Generation and characterization of high affinity human monoclonal antibodies that neutralize staphylococcal enterotoxin B

Abstract

BackgroundStaphylococcal enterotoxins are considered potential biowarfare agents that can be spread through ingestion or inhalation. Staphylococcal enterotoxin B (SEB) is a widely studied superantigen that can directly stimulate T-cells to release a massive amount of proinflammatory cytokines by bridging the MHC II molecules on an antigen presenting cell (APC) and the Vβ chains of the T-cell receptor (TCR). This potentially can lead to toxic, debilitating and lethal effects. Currently, there are no preventative measures for SEB exposure, only supportive therapies.MethodsTo develop a potential therapeutic candidate to combat SEB exposure, we have generated three human B-cell hybridomas that produce human monoclonal antibodies (HuMAbs) to SEB. These HuMAbs were screened for specificity, affinity and the ability to block SEB activity in vitro as well as its lethal effect in vivo.ResultsThe high-affinity HuMAbs, as determined by BiaCore analysis, were specific to SEB with minimal crossreactivity to related toxins by ELISA. In an immunoblotting experiment, our HuMAbs bound SEB mixed in a cell lysate and did not bind any of the lysate proteins. In an in vitro cell-based assay, these HuMAbs could inhibit SEB-induced secretion of the proinflammatory cytokines (INF-γ and TNF-α) by primary human lymphocytes with high potency. In an in vivo LPS-potentiated mouse model, our lead antibody, HuMAb-154, was capable of neutralizing up to 100 μg of SEB challenge equivalent to 500 times over the reported LD50 (0.2 μg) , protecting mice from death. Extended survival was also observed when HuMAb-154 was administered after SEB challenge.ConclusionWe have generated high-affinity SEB-specific antibodies capable of neutralizing SEB in vitro as well as in vivo in a mouse model. Taken together, these results suggest that our antibodies hold the potential as passive immunotherapies for both prophylactic and therapeutic countermeasures of SEB exposure.

Identification of Anti-Alpha Toxin Monoclonal Antibodies That Reduce the Severity of Staphylococcus aureus Dermonecrosis and Exhibit a Correlation between Affinity and Potency

“…They exhibited similar affinity constants for AT, thus precluding a similar comparison between affinity and potency. One example where affinity correlated with antitoxin potency was reported for MAbs against staphylococcal enterotoxin B (SEB); however, the potencies of the different MAbs were not examined in vivo (12). The number of MAbs compared in our study and the Drozdowski study (12) is small, yet the results provide support for the hypothesis that in some instances an increase in affinity will result in increased potency.…”

Mechanisms Mediating Enhanced Neutralization Efficacy of Staphylococcal Enterotoxin B by Combinations of Monoclonal Antibodies

“…In some cases, a combination of mAbs was required to achieve optimal protection (8 -13). However, the administration of potent neutraliz-ing SEB-specific mAbs, either individually or as cocktails (14,15), constitutes a challenge, because the onset of life-threatening symptoms after aerosol exposure occurs within 24 h (16). Given the short window for therapeutic intervention after exposure, lead clinical mAb candidates need to be optimized for postexposure treatment against SEB intoxication.…”

Synthetic Human Monoclonal Antibodies toward Staphylococcal Enterotoxin B (SEB) Protective against Toxic Shock Syndrome

“…Previous studies using human anti-SEB antibodies reported by other investigators showed partial protection even when used in a prophylactic setting (33). In another report by Drozdowski et al (34), a human anti-SEB antibody protected 90% of mice when administered at the time of challenge with SEB, whereas the protection dropped to 50 or 10% when antibody was administered 30 min or 1 hour postexposure, respectively. In contrast, three of the lead human anti-SEB antibodies reported here showed complete protection over a wide range of challenge doses when administered 1 h postchallenge.…”