Objectives: The primary goal of the present study is to determine the breadth of neutralizing activity of human antibodies against superantigens of S. aureus and S. pyogenes elicited by natural exposure. The secondary objective is to determine the range of cross reactivity of toxin-specific human polyclonal antibodies purified by affinity purification. The long term objective is to explore the possibility of developing hyperimmune human polyclonal antibodies with broad reactivity toward superantigenic toxins produced by S. aureus and S. pyogenes.
Methods: Twenty eight purified commercial IVIG batches and thirty individual plasma samples from healthy donors were tested by ELISA to identify the titers against SEA, SEB, TSST-1, SED, SpeA, and SpeC. In vitro toxin neutralization activity (TNA) assays based on T-cell proliferation and cytokine responses were performed in human peripheral blood mononuclear cells and the TNA titer of all samples for each toxin was identified. Specific human anti-toxin polyclonal antibodies (pAb) were purified by affinity columns from pooled IVIG. The breadth of TNA activity of each purified pAb was determined toward all the other toxins. Finally, the therapeutic efficacy of pooled and purified antibodies was determined in a mouse model of toxic shock.
Results: All IVIG samples display low to moderate titers against the tested superantigens. The highest activity was observed toward SEB, SEC, and TSST-1 and the lowest reactivity for SED. The difference in ELISA titers generally correlated with the TNA titers. The studies with purified pAb showed that anti-SEB antibodies cross react to varying degree with all other superantigens except for SpeC and TSST-1. Studies with other purified pAbs and in vivo efficacy studies are underway and will be presented.
Conclusions: Preliminary findings support the notion that highly effective human antibody therapeutics can be developed to treat toxic shock induced by staphylococcal and streptococcal superantigens. However, the levels of anti-toxin activity in IVIG preparations may be insufficient for a reliable therapeutic outcome. Approaches to produce hyperimmune IVIG may be needed to develop a clinically effective therapeutic.