人工多能性幹細胞

iPS cells are generated by introducing viral vectors containing genes for specific transcription factors—Oct4, Sox2, Klf4, and c-Myc—into differentiated adult cells like skin cells. When these transcription factors are expressed, they reprogram the mature cells, causing them to dedifferentiate over several generations and return to a pluripotent stem cell state capable of forming most body cell types.

iPS cells avoid ethical concerns associated with embryonic stem cells because they originate from adult cells rather than embryos. Additionally, using a patient's own cells for iPS cell generation minimizes transplant rejection risk through autologous transplantation, where cells are derived from and returned to the same individual's body.

Scientists confirm iPS cell transformation by checking for teratoma formation, an encapsulated benign tumor composed of tissues from all three germ layers—endoderm, mesoderm, and ectoderm. Additional markers include unlimited proliferation capacity, long telomeres, and expression of pluripotent stem cell markers such as Oct4, c-Myc, and Nanog.

The first iPS cell clinical trial involved transplanting retinal cells into patients with age-related macular degeneration. Since then, approved trials have expanded to treat Parkinson's disease, heart disease, and spinal cord injury. iPS cells are also used to study patient-derived diseases in laboratory settings, providing valuable research models.

Generating iPS cells is inefficient and time-consuming, taking up to four weeks with only 0.01 to 1% of somatic cells successfully forming pluripotent stem cells. Viral vectors may insert genes at undesired genomic locations, and c-Myc overexpression poses a cancer risk, as this oncogene can activate genes that cause malignant transformation.

All four OSKM factors—Oct4, Sox2, Klf4, and c-Myc—must be expressed in precise amounts within a single cell to achieve successful reprogramming to pluripotency. Imbalanced expression of these factors prevents complete dedifferentiation, reducing the efficiency of iPS cell formation and increasing the likelihood of incomplete or failed reprogramming.

Autologous transplantation uses cells generated from a patient's own body, eliminating the immunological mismatch that occurs when tissues are transplanted between different individuals. This approach significantly reduces transplant rejection risk, improving clinical outcomes and reducing the need for immunosuppressive medications.