The capacity of CIITA-dependent MHC class II expressing tumor cells to serve as APC in vivo raises the question of whether these cells possess or acquire the expression of co-stimulatory molecules, such as B7.1 (CD80) and B7.2 (CD86) that may serve as “signal 2” in triggering antigen-specific naïve TH cells upon interaction with CD28 (50), as previous studies of another group has shown that prevention of tumor growth in vivo of CIITA-modified tumor cells in a distinct model of mammary carcinoma in H-2q model required also expression of CD80 (51). Here, CD86 is linked to breast carcinoma.