The team at Stanford University confirmed that iPSCs from mice and humans have similar expression levels of antigens to those found in different cancers.
Previous cancer vaccines have had limited success because only one antigen has generally been targeted, results have initially been promising but then resistance develops as cancer cells without the target antigen proliferate. The idea that stem cells and cancer cells have similar antigen profiles is not new and has the advantage that several known and unknown antigens can be presented to the immune system at the same time, allowing for a more effective immune response.
Studies have established that embryonic stem cells can protect mice from transplanted tumour but using inactivated iPSCs as an immunotherapy against cancer has the advantage that while embryonic stem cell rely on the availability of embryonic tissue and therefore have ethical and feasibility issues, iPSCs can be derived from adult cells.
'What surprised us most was the effectiveness of the iPSC vaccine in re-activating the immune system to target cancer,' said Dr Joseph Wu, lead author of the study. 'This approach may have clinical potential to prevent tumour recurrence or target distant metastases.'
The group used iPSCs created from mouse fibroblasts, in addition to an immune-boosting bacterial DNA fragment, to vaccinate mice before transplanting them with either breast, skin or lung cancer. While the control animals developed considerable tumours, the treated mice presented with smaller tumours or with tumour regression. These results highlight a potential prophylactic application of the vaccine, for example in the elderly or other groups who are prone to the development of cancers.
To confirm that the immune response is specific to cancer, the researchers transferred T cells from vaccinated animals into non-vaccinated animals with breast cancer and found that the tumours in the non-vaccinated animals also showed signs of regression. This approach did not work in mice with skin cancer, however, it was found to prevent regrowth of skin tumours after partial surgery, indicating a possible usefulness in real life skin cancer scenarios.
While the scientists note that there were no signs of an autoimmune reaction or other serious adverse effects, they caution that this therapeutic approach is far from being proven in humans. Professor Daniel Davis, Professor of Immunology at the University of Manchester, who was not involved in the study, added: 'As the authors say themselves, we have no idea if something like this could work in humans. If it does, this type of cancer treatment is most likely to be useful in combination with other therapies. In the meantime, as scientists often quip, this is good news for mice.'