The present invention relates to a method of treating or preventing an infection, a neoplastic disease or an immune-related disease in a subject in need thereof, the method comprising contacting a therapeutically effective or immuno-effective amount of an TLR9 agonist, specifically CpG oligodeoxynucleotide 2216 (CpG ODN), with a precursor dendritic cell (pre-DC), wherein the TLR9 agonist stimulates the pre-DC to secrete one or more cytokines such as TNF-alpha and IL-12p40, to thereby activate or increase the subject's immune response for treating or preventing the infection, the neoplastic disease or the immune-related disease. The present invention also relates to immunogenic or adjuvant compositions comprising the TLR9 agonist. A method of diagnosing a deficient immune system in a subject, comprising contacting a sample comprising pre-DC from the subject with one or more TLR 9 agonists and kits thereof are also disclosed.
