Measuring quantity and function of pneumococcal antibodies in immunoglobulin products

Abstract

BACKGROUND Immunoglobulin replacement therapy is a cornerstone of the treatment of primary immunodeficiencies. Preparations used for replacement therapy are processed by purifying immunoglobulins from large pools of plasma, which were obtained from healthy donors. The constituent antibodies in these products depend on the immune history of the donor pool as well as manufacturing processes that differ among manufacturers. For these reasons various methods have been proposed to examine the levels and function of antibodies to organisms such as Streptococcus pneumoniae, which frequently causes infections in patients with immunodeficiencies. Pneumococcal antibody levels or antibody function can be measured with enzyme‐linked immunosorbent assay (ELISA) or multiplexed opsonophagocytosis assay (MOPA). Although these assays were developed initially to assess the immunogenicity of pneumococcal vaccines, the techniques have been adapted to evaluate immunoglobulin products as well. STUDY DESIGN AND METHODS This article provides a concise review of the analytic techniques for measuring pneumococcal antibodies and prior studies of immunoglobulin products utilizing these methods. RESULTS Studies utilizing these assays have demonstrated that antibody levels of immunoglobulin products can vary with time, location, and manufacturer. CONCLUSIONS We highlight current issues and future considerations concerning measurement of pneumococcal antibodies in immunoglobulin products, and the assays used for this purpose.

Overview of antibody‐mediated immunity to S. pneumoniae: pneumococcal infections, pneumococcal immunity assessment, and recommendations for IG product evaluation

“…OPA assays have undergone significant developments that have improved its availability, its use to assess immunity to many different S. pneumoniae serotypes, its standardization and the availability of reference sera. [30][31][32][33][34] When applied to the assessment of vaccine responses 35 and therapeutic IgG preparation, OPA has offered a welcome improvement over previous use of experimental animals to test the ability of passively administered human antibodies to prevent lethal infections with a single pneumococcal serotype. 36,37…”

“…OPA assays have undergone significant developments that have improved its availability, its use to assess immunity to many different S. pneumoniae serotypes, its standardization and the availability of reference sera …”

Antibodies to vaccine antigens in pooled polyclonal human IgG products

“…In general, binding assays in which killed organisms or isolated antigen(s) are immobilized on a solid phase such as a plastic enzyme‐linked immunoadsorbent assay (ELISA) plate or a visible or fluorescent microparticle are generally more rapid, more reproducible and easier to standardize than are assays of biological functions such as neutralization (prevention of infection of cells in vitro) or opsono‐phagocytic killing . Functional assays require viable target cells and/or phagocytes, which may be difficult to maintain and which are much more variable than isolated antigen molecules . A priori, we expect that neutralization or killing assays will correlate well with protection against infection and therefore are likely to be more informative than binding assays, which might be measuring antibodies against irrelevant antigens.…”

“…22,23 Functional assays require viable target cells and/or phagocytes, which may be difficult to maintain and which are much more variable than isolated antigen molecules. 22,24 A priori, we expect that neutralization or killing assays will correlate well with protection against infection 25 and therefore are likely to be more informative than binding assays, which might be measuring antibodies against irrelevant antigens. In fact, however, all laboratory assays are model systems which are merely surrogates for protection.…”

Assuring immune globulin potency in a world of changing pathogen challenges

“…Considerable attention was given to S. pneumoniae because it has been a major cause of pneumonia and invasive disease in untreated and undertreated patients with PI. Test methods and standards have evolved since 2007, although some commercial assays yield conflicting results, and ELISA titers do not always correlate with functional opsonophagocytic assays . It was generally agreed that an opsonophagocytosis assay or a multiplex version of the opsonophagocytosis assay were most attractive, as they provide antibody functionality, are reproducible, and may be relatively stable over time.…”