An adenovirus vectored mucosal adjuvant augments protection of mice immunized intranasally with an adenovirus-vectored foot-and-mouth disease virus subunit vaccine.

Foot-and-mouth disease virus (FMDV) is a highly contagious pathogen that causes severe morbidity and economic losses to the livestock industry in many countries. The oral and respiratory mucosae are the main ports of entry of FMDV, so the stimulation of local immunity in these tissues may help prevent initial infection and viral spread. E. coli heat-labile enterotoxin (LT) has been described as one of the few molecules that have adjuvant activity at mucosal surfaces. The objective of this study was to evaluate the efficacy of replication-defective adenovirus 5 (Ad5) vectors encoding either of two LT-based mucosal adjuvants, LTB or LTR72. These vectored adjuvants were delivered intranasally to mice concurrent with an Ad5-FMDV vaccine (Ad5-A24) to assess their ability to augment mucosal and systemic humoral immune responses to Ad5-A24 and protection against FMDV. Mice receiving Ad5-A24 plus Ad5-LTR72 had higher levels of mucosal and systemic neutralizing antibodies than those receiving Ad5-A24 alone or Ad5-A24 plus Ad5-LTB. The vaccine plus Ad5-LTR72 group also demonstrated 100% survival after intradermal challenge with a lethal dose of homologous FMDV serotype A24. These results suggest that Ad5-LTR72 could be used as an important tool to enhance mucosal and systemic immunity against FMDV and potentially other pathogens with a common route of entry.

Xenoepitope substitution avoids deceptive imprinting and broadens the immune response to foot-and-mouth disease virus.

Many RNA viruses encode error-prone polymerases which introduce mutations into B and T cell epitopes, providing a mechanism for immunological escape. When regions of hypervariability are found within immunodominant epitopes with no known function, they are referred to as "decoy epitopes," which often deceptively imprint the host's immune response. In this work, a decoy epitope was identified in the foot-and-mouth disease virus (FMDV) serotype O VP1 G-H loop after multiple sequence alignment of 118 isolates. A series of chimeric cyclic peptides resembling the type O G-H loop were prepared, each bearing a defined "B cell xenoepitope" from another virus in place of the native decoy epitope. These sequences were derived from porcine respiratory and reproductive syndrome virus (PRRSV), from HIV, or from a presumptively tolerogenic sequence from murine albumin and were subsequently used as immunogens in BALB/c mice. Cross-reactive antibody responses against all peptides were compared to a wild-type peptide and ovalbumin (OVA). A broadened antibody response was generated in animals inoculated with the PRRSV chimeric peptide, in which virus binding of serum antibodies was also observed. A B cell epitope mapping experiment did not reveal recognition of any contiguous linear epitopes, raising the possibility that the refocused response was directed to a conformational epitope. Taken together, these results indicate that xenoepitope substitution is a novel method for immune refocusing against decoy epitopes of RNA viruses such as FMDV as part of the rational design of next-generation vaccines.