The present invention provides compositions and methods for the prevention and treatment of primary and metastatic neoplastic diseases and infectious diseases, for stimulating an immune response in a subject, and for use as an alternative to interleukin-12 (IL-12) treatment. In particular, the present invention provides Apicomplexa-related proteins (ARPs) that have immune stimulatory activity and thus have uses in the treatment and prevention of cancer and infectious diseases and in immune modulation. Compositions comprising an ARP are provided. Methods of use of an ARP for the prevention and/or treatment of cancer and/or infectious diseases, for use as an alternative to interleukin-12 (IL-12) treatment, and for eliciting an immune response in a subject, are also provided.