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Since pioneering studies advocate cell replacement as a long-standing and realistic goal for Parkinson’s Disease treatment, transplantation cells can be sourced from the tissue of the fetal brain or stem cells. However, once the transplantation is carried out, the dopamine (DA) neurons are seen as minor components of the grafts. It has remained a challenge to determine the identity of other cell types. Functional and authentic midbrain dopamine (DA) neurons and their progenitors can now be generated from human pluripotent stem cells (hPSCs) using a floor plate intermediate. This type of cell preparations is both functional and safe when transplanted to animal models of Parkinson’s disease.

However, these therapeutic cells are a minor component of the grafts which is the case for transplants from fetal brain tissue, although the resulting grafts from the hPSCs contain large quantities of desired dopamine neutrons. A comprehensive understand of these graft’s cellular compositions remains a challenge due to the limitations in histological methods that depend significantly on pre-conceived notions concerning the cell types likely to be present in the grafts.

When single-cell RNA sequencing was combined with histological analyses to characterize intracerebral grafts from ventral midbrain (VM)-patterned human embryonic stem cells (hESCs) and VM fetal tissue after long-term survival and functional maturation in a preclinical rat model of PD. The analysis also showed that while both the cell preparations gave rise to the astrocytes and neurons, the only cell identified in the fetal tissue graft was oligodendrocytes. In addition, a cell type a lot like the class of newly identified perivascular-like cells was also identified as a previously unknown component of hESC-derived grafts.

An in-depth analysis of graft composition uniquely showed the discern similarities and potential differences between the cellular composition of fetal- and hESC-derived grafts after transplantation. Accordingly, two of the clusters (astrocyte and neuronclusters) contained cells both from grafted VM-patterned hESCs and fetal cells.

In that analysis, the presence of VLMCs was also confirmed through histological analysis of brain sections of animals grafted in parallel with the same batches of cells that were used for scRNA-seq. The histological analysis also showed that the hESC-derived VLMCs were intermixed with rat cells of similar location and appearance within the transplants. Furthermore, it was also confirmed the presence of graft-derived oligodendrocyte progenitors expressing OLIG2 and PDGFRA at the edge of fetal VM grafts.

Both stem cell and fetal cell-derived grafts are highly heterogeneous with respect to the composition of cell type. Moreover, all the reports of graft composition to date make use of the histological methods that depend on pre-conceived notions related to cell types are more likely to be present in the grafts.


Tiklová, K., Nolbrant, S., Fiorenzano, A., Björklund, Å. K., Sharma, Y., Heuer, A., … & Parmar, M. (2020). Single cell transcriptomics identifies stem cell-derived graft composition in a model of Parkinson’s disease. Nature communications, 11(1), 1-11.

Birtele, M., Sharma, Y., Storm, P., Kajtez, J., Sozzi, E., Nilsson, F., … & Parmar, M. (2020). Single cell transcriptional and functional analysis of human dopamine neurons in 3D fetal ventral midbrain organoid like cultures. bioRxiv.