Proof-of-principle study of the first-ever autologous iPSC-derived cell transplant in non-human primates
Background: The Promise and Problems of iPSCs
Shinya Yamanaka won the Nobel Prize in Medicine for his work on cellular reprogramming and creating induced pluripotent stem cells (iPSCs). He identified four transcription factors — Oct-3/4, Sox2, c-Myc, and Klf4 — that control pluripotency. Using these factors, he reprogrammed differentiated adult cells into pluripotent cells, which can then be turned back into specialized tissue. This raised great hope for cellular therapy and regenerative medicine.
But the path to using iPSCs as therapy is long and complicated. Researchers first believed iPSCs would avoid any immune response, since they can be made from a patient’s own cells. Zhao et al. challenged that idea. They found that iPSCs made from C57BL/6 (B6) mice with standard retroviral methods formed teratomas after transplant into syngenic host mice — and triggered a fast, T cell-dependent immune response1.
A New Proof-of-Principle in Primates
A research group led by Dr. Su-Chun Zhang at the Waisman Center, University of Wisconsin-Madison, has now shown that autologous iPSC-based cell therapy is possible — without triggering immune rejection. Dr. Zhang was the first to derive neural cells from both embryonic stem cells (ESCs) and iPSCs. This new work is the first proof-of-principle that autologous iPSC-derived cells can engraft and survive in the primate brain.
In a study in Cell Reports, Zhang’s group did the following:
- Generated iPSCs from fibroblasts of 8-10 year old rhesus monkeys (Macaca mulatta), using retroviruses carrying the four Yamanaka factors.
- Differentiated the iPSCs into neurons.
- Transplanted the neurons back into the same donor monkeys2.
The rhesus iPSCs formed neuroepithelia with the characteristic neural tube-like rosettes, and expressed the neuroectoderm transcription factors Pax6 and Sox1. The team expanded and further differentiated these rosettes. By day 42 (the day of transplant), the cell mix was 37% βIII-tubulin+ neurons, 16% S100β+ immature astrocytes, and 47% Nestin+ progenitors.
Modeling Parkinson’s Disease in Rhesus Monkeys
To test whether this approach could work for Parkinson’s disease, Zhang’s team gave the monkeys parkinsonism using a single intracarotid artery injection of the neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine). Twelve to 18 months later, all the monkeys had a stable, one-sided parkinsonian condition, with tremors, slowed movement, poor balance, and impaired motor skills.
At day 30 of cell culture, the team labeled the iPSC-derived neural progenitors with a GFP (green fluorescent protein) lentivirus. At day 42, they transplanted these labeled cells into the striatum and substantia nigra — back into the same monkey the iPSCs came from.
Engraftment Without Immune Rejection
The monkeys received no immune suppression. Six months after transplant, researchers checked engraftment of the GFP-labeled cells using stereological analysis on serial coronal sections. They found distinct grafts in the injected regions, made up of:
- 63% MAP2+ neurons (microtubule-associated protein 2)
- 22% GFAP+ astrocytes (glial fibrillary acidic protein)
- 10% MBP+ oligodendrocytes (myelin basic protein)
The GFP+ neurons grew long fibers into the surrounding host tissue, and some neurons outside the graft region showed markers of mature neurons. There was no sign of pluripotent stem cell markers (OCT4, NANOG, SOX17, and Brachyury) and no Ki67 staining (a marker of dividing cells) — meaning the grafted progenitors had fully matured.
Zhao et al. had shown that teratomas from transplanted iPSCs were rejected by the immune system in syngenic mice1. Zhang’s study found something different: the autologous iPSC-derived neural transplants in the primate brain did not trigger immune rejection. There was no CD3 or CD8 staining (lymphocyte markers) to suggest an immune attack. The brain’s own glial cells (astrocytes and microglia) also showed little reaction — HLA-DR staining (a microglia and macrophage marker) looked the same throughout the brain, including in the grafted areas.
Why No Behavioral Improvement?
Even though the transplanted cells engrafted and matured well, the parkinsonian monkeys showed no improvement in behavior. One likely reason: most of the GFP+ neurons were γ-Aminobutyric acid (GABA+) neurons, and few were tyrosine hydroxylase (TH+) neurons. TH drives the rate-limiting step in making dopamine, and low TH has been linked to parkinsonian symptoms3. It’s also possible the researchers simply transplanted too few cells to replace the dopamine-producing cells lost in the primate brain.
What This Study Means for Cell Therapy
Even without behavioral improvement, this study is real cause for hope in cell therapy using autologous iPSC-derived cells. The transplanted neural progenitors survived and matured into neurons, astrocytes, and oligodendrocytes in the primate brain — with no immune rejection and no teratomas. The cells structurally integrated into the host brain: they grew long neuron-like processes, and myelin basic protein staining suggested the oligodendrocytes were myelinating properly. As the first-ever transplant of iPSC-derived cells back into the same non-human primate, this proof-of-principle study offers hope for personalized regenerative medicine and for patients with neurodegenerative disease.
Further reading:
1. Zhao, Tongbiao; Zhang, Zhen-Ning; Rong, Zhili; and Xu, Yang. Immunogenicity of induced pluripotent stem cells. Nature. 474, 212–215, 9 June 2011
2. Emborg ME, Liu Y, Xi J, Chang X, Yin Y, Lu J, Joers V, Swanson C, Holden JE, and Zhang Su. Induced pluripotent stem cell-derived neural stem cells survive and mature in the nonhuman primate brain. Cell Reports 3, 1-5, March 28, 2013.
3. Goodwill KE, Sabatier C, Marks C, Raag R, Fitzpatrick PF, Stevens RC. Crystal Structure of tyrosine hydroxylase at 2.3a and its implications for inherited neurodegenerative diseases. Nature Structural Biology 4 (7): 578–585, 1997
