Vaccine candidates in STD.

Sexually transmitted diseases (STDs) are caused by organisms that infect the mucosal surfaces of the genitourinary tract. In spite of its public health importance, particular scientific problems have delayed the development of an STD vaccine, such as incomplete attenuation (human herpes simplex virus type 2), accentuated immunopathology (Chlamydia trachomatis), poor immunogenicity (Treponema pallidum), and broad antigenic heterogeneity (Neisseria gonorrhoeae). Nevertheless, efforts continue with the use of protein antigens: for example, the haemolysin toxoid of Haemophilus ducreyi; the major outer membrane protein(s) of N. gonorrhoeae and C. trachomatis; the glycoprotein D of human herpes simplex virus type 2; and the proteins E6 and E7 of the human papillomavirus. It could be predicted that eventual STD vaccines (administered either for prophylaxis or for therapy) will use approaches that will include (1) live-attenuated viruses, (2) subunit proteins or inactivated whole organisms given with mucosal adjuvants or with cellular immune response adjuvants, or (3) DNA plasmids expressing the vaccine antigen.