Engineering adult stem cells for cancer immunotherapy

Stem cells are rare populations of multipotent and undifferentiated progenitors, demonstrating an unlimited self-renewal capacity and high plasticity. After isolation from embryonic or adult tissues, stem cells can be expanded and manipulated ex vivo for therapeutic use. With recent advances in our understanding of stem cell biology, their pluripotency and longevity, and especially, the realization of their tumoritropic migratory property, stem cells are thought to be ideal candidates as vehicles for long-term and tissue-specific transgene delivery for cancer therapeutics. Stem cell-based approaches directly modifying, attracting, or enhancing the function of immune effector cells, such as T cells or APCs, and enhancing tumor killing have been proven feasible. However, the clinical efficacy of the engineered adult stem cells for specific and targeted cancer treatment has yet to be attested. With increased venues of stem cell generation, separation, ex vivo expansion, and improvement in targeted gene delivery vehicles, it is expected that broadened applications and improved clinical outcome of adult stem cell-based cancer treatment could be realized in the near future. Here, we review the rationale and current status of adult stem cell-based cancer immune therapy in experimental models and early clinical trials and extend our discussion to prospects for clinical application.