Viral Clearance
Individual plasma units which are obtained for the production of EVICEL® are evaluated by FDA-licensed serological tests for hepatitis B surface antigen (HBsAg), human immunodeficiency virus (HIV) 1 & 2 antibody and hepatitis C virus (HCV) antibody as well as with FDA-licensed nucleic acid testing (NAT) methods for HCV and HIV-1.
Some viruses such as hepatitis A virus (HAV) and parvovirus B19 are particularly difficult to remove or inactivate. Parvovirus B19 most seriously affects pregnant women or immune-compromised individuals. The plasma units are tested by NAT for HAV and hepatitis B virus (HBV). All tests for HIV, HCV, HBV and HAV must be negative (non-reactive). However, since the effectiveness of these test methods in detecting low levels of viral material is still under investigation, the significance of a negative result for these viruses is unknown. NAT for parvovirus B19 is also performed, and the level of contamination is not permitted to exceed 10,000 copies/ml. This limit is applied to restrict the viral load of parvovirus B19 in the starting plasma pool.
In addition to the screening of plasma, each manufacturing pool is tested for HBsAg, HIV-1 & 2 antibody, HCV by NAT and for parvovirus B19 by NAT. Manufacturing pool testing, however, has a lower sensitivity than that of individual unit testing.
The manufacturing procedure for EVICEL® includes processing steps which are designed to reduce the risk of viral transmission. Both BAC2 and Thrombin undergo two discrete virus inactivation/removal steps, summarized in Table 6:
Table 6: Steps for the Reduction of Viral Transmission Risk| Step | Component |
|---|
| BAC2 | Thrombin |
|---|
| 1 | Solvent/detergent treatment (1% TnBP, 1% Triton X-100) for 4 hours at 30°C | Solvent/detergent treatment (1% TnBP, 1% Triton X-100) for 6 hours at 26°C |
| 2 | Pasteurization (10 hours at 60°C) | Nanofiltration |
BAC2 is manufactured by treatment of cryoprecipitate with aluminum hydroxide gel to adsorb the Vitamin K dependent clotting factors and it is then incubated with a solvent detergent (SD) mixture (1% TnBP, 1% Triton X-100) for 4 hours at 30°C. The SD reagents are removed by castor oil extraction and reverse phase chromatography (C-18 column) and the preparation is subsequently treated by pasteurization.
Prior to pasteurization, sucrose and glycine are added as stabilizers. The solution is heated to 60±0.5°C and maintained at that temperature for 10 hours. After pasteurization, the stabilizers used for heat treatment are removed by diafiltration and the product is concentrated by ultrafiltration. An affinity chromatography step is then used to remove plasminogen from the product, after which it is concentrated. After concentration the solution is formulated, sterile filtered and aseptically filled and frozen.
Thrombin is manufactured by chromatographic purification of prothrombin from cryo-poor plasma followed by activation with calcium chloride. The manufacturing process includes two separate steps for inactivation or removal of viruses. The first of these is treatment with a SD mixture (1% TnBP, 1% Triton X-100) for 6 hours at 26°C to inactivate lipid enveloped viruses.
The SD reagents are removed by cation exchange chromatography. Mannitol and human albumin are used to stabilize the solution, which undergoes nanofiltration for removal of both enveloped and non-enveloped viruses. After nanofiltration, the solution is formulated with calcium chloride, sterile filtered and aseptically filled and frozen.
The efficiency of the virus inactivation/removal procedures in reducing the level of a range of viruses has been assessed using viruses with a range of physico-chemical characteristics. The results of virus removal/inactivation validation studies are summarized in Table 7:
Tables 7a,b: Results of Virus Removal/Inactivation in Validation Studies
Table 7a: BAC2| Virus | HIV-1 | BVDV | PRV | EMCV | HAV | CPV |
|---|
| Reduction factor (log10) |
| SD Treatment | >4.4 | >4.3 | >3.8 | Not Done | Not Done | 0 |
| Pasteurization | >4.4 | >5.4 | 6.0 | 3.7 | >5.8 | 1.3 |
| Global Reduction Factor | >8.8 | >9.7 | >9.8 | 3.7 | >5.8 | 1.3 |
Table 7b: Thrombin| Virus | HIV-1 | SBV | BVDV | PRV | EMCV | HAV | MVM |
|---|
HIV-1: Human immunodeficiency virus Type 1; SBV: Sindbis virus; BVDV: Bovine viral diarrhea virus; PRV: Pseudorabies virus; EMCV: Encephalomyocarditis virus; HAV: Hepatitis A virus; CPV: Canine parvovirus; MVM: Minute virus of mouse. |
| Reduction factor (log10) |
| SD Treatment | >5.8 | >5.0 | >4.6 | >4.2 | Not Done | Not Done | Not Done |
| Nanofiltration | >4.6 | Not Done | >5.6 | >5.7 | >7.4 | >7.5 | >6.3 |
| Global Reduction Factor | >10.4 | >5.0 | >10.2 | >9.9 | >7.4 | >7.5 | >6.3 |