Development and validation of a monocyte activation test for the control/safety testing of an OMV-based meningococcal B vaccine.

It is imperative to ensure biological products are free of contaminating pyrogenic material prior to administration to patients. Historically the rabbit pyrogen test (RPT) was used to screen for such contamination in medicines for intravenous delivery. This test was adapted for use to screen vaccines. However, some, including meningococcal vaccines containing outer membrane vesicles, are intrinsically pyrogenic. Indeed, this is the case for Bexsero which contains relatively high levels of endotoxin and other potential pyrogens such as lipoproteins and porins. The RPT proved a difficult method for measuring the pyrogenic content of Bexsero and differences between laboratories in different countries made repeat testing at the control laboratories problematic resulting in batches being wrongly identified as unsafe. At NIBSC a monocyte activation test (MAT) was adapted and validated as an alternative. This required setting of a specification in-house and deciding on a decisional procedure using multiple donors, allowing batches equally pyrogenic or less, than those batches shown to be safe in a clinical trial, to be certified as safe. The resulting format was a reference comparison method with an upper limit of 1.8 relative pyrogen units (RPU). The batch passed if an initial four donors had a response equal to or less than 1.8 RPU, if one donor is above this limit the batch was tested in a further four donors and seven of the eight must be equal to or below 1.8 RPU. If two donors have a response greater than 1.8 the batch failed.

Evaluation of the monocyte activation test for the safety testing of meningococcal B vaccine Bexsero: A collaborative study.

The aim of this collaborative study was to evaluate the robustness of the monocyte activation test (MAT) for quantifying the pyrogenic content in the outer membrane vesicle (OMV)-containing vaccine Bexsero: the first meningococcal B vaccine to be licenced. We analysed datasets from 9 laboratories covering 15 test systems for 3 batches of Bexsero with higher, equivalent and lower activity relative to a reference lot in the MAT. Activity was measured in terms of relative pyrogen units (RPU) based on European Pharmacopoeia (Ph. Eur.) MAT Chapter 2.6.30 Method C: Reference Lot Comparison Test. We report that all 15 test systems were consistent in that they showed sample A to be the most active in the MAT; that 13 of 15 test systems had an accuracy of more than 80% and an overall geometric mean RPU of 1.03 with lower and upper 95% confidence limits of 0.97 and 1.09 respectively for a sample with an expected value of 1.00 RPU. We also report larger variability in the results for test systems involving cells from individual blood donations for sample A suggesting that there could be donor to donor differences in sensitivity to the vaccine constituents responsible for the higher activity of this batch. Overall, the consistency and accuracy of the MAT was remarkable given the range of test systems used by participants, all of which are permitted by the Ph. Eur. General MAT Chapter. This is important given the limitations of the rabbit pyrogen test for the control of pyrogenicity in general and particularly with products with intrinsic pyrogenicity such as Bexsero.

Quantification of cells with specific phenotypes I: determination of CD4+ cell count per microliter in reconstituted lyophilized human PBMC prelabeled with anti-CD4 FITC antibody.

A surface-labeled lyophilized lymphocyte (sLL) preparation has been developed using human peripheral blood mononuclear cells prelabeled with a fluorescein isothiocyanate conjugated anti-CD4 monoclonal antibody. The sLL preparation is intended to be used as a reference material for CD4+ cell counting including the development of higher order reference measurement procedures and has been evaluated in the pilot study CCQM-P102. This study was conducted across 16 laboratories from eight countries to assess the ability of participants to quantify the CD4+ cell count of this reference material and to document cross-laboratory variability plus associated measurement uncertainties. Twelve different flow cytometer platforms were evaluated using a standard protocol that included calibration beads used to obtain quantitative measurements of CD4+ T cell counts. There was good overall cross-platform and counting method agreement with a grand mean of the laboratory calculated means of (301.7 ± 4.9) µL(-1) CD4+ cells. Excluding outliers, greater than 90% of participant data agreed within ±15%. A major contribution to variation of sLL CD4+ cell counts was tube to tube variation of the calibration beads, amounting to an uncertainty of 3.6%. Variation due to preparative steps equated to an uncertainty of 2.6%. There was no reduction in variability when data files were centrally reanalyzed. Remaining variation was attributed to instrument specific differences. CD4+ cell counts obtained in CCQM-P102 are in excellent agreement and show the robustness of both the measurements and the data analysis and hence the suitability of sLL as a reference material for interlaboratory comparisons and external quality assessment.

The effect of storing whole blood at 22 degrees C for up to 24 hours with and without rapid cooling on the quality of red cell concentrates and fresh-frozen plasma.

BACKGROUND: Storage of whole blood (WB) for less than 24 hours at ambient temperature is permitted in Europe, but data directly comparing storage with and without active cooling are lacking, which was investigated and compared to current standard methods. STUDY DESIGN AND METHODS: WB was stored in one of four different ways for 24 hours after donation before processing on Day 1 to red cell concentrates (RCCs) in saline-adenine-glucose-mannitol and fresh-frozen plasma (FFP; n = 20 each): 1) at 22 degrees C in plastic trays, 2) in cooling devices (Compocool II, NPBI), 3) at 4 degrees C, or 4) processed from WB without storage less than 8 hours from donation (Day 0). RESULTS: 2,3-Diphosphoglycerate (2,3-DPG) in RCCs were lower after ambient storage compared with those processed on Day 0 or after 4 degrees C storage. Rapid cooling slowed the loss of 2,3-DPG but levels were undetectable by Day 21 with any method. On Day 42 of RCC storage, there was no significant difference between storage methods in levels of adenosine triphosphate or hemolysis. Potassium levels were lower in RCCs from WB stored at ambient compared with those produced on Day 0, regardless of the use of cooling plates. FFP produced from WB on Day 0 or after storage at ambient with or without active cooling met UK specifications (>75% of units >0.70 IU/mL Factor VIII). CONCLUSION: These data suggest that RCCs and FFP produced from WB that has been stored at ambient temperature with or without active cooling are of acceptable quality compared with those produced using current standard methods in the United Kingdom.

Persistence of HTLV-I in blood components after leukocyte depletion.

The human T-cell leukemia virus HTLV-I is a transfusion-transmissible retrovirus targeting T lymphocytes for which screening is not currently undertaken in United Kingdom blood donors. The introduction of universal leukocyte depletion (LD) of the United Kingdom blood supply raises the question as to the degree of protection afforded by this procedure against HTLV-I transmission by blood components. HTLV-I viral DNA removal by leukocyte-depleting filters was assessed in units of whole blood and platelets by real-time quantitative polymerase chain reaction (PCR) and by nested PCR for HTLV-I Tax DNA. We examined HTLV-I removal by LD filters using a model system of blood units containing exogenous spiked HTLV-I-positive MT-2 cells at a relevant concentration and whole blood donations from asymptomatic HTLV-I carriers. T-lymphocyte removal was assessed in parallel by measurement of endogenous subset-specific CD3 mRNA. In the MT-2 model system we observed 3.5 log(10) to 4 log(10) removal of HTLV-I Tax DNA by filtration of whole blood and 2 log(10) to 3 log(10) removal across platelet filters with 13 of 16 whole blood and 8 of 8 platelet units still positive after filtration. Despite 3 log(10) to 4 log(10) viral removal, HTLV-I Tax DNA could be detected after whole blood filtration in asymptomatic carriers with viral loads above 10(8) proviral DNA copies/L. T-lymphocyte removal was also between 3.5 log(10) and 4.5 log(10). HTLV-I provirus removal was incomplete in the model system and in asymptomatic carriers with viral loads greater than 10(8) copies/L. These results suggest that LD alone may not provide complete protection from HTLV-I transmission by transfusion.