RESUMEN
Secreted alpha-toxin and surface-localized clumping factor A (ClfA) are key virulence determinants in Staphylococcus aureus bloodstream infections. We previously demonstrated that prophylaxis with a multimechanistic monoclonal antibody (MAb) combination against alpha-toxin (MEDI4893*) and ClfA (11H10) provided greater strain coverage and improved efficacy in an S. aureus lethal bacteremia model. Subsequently, 11H10 was found to exhibit reduced affinity and impaired inhibition of fibrinogen binding to ClfA002 expressed by members of a predominant hospital-associated methicillin-resistant S. aureus (MRSA) clone, ST5. Consequently, we identified another anti-ClfA MAb (SAR114) from human tonsillar B cells with >100-fold increased affinity for three prominent ClfA variants, including ClfA002, and potent inhibition of bacterial agglutination by 112 diverse clinical isolates. We next constructed bispecific Abs (BiSAbs) comprised of 11H10 or SAR114 as IgG scaffolds and grafted anti-alpha-toxin (MEDI4893*) single-chain variable fragment to the amino or carboxy terminus of the anti-ClfA heavy chains. Although the BiSAbs exhibited in vitro potencies similar to those of the parental MAbs, only 11H10-BiSAb, but not SAR114-BiSAb, showed protective activity in murine infection models comparable to the respective MAb combination. In vivo activity with SAR114-BiSAb was observed in infection models with S. aureus lacking ClfA. Our data suggest that high-affinity binding to ClfA sequesters the SAR114-BiSAb to the bacterial surface, thereby reducing both alpha-toxin neutralization and protection in vivo These results indicate that a MAb combination targeting ClfA and alpha-toxin is more promising for future development than the corresponding BiSAb.
Asunto(s)
Anticuerpos Monoclonales/uso terapéutico , Anticuerpos Neutralizantes/uso terapéutico , Bacteriemia/tratamiento farmacológico , Toxinas Bacterianas/inmunología , Coagulasa/inmunología , Proteínas Hemolisinas/inmunología , Staphylococcus aureus Resistente a Meticilina/efectos de los fármacos , Infecciones Estafilocócicas/tratamiento farmacológico , Animales , Anticuerpos Antibacterianos/inmunología , Anticuerpos Antibacterianos/uso terapéutico , Anticuerpos Monoclonales/inmunología , Anticuerpos Monoclonales Humanizados , Anticuerpos Neutralizantes/inmunología , Bacteriemia/microbiología , Anticuerpos ampliamente neutralizantes , Femenino , Staphylococcus aureus Resistente a Meticilina/inmunología , Staphylococcus aureus Resistente a Meticilina/patogenicidad , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Infecciones Estafilocócicas/inmunología , Factores de VirulenciaRESUMEN
Accumulation and deposition of beta amyloid (Abeta) play a critical role in the pathogenesis of Alzheimer's Disease (AD), and numerous approaches to control Abeta aggregation are being actively pursued. Brain Abeta levels are controlled by the action of several proteolytic enzymes such as neprilysin (NEP), insulin degrading enzyme (IDE) and plasmin. While up-regulation of these enzymes increased clearance of Abeta in transgenic mouse models of AD, these enzymes have other natural substrates and multiple cleavage sites in Abeta complicating their use for treating AD. Alternatively, immunotherapeutic approaches to clear Abeta are gaining interest. Active and passive immunization studies with Abeta can reduce plaque burden and memory loss, but clinical trials were stopped due to meningioencephalitis in some patients. Naturally occurring proteolytic antibodies have been shown to cleave Abeta, and their serum titers are increased in patients with AD reflecting a protective autoimmune response. These antibodies however cannot cross the blood brain barrier and depend entirely on peripheral clearance to clear Abeta. A potentially non-inflammatory approach to facilitate Abeta clearance and reduce toxicity is to promote hydrolysis of Abeta at its alpha-secretase site using affinity matured single chain antibody fragments (scFvs). Bispecific antibodies consisting of a proteolytic scFv and a targeting scFv can be engineered to selectively supplement and target extracellular alpha-secretase activity and to target toxic Abeta forms facilitating their degradation and clearance without generating an immune response. This strategy represents a suitable paradigm for treating other neurological diseases such as Parkinson's Disease, Lou Gehrig's Disease, and spongiform encephalopathies.