A novel bioactivity assay for monoclonal antibodies directed against IgE

Assessment of three human FcepsilonRI-transfected RBL cell-lines for identifying IgE induced degranulation utilizing peanut-allergic patient sera and peanut protein extract

Specific IgE sera screening studies are employed to investigate protein cross-reactivity. Such nonfunctional immunochemical methods cannot measure the biological activity of proteins. Therefore, an assay using RBL cells transfected with human FcepsilonRI was developed. Our objective was to evaluate the degranulation of three cell-lines expressing either the alpha-(RBL-hEI(a)-2B12 and RBL-30/25cells) or alpha-, beta-, and gamma-subunits (RBL SX-38) of the human FcepsilonRI by beta-hexosaminidase release. Purified human IgE and serum-derived polyclonal IgE from peanut-allergic subjects following challenge with anti-IgE or peanut protein extract, respectively, were utilized. Robust degranulation was induced in all three: RBL-30/25 (84%), -hEI(a)-2B12 (54%), SX-38 (94%), respectively, using purified IgE+anti-human IgE. Good release (18%, 40-45%, and 65%, respectively) occurred for one peanut-allergic subject+peanut extract with all cell-lines. With serum from three other peanut-allergic subjects, no beta-hexosaminidase release occurred with RBL-hEI(a)-2B12 cells+peanut extract, while only serum from one subject induced good degranulation, 30% and 60%, respectively, with RBL-30/25 and RBL SX 38 cells. Consistent degranulation with a potent food allergen (peanuts) was not observed. The assay's utility in safety assessment, predictive value and reproducibility for evaluating the cross-reactivity of proteins with allergens needs further investigation with additional proteins and well-characterized sera.

Human serum IgE-mediated mast cell degranulation shows poor correlation to allergen-specific IgE content

BACKGROUND

Although allergen-specific IgE content in serum can be determined immunochemically, little is known about the relationship between this parameter and the strength of the degranulation response upon allergen triggering.

OBJECTIVES

Analyse the degranulation capacity of immunochemically defined purified and serum IgE after challenge with anti-IgE or allergen using a rat mast cell line (RBL) transfected with the alpha-chain of the human high-affinity IgE receptor (FcepsilonRI).

METHODS

Purified IgE specific for 4-hydroxy-3nitrophenylacetyl, purified IgE of unknown specificity, and sera from allergic patients sensitive to Dermatophagoides pteronyssinus and Dactylis glomerata were assessed. Degranulation was measured by a beta-hexosaminidase release assay after anti-IgE or allergen-specific challenge.

RESULTS

For purified monoclonal IgE a significant correlation (r = 0.97) was found between the proportion of bound allergen-specific IgE and the strength of the degranulation response. In contrast, no correlation (r = 0.27) was detected after sensitization with serum IgE.

CONCLUSION

Our studies demonstrate that mast cell activation mediated through IgE from allergic patients is a result of complex relationships that are not only dependent on allergen-specific IgE content but also relate to the capacity to efficiently sensitize and trigger the signalling responses that lead to degranulation.

Efficacy of immunotherapy to ragweed antigen tested by controlled antigen exposure

BACKGROUND

Immunotherapy is a recognized component in the management of allergic rhinitis. Its efficacy has been evaluated in a number of clinical field trials. These methods of evaluation are limited by control of antigen exposure.

OBJECTIVE

A study was designed to evaluate the efficacy of immunotherapy in ragweed-induced rhinoconjunctivitis using an environmental exposure unit.

METHODS

Forty-three subjects were grouped into (1) immunotherapy group: ragweed-allergic subjects on maintenance ragweed immunotherapy for at least 2 years (N = 16), (2) positive control group: ragweed-allergic subjects who had never received immunotherapy (n = 16), and (3) negative control group: ragweed-nonallergic subjects (N = 11). Ragweed specific skin tests and ragweed IgE levels were obtained prior to exposure. The study was done in a room where levels of 2,500 to 3,000 grains m3 of ragweed were maintained over three hours. Symptoms were recorded every 15 minutes.

RESULTS

Nasal symptoms in the immunotherapy group were significantly less than in the positive control group after 45 minutes (P = .025). Significant differences were not observed for ocular symptoms. Combined nasal and ocular scores were 50% less in the immunotherapy group than in the positive control group by 75 minutes (P = .039). Ragweed-specific skin tests and IgE were significantly less in the immunotherapy group than in the positive control group. Rhinoconjunctivitis symptoms in the negative control group were absent throughout.

CONCLUSIONS

Controlled ragweed pollen exposure in this setting demonstrated that ragweed immunotherapy significantly reduced symptoms of ragweed-allergic rhinitis but had no significant effect on ocular symptoms. This system presents opportunities for additional studies on immunotherapy for allergic respiratory conditions.

Binding of cynomolgus monkey IgE to a humanized anti-human IgE antibody and human high affinity IgE receptor

Antibodies which block IgE binding to its high affinity receptor have the therapeutic potential for treating allergic diseases. A humanized anti-human IgE antibody (E25) was developed for this purpose. Cynomolgus monkeys were used for preclinical studies of E25. We studied the binding of purified human IgE and cynomolgus monkey IgE to E25 and the human high affinity IgE receptor alpha-chain-IgG fusion molecule (Fc epsilon RI-IgG) by surface plasmon resonance. Human IgE and cynomolgus monkey IgE bound to immobilized E25 with similar affinity (apparent Kd = 0.06 and 0.19 nM, respectively). Human IgE and cynomolgus monkey IgE also bound to immobilized Fc epsilon RI-IgG with similar affinity (apparent Kd = 0.28 and 0.30 nM, respectively). These data suggest that the cynomolgus monkey is a valid model for preclinical studies of the E25 antibody and probably for other antibodies which block IgE binding to its receptor. An enzyme-linked immunosorbent assay (ELISA) for measuring cynomolgus monkey IgE was developed to support preclinical studies. This ELISA used FcERI-IgG for capture and peroxidase labelled goat polyclonal antibody to human IgE for detection. Using purified cynomolgus monkey IgE as the standard, the serum IgE levels in six cynomolgus monkeys measured were 4-23 micrograms/ml.

Anti-IgE in allergic sensitization

Anti-IgE autoantibodies exist predominantly in the sera of patients with atopic disease. For some time such anti-IgE autoantibodies have been considered a phenomenon that may not be of clinical importance. The cloning of such anti-IgE autoantibodies has eliminated doubts of whether these antibodies exist, but it is still unclear whether such autoantibodies play a pathophysiological role. However, there are ongoing clinical trials that use humanized anti-IgE antibodies for passive immunization of atopic individuals. While this approach may not definitely clarify the role of anti-IgE autoantibodies, it will nevertheless clarify the role of IgE.

Allergen-induced histamine release in rat mast cells transfected with the alpha subunits of Fc epsilon RI

A rat mast cell histamine assay (RMCHA) has been developed to quantitate the biological activity of a recombinant humanized, monoclonal anti-IgE antibody (rhuMAbE25). Rat mast cells (RBL 48), transfected with the alpha subunit of the high affinity human IgE receptor (Fc epsilon RI), were presensitized for 2 h with human plasma containing IgE specific for ragweed and challenged with ragweed allergen in the presence of 50% D2O. Histamine release plateaus at 0.1 micrograms/ml of ragweed. The release of histamine was time, temperature and Ca2+ dependent. This ragweed-induced histamine release could be inhibited by rhuMAbE25 in a dose-dependent fashion with an IC50 of 1.19 +/- 0.31 micrograms/ml (n = 25). Other humanized MAbs and recombinant human growth factors neither trigger histamine release nor inhibit ragweed-induced histamine release. This RMCHA correlates well with the human basophil histamine assay (HBHA) (Fei et al., 1994) with a correlation coefficient of 0.93 (n = 59, p < 0.0001). Histamine was also released when the cells were presensitized with human plasma containing the respective allergen-specific IgE and then challenged with standardized mite, D. farinae, house dust mix, standardized cat pelt, or Alternaria tenuis. Comparison of allergen-induced histamine release showed a good correlation between RMCHA and HBHA with a correlation coefficient of 0.69 (n = 37, p = 0.0001). We conclude that RMCHA provides a useful tool to confirm allergen-specific IgE in allergic patients and can be used to evaluate the biological activity of any anti-IgE monoclonal antibody. Moreover, RMCHA provides an unique opportunity to study the mechanism of IgE-mediated histamine release in the absence of interfering proteins and growth factors normally present in whole blood.