clinical treatment options such as nucleoside analogues, retinoic acid derivatives, quinolone antibiotics, and catechin derivatives. There are also other molecular genetic-based methods of inhibiting telomerase, such as antisense therapy and RNA interference. hTERT peptide fragments have been shown to induce a cytotoxic T-cell reaction against telomerase-positive tumor cells in vitro. The response is mediated by dendritic cells, which can display hTERT-associated antigens on MHC class I and II receptors following adenoviral transduction of an hTERT plasmid into dendritic cells, which mediate T-cell responses. Dendritic cells are then able to present telomerase-associated antigens even with undetectable amounts of telomerase activity, as long as the hTERT plasmid is present. Immunotherapy against telomerase-positive tumor cells is a promising field in cancer research that has been shown to be effective in in vitro and mouse model studies. Medical implications iPS cells Induced pluripotent stem cells (iPS cells) are somatic cells that have been reprogrammed into a stem cell-like state by the introduction of four factors (Oct3/4, Sox2, Klf4, and c-Myc). iPS cells have the ability to self-renew indefinitely and contribute to all three germ layers when implanted into a blastocyst or use in teratoma formation. Early development of iPS cell lines were not efficient, as they yielded up to 5% of somatic cells successfully reprogrammed into a stem cell-like state. By using immortalized somatic cells (differentiated cells with hTERT upregulated), iPS cell reprogramming was increased by twentyfold compared to reprogramming using mortal cells. The reactivation of hTERT, and subsequently telomerase, in human iPS cells has been used as an indication of pluripotency and reprogramming to an ES (embryonic stem) cell-like state when using mortal cells. Reprogrammed cells that do not express sufficient hTERT levels enter a quiescent state following a number of replications depending on the length of the telomeres while maintaining stem cell-like abilities to differentiate. Reactivation of TERT activity can be achieved using only three of the four reprogramming factors described by Takahashi and Yamanaka: To be specific, Oct3/4, Sox2 and Klf4 are essential, whereas c-Myc is not. However, this study was done with cells containing endogenous levels of c-Myc that may have been sufficient for reprogramming. Telomere length in healthy adult cells elongates and acquires epigenetic characteristics similar to those of ES cells when reprogrammed as iPS cells. Some epigenetic characteristics of ES cells include a low density of tri-methylated histones H3K9 and H4K20 at telomeres, as well as an increased