ABSTRACT
Following the success of immune checkpoint blockade therapy against cancer, agonistic antibodies targeting T-cell costimulatory pathways are in clinical trials. The TNF superfamily of receptors (TNFRSF) members CD137 and OX40 are costimulatory receptors that stimulate T-cell proliferation and activation upon interaction with their cognate ligands. Activating CD137 and OX40 with agonistic mAbs stimulates the immune system due to their broad expression on CD4+ and CD8+ T cells and natural killer cells and has antitumor effects in preclinical models. Most TNFRSF agonist antibodies require crosslinking via Fcγ receptors (FcγR), which can limit their clinical activity. FS120 mAb2, a dual agonist bispecific antibody targeting CD137 and OX40, activated both CD4+ and CD8+ T cells in an FcγR-independent mechanism, dependent on concurrent binding. A mouse surrogate version of the bispecific antibody displayed antitumor activity in syngeneic tumor models, independent of T regulatory cell depletion and of FcγR interaction, but associated with peripheral T-cell activation and proliferation. When compared with a crosslink-independent CD137 agonist mAb, the FS120 surrogate induced lower liver T-cell infiltration. These data support initiation of clinical development of FS120, a first-in-class dual agonist bispecific antibody for the treatment of human cancer.
Subject(s)
Antibodies, Bispecific/pharmacology , Colonic Neoplasms/therapy , Killer Cells, Natural/immunology , Lymphocyte Activation/immunology , Receptors, OX40/immunology , T-Lymphocytes, Regulatory/immunology , Tumor Necrosis Factor Receptor Superfamily, Member 9/immunology , Animals , Apoptosis , Cell Proliferation , Colonic Neoplasms/immunology , Colonic Neoplasms/metabolism , Colonic Neoplasms/pathology , Female , Humans , Immunotherapy , Mice , Mice, Inbred BALB C , Tumor Cells, Cultured , Xenograft Model Antitumor AssaysABSTRACT
Although specific antibody induced by pathogens or vaccines is a key component of protection against infectious threats, some viruses, such as dengue, induce antibody that enhances the development of infection. In contrast, antibody-dependent enhancement of bacterial infection is largely unrecognized. Here, we demonstrate that in a significant portion of patients with bronchiectasis and Pseudomonas aeruginosa lung infection, antibody can protect the bacterium from complement-mediated killing. Strains that resist antibody-induced, complement-mediated killing produce lipopolysaccharide containing O-antigen. The inhibition of antibody-mediated killing is caused by excess production of O-antigen-specific IgG2 antibodies. Depletion of IgG2 to O-antigen restores the ability of sera to kill strains with long-chain O-antigen. Patients with impaired serum-mediated killing of P. aeruginosa by IgG2 have poorer respiratory function than infected patients who do not produce inhibitory antibody. We suggest that excessive binding of IgG2 to O-antigen shields the bacterium from other antibodies that can induce complement-mediated killing of bacteria. As there is significant sharing of O-antigen structure between different Gram-negative bacteria, this IgG2-mediated impairment of killing may operate in other Gram-negative infections. These findings have marked implications for our understanding of protection generated by natural infection and for the design of vaccines, which should avoid inducing such blocking antibodies.
Subject(s)
Antibody-Dependent Enhancement/immunology , Blood Bactericidal Activity/immunology , Immunoglobulin G/blood , Immunoglobulin G/immunology , O Antigens/immunology , Pseudomonas Infections/blood , Pseudomonas aeruginosa , Respiratory Tract Infections/blood , Respiratory Tract Infections/immunology , Antibodies, Blocking/blood , Bronchiectasis/blood , Bronchiectasis/immunology , Bronchiectasis/physiopathology , Complement System Proteins/immunology , Humans , Pseudomonas Infections/immunology , Pseudomonas Infections/physiopathology , Pseudomonas aeruginosa/immunology , Respiratory Tract Infections/physiopathologyABSTRACT
Nontyphoidal Salmonellae commonly cause fatal bacteraemia in African children lacking anti-Salmonella antibodies. These are facultative intracellular bacteria capable of cell-free and intracellular survival within macrophages. To better understand the relationship between extracellular and intracellular infection in blood and general mechanisms of Ab-related protection against Salmonella, we used human blood and sera to measure kinetics of Ab and complement deposition, serum-mediated bactericidal killing and phagocytosis of invasive African Salmonella enterica serovar Typhimurium D23580. Binding of antibodies peaked by 30 s, but C3 deposition lagged behind, peaking after 2-4 min. C5b-9 deposition was undetectable until between 2 and 6 min and peaked after 10 min, after which time an increase in serum-mediated killing occurred. In contrast, intracellular, opsonized Salmonellae were readily detectable within 5 min. By 10 min, around half of monocytes and most neutrophils contained bacteria. The same kinetics of serum-mediated killing and phagocytosis were observed with S. enterica Typhimurium laboratory strain SL1344, and the S. enterica Enteritidis African invasive isolate D24954 and laboratory strain PT4. The differential kinetics between cell-free killing and phagocytosis of invasive nontyphoidal Salmonella allows these bacteria to escape the blood and establish intracellular infection before they are killed by the membrane attack complex.
Subject(s)
Antibodies, Bacterial/immunology , Complement Membrane Attack Complex/immunology , Phagocytosis/immunology , Salmonella enteritidis/immunology , Salmonella typhimurium/immunology , Adult , Blood Bactericidal Activity , Complement C3/immunology , Complement C5b/immunology , Flow Cytometry , Host-Pathogen Interactions/immunology , Humans , Kinetics , Microbial Viability/immunology , Monocytes/cytology , Monocytes/immunology , Monocytes/microbiology , Neutrophils/cytology , Neutrophils/immunology , Neutrophils/microbiology , Opsonin Proteins/immunology , Salmonella enteritidis/physiology , Salmonella typhimurium/physiology , Serum/immunology , Serum/microbiology , Time FactorsABSTRACT
Salmonella enterica is a major cause of morbidity worldwide and mortality in children and immunocompromised individuals in sub-Saharan Africa. Outer membrane proteins of Salmonella are of significance because they are at the interface between the pathogen and the host, they can contribute to adherence, colonization, and virulence, and they are frequently targets of antibody-mediated immunity. In this study, the properties of SadA, a purported trimeric autotransporter adhesin of Salmonella enterica serovar Typhimurium, were examined. We demonstrated that SadA is exposed on the Salmonella cell surface in vitro and in vivo during infection of mice. Expression of SadA resulted in cell aggregation, biofilm formation, and increased adhesion to human intestinal Caco-2 epithelial cells. Immunization of mice with folded, full-length, purified SadA elicited an IgG response which provided limited protection against bacterial challenge. When anti-SadA IgG titers were enhanced by administering alum-precipitated protein, a modest additional protection was afforded. Therefore, despite SadA having pleiotropic functions, it is not a dominant, protective antigen for antibody-mediated protection against Salmonella.
Subject(s)
Adhesins, Bacterial/metabolism , Bacterial Adhesion/physiology , Biofilms , Gene Expression Regulation, Bacterial/physiology , Membrane Proteins/metabolism , Salmonella typhimurium/metabolism , Adhesins, Bacterial/genetics , Alum Compounds , Animals , Bacterial Adhesion/genetics , Caco-2 Cells , Escherichia coli K12/metabolism , Humans , Immunoglobulin G , Membrane Proteins/genetics , Mice , Phylogeny , Salmonella typhimurium/genetics , Salmonella typhimurium/pathogenicity , VirulenceABSTRACT
Salmonella enterica is a major cause of morbidity worldwide and mortality in children and immunocompromisedindividuals in sub-Saharan Africa. Outer membrane proteins of Salmonella are of significance becausethey are at the interface between the pathogen and the host, they can contribute to adherence, colonization, and virulence, and they are frequently targets of antibody-mediated immunity. In this study, the properties of SadA,a purported trimeric autotransporter adhesin of Salmonella enterica serovar Typhimurium, were examined. Wedemonstrated that SadA is exposed on the Salmonella cell surface in vitro and in vivo during infection of mice.Expression of SadA resulted in cell aggregation, biofilm formation, and increased adhesion to human intestinalCaco-2 epithelial cells. Immunization of mice with folded, full-length, purified SadA elicited an IgG responsewhich provided limited protection against bacterial challenge. When anti-SadA IgG titers were enhanced byadministering alum-precipitated protein, a modest additional protection was afforded. Therefore, despite SadAhaving pleiotropic functions, it is not a dominant, protective antigen for antibody-mediated protection againstSalmonella.