Removal of natural anti-αGal antibodies elicits protective immunity against Gram-negative bacterial infections.

Antibody-dependent enhancement (ADE) of bacterial infections occurs when blocking or inhibitory antibodies facilitate the infectivity of pathogens. In humans, antibodies involved in ADE of bacterial infections may include those naturally produced against Galα1-3Galß1-4GlcNAcß (αGal). Here, we investigate whether eliminating circulating anti-αGal antibodies using a soluble αGal glycopolymer confers protection against Gram-negative bacterial infections. We demonstrated that the in vivo intra-corporeal removal of anti-αGal antibodies in α1,3-galactosyltransferase knockout (GalT-KO) mice was associated with protection against mortality from Gram-negative sepsis after cecal ligation and puncture (CLP). The improved survival of GalT-KO mice was associated with an increased killing capacity of serum against Escherichia coli isolated after CLP and reduced binding of IgG1 and IgG3 to the bacteria. Additionally, inhibition of anti-αGal antibodies from human serum in vitro increases the bactericidal killing of E. coli O86:B7 and multidrug-resistant Klebsiella pneumoniae and Pseudomonas aeruginosa. In the case of E. coli O86:B7, there was also an improvement in bacteria opsonophagocytosis by macrophages. Both lytic mechanisms were related to a decreased binding of IgG2 to the bacteria. Our results show that protective immunity against Gram-negative bacterial pathogens can be elicited, and infectious diseases caused by these bacteria can be prevented by removing natural anti-αGal antibodies.

Poly-L-Lysine-Based αGal-Glycoconjugates for Treating Anti-αGal IgE-Mediated Diseases.

Anti-αGal IgE antibodies mediate a spreading allergic condition known as αGal-syndrome (AGS). People exposed to hard tick bites are sensitized to αGal, producing elevated levels of anti-αGal IgE, which are responsible for AGS. This work presents an immunotherapy based on polymeric αGal-glycoconjugates for potentially treating allergic disorders by selectively inhibiting anti-αGal IgE antibodies. We synthesized a set of αGal-glycoconjugates, based on poly-L-lysine of different degrees of polymerization (DP1000, DP600, and DP100), to specifically inhibit in vitro the anti-αGal IgE antibodies in the serum of αGal-sensitized patients (n=13). Moreover, an animal model for αGal sensitization in GalT-KO mice was developed by intradermal administration of hard tick' salivary gland extract, mimicking the sensitization mechanism postulated in humans. The in vitro exposure to all polymeric glycoconjugates (5-10-20-50-100 µg/mL) mainly inhibited anti-αGal IgE and IgM isotypes, with a lower inhibition effect on the IgA and IgG, respectively. We demonstrated a differential anti-αGal isotype inhibition as a function of the length of the poly-L-lysine and the number of αGal residues exposed in the glycoconjugates. These results defined a minimum of 27 αGal residues to inhibit most of the induced anti-αGal IgE in vitro. Furthermore, the αGal-glycoconjugate DP1000-RA0118 (10 mg/kg sc.) showed a high capacity to remove the anti-αGal IgE antibodies (≥75% on average) induced in GalT-KO mice, together with similar inhibition for circulating anti-αGal IgG and IgM. Our study suggests the potential clinical use of poly-L-lysine-based αGal-glycoconjugates for treating allergic disorders mediated by anti-αGal IgE antibodies.