The present invention provides vaccine compositions useful in prevention and treatment of Chlamydia sp. (e.g., C. trachomatis or C. pneumoniae) infection. Provided are polypeptide vaccine antigens comprising Chlamydia HtrA-derived sequences, including epitopic fragments, analogs, derivatives, and variants. Also provided are a method for inducing an immune response to a subject against Chlamydia infection, a method for preventing Chlamydia infection, or a method for treating a disease or symptom caused by or resulting from infection with Chlamydia, for instance, C. trachomatis or C. pneumoniae. In one embodiment, the present invention is drawn to C. trachomatis HtrA, which induces a cellular immune response and imparts partial protective immunity in vivo.