Sequence-specific binding of normal serum immunoglobulin M to exposed protein C-termini

Engineering Phages to Fight Multidrug-Resistant Bacteria

Facing the global "superbug" crisis due to the emergence and selection for antibiotic resistance, phages are among the most promising solutions. Fighting multidrug-resistant bacteria requires precise diagnosis of bacterial pathogens and specific cell-killing. Phages have several potential advantages over conventional antibacterial agents such as host specificity, self-amplification, easy production, low toxicity as well as biofilm degradation. However, the narrow host range, uncharacterized properties, as well as potential risks from exponential replication and evolution of natural phages, currently limit their applications. Engineering phages can not only enhance the host bacteria range and improve phage efficacy, but also confer new functions. This review first summarizes major phage engineering techniques including both chemical modification and genetic engineering. Subsequent sections discuss the applications of engineered phages for bacterial pathogen detection and ablation through interdisciplinary approaches of synthetic biology and nanotechnology. We discuss future directions and persistent challenges in the ongoing exploration of phage engineering for pathogen control.

Engineered Bacteriophage Therapeutics: Rationale, Challenges and Future

The current problems with increasing bacterial resistance to antibacterial therapies, resulting in a growing frequency of incurable bacterial infections, necessitates the acceleration of studies on antibacterials of a new generation that could offer an alternative to antibiotics or support their action. Bacteriophages (phages) can kill antibiotic-sensitive as well as antibiotic-resistant bacteria, and thus are a major subject of such studies. Their efficacy in curing bacterial infections has been demonstrated in in vivo experiments and in the clinic. Unlike antibiotics, phages have a narrow range of specificity, which makes them safe for commensal microbiota. However, targeting even only the most clinically relevant strains of pathogenic bacteria requires large collections of well characterized phages, whose specificity would cover all such strains. The environment is a rich source of diverse phages, but due to their complex relationships with bacteria and safety concerns, only some naturally occurring phages can be considered for therapeutic applications. Still, their number and diversity make a detailed characterization of all potentially promising phages virtually impossible. Moreover, no single phage combines all the features required of an ideal therapeutic agent. Additionally, the rapid acquisition of phage resistance by bacteria may make phages already approved for therapy ineffective and turn the search for environmental phages of better efficacy and new specificity into an endless race. An alternative strategy for acquiring phages with desired properties in a short time with minimal cost regarding their acquisition, characterization, and approval for therapy could be based on targeted genome modifications of phage isolates with known properties. The first example demonstrating the potential of this strategy in curing bacterial diseases resistant to traditional therapy is the recent successful treatment of a progressing disseminated Mycobacterium abscessus infection in a teenage patient with the use of an engineered phage. In this review, we briefly present current methods of phage genetic engineering, highlighting their advantages and disadvantages, and provide examples of genetically engineered phages with a modified host range, improved safety or antibacterial activity, and proven therapeutic efficacy. We also summarize novel uses of engineered phages not only for killing pathogenic bacteria, but also for in situ modification of human microbiota to attenuate symptoms of certain bacterial diseases and metabolic, immune, or mental disorders.

Bacteriophages engineered to display foreign peptides may become short-circulating phages

Bacteriophages draw scientific attention in medicine and biotechnology, including phage engineering, widely used to shape biological properties of bacteriophages. We developed engineered T4-derived bacteriophages presenting seven types of tissue-homing peptides. We evaluated phage accumulation in targeted tissues, spleen, liver and phage circulation in blood (in mice). Contrary to expectations, accumulation of engineered bacteriophages in targeted organs was not observed, but instead, three engineered phages achieved tissue titres up to 2 orders of magnitude lower than unmodified T4. This correlated with impaired survival of these phages in the circulation. Thus, engineering of T4 phage resulted in the short-circulating phage phenotype. We found that the complement system inactivated engineered phages significantly more strongly than unmodified T4, while no significant differences in phages' susceptibility to phagocytosis or immunogenicity were found. The short-circulating phage phenotype of the engineered phages suggests that natural phages, at least those propagating on commensal bacteria of animals and humans, are naturally optimized to escape rapid neutralization by the immune system. In this way, phages remain active for longer when inside mammalian bodies, thus increasing their chance of propagating on commensal bacteria. The effect of phage engineering on phage pharmacokinetics should be considered in phage design for medical purposes.

In vivo selection and validation of liver-specific ligands using a new T7 phage peptide display system

In vivo phage display is a powerful source of new peptide ligands for specific organ targeting by drugs and gene therapy vectors. Since the introduction of this methodology a decade ago, a number of peptides that preferentially react with organ-specific endothelium and parenchymal markers have been selected. One organ that has been conspicuously missing from these selection studies is the liver, which possesses a multitude of acquired and hereditary disorders and represents a highly important therapeutic target. Herein, we set out to fill this gap by introducing a novel peptide display system containing cloned sequences in the tail fiber protein (p17) of phage T7. The p17 display effectively avoids the innate immune system and is well suited both for selection of new liver-specific ligands and for validation of protein sequences that have been implicated in liver targeting by the use of conventional biochemical methods.

The acquisition of narrow binding specificity by polyspecific natural IgM antibodies in a semi-physiological environment

Natural IgM antibodies (Abs) play an important role in clearing pathogens, enhancing immune responses, and preventing autoimmunity. However, the molecular mechanisms that mediate the functions of natural IgM Abs are understood only to a limited degree. This shortcoming is largely due to the fact that isolated natural IgM Abs are commonly polyspecific and recognize a variety of antigens (Ags) with no apparent structural homology. It is generally believed that polyspecificity is an inherent property of natural Abs. However, there is increasing evidence that polyspecificity may be induced by mild denaturing conditions. In this study, we compared the specificity of three polyspecific IgM Abs in conventional buffers and undiluted sera deficient in immunoglobulins. All three Abs lost their polyspecificity in serum. They no longer reacted with conventional screening Ags, including hapten-BSA conjugates, ssDNA, thyroglobulin and myosin, but fully retained their reactivity with cognate peptide Ags selected from a T7 phage library. The acquisition of narrow specificity by polyspecific IgM in serum was also observed with muscle tissue sections used as a source of endogenous Ags. The loss of polyspecificity by different Abs was apparently dependent on the presence of different serum constituents. The results of this study suggest that the seemingly inherent polyspecificity of many natural IgM Abs may be largely an in vitro phenomenon related to the lack of normal serum components in the medium. Potential mechanisms underlying the loss of polyreactivity are discussed.