An unexpected potential use for embryonic stem (ES) cells: "One of the most auspicious, yet challenging, avenues for combating malignancies is to enlist the immune system to come to the defense of the patient. However, myriad components of the immune system interact in extraordinarily complex ways with active or dormant neoplastic cells, an interaction matrix that is incompletely understood at best. ... [Researchers] reason that exposure of the immune system to novel tumor-associated antigens might boost an otherwise inadequate immune response into an effective antitumor action. What distinguishes the study is the source of these tumor-associated antigens: human ES and iPS cells. Specifically, the study investigated whether vaccination of mice with human ES or iPS cell lines would trigger an enhanced immunological response against shared antigens expressed by the primitive normal cells and the colon carcinoma cell line CT26 ... vaccination of mice with the human ES cell line H9 induced both strong cellular and humoral immune responses against CT26 colon carcinoma. ... There is a certain irony in the fact that human ES cells, which themselves possess many features of neoplastic cells - including sustained telomerase activity, formation of tumors after injection into mice, and infinite growth - would be exploited against cancer. By analogy, it is like fighting fire with fire."