Intranasal immunization against herpes simplex virus infection by using a recombinant glycoprotein D fused with immunomodulating proteins, the B subunit of Escherichia coli heat-labile enterotoxin and interleukin-2.

To establish a novel strategy of mucosal immunization against herpes simplex virus type 1 (HSV-1) infection, we studied the immune responses elicited by intranasal immunization with several forms of a recombinant glycoprotein D (gD) of HSV-1. A truncated gD (t-gD) co-administered with heat-labile enterotoxin B subunit (LTB) from Escherichia coli induced both a mucosal immune response involving secretion of anti-gD IgA and serum IgG production. The levels of these responses are comparable to those in mice which have recovered from intranasal HSV-1 infections. The fusion protein (t-gD-LTB), consisting of t-gD and LTB, induced the responses more efficiently than did co-administration of t-gD and LTB, although GM1 ganglioside binding activity was significantly reduced in t-gD-LTB. We found that another fusion protein, consisting of t-gD and human interleukin-2 (t-gD-IL-2), also elicited antibody responses comparable to those induced by t-gD-LTB. Immunity acquired by intranasal immunization with t-gD-IL-2 protected mice from intraperitoneal HSV-1 infections, whereas t-gD-LTB or t-gD alone failed to provide protection against infection. Even in a mouse strain that responded highly to subcutaneously administered gD, intranasally administered t-gD did not elicit antibody responses. The lack of response to gD was clearly abrogated by co-administration with IL-2, and administration of t-gD-IL-2 induced an excellent level of antibody responses in this strain. These results suggest that the IL-2 fusion strategy yields a new type of mucosal immunization, the mechanism of which differs from that speculated for the mucosal adjuvant activity of LTB.