Transitioning from development to commercial: risk-based guidance for critical materials management in cell therapies

A key hurdle to ensuring patient access to cell and gene therapies (CGTs) and continued growth of the industry is the management of raw materials. The combination of rapid growth, individual product and process complexity and limited industry-specific guidance or awareness presents non-obvious risk mitigation challenges for transitioning from development to clinical application. Understanding, assessing and mitigating the varied raw material risks for CGT products during product and clinical development are critical for ensuring smooth transitions into commercialization and for preventing interruption of product supply to patients. This article presents a risk-based approach driven by concerns for patient safety that can help focus and coordinate efforts to address the most critical risk factors. Highlighted are some of the highest risk materials common to the manufacture of many CGTs, including the primary starting material, culture media, reagents and single-use components. Using a hypothetical gene-edited cell therapy as an example, we describe the general manufacturing process and subsequently incorporate the described methodology to perform a sample risk assessment. The practical approach described herein is intended to assist CGT manufacturers and suppliers in actively assessing materials early in development to provide a basic starting point for mitigating risks experienced when translating CGT products for clinical and long-term commercial application.

Concise Review: Process Development Considerations for Cell Therapy

The development of robust and well-characterized methods of production of cell therapies has become increasingly important as therapies advance through clinical trials toward approval. A successful cell therapy will be a consistent, safe, and effective cell product, regardless of the cell type or application. Process development strategies can be developed to gain efficiency while maintaining or improving safety and quality profiles. This review presents an introduction to the process development challenges of cell therapies and describes some of the tools available to address production issues. This article will provide a summary of what should be considered to efficiently advance a cellular therapy from the research stage through clinical trials and finally toward commercialization. The identification of the basic questions that affect process development is summarized in the target product profile, and considerations for process optimization are discussed. The goal is to identify potential manufacturing concerns early in the process so they may be addressed effectively and thus increase the probability that a therapy will be successful.

SIGNIFICANCE

The present study contributes to the field of cell therapy by providing a resource for those transitioning a potential therapy from the research stage to clinical and commercial applications. It provides the necessary steps that, when followed, can result in successful therapies from both a clinical and commercial perspective.

Concise review: guidance in developing commercializable autologous/patient-specific cell therapy manufacturing

Cell therapy is poised to play an enormous role in regenerative medicine. However, little guidance is being made available to academic and industrial entities in the start-up phase. In this technical review, members of the International Society for Cell Therapy provide guidance in developing commercializable autologous and patient-specific manufacturing strategies from the perspective of process development. Special emphasis is placed on providing guidance to small academic or biotech researchers as to what simple questions can be addressed or answered at the bench in order to make their cell therapy products more feasible for commercial-scale production. We discuss the processes that are required for scale-out at the manufacturing level, and how many questions can be addressed at the bench level. The goal of this review is to provide guidance in the form of topics that can be addressed early in the process of development to better the chances of the product being successful for future commercialization.

Mechanisms of T-cell protection from death by IRX-2: a new immunotherapeutic

OBJECTIVES

IRX-2 is a novel immunotherapeutic containing physiologic quantities of several cytokines which protects human T lymphocytes from tumor-induced or drug-induced apoptosis. Here, we investigate the mechanisms responsible for IRX-2-mediated protection of T lymphocytes exposed to tumor-derived microvesicles (TMV).

METHODS

Jurkat cells or primary human T cells ± IRX-2 were co-incubated with TMV and then examined by flow cytometry or Western blots for expression of molecules regulating cell survival (FLIP, Bcl-2, Bcl-xL, Mcl-1) or death (Fas, caspase 8, caspase 9, Bax, Bid). ANX V binding, caspase activation or cytochrome c release were also measured ± cycloheximide (CHX) or ± the Akt-specific inhibitor. Jurkat cells transfected with the cFLIP gene were used to evaluate the role of cFLIP in IRX-2-mediated protection. Effects of CHX on IRX-2-mediated protection and activation of NF-κB upon the TMV/IRX-2 treatment were also measured.

RESULTS

IRX-2 protected T cells from apoptosis by preventing Fas overexpression induced by TMV and blocking caspase 8 activation by up-regulating cFLIP. Jurkat cells overexpressing cFLIP were more resistant to TMV-induced apoptosis than the mock-transfected cells (p < 0.02). Signaling via the PI3K/Akt pathway, IRX-2 corrected the imbalance of pro- versus anti-apoptotic proteins induced by TMV and promoted NF-κB translocation to the nucleus. CHX abolished IRX-2-mediated protection in T cells, suggesting that IRX-2 induces de novo synthesis of one or more proteins that are required for protection.

CONCLUSIONS

This biologic may be therapeutically useful for protection of activated T cells from tumor-induced immune suppression and death.

The Influence of Various Hematology Analyzers on Component Platelet Counts

Hematology analyzers designed to count platelets in samples of whole blood are used to enumerate the total number of platelets in components prepared for transfusion. This report addresses the issue of variability in platelet counts obtained with different models of hematology analyzers. The influence of a common calibration procedure, involving one level of porcine platelets, on the extent of variability was also evaluated. Identical sets of samples of simulated and apheresis-derived human platelets were counted by multiple laboratories in 3 separate studies. In the first 2 exercises, 7 samples of both porcine platelets and modified goat erythrocytes with targeted platelets counts from 0.2 to 4.0 x 10(12)/L were counted without prior dilution. In both exercises, the samples were counted multiple times after routine calibration using instructions provided by the manufacturers of the various hematology analyzers used. In the second exercise, the samples were recounted after the hematology analyzers were recalibrated with a common calibrant consisting of porcine platelets at a targeted concentration of 0.5 x 10(12)/L. In the first and second exercises, 20 and 18 hematology analyzers were used, respectively. In the third exercise, 6 samples prepared from a single unit of apheresis platelets with targeted counts from 0.2 to 1.64 x 10(12)/L were shipped by an overnight courier and counted in triplicate on the day of arrival. Eleven hematology analyzers were used. The influence of recalibration was evaluated statistically by using the 95% prediction interval for the mean of a future set of observations. The platelet counts measured with a specific type of hematology analyzer provided the data to calculate the 95% prediction interval. With routine calibration, a wide variability in platelet counts was observed with all levels of both simulated and apheresis-derived human platelets. For example, with porcine platelets at a targeted level of 0.4 x 10 (12)/L, the platelet counts ranged from 0.31 to 0.47 x 10(12)/L. Recalibration reduced the extent of variability observed with all levels of simulated and apheresis-derived human platelets by increasing the observed platelet counts determined with a subset of hematology analyzers that produced platelet counts in the lower portion of the range. With recalibration, the mean platelet counts obtained with most hematology analyzers, especially with samples having targeted platelet levels no greater than 1.0 x 10(12)/L, were within or near the 95% prediction interval determined with the instruments that provided the highest platelet counts with routine calibration. With recalibration, the reproducibility of the platelet counts was considered to be good for all hematology analyzers with all levels of simulated and apheresis-derived human platelets for most of the instruments. The coefficient of variance did not exceed 6%, with most of the values ranging from 1% to 3%. This study therefore found that the platelet counts of platelet concentrates can be markedly influenced by the type of hematology analyzer used. A common calibration procedure designed specifically for the range of platelet counts in platelet products may be beneficial considering that many different hematology analyzers are being used to count platelets.

Method for qualifying microbial removal performance of 0.1 micron rated filters. Part III: bacterial challenge tests on 0.2/0.22 and 0.1 micron rated filter cartridges with Hydrogenophaga (formerly Pseudomonas) pseudoflava

We have previously reported on the preliminary characterization of Hydrogenophaga (formerly Pseudomonas) pseudoflava for potential use as a standard challenge organism to qualify 0.1 microm rated filters. This article reports on the retention efficiencies of a large panel of 0.2/0.22 microm and 0.1 microm rated filter cartridges for H. pseudoflava (ATCC 700892) versus the retention capabilities of the same filters for Brevundimonas diminuta (ATCC 19146). A total of thirty-two 0.2/0.22 microm rated filter cartridges, spanning nine different "sterilizing grade" filter types from four different filter manufacturers, were challenged with H. pseudoflava at challenge levels exceeding 10(7) cfu/cm2. H. pseudoflava was shown to penetrate every 0.2/0.22 microm rated filter tested, with log titer reduction (LTR) values ranging from 3.5 to 7.7 logs. H. pseudoflava was shown to be more penetrative than B. diminuta under the same challenge conditions. B. diminuta was fully retained by nineteen of the twenty 0.2/0.22 microm rated filters that were challenged with both organisms. In the case of 0.1 microm rated filters, eighteen filter cartridges, spanning five different filter types from three manufacturers were tested. H. pseudoflava was consistently retained by four out of the five filter types tested, with LTR values in excess of 11.5 to 12.2 logs. The 0.1 microm rated filter type that was penetrated by H. pseudoflava has been previously demonstrated to be not fully retentive for naturally occurring bacteria. The data show that H. pseudoflava penetrates 0.2/0.22 microm rated filters just as readily as B. diminuta penetrates 0.45 microm rated filters. In addition, titer reductions provided by 0.2/0.22 microm rated filters for H. pseudoflava are comparable to those reported for A. laidlawii mycoplasma, albeit under different conditions. This study demonstrates that H. pseudoflava meets all criteria for use as a standard organism for qualifying the microbial removal performance of 0.1 microm rated filters for enhanced sterility assurance.

Method for qualifying microbial removal performance of 0.1 micron rated filters. Part I: characterization of water isolates for potential use as standard challenge organisms to qualify 0.1 micron rated filters

Although 0.1 microm rated filters intended for pharmaceutical sterilization applications have been commercially available for at least 15 years, there is no industry-wide standard for qualifying the microbial removal performance of these filters. In this article, we report on the bacterial challenge methodology used to screen four bacterial species for potential utility as a standard challenge organism to qualify 0.1 microm rated filters. These isolates were, in their natural state, demonstrated to penetrate 0.2/0.22 microm rated filters in prior studies. In the screening challenges described in this study, three out of these four candidates tested demonstrated consistent penetration of one 0.22 microm rated filter type tested (when cultured in a low nutrient medium under standard laboratory conditions). These included 6204-22 (FAME ID Acidovorax avenae citrulli), 6266-15 (FAME ID Comamonas acidovorans), and 6266-34 (FAME ID Hydrogenophaga pseudoflava). Of these, H. pseudoflava (6266-34) was chosen for additional experiments with other 0.2 microm rated filter membranes. In total, seventeen 0.2 and 0.22 microm rated filter discs, spanning five different "sterilizing grade" filter types from three different filter manufacturers were tested. H. pseudoflava penetration was observed for every filter tested. Under the same challenge conditions, H. pseudoflava was consistently retained by a 0.1 microm rated hydrophilic PVDF (polyvinylidenefluoride) filter with a specified high titer reduction claim for Acholeplasma laidlawii. In order to ensure selection of the most stable penetrative phenotype (i.e., select for nonrevertants), H. pseudoflava was subjected to three rounds of "filter cloning," and these results are described herein. The advantages of using H. pseudoflava for qualifying the microbial removal performance of 0.1 microm rated filters are also discussed.

Method for qualifying microbial removal performance of 0.1 micron rated filters. Part II: preliminary characterization of Hydrogenophaga (formerly Pseudomonas) pseudoflava for use as a standard challenge organism to qualify 0.1 micron rated filters

In this article, we report on the preliminary characterization of Hydrogenophaga (formerly Pseudomonas) pseudoflava for potential use as a standard challenge organism to qualify 0.1 microm rated filters. Filter-cloned H. pseudoflava (ATCC 700892) was easily cultured in a low nutrient broth (R2A broth) under standard laboratory conditions, reaching high titers of 10(8)-10(9) cfu/mL within 48-65 hours of incubation at 25+/-5 degrees C. Under these conditions, H. pseudoflava is a rod-shaped bacterium, averaging 0.25+/-0.03 microm by 1.65+/-0.35 microm, and appears to be smaller than Brevundimonas diminuta in width (0.31+/-0.03 microm), but somewhat longer in length (0.88+/-0.19 microm), which may partly explain the observed penetration. In total, thirty-five 0.2/0.22 microm rated filter discs, spanning five different "sterilizing grade" filter types from two different filter manufacturers were challenged with H. pseudoflava. In all cases, H. pseudoflava was shown to consistently penetrate every 0.2/0.22 microm rated filter disc tested. These tests also spanned three different challenge durations, including short-term challenges (30-40 minutes), and two different challenge fluids. The use of serial (double) 0.22 mm rated filters, which is a common industry practice to reduce the prefiltration bioburden to the final "sterilizing" filter, was also shown to be inadequate to fully retain H. pseudoflava under the challenge condition used. In contrast, two different 0.1 microm rated filter types functionally qualified with a specified high titer reduction claim for Acholeplasma laidlawii, were shown to consistently and fully retain H. pseudoflava, and retention by these two filter types was shown to be robust and independent of the challenge duration.

Retention of water-borne bacteria by membrane filters. Part I: Bacterial challenge tests on 0.2 and 0.22 micron rated filters

The results of bacterial challenge tests conducted on several 0.2 and 0.22 micron rated "sterilizing grade" filter cartridge types with bacteria from a natural water source are presented. Eight different 0.2/0.22 micron rated "sterilizing grade" filter types from four different filter manufacturers, claimed to be capable of retaining Brevundimonas diminuta at a challenge level of 10(7) CFU/cm2, were tested. The filters tested included nylon 6.6 and polyamide filters from two manufacturers, modified or hydrophilic PVDF filters from two manufacturers, modified or asymmetric PES filters from three manufacturers, and cellulose acetate filters from a single manufacturer. Consistent bacterial penetration was observed, over the 18-24 h challenge period, for all twenty-five integral 0.2 and 0.22 micron rated filter cartridges tested, at challenge levels of about 10(1)-10(4) CFU/cm2, indicating that natural waterborne bacteria were more penetrative than B. diminuta. The observed penetration was thus qualitatively independent of filter media type or manufacturer. These results add to the growing body of evidence that shows 0.2 and 0.22 micron rated filters may not remove all microorganisms under all conditions. These results further establish that bacterial penetration of 0.2/0.22 micron rated filters is not limited just to (1) specific membrane types, or (2) extended duration challenges (>> 24 h), or (3) extremely high challenge levels, or (4) bacteria that can only exist in a penetrative state in an artificial laboratory setting.

Retention of water-borne bacteria by membrane filters. Part III: Bacterial challenge tests on 0.1 micron rated filters

Clear performance differences were observed between different 0.1 micron rated filters in terms of their microbial removal efficiency when challenged with naturally occurring waterborne bacteria from a water source. Penetration occurred with three 0.1 micron rated "sterilizing grade" filter types tested, from three different filter manufacturers, that did not have a specific high titer reduction claim for Acholeplasma laidlawii. Bacteria shown to penetrate these 0.1 micron rated filters were quite similar to those recovered downstream of 0.2.0.22 micron rated filters (described in Part II). All of the isolates identified via FAME analyses were common environmental or ubiquitous organisms, and some, such as Acidovorax sp. and Hydrogenophaga pseudoflava, have also been isolated from pharmaceutical water systems. In contrast, four different 0.1 micron rated "sterilizing grade" filter types from two different manufacturers, which had been qualified with both B. diminuta and A. laidlawii, consistently produced sterile effluents under similar test conditions. This study thus highlights the need for an industry or regulatory standard method of defining the microbial removal performance of 0.1 micron rated filters, and supports the use of functionally qualified 0.1 micron rated filters as sterilizing grade filters in pharmaceutical operations for enhanced sterility assurance.

Retention of water-borne bacteria by membrane filters. Part II: Scanning electron microscopy (SEM) and fatty acid methyl ester (FAME) characterization of bacterial species recovered downstream of 0.2/0.22 micron rated filters

The results of scanning electron microscopic (SEM) and fatty acid methyl ester (FAME) characterization of the bacterial species shown to penetrate conventional 0.2/0.22 micron rated "sterilizing grade" filters are presented. SEM data suggest that retention of bacteria by these filters appears to be strongly influenced by the morphology, and especially the width of bacteria and less so by length. When the bacterial cell width is small, less than 0.3 micron or so, the cell length does not appear to limit the ability to penetrate 0.2/0.22 micron rated filters. As the bacterial width increases, there is also a strong, almost exponential, decrease in the allowable length for penetration, with most penetrative cells tending to be coccoid beyond a width of 0.5 micron. Significant percentages of the bacteria (40-50%) that were observed downstream of these filters were larger than B. diminuta, the standard organism used to qualify 0.2/0.22 micron rated filters. The average sizes of natural waterborne bacteria that penetrated the filters tested were 20-40% larger in width, and 40-70% larger in length, compared to B. diminuta. These results indicate that size exclusion is not the sole mechanism governing bacterial retention. All isolates identified via FAME analyses were common environmental or ubiquitous organisms, and some, such as Acidovorax sp. and Hydrogenophaga pseudoflava, have also been isolated from pharmaceutical water systems. Most of the bacteria recovered downstream of 0.2/0.22 micron rated filters were gram negative, oxidase positive, motile, nonfermentors.

Membrane filtration for virus removal

Incorporation of adequate clearance methodologies for viral safety assurance constitutes an integral part of the manufacturing process for plasma-derived biologicals. Filtration, being non-invasive, non-destructive and a <<robust>> mechanism for virus removal is often the method of choice. This paper discusses the virus filter performance characteristics and other process-related issues specifically applying to the Pall Ultipor VF filters (Grade DV50 and Grade DV20), which are operated in the direct flow filtration (DFF) mode and the Pall Filtron Omega VR filters (the Omega 300 K and Omega 100 K), which are operated in the tangential flow filtration (TFF) mode.

Application of membrane filtration for removal of diminutive bioburden organisms in pharmaceutical products and processes

In this report, we present results of a recent investigation in our laboratories demonstrated the effect of process conditions and/or drug product composition on the ability of 0.2 micron and 0.22 micron sterilizing grade filters to fully retain Ralstonia (formerly Burkholderia, formerly Pseudomonas) pickettii. R. pickettii is a opportunistic pathogen widely distributed in nature as well as clinical specimens and there have been several reports of nosocomial infections due to intrinsic manufacture-related R. pickettii contamination in filter-sterilized parenteral fluids. This study documents the penetration of 0.2 micron nylon 66 and 0.22 micron modified PVDF sterilizing grade filters by R. pickettii (grown and challenged) in a drug solution under conditions that simulated a pharmaceutical filling operation. Penetration was not observed for every filter disc tested, and this may be explained, in part, by the stochastic nature (i.e., governed by the rules of probability) of the retention mechanisms involved. Scanning electron microscopy revealed significant changes in the microorganism's size and morphology as a result of exposure to the drug solution; these changes are consistent with those reported for bacteria subjected to nutrient deprivation. The SEM analyses of R. pickettii challenge suspensions in the drug solution showed that the average cell length decreased from 1.25 +/- 0.27 microns to 0.84 +/- 0.17 micron between zero and 24 hours. In addition, significant changes were observed in the size (length) distributions, with approximately 35% of the cells at 24 hours being smaller than any cell observed at the start of the challenge. These data suggest that the significant reduction in bioburden size and morphology that occurred as a result of exposure to the drug solution may play a role in the reduced ability of the 0.2 micron and 0.22 micron filters tested in this study to retain these organisms. Under the same test conditions where penetration of 0.2/0.22 micron filters was observed, 0.1 micron rated membrane filters qualified with both B. diminuta and Acholeplasma laidlawii mycoplasma consistently provided sterile effluent. Bacterial penetration of 0.2 (or 0.22) micron sterilizing grade filters was not observed under identical test conditions with either R. pickettii in a standardized solution (saline lactose broth) routinely used in challenge testing filters, or with the standard test organism, B. diminuta, in the drug solution. This study thus supports the renewed emphasis on both product- and process specific validation as well as routine bioburden monitoring expressed by regulatory agencies, and the use of enhanced bacterial removal efficiency 0.1 micron rated filters to provide enhanced sterility assurance in pharmaceutical processes.

Process control procedures to augment quality control of leukocyte-reduced red cell blood products

Quality control of leukocyte-reduced packed red cell units (LRprc) produced in blood facilities must conform to regulatory criteria, which state that units may not contain more than 1 x 10(6) to 5 x 10(6) white blood cells (WBC) per unit. The post-filtration WBC content of a total of n = 386 LRprc units was counted with a Nageotte chamber to model the probability that a unit would not meet the regulatory criteria. The distribution of the residual leukocyte counts is close to a negative binomial distribution (NBD) and is independent of the packed red cell volume filtered. The observed probability that a unit of blood has a residual WBC greater than 5 x 10(6) is 2.6 +/- 2.6 x 10(-3). A power analysis of the two-sample Kolmogorov-Smirnov (KS) test in this application shows that a sample size of 20 is sufficient for determining that the process is in control when an out of control process has a k NBD parameter greater than or equal to that of the in control process. The three out of control processes observed to date appear to have this property. A sample of size 80 may be necessary for confirming that process validation data sets conform to the larger 'reference' database (n = 386) for processes that are out of control in such a way that their k NBD parameter is less than the k parameter of the in control process.

Application of bacteriophages as surrogates for mammalian viruses: a case for use in filter validation based on precedents and current practices in medical and environmental virology

Infectivity-based assays are the assays of choice for the detection of pathogenic mammalian viruses. While it is intuitively appropriate to conduct testing and validation studies with the known viral burden or a closely related mammalian species, logistic considerations often dictate otherwise. Consequently, bacteriophages have served as suitable surrogates for mammalian viruses in both medical and environmental virology applications. The wide range of bacteriophages available offers a powerful analytical tool amenable to several different applications: filter validation studies (where removal is based on size exclusion), investigations into virus contamination control issues, evaluation of barrier materials, etc. There is a considerable body of evidence to suggest and support the use of bacteriophages as surrogates for mammalian viruses. Use of appropriately sized bacteriophages provides an innocuous, efficacious and expeditious method for economical testing and validation of viral clearance capabilities of virus removal filters, thus facilitating performance of filter validation studies in biopharmaceuticals under product- and process-specific conditions in an overall effort towards ensuring the virological safety of biologicals. This paper discusses the limitations associated with mammalian virus assays and provides a rationale for the use of bacteriophages as surrogates for mammalian viruses. Data from published literature documenting applicability of bacteriophages in filter validation studies, especially when removal is based on size exclusion, is reviewed along with examples of studies from the fields of medical and environmental virology.

Lack of clinically significant contact system activation during platelet concentrate filtration by leukocyte removal filters

When blood (plasma) contacts certain foreign surfaces, factor XII can activate and trigger a series of reactions leading to cleavage of kininogens with subsequent release of bradykinin. In this study, we investigated two different widely used leukocyte removal filters, Pall PXL8K (A) and Asahi PLS-5A (B), to test whether clinically significant contact activation occurred during leukodepletion of platelet-rich plasma (PRP). Kininogens were measured by particle concentration fluorescence immunoassay (PCFIA), which can detect cleavage of high and low molecular weight kininogens (HK and LK), the parent molecules of bradykinin, to determine if contact activation had occurred. A slight, nonsignificant decrease in HK and LK was observed with filter A after the first 5 mL was filtered that returned to prefiltration levels by the end of the filtration. Specific TotK (the combined measurement of HK and LK heavy chains divided by plasma protein concentration) showed a small, significant decrease with filter A after the first 5 mL of platelet concentrates was filtered that returned to prefiltration levels by the end of the filtration. There were no significant increases or decreases in the cleaved kininogen index (CKI), an index of HK proteolytic activation or HK and LK destruction (with release of bradykinin). These data suggest that small amounts of both HK and LK initially adsorb to filter A and then desorb, primarily intact. These data also indicate that no significant contact activation, as measured by PCFIA, occurs during leukodepletion of platelet concentrates with either filter A or B.

Virus retention by a hydrophilic triple-layer PVDF microporous membrane filter

Retention of bacteriophages (phi 6, PR772, T1, and PP7) and mammalian viruses (poliovirus and influenza A virus) by a hydrophilic triple layer PVDF microporous membrane, the Ultipor VF grade DV50 membrane, was evaluated. Challenges of membrane discs or pleated filter cartridges were performed at concentrations of 10(6)-10(8) PFU/mL in one or more of the following carrier fluids: water, saline, gelatin (0.1%) in phosphate buffer, Dulbecco's Modified Eagle Medium (MEM), and MEM supplemented with 10% fetal bovine serum (MEM + 10). The data demonstrate a minimum log titer reduction (LTR) of 6 for viruses larger than 50 nm irrespective of the carrier fluid. Protein transmission levels of greater than 95% for IgG and albumin were achieved. For integral pleated filter cartridges, correlation between a nondestructive integrity test (using the forward flow integrity test method) and virus retention was demonstrated. The Ultipor VF grade DV50 filter can be applicable in the manufacture of biologicals and biopharmaceuticals, where high protein transmission and consistent viral titer reduction are desired.

Removal of Mycobacterium species by breathing circuit filters

Breathing circuit filters (BCFs) are used in respiratory and critical-care settings for humidification of air and to limit transmission of respiratory pathogens. Three types of BCFs (Pall BB 25A, BB 100, and HME 15-22) were evaluated (in triplicate) for removal of Mycobacterium species. Filters were challenged with aerosolized Mycobacterium bovis (a surrogate for Mycobacterium tuberculosis), at minimum total concentrations of 10(4) colony-forming units. No M bovis was recovered in the effluent, providing removal efficiencies of > 99.99% to > 99.999% for the filters tested.

Practical guidelines for process validation and process control of white cell-reduced blood components: report of the Biomedical Excellence for Safer Transfusion (BEST) Working Party of the International Society of Blood Transfusion (ISBT)

BACKGROUND

The increased use of white (WBC)-reduced blood components has prompted many institutions to develop quality assurance programs directed to such component preparation processes. For consistent preparation of WBC-reduced blood components that meet clinical needs as well as national standards, a program of process validation and control should be instituted. This involves controlling key factors that affect WBC reduction as well as periodic monitoring of the residual cellular content of components. Practical guidelines for the implementation of such a program are provided.

STUDY DESIGN AND METHODS

A program involving three phases of monitoring was developed by individuals belonging to an international working party of the International Society of Blood Transfusion.

RESULTS

The first phase, process validation, evaluates a minimum of 20 consecutive units (a minimum of 60 units when nonparametric measurements are used) to document the successful local implementation of a new or substantially modified process. Ongoing process control employing Levey-Jennings type control charts is used to demonstrate that the process remains stable over time. Process capability assessment and conformance with standards are evaluated once residual WBCs are counted in a sufficient number of units. This enables a facility to claim with a specified degree of confidence that a stated proportion of WBC-reduced units will meet national standards. Two approaches to determine the number of units that should be selected for counting are presented. The first approach considers units as either acceptable or not acceptable and assumes that the distribution of failed (or nonconforming) units approximates the Poisson distribution. The second approach takes into consideration the observed WBC content of the tested units, with the assumption that the residual WBC content in WBC-reduced components follows a lognormal distribution. A method to assess the lognormal distribution of residual WBCs is presented. Specific tables based on each of these approaches are provided to guide the reader in the design of a program that will verify conformance with any national standard at specific confidence levels. The approach can be generalized to other process control applications.

CONCLUSION

Guidelines are presented for process validation, process control, and assessment of conformance in the production of WBC-reduced blood components. Policy makers retain the responsibility to establish, on the basis of the expected use of WBC-reduced components, requirements for the frequency of testing and for the proportion of prepared units that are expected with a stated degree of confidence to meet the standards. Facilities preparing WBC-reduced components can monitor key factors that influence the preparation of WBC-reduced blood, can periodically assess their conformance with the standards, and can intervene to correct adverse changes in the process. This approach can be used to ensure the consistent quality of WBC-reduced blood components.

Multicenter evaluation of the 3% paraformaldehyde method for white cell counting in leukocyte-reduced red blood cells. BEST (Biomedical Excellence for Safer Transfusion) Working Party of the International Society of Blood Transfusion

BACKGROUND/AIM

The 3% paraformaldehyde (PFA) method is a simple technique for counting residual white blood cells (WBC) in leukocyte-depleted red blood cells (RBC). Preliminary data suggested that its sensitivity is at least equal to PCR and flow cytometry. We report the results of a multicenter study conducted by the BEST Working Party to determine precision and accuracy of the 3% PFA method.

STUDY DESIGN

In the 7 participating laboratories, 5 sets of samples containing nominal concentrations of 200, 100, 50, and 10 WBC/ml were prepared by diluting whole blood into 'WBC-free' RBC. Ten milliliters of each sample were processed using the 3% PFA method, which is based on erythrocyte lysis and WBC concentration into 5% of the original sample volume; a Nageotte chamber is used to count concentrated WBC.

RESULTS

The precision of the technique varied according to the nominal concentration, ranging from a CV of 12% at 200 WBC/ml to 57% at 10 WBC/ml. The technique measured fewer than the nominal WBC concentrations (mean of all laboratories, -12.4%); underestimation was probably due to cell loss during sample manipulation. Overall accuracy was however acceptable, because statistical considerations establish that the actual WBC concentration would unlikely exceed 2 times the estimated count.

CONCLUSIONS

The 3% PFA method is suitable for the enumeration of residual WBC at concentrations > or = 50/ml. It represents a useful tool for evaluation of high performance filters by reference laboratories.

Chemiluminescent detection of DNA on nylon membranes

Two types of nonradioactive DNA detection systems were optimized for use with nylon membranes in Southern transfers. A luminol substrate system (consisting of an enhanced chemiluminescent reaction utilizing luminol enzyme substrate) was used with peroxidase-labeled probe DNA, and a dioxetane-based substrate was used with alkaline phosphatase/antibody and digoxigenin-labeled probe DNA. Chemiluminescence was detected by autoradiography. Methods for reprobing the membranes were also optimized for both systems; blots could be reprobed at least ten times. Results showed that excellent sensitivity and low background can be achieved on both amphoteric and positively charged nylon membranes, using either detection system.

Blinded, two-laboratory comparative analysis of Escherichia coli heat-stable enterotoxin production by using monoclonal antibody enzyme-linked immunosorbent assay, radioimmunoassay, suckling mouse assay, and gene probes

Heat-stable enterotoxin (ST)-producing enterotoxigenic Escherichia coli (ETEC) can be identified by a variety of assays, including the suckling mouse assay (SMA), radioimmunoassay (RIA), polyclonal or monoclonal antibody enzyme-linked immunosorbent assay (ELISA), and DNA hybridization with STh and STp gene probes. To compare the sensitivity and reliability of these assays, 100 coded ETEC and non-ETEC isolates were blindly tested in two independent laboratories. SMA, RIA, and monoclonal ELISA were performed in Cincinnati, Ohio, while gene probe analysis was performed in Baltimore, Md. The method of storage of organisms had a profound effect on the stability of plasmids in certain strains. Hybridization experiments to determine the presence or absence of the enterotoxin gene showed that strains stored on Dorset egg medium at room temperature better retained their plasmids than strains stored frozen in skim milk. Forty-four of the 100 organisms obtained from the skim milk stock were found to produce STa in liquid culture by the RIA, SMA, and monoclonal ELISA (100% agreement). However, 50 of 54 of the strains stored on Dorset egg medium which were originally classified as STa+ or ST+ LT+ (positive for both heat-stable and heat-labile [LT] enterotoxins) were found to produce STa and retain the plasmid by each of these assays. Three additional strains were found which harbored the plasmid but did not elaborate STa by any of the assays (3% discrepancy). The monoclonal antibody ELISA appears to be highly reliable for determination of STa production by ETEC and can be easily scored visually even by untrained personnel. Furthermore, when this STa assay is coupled with a polyclonal antibody assay, it is possible to predict the genotype of STh- and STp-producing organisms.

Production of neutralizing monoclonal antibodies to Escherichia coli heat-stable enterotoxin

In an effort to develop new approaches to the study and control of infectious diarrhea, we prepared murine monoclonal antibodies to the Escherichia coli heat-stable enterotoxin (STa). The toxin was purified from E. coli culture media and conjugated to bovine serum albumin. The STa-bovine serum albumin conjugate was used to immunize BALB/c mice, and the immune spleen cells from these mice were fused with SP2/0 myeloma cells. Resultant hybridomas were screened in an enzyme-linked immunosorbent assay protocol against 500 ng of STa-bovine serum albumin bound to microtiter wells as the solid-phase antigen. Five stable clones were selected and grown further in ascites fluid, which demonstrated anti-STa activity at dilutions of up to 1:500,000 in the enzyme-linked immunosorbent assay for heat-stable enterotoxin. In a competitive enzyme-linked immunosorbent assay format, the antibodies recognized several human and porcine strains of STa to various extents, but did not recognize E. coli heat-labile toxin, cholera toxin, or staphylococcal enterotoxin B. The antibodies were all able to bind lactoperoxidase-labeled [125I]STa, and antibody 20B3 was also able to dissociate [125I]STa bound to toxin receptors on rat jejunal villous cells. Preincubation of STa with antibodies 20B3 or 20F5 led to a concentration-dependent neutralization of toxin activity in a suckling mouse intestinal secretion assay. These antibodies are likely to provide new tools for the continued study of STa structure-function relationships and may lead to improved diagnosis and treatment of E. coli-induced infectious diarrhea.

Simple and reliable enzyme-linked immunosorbent assay with monoclonal antibodies for detection of Escherichia coli heat-stable enterotoxins

We have developed a sensitive and specific competitive enzyme-linked immunosorbent assay for Escherichia coli heat-stable enterotoxins consisting of methanol-soluble, suckling mouse active peptides with similar core sequences (STa) by using monoclonal antibodies prepared against STa purified from a human isolate. The assay can detect 3 to 20 pg of purified STa, depending on the monoclonal antibody used in the assay. The assay is rapid, requiring ca. 1 h to complete. With this competitive enzyme-linked immunosorbent assay, we measured STa production by enterotoxigenic E. coli directly in Casamino Acid-yeast extract culture supernatants. The assay was suitable for measuring STa in culture supernatants from human, bovine, and porcine E. coli isolates. No cross-reactivity was observed with heat-labile enterotoxin, cholera toxin, or heat-stable enterotoxin STb, which is a methanol-insoluble peptide(s) active in the ligated pig jejunal loop test. A 100% correlation of toxin production was found by comparing the enzyme-linked immunosorbent assay with the previously established radioimmunoassay for STa and with suckling mouse activity.

Production and characterization of monoclonal antibodies to soluble rat lung guanylate cyclase

Four monoclonal antibodies to rat lung soluble guanylate cyclase [GTP pyrophosphate-lyase (cyclizing) EC 4.6.1.2] have been produced by fusing spleen cells from immunized BALB/c mice with SP-2/0 myeloma cells. The antibodies were detected by their ability to bind immobilized guanylate cyclase and by immunoprecipitation of purified enzyme in the presence of second (rabbit anti-mouse) antibody. After subcloning by limiting dilution, hybridomas were injected intraperitoneally into mice to produce ascitic fluid containing 2-5 mg of antibody per ml. The four antibodies obtained had titers of between 1:1580 and 1:3160 but were detectable at dilutions greater than 1:20,000. Soluble guanylate cyclase from several rat tissues were crossreactive with the four monoclonal antibodies, suggesting that the soluble enzyme from different rat tissues is antigenically similar. The antibodies also recognized soluble lung enzyme from rat, beef, and pig, while enzyme from rabbit was not crossreactive and mouse enzyme was recognized by only one of the antibodies. Particulate guanylate cyclase from a number of tissues had only minimal crossreactivity with the antibodies. Immunoprecipitated guanylate cyclase retained catalytic activity, could be activated with sodium nitroprusside, and was inhibited by cystamine. None of the antibodies were inhibitory under the conditions examined. These antibodies will be useful probes for the study of guanylate cyclase regulation and function under a variety of physiological conditions.