular stomatitis Indiana virus (VSIV); (c) inactivation kinetics of bovine viral diarrhoea virus (BVDV); (d) inactivation kinetics of pseudorabies virus (PRV) (from ref. 107).

Figure 8

PEN110 kinetics of viral reduction of six non-enveloped viruses in CPD/AS-1, CP2D/AS-3, or CPD/AS-5 red blood cell concentrate (RBCC) units at 22±2 °C for up to 22±2 hours. ♦, CPD/AS-1; ▪, CP2D/AS-3; ▴, CPD/AS-5; ●, limit of detection. (a) Inactivation kinetics of porcine parvovirus (PPV); (b) inactivation kinetics of reovirus 3 (Reo-3); (c) inactivation kinetics of human adenovirus 2 (Adeno-2); (d) inactivation kinetics of vesicular exanthema of swine virus (VESV); (e) inactivation kinetics of foot and mouth disease virus (FMDV); (f) inactivation kinetics of bluetongue virus (BTV) (from ref. 107).