An anti-idiotopic antibody-based enzyme-linked immunosorbent assay for the quantification of the monoclonal anti-D BRAD-5

Single molecule distribution of RhD binding epitopes on ultraflat erythrocyte ghosts

The Rh blood group system plays a key role in transfusion and organ transplant medicine. The complex transmembrane Rh polypeptides RhD and RhCE carry numerous antigens, including the extremely immunogenic D antigen. The Rh polypeptides form multimolecular Rh complexes with certain transmembrane and skeletal proteins, with so far only incompletely understood physiological functions. Determination of the energy landscape of individual Rh binding epitopes towards their specific interaction partners as well as their localization across the red blood cell (RBC) membrane requires single molecule approaches including large area high resolution recognition imaging. Atomic force microscopy based molecular recognition force spectroscopy in combination with single molecule recognition imaging fulfills these requirements. For unbiased single molecule results, nano-mechanical influences due to cell elasticity have to be eliminated. This is realized by generation of ultra flat erythrocyte ghosts on a solid support. We developed a protocol for the preparation of complete ultraflat erythrocyte ghosts and determined the molecular binding behaviour of different anti-D antibodies towards their binding epitopes on RhD positive and negative erythrocytes. Performing optimized topography and recognition imaging at 16 Mpixel resolution allowed localisation of individual RhD molecules at the single molecule level across an entire RBC. A map of Rh antigens across integer ultraflat RBC ghosts was generated with nanometer resolution. Here we show a homogeneous distribution on rim and dimple regions with comparable receptor densities. Furthermore, differences in the energy landscape between specific monoclonal antibodies were determined at the single molecule level.

Generation of anti-idiotype scFv for pharmacokinetic measurement in lymphoma patients treated with chimera anti-CD22 antibody SM03

Pre-clinical and clinical studies of therapeutic antibodies require highly specific reagents to examine their immune responses, bio-distributions, immunogenicity, and pharmacodynamics in patients. Selective antigen-mimicking anti-idiotype antibody facilitates the assessment of therapeutic antibody in the detection, quantitation and characterization of antibody immune responses. Using mouse specific degenerate primer pairs and splenocytic RNA, we generated an idiotype antibody-immunized phage-displayed scFv library in which an anti-idiotype antibody against the therapeutic chimera anti-CD22 antibody SM03 was isolated. The anti-idiotype scFv recognized the idiotype of anti-CD22 antibody and inhibited binding of SM03 to CD22 on Raji cell surface. The anti-idiotype scFv was subsequently classified as Ab2γ type. Moreover, our results also demonstrated firstly that the anti-idiotype scFv could be used for pharmacokinetic measurement of circulating residual antibody in lymphoma patients treated with chimera anti-CD22 monoclonal antibody SM03. Of important, the present approach could be easily adopted to generate anti-idiotype antibodies for therapeutic antibodies targeting membrane proteins, saving the cost and time for producing a soluble antigen.

Generation of internal image monoclonal anti-idiotypic antibodies against idiotypic antibodies to GP5 antigen of porcine reproductive and respiratory syndrome virus

Syngeneic monoclonal anti-idiotypic antibodies (Mab2s) were generated against idiotypic antibodies to membrane glycoprotein GP5 of porcine reproductive and respiratory syndrome virus (PRRSV) using the sequential immunization method. Six of 12 Mab2s possessed potential internal image characteristics by recognizing a common idiotype on murine and swine anti-GP5 antibodies. Further serological characterization demonstrated that one of the Mab2 (Mab2-5G2) represents internal image anti-idiotope which mimicked the GP5 antigen that inhibited the interaction between idiotypic anti-GP5 antibodies and GP5 antigen, its reaction with the idiotypic anti-GP5 antibody was inhibited by GP5 antigen and detected the common Id on anti-PRRSV antibodies from pigs that were experimentally infected with PRRSV. In addition, Mab2-5G2 identified a soluble protein on MA-104 and porcine alveolar macrophages. These results indicate that Mab2-5G2 may be a useful candidate as an alternative PRRSV serodiagnostic reagent and a useful probe to study PRRSV-cell interaction.

Management and outcome of 200 cases of fetomaternal alloimmune thrombocytopenia

BACKGROUND

Fetomaternal alloimmune thrombocytopenia (FMAIT) is the commonest cause of severe thrombocytopenia in term neonates but its management remains controversial.

STUDY DESIGN AND METHODS

A 7-year prospective observational study of 200 cases of FMAIT evaluated the relationship between human platelet antigen (HPA) antibody specificity, clinical presentation, morbidity, mortality, and therapeutic interventions in the antenatal and postnatal period, with long-term follow-up of neonates with intracranial hemorrhage (ICH).

RESULTS

In 1148 referrals for FMAIT, HPA antibodies were confirmed in 200 (17%). The commonest specificities were anti-HPA-1a, 150 (75%); anti-HPA-5b, 31 (15.5%); and anti-HPA-15b, 8 (4%). Of 123 (62%) cases (two sets of twins) with no previous history of FMAIT, intrauterine deaths occurred in 5: anti-HPA-1a alone, 3; in combination with anti-HPA-5b, 1; and anti-HPA-15b, 1. Of the 120 live neonates, 103 had severe thrombocytopenia and 17 (14%) developed ICH (anti-HPA-1a, 13; anti-HPA-5b, 3; anti-HPA-15b, 1). Postnatal care varied widely with 37 percent of neonates receiving random rather than HPA-1a and -5b-negative platelets. Of the remaining 77 cases with a history of FMAIT, 40 received intrauterine transfusions. Six (15%) of these fetuses died in utero and an additional 2 developed ICH postnatally. Of the 19 children with ICH, 1 (anti-HPA-15b) died on Day +1, and neurologic sequelae persist in 13 (mean follow-up, 2.5 years).

CONCLUSION

HPA-1a antibodies are most commonly implicated in severe thrombocytopenia but HPA-5b and HPA-15b antibodies can also result in poor outcome. Postnatal transfusion management is extremely variable, and fetal transfusions are associated with significant morbidity and mortality.

High Prevalence of Human Anti‐bovine IgG Antibodies as the Major Cause of False Positive Reactions in Two‐Site Immunoassays Based on Monoclonal Antibodies

A sandwich ELISA for quantification of the endometrial protein PP14 revealed false positive reactions in 81% of male sera (n = 54). The PP14 ELISA was based on two monoclonal antibodies (Mabs) with different epitope specificities--a catcher and a biotinylated indicator. The monoclonal antibodies were purified by protein G affinity chromatography from culture supernatant containing 10% (v/v) fetal calf serum (FCS). Human anti-animal IgG (bovine, mouse, horse, and swine) antibodies and human anti-bovine serum albumin antibodies were measured using an ELISA design, with direct bridging of the solid phase and biotinylated antigens. The false positive reactions were abolished by addition of 1% (v/v) bovine serum to the dilution buffer (DB). Human anti-bovine IgG antibodies (HABIA) were detected in 99 out of 104 sera from blood donors (50 females; 54 males). HABIA levels in male sera (n = 54) were positively correlated to the false positive signals in the PP14 ELISA (r = 0.923; p < 0.0001). Antibodies to IgG from other mammalian species (mouse, horse, and swine) were also detected in the donor sera, but levels and frequencies were lower compared to that of HABIA. Furthermore, HABIA were positively correlated to human anti-bovine serum albumin antibodies in the donor sera (r = 0.639; p < 0.0001; n = 103). HABIA (prevalence 95%) cause false positive reactions due to crossbinding of contaminating bovine IgG and/or crossreaction with mouse IgG in two-site immunoassays. The apparent presence of human anti-mouse IgG antibodies (HAMA), described to create false positive results, may be due to a crossreacting fraction of the polyclonal circulating antibodies against bovine IgG.

Monoclonal anti-D for immunoprophylaxis

Routine antenatal prophylaxis with anti-D has become accepted as desirable, but concerns have been expressed about the adequacies of supply and safety of polyclonal anti-D. Human monoclonal anti-D has been produced using Epstein-Barr virus (EBV)-transformed peripheral B cells, sometimes coupled with fusions to myeloma cell lines. More recently, molecular biology techniques have been used to produce human monoclonal anti-D in a variety of different ways. Many monoclonal antibodies (mAbs) have been characterized for fine specificity and in vitro functional activity in International Workshops. Two mAbs have been shown to cause red cell clearance and immunosuppression in male volunteers. Considerations for the future development of monoclonal anti-D for prophylactic use are reviewed.