Mark Fung, M.D., Ph.D., Transfusion Medicine Fellow
Darrell J. Triulzi, M.D., Medical Director, The Institute for Transfusion Medicine

INTRODUCTION

Significant progress has been made in improving the safety of both cellular and acellular blood components, such that the current estimated risk of transmission of HIV, HCV, HTLV, and HBV ranges from 0.5 to 7 per million transfusions.  These advances include: better donor screening, viral nucleic acid testing (NAT) of donated blood, purification of plasma and plasma-derived products (affinity-purified coagulation factors, nanofiltration, solvent-detergent treatment), and recombinant factor concentrate production technology.

With these improvements in reducing viral transmission risk, the focus of blood product safety improvement has shifted to reducing the rate of bacterial contamination.  Currently, one in 500 to 2,000 platelet concentrates is bacterially contaminated.¹ In addition, the growing list of blood-borne pathogens is outpacing our ability to devise and implement new screening tests. 

With these issues in mind, the use of broadly active pathogen inactivation technologies is actively being studied.  Specifically, compounds are being developed that have a high affinity for nucleic acids and, upon entering the nucleic acid strand, permanently damage it, preventing further replication.  These compounds include psoralen-derivatives, riboflavin, ethylene imines, and methylene blue.  For psoralen-derivatives and riboflavin, some form of photo-activation (UV irradiation or visible light) is required.  Light-independent compounds that target nucleic acids have also been developed for red cell concentrates. These include S-303 and PEN110, proprietary compounds developed by Cerus Inc. and Vitex Inc., respectively.  Both of these products are in phase II/III clinical trials.

For a more detailed history and description of pathogen inactivation methods, the review article by Bopp et al.² is recommended.

CLOTTING FACTOR CONCENTRATES AND IMMUNOGLOBULINS

Recombinant factors VIII and IX are available for treatment of hemophilia A and B, but patients with von Willebrand factor deficiencies still require plasma-derived concentrates.  Intravenous immunoglobulins (IVIG), anti-Rh immunoglobulin (RhIg), and albumin are widely used blood-derived products that routinely undergo pathogen inactivation. 

Pasteurization is perhaps the oldest of the pathogen inactivation techniques. With pasteurization as the sole method of pathogen inactivation, no cases of transmission of HBV, HAV, HIV, HCV, or HGV (hepatitis G) have been documented.³ Another currently used method is solvent-detergent treatment, which is effective against lipid-encapsulated viruses (HBV, HCV, HIV), but not against HAV and parvovirus, which are not lipid encapsulated.  For these reasons, a multi-tier system of virus decontamination has been adopted which includes plasma fractionation steps, affinity chromatography, and nanofiltration.  No cases of viral transmission have been reported where two or more decontamination steps have been used. 

Recent concerns for transmissible spongiform encephalopathies (e.g. “Mad Cow disease”) have led to modifications in donor criteria, as well as, a re-examination of the efficacy of current pathogen inactivation methods.  Currently, there is no human evidence of transmission by exposure to blood-products, only a theoretical risk based on animal studies.^4,5,6 Some evidence suggests that plasma fractionation and nanofiltration, may reduce this risk.^7,8,9 Gamma irradiation studies with human albumin preparations have found only a modest reduction (1.5 log) in prion infectivity.¹⁰

FRESH FROZEN PLASMA

Solvent detergent treatment of FFP is used in Europe, but is no longer available in the US due to concerns over pooling during manufacture (2,500donors/batch)andthromboticcomplication.Currently, there are no approved pathogen inactivation systems for FFP. The only method available to further reduce the low risk of donor-associated disease transmission is quarantine of FFP units until the donor returns for a subsequent donation and standard viral screening tests are negative (donor re-tested plasma).  While this is theoretically possible due to the one-year shelf life of FFP, it is impractical because it would only be applicable to units from frequent donors.

The use of a psoralen-based compound (S-59) to photoinactivate bacteria and viruses in FFP is in clinical trials.  In vitro experiments with S-59 show elimination of bacteria, viruses, and parasites on the order of 5 logs. Studies in healthy volunteers show no change in vivo recovery of coagulation factors with S-59 treated FFP.¹¹ Similarly, patients with end-stage liver disease showed equivalent effectiveness of treated and untreated FFP.¹²  Other methods using nucleic acid-targeted pathogen inactivation are in pre-clinical trials, including riboflavin photoinactivation.^13,14

PLATELET AND RED CELL CONCENTRATES

There are currently no approved methods for pathogen inactivation of platelet or red cell concentrates in the US.  A European trial of S-59 treated whole blood-derived platelets showed comparable efficacy to control platelet concentrates in thrombocytopenic patients.¹⁵ Similar results were found in the corresponding American study using single donor platelets.¹⁶ In both studies, however, more treated platelet units were required to achieve the same clinical endpoint due to platelet loss during treatment.

Due to the photoabsorptive effects of hemoglobin in red cells, S-59 treatment and photoactivation with UV-A is not effective, though riboflavin treatment with visible light activation is apparently not impaired.¹⁷ Phase I and II studies with PEN110, and S-303, light-independent inactivating compounds with high affinity to nucleic acids, showed efficacy with no adverse effects.¹⁸ Phase III studies have recently begun.

SUMMARY

The nucleic acid-based pathogen inactivation methods that are currently in clinical trials are quite promising.  These new methods would provide a broad pathogen inactivation process and do not appear to affect the clinical efficacy of blood products.  The long history of minimal toxicities associated with psoralen-based compounds and riboflavin is also encouraging, but further investigation is needed before implementation as a standard process.

REFERENCES

1. Engelfriet et al., Vox Sang 78:59-67, 2000.

2. Bopp et al., Transfusion Med 11:149-175,2001.

3. Kreuz et al., Sem Thromb & Hemostas 28 (S1):57 62, 2002.

4. Brown et al., Transfusion 38:810-816, 1998.

5. Brown et al., Transfusion 39: 1169-78, 1999.

6. Houston et al., Lancet 356:999-1000, 2000.

7. Lee et al., J Virol Meth 84:77-89, 2000.

8. Lee et al., Transfusion 41:449-55, 2001.

9. Tateishi et al., Biologicals 29:17-25, 2001.

10. Miekka et al., Vox Sang 84:36-44, 2003.

11. Hambleton et al., Transfusion 42:1302-1307, 2002.

12. Mintz et al., Transfusion 42 (suppl): 15S, 2002

13. Goodrich, Vox Sang 78 (suppl 2): 211-215, 2000.

14. Goodrich et al., Transfusion 42 (suppl): 16S, 2002.

15. Van Rhenen et al., Blood 101:2426-33, 2003.

16. Slichter et al., Blood 100 (11); Abstr. 4048,2003.

17. Reddy et al., Transfusion 42 (suppl): 16S, 2002.

18. AuBuchon et al., Transfusion 42:146-152, 2002.

Copyright ©2003, Institute For Transfusion Medicine 

Editor: Donald L. Kelley, M.D., MBA: dkelley@itxm.org