ODN 1585 is a Type A murine TLR9 agonist whose mechanism of action preferably involves indirect activation of the natural killer cells, induced regression of the MHC class I-deficient tumors TC1/A9 but not of the MHC class I proficient tumors TC-1. The synthetic CpG ODN have a potential for the therapy of both MHC class I-proficient and -deficient tumors and thus could be also used against tumors that tend to downregulate their MHC class I expression.