Rare intercellular material transfer as a confound to interpreting inner retinal neuronal transplantation following internal limiting membrane disruption

Intercellular cytoplasmic material transfer (MT) occurs between transplanted and developing photoreceptors and ambiguates cell origin identification in developmental, transdifferentiation, and transplantation experiments. Whether MT is a photoreceptor-specific phenomenon is unclear. Retinal ganglion cell (RGC) replacement, through transdifferentiation or transplantation, holds potential for restoring vision in optic neuropathies. During careful assessment for MT following human stem cell-derived RGC transplantation into mice, we identified RGC xenografts occasionally giving rise to labeling of donor-derived cytoplasmic, nuclear, and mitochondrial proteins within recipient Müller glia. Critically, nuclear organization is distinct between human and murine retinal neurons, which enables unequivocal discrimination of donor from host cells. MT was greatly facilitated by internal limiting membrane disruption, which also augments retinal engraftment following transplantation. Our findings demonstrate that retinal MT is not unique to photoreceptors and challenge the isolated use of species-specific immunofluorescent markers for xenotransplant identification. Assessment for MT is critical when analyzing neuronal replacement interventions. [Display omitted] •Human RGC transplantation is associated with material transfer to host Müller glia•Transferred materials include cytoplasmic, nuclear, and mitochondrial proteins•Nuclear morphology is distinct between human and murine retinal neurons•Definitive cell origin identification is critical in neuronal transplantation Transfer of cellular material from donor to host cells confounds evaluation of transplantation experiments. Zhang et al. demonstrate that transplanted human retinal ganglion cells transfer cytoplasmic, nuclear, and mitochondrial antigens to host murine Müller glia. While this observation undermines use of species-specific antigens for cell origin identification, nuclear morphology can effectively parse human and mouse retinal cells in xenotransplant paradigms.