Considerations of pool size in the manufacture of plasma derivatives.

BACKGROUND: The pooling of human plasma from many donors for the purpose of manufacturing therapeutic proteins increases the risk of exposing recipients of these proteins to pathogens that may contaminate 1 or a few units included in the pool. STUDY DESIGN AND METHODS: This risk is estimated for a range of manufacturing scales that would derive material from a varied number of donors and for a number of hypothetical infectious agents that may exist in the donor population over a wide range of prevalence. Risk is also calculated both for recipients of single doses of a plasma protein and for those who depend on long-term treatment with plasma derivatives. RESULTS: Risk of exposure increases with pool size and the prevalence of the agent in question and accumulates with repeated treatments with material manufactured from different pools. CONCLUSION: Reducing pool size would at best decrease this risk in proportion to the reduction in manufacturing scale. However, for individuals requiring repeated or continuous treatments, the risk of exposure to all but the rarest infectious agents would be only minimally affected, even by large reductions in manufacturing scale.

Fibrin sealant: summary of a conference on characteristics and clinical uses.

The 2-day conference clearly outlined the formulations of products that are being developed or are commercially available in Europe. The major difference between products in the United States and those in Europe is that US manufacturers are preparing fibrin sealant that does not contain aprotinin, epsilon amino caproic acid, or any other type of antifibrinolytic agent, whereas antifibrinolytic agents are included in all such preparations used in Europe. The conference provided no clear consensus that such agents are essential to the efficacy of the product. Although many investigators believe in the clinical benefit of fibrin sealant, most of the studies to demonstrate efficacy have not been performed in a well-controlled fashion. However, fibrin sealant, if found in a controlled trial to have clinical efficacy, could be approved by the FDA for a narrow indication. Opportunities remain for greater exploration of different forms of the product, not only as a hemostatic agent, but as an adjunct to wound healing and as a matrix for delivery of drugs and proteins with other biologic activities.

The effect on the safety of intravenous immunoglobulin of testing plasma for antibody to hepatitis C.

BACKGROUND: The safety of intravenous immunoglobulin (IGIV), manufactured from units testing negative for antibody to hepatitis C virus (anti-HCV), was investigated. STUDY DESIGN AND METHODS: A study involving five chimpanzees was performed to determine whether the safety of IGIV would be compromised if units of plasma that reacted for anti-HCV were withheld from pools from which IGIV is manufactured. In the first phase of the experiment, two chimpanzees were infused with 25 mL per kg of unprocessed, pooled plasma from 2887 donors who did not react for anti-HCV in single-antigen (c100-3) enzyme-linked immunosorbent assays. In the second phase, each of three chimpanzees was infused with 1000 mg per kg of IGIV manufactured from the same plasma units. The immunoglobulin was made by seven United States-licensed manufacturers, each using its own approved method. Each chimpanzee received an equal dose of each manufacturer's IGIV. RESULTS: The two chimpanzees that received anti-c100-3-nonreactive, unprocessed pooled plasma became infected with HCV. The three chimpanzees infused with IGIV did not show any evidence of infection with HCV 15 months after inoculation. Two of these animals were challenged with human non-A,non-B hepatitis-infectious plasma, and both subsequently showed evidence of HCV infection. CONCLUSION: These studies demonstrate that, as determined by infectivity for chimpanzees, 1) the withholding of plasma units that react for anti-c100-3 from pools from which plasma products are manufactured does not render the source material noninfectious, and 2) the safety of IGIV manufactured from such plasma pools is not compromised by withholding the units that react for anti-c100-3.

Immunoglobulin G dimer: an idiotype-anti-idiotype complex.

Immunoglobulin G (IgG) prepared from pooled human plasma contains variable amounts (up to 40%) of IgG dimer whereas IgG isolated from the plasma of a single individual is essentially monomeric. The amount of dimer increases with the number of donors contributing to the plasma pool from which the IgG is prepared. Dimerization is reversed by increasing the temp or decreasing the pH. Two intact antibody-combining sites (paratopes) are required for optimal dimer formation; the Fc region is unnecessary. These findings strongly suggest that IgG dimer consists of idiotype-anti-idiotype pairs formed between molecules of IgG from different individuals, and that a mechanism exists for suppressing idiotype-anti-idiotype formation in vivo.

Interaction between various polymerized human albumins and hepatitis B surface antigen.

A variety of albumin polymers were prepared and tested for binding with hepatitis B surface antigen (HBsAg): synthetic polymers cross-linked by either glutaraldehyde or carbodiimide; heat-aggregated polymers made by heating albumin solutions at 60 degrees C for 10 h with or without albumin stabilizer; and polymers isolated from fresh or long-stored commercial therapeutic albumin solutions. A sensitive solid-phase, competitive-inhibition radioimmunoassay, which can detect as little as 10 ng of glutaraldehyde-cross-linked human albumin polymer (PHALB-G), was developed and used to measure binding. The binding of PHALB-G with HBsAg was 150- to 1,000-fold greater than that of any other albumin polymer. Glutaraldehyde-cross-linked bovine albumin polymer showed no binding. Albumin monomer and dimer fractions produced by glutaraldehyde treatment exhibited some binding, albeit much weaker than PHALB-G. As measured by a direct-binding assay with solid-phase PHALB-G, the attachment of HBsAg particles from sera positive for antibody to the e antigen was less efficient than that from sera positive for e antigen, even when all sera were tested at equal HBsAg concentrations. In protein blot experiments with radiolabeled albumin preparations, PHALB-G bound almost exclusively to HBsAg polypeptide P31 and showed no binding with the major polypeptides P23 and P26. None of the other radiolabeled albumin polymers was reactive. These results indicate that the interaction between PHALB-G and HBsAg is not due to polymerization of albumin per se, but rather is unique and site specific.

Quantitative determination of the stabilizers octanoic acid and N-acetyl-DL-tryptophan in human albumin products.

Methods were developed for the determination of octanoic acid and N-acetyl-DL-tryptophan, which are used as stabilizers in the human blood-derived therapeutic products normal serum albumin and plasma protein fraction. The method for octanoic acid uses GC; quantitation is achieved using heptanoic acid as the internal standard. The method for N-acetyl-DL-tryptophan is based on UV spectrophotometry of the acid-soluble fraction remaining after precipitation of the protein (epsilon 280 for N-acetyl-DL-tryptophan, 5250). The coefficient of variation for replicate determinations of octanoic acid averaged 3.9% (range 2.1-5.5%); that of N-acetyl-DL-tryptophan averaged 1.9% (range 0.5-4.0%). Use of these methods for the analysis of 138 lots of commercial products for octanoic acid and 159 lots for N-acetyl-DL-tryptophan showed that the stabilizer contents of 132 and 158 of these lots, respectively, were within 20% of the value indicated on the product label.

Kinetics of activation and autoactivation of human factor XII.

The kinetics of the enzymic reactions that participate in the contact activation system of human plasma were examined. These reactions are potentiated by dextran sulfate, a negatively charged solute that mimics many of the effects of glass or kaolin on this system. The reactions of reciprocal activation, consisting of activation of factor XII by kallikrein and of prekallikrein by activated factor XII, follow Michaelis-Menten kinetics; values of kcat and Km for each of these reactions were determined in the presence of dextran sulfate and in its absence. In the presence of dextran sulfate, the catalytic efficiency for factor XII activation was increased 11 000-fold, and that for prekallikrein was increased 70-fold. Autoactivation of factor XII in the presence of dextran sulfate also follows Michaelis-Menten kinetics with kcat = 0.033 s-1 and Km = 7.5 microM. This finding supports the concept that autoactivation is an enzymic process, initiated by traces of activated factor XII which are invariably present in factor XII preparations. At prekallikrein and factor XII levels equal to those in plasma, reciprocal activation is approximately 2000-fold more rapid than autoactivation. Thus, reciprocal activation is the predominant mode of factor XII activation in normal plasma.

Thermal stability of human albumin measured by differential scanning calorimetry. II. Effects of isomers of N-acetyltryptophanate and tryptophanate, pH, reheating, and dimerization.

Thermal stability of undefatted human albumin preparations at 5% concentration and neutral pH in 145 mM Na+ was investigated by differential scanning calorimetry. At 30 and 4 mM N-acetyltryptophanate, the thermogram for previously unheated albumin monomer is independent of the stereochemistry of this ligand; thus, the affinity of the protein must be the same for the L- and D-isomers in the temperature range of thermal denaturation (62-86 degrees C). 26 mM L-tryptophanate bestows a slight increase in stability on previously unheated monomer, whereas 27 mM D-tryptophanate has no effect, a result consistent with the reported weaker binding of the D-isomer. Previously unheated albumin monomer shows slightly greater thermal stability at pH 6.4 than at pH 7.4. The tracing of differential heat capacity versus temperature (thermogram) for monomer from once heated albumin, i.e. once processed and once heated normal serum albumin (NSA), is almost identical to that for previously unheated monomer. Monomer prepared from outdated, multiply reprocessed, multiply reheated NSA (old monomer) had the same corresponding denaturation temperatures as previously unheated monomer; the corresponding dimer (old dimer) is slightly less stable. Thermograms for old monomer and old dimer, like those for previously unheated monomer, comprise two denaturation peaks (endotherms). Their endotherms, however, are very broad, reflecting the great heterogeneity of the old proteins. The thermogram for old monomer remains broad even in the presence of N-acetyltryptophanate and/or caprylate. Old dimer does not dissociate when undergoing thermal denaturation.

Stabilization of human albumin by caprylate and acetyltryptophanate.

The thermal stabilization of human albumin by caprylate (CA) and acetyltryptophanate (AT) was studied by monitoring the formation of albumin polymer (defined as species larger than dimer) on the basis of its molecular size as well as its characteristic migration as alpha-globulin. Heating 5% protein solutions of purified albumin monomer, cohn fraction V, and fraction IV-4 + V at 60 degrees C in 0.1 M sodium phosphate or 145 mM sodium chloride, pH 7.0, established the following order of stabilizer effectiveness: 4 mM CA + 4 mM AT approximately 4 mM CA greater than 8 mM AT greater than or equal to 2 mM CA greater than 4 mM AT. However, albumin was more thermally stable in the chloride medium. Raising the CA concentration above 4 mM provided little additional stabilization. The D- and L-enantiomers of AT were equally effective, but 16 mM AT was needed to equal the effect of 4 mM CA. L-Tryptophanate exerted only slight stabilization, even at 32 mM; D-tryptophanate was even less effective. The albumin polymer level increased progressively with time at 60 degrees C in 2 mM CA or 4 mM AT, whereas in 4 mM CA it reached a plateau in 4-6 h. Acetone drying of albumin-rich fractions was shown to remove nearly all endogenous fatty acid, rendering the protein thermally labile unless sufficient exogenous stabilizer(s) was added. Even in the presence of 145 mM sodium chloride and 4 mM CA + 4 mM AT or 4 mM CA, the stabilizing effect of endogenous fatty acid was still detectable.

Thermal stability of human albumin measured by differential scanning calorimetry. I. Effects of caprylate and N-acetyltryptophanate.

The thermal stability of 5% previously unheated, undefatted human albumin monomer in 145 mM Na+, pH 7.0 was investigated by differential scanning calorimetry (DSC) as a function of added caprylate and/or N-acetyl-DL-tryptophanate. Caprylate was substantially more effective than N-acetyl-DL-tryptophanate in protecting the protein against thermal denaturation at a given level or at a saturating level of stabilizer. The tracing of the differential heat capacity versus temperature (thermogram) for this undefatted monomer that contained 1.5 mol endogenous, long-chain fatty acid (LCFA)/mol monomer exhibits two denaturation peaks (endotherms) in the absence of stabilizer. The endotherm with the lower denaturation temperature (Td) comprises 70% of the total heat of denaturation and also corresponds to irreversible denaturation and precipitation of 70% of the albumin. This endotherm is associated with more thermally labile protein species containing low levels of LCFA. The endotherm with the higher Td is associated with more stable protein species containing high levels of LCFA. Thus, the two endotherms are not related to the proposed domain structure of the protein but result from an uneven LCFA distribution that is due to preexisting heterogeneity in the albumin and/or heterogeneity that arises during the DSC experiment. Binding data do not support a preexisting uneven distribution of sufficient magnitude to explain the experimental results. A complementary explanation is that an uneven fatty acid distribution arises during the DSC experiment by migration of LCFA from the more labile species to the more stable as the former unfold; such migration would cause further stabilization of the latter.

Activation of factor XII by dextran sulfate: the basis for an assay of factor XII.

A system was developed for studying the activation of factor XII (Hageman factor) in the presence of dextran sulfate (DS). Salient features of the system included low ionic strength (0.08), low concentration of factor XII (approximately 1/10,000 that in normal plasma), and an excess of exogenous prekallikrein (PK). In this system, factor XII was rapidly converted to the 80,000 molecular weight (mol wt) form of factor XIIa (alpha-factor-XIIa). Once formed, the factor XIIa converted PK to kallikrein at a rate that was proportional to the amount of factor XII originally present in the incubation mixture. This system was used to construct a simple sensitive assay for factor XII in plasma and other biologic samples. The kallikrein produced was measured spectrophotometrically with the chromogenic substrate (H-D-Pro-Phe-Arg-p-nitroanilide (S-2302). This assay was shown to be independent of the high molecular weight kininogen and the PK content of the sample being analyzed. The measurements obtained were consistent with fundamental enzymologic principles and, if desired, could be processed with a simple calculator program to achieve linear standard curves. When applied to the quantitation of factor XII in plasma, the assay yielded values in close agreement with those determined by coagulant assay or by radial immunodiffusion.