Immune tolerance induced by polyethylene glycol-conjugate of protein antigen: clonal deletion of antigen-specific Th-cells in the thymus

Bioconjugate Strategies for the Induction of Antigen-Specific Tolerance in Autoimmune Diseases

Antigen-specific immunotherapy (ASI) holds great promise for the treatment of autoimmune diseases. In mice, administration of major histocompatibility complex (MHC) binding synthetic peptides which modulate T cell receptor (TCR) signaling under subimmunogenic conditions induces selective tolerance without suppressing the global immune responses. However, clinical translation has yielded limited success. It has become apparent that the TCR signaling pathway via synthetic peptide antigen alone is inadequate to induce an effective tolerogenic immunity in autoimmune diseases. Bioconjugate strategies combining additional immunomodulatory functions with TCR signaling can amplify the antigen-specific immune tolerance and possibly lead to the development of new treatments in autoimmune diseases. In this review, we provide a summary of recent advances in the development of bioconjugates to achieve antigen-specific immune tolerance in vivo, with the discussion focused on the underlying design principles and challenges that must be overcome to target these therapies to patients suffering from autoimmune diseases.

Microbiome precision editing: Using PEG as a selective fermentation initiator against methicillin-resistant Staphylococcus aureus

Recent creation of a Unified Microbiome Initiative (UMI) has the aim of understanding how microbes interact with each other and with us. When pathogenic Staphylococcus aureus infects the skin, the interplay between S. aureus and skin commensal bacteria occurs. Our previous data revealed that skin commensal bacteria can mediate fermentation against the growth of USA300, a community-acquired methicillin-resistant S. aureus MRSA. By using a fermentation process with solid media on a small scale, we define poly(ethylene glycol) dimethacrylate (PEG-DMA) as a selective fermentation initiator which can specifically intensify the probiotic ability of skin commensal Staphylococcus epidermidis bacteria. At least five short-chain fatty acids including acetic, butyric and propionic acids with anti-USA300 activities are produced by PEG-DMA fermentation of S. epidermidis. Furthermore, the S. epidermidis-laden PEG-DMA hydrogels effectively decolonized USA300 in skin wounds in mice. The PEG-DMA and its derivatives may become novel biomaterials to specifically tailor the human skin microbiome against invading pathogens.

PEGylated helper-dependent adenoviral vectors: highly efficient vectors with an enhanced safety profile

Transgene expression from helper-dependent adenoviral (HD-Ad) vectors is effective and long lasting, but not permanent. Their use is also limited by the host response against capsid proteins that precludes successful gene expression upon readministration. In this report, we test the hypothesis that PEGylation of HD-Ad reduces its toxicity and promotes transgene expression upon readministration. PEGylation did not compromise transduction efficiency in vitro and in vivo and reduced peak serum IL-6 levels two-fold. IL-12 and TNF-alpha levels were reduced three- and seven-fold, respectively. Thrombocytopenia was not detected in mice treated with the PEGylated vector. Serum transaminases were not significantly elevated in mice treated with either vector. Mice immunized with 1 x 10(11) particles of unmodified HD-Ad expressing human alpha-1 antitrypsin (hA1AT) were rechallenged 28 days later with 8 x 10(10) particles of unmodified or PEG-conjugated vector expressing beta-galactosidase. Trace levels of beta-galactosidase (52.23+/-19.2 pg/mg protein) were detected in liver homogenates of mice that received two doses of unmodified HD-Ad. Mice rechallenged with PEGylated HD-Ad produced significant levels of beta-galactosidase (5.1+/-0.4 x 10(5) pg/mg protein, P=0.0001). This suggests that PEGylation of HD-Ad vectors may be appropriate for their safe and efficient use in the clinic.

Phenylalanine ammonia-lyase modified with polyethylene glycol: potential therapeutic agent for phenylketonuria

Phenylketonuria (PKU) is an autosomal recessive genetic disease caused by the defects in the phenylalanine hydroxylase (PAH) gene. Individuals homozygous for defective PAH alleles show elevated levels of systemic phenylalanine and should be under strict dietary control to reduce the risk of neuronal damage associated with high levels of plasma phenylalanine. Researchers predict that plant phenylalanine ammonia-lyase (PAL), which converts phenylalanine to nontoxic t-cinnamic acid, will be an effective therapeutic enzyme for the treatment of PKU. The problems of this potential enzyme therapy have been the low stability in the circulation and the antigenicity of the plant enzyme. Recombinant PAL originated from parsley (Petroselinum crispum) chemically conjugated with activated PEG2 [2,4-bis(O-methoxypolyethyleneglycol)-6-chloro-s-triazine] showed greatly enhanced stability in the circulation and was effective in reducing the plasma concentration of phenylalanine in the circulation of mice. PEG-PAL conjugate will be an effective therapeutic enzyme for the treatment of PKU.