Immunohistochemical toolkit for tracking and quantifying xenotransplanted human stem cells

Aim. Tracking human cells xenotransplanted into animal models is crucial for studying their in vivo biologic potential and essential to follow their fate in the field of cell therapy or tumor xenografting. Preclinical assessment for cellular therapy requires data on biodistribution, viability, integration into host tissue, differentiation into functional cells, tumorigenic potential and safety of delivery. Often injected in limited amount, these cells, from human origin, must be recognized with high sensitivity. Post-mortem immunohistochemistry is currently the most sensitive method for cell tracking affording the detection of specific cell populations, while preserving both their morphology and that of the surrounding environment. Here, we focused our work on the specific expression throughout the human body of three human-specific biomarkers: Ku80, human mitochondria (hMito) and Alu after transplantation of human stem cell in animals. Results. We showed that Ku80, hMito and Alu biomarkers are broadly expressed in human tissues with no or low cross-reactivity towards rat, mouse or pig tissues. Through in vitro studies, we demonstrated that the expression of Ku80 and Alu biomarkers is stable over time and does not change upon the differentiation process of human-derived induced pluripotent stem cells or glial-restricted precursors. We also showed that these human biomarkers could be reliably used to track human neural or human glial stem cells transplanted in the rodent spinal cord. Using computer-assisted image analysis, we were able to quantify the engraftment of these human stem cells in animal tissue. Human-specific antibodies helping at detecting apoptotic, proliferative or neural-committed cells were also characterized. Conclusions. Based on immunohistochemistry and in situ hybridization, this methodological study assesses the human-species specificity of Ku80, hMito and Alu biomarkers and proposes useful tools for the critical analysis of human stem cells tracking after transplantation, which is needed for both preclinical cell therapy evaluation and tumor xenografting analysis.