Functional Antibodies Targeting IsaA of Staphylococcus aureus Augment Host Immune Response and Open New Perspectives for Antibacterial Therapy

Abstract

Staphylococcus aureusis the most common cause of nosocomial infections. Multiple antibiotic resistance and severe clinical outcomes provide a strong rationale for development of immunoglobulin-based strategies. Traditionally, novel immunological approaches against bacterial pathogens involve antibodies directed against cell surface-exposed virulence-associated epitopes or toxins. In this study, we generated a monoclonal antibody targeting the housekeeping protein IsaA, a suggested soluble lytic transglycosylase ofS. aureus, and tested its therapeutic efficacy in two experimental mouse infection models. A murine anti-IsaA antibody of the IgG1 subclass (UK-66P) showed the highest binding affinity in Biacore analysis. This antibody recognized allS. aureusstrains tested, including hospital-acquired and community-acquired methicillin-resistantS. aureusstrains. Therapeutic efficacyin vivoin mice was analyzed using a central venous catheter-related infection model and a sepsis survival model. In both models, anti-IsaA IgG1 conferred protection against staphylococcal infection.Ex vivo, UK-66P activates professional phagocytes and induces highly microbicidal reactive oxygen metabolites in a dose-dependent manner, resulting in bacterial killing. The study provides proof of concept that monoclonal IgG1 antibodies with high affinity to the ubiquitously expressed, single-epitope-targeting IsaA are effective in the treatment of staphylococcal infection in different mouse models. Anti-IsaA antibodies might be a useful component in an antibody-based therapeutic for prophylaxis or adjunctive treatment of human cases ofS. aureusinfections.

Characterization of the biological anti-staphylococcal functionality of hUK-66 IgG1, a humanized monoclonal antibody as substantial component for an immunotherapeutic approach

“…The equilibrium dissociation constant (K D ) for hUK-66 was 4.8 nM and that for murine UK-66P was 1.7 nM. 9 The association (k a ) and dissociation (k d ) rate constants for the interaction between hUK-66 and rIsaA were 3. , respectively. These results show that hUK-66 IgG1 binds specifically to rIsaA with high affinity (rapid association and relatively slow dissociation), and confirming, that the hUK-66 antibody retains its high affinity for IsaA after humanization.…”

“…9 These encouraging results prompted us to select UK-66P for humanization as a prerequisite for further clinical development as a component for passive immunotherapeutic approach to treating S. aureus infections. Based on the mouse VH and VL sequences, the UK-66 antigen binding site was humanized by grafting the CDRs onto human frameworks obtained from the closest human germline V segments.…”

“…9 We selected IsaA, a supposed lytic transglycosylase, as the target for antibody-based therapy, because all analyzed patients surviving staphylococcal sepsis produced significant levels of IsaA-specific antibodies. 10 Moreover, IsaA is expressed on the surface of S. aureus, and is evolutionary highly conserved.…”

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

“…The difficulty of treatment and the slowed progress in the identification of new antibiotics necessitate the development of new approaches to antibacterial prophylaxis and therapy (29,32). One alternate strategy being explored is the use of monoclonal antibodies (MAbs) directed against a surface determinant on the pathogen and/or virulence factors produced by the invading pathogen to be used in prophylaxis or as adjunctive therapy with antibiotics (13,14,22,30,36). Antigens for which there are promising preclinical data on the use of MAbs against S. aureus include IsaA, IsdB, ClfA, and alpha toxin (AT).…”

Physiology and Pathology of Multidrug-Resistant Bacteria: Antibodies- and Vaccines-Based Pathogen-Specific Targeting

“…Similarly, protection was conferred by a mAb speciic to IsaA in a mouse model [75]. The mode of action of mAb is mainly through activation of professional phagocytes and induction of oxidative burst activity of neutrophil.…”