Oral immunization with a Lactobacillus casei vaccine expressing human papillomavirus (HPV) type 16 E7 is an effective strategy to induce mucosal cytotoxic lymphocytes against HPV16 E7.

Although many clinical trials on human papillomavirus (HPV) therapeutic vaccines have been performed, clinical responses have not been consistent. We have addressed mucosal cytotoxic cellular immune responses to HPV16 E7 after oral immunization of mice with recombinant Lactobacillus casei expressing HPV16 E7 (LacE7). C57BL/6 mice were orally exposed to 0.1-100mg/head of attenuated LacE7 or vehicle (Lac) vaccines at weeks 1, 2, 4, and 8. Responses to subcutaneous or intramuscular injection of an HPV16 E7 fusion protein using the same timing protocol were used for comparison. Oral immunization with LacE7 elicited E7-specific IFN gamma-producing cells (T cells with E7-type 1 immune responses) among integrin alpha 4 beta 7(+) mucosal lymphocytes collected from gut mucosa. An induction of E7-specific granzyme B-producing cells (E7-CTL) exhibiting killer responses toward HPV16 E7-positive cells was also observed. The induction of T cells with specific mucosal E7-type 1 immune responses was greater after oral immunization with LacE7 when compared to subcutaneous or intramuscular antigen delivery. Oral immunization with Lactobacillus-based vaccines was also able to induce mucosal cytotoxic cellular immune responses. This novel approach at a therapeutic HPV vaccine may achieve more effective clinical responses through its induction of mucosal E7-specific CTL.