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How do we Test for Immunogenicity of Human iPSC-Derived Cells?

Review of “Putative Immunogenicity Expression Profiling Using Human Pluripotent Stem Cells and Derivatives” from Stem Cells TM by Stuart P. Atkinson

 Alongside the potential for tumorigenesis, the immune response to cells derived from induced pluripotent stem cells (iPSCs) remains a possible stumbling block for the transfer of iPSC technology from bench to bedside. The first study of this kind found that teratomas derived from mouse iPSCs, but not mouse embryonic stem cells (ESCs), could elicit an immune response [1], although further mouse studies did not fully corroborate this finding [2, 3]. Human iPSC/ESC studies have been reported [4-6] and, to further expand upon these findings, the group of James A. Byrne (UCLA) have assessed a wide range of iPSCs and their differentiated progeny for the expression of the human homologs of two putative mouse “immunogenicity” genes (ZG16 and HORMAD1) and the resulting immune response these iPSCs elicit using a peripheral blood mononuclear cell (PBMC) co-culture assay [7].

 The authors initially replicated the teratoma-based iPSC-specific immune response assay used in previous studies to assess a wide range of iPSCs/ESCs for HORMAD1 and ZG16 expression. These two putative immunogenicity genes previously correlated to an in vivo T cell-mediated immune response in the mouse [1]. While HORMAD1 expression remained low and cells expressed ZG16 at a higher level, gene expression levels were highly variable, most likely due to line-to-line and clonal variation (See Figure). Analysis of differentiated cells began using embryoid body (EB)-mediated non-directed differentiation. Again, HORMAD1 expression remained low and, while ZG16 expression was higher in comparison, this level was much lower as compared to ZG16 expression observed in teratomas. These expression levels also remained heterogeneous, and the researchers found no correlation between different cell numbers and time points across all lines tested. They also observed similar findings following the assessment of cells representing specific early derivatives of the three embryonic germ layers following directed differentiation. Further differentiation of iPSCs/ESCs to clinically relevant cell types (oligodendrocyte progenitor cells (OPCs), hepatocytes, and cardiomyocytes) using strict directed differentiation protocols found a trend for increased expression of HORMAD1, although this still represented a very low expression level which is unlikely to cause an immune response. ZG16 levels also definitively and reproducibly increased, although the data the authors have generated highlights inherent intra- and interline variability, which would preclude ZG16 assessment as a useful immunogenicity screening tool. The group then moved on to their in vitro acute immune response assay using a PBMC co-culture assay, and discovered that ZG16 expression was unable to induce IFN-expression (the assay output) or cause gross changes in MHC presentation, and so is not acutely immunogenic.

Overall, this study provides evidence that currently used means of assessing immunogenicity are insufficient to test for immunogenicity in humans. Hopefully this study will provoke the search for a better assessment of immunogenicity which will be able to quickly and decisively demonstrate the immunogenicity inherent in iPSCs and their derivatives.

References

  1. Zhao T, Zhang ZN, Rong Z, et al. Immunogenicity of induced pluripotent stem cells. Nature 2011;474:212-215.
  2. Araki R, Uda M, Hoki Y, et al. Negligible immunogenicity of terminally differentiated cells derived from induced pluripotent or embryonic stem cells. Nature 2013;494:100-104.
  3. Guha P, Morgan JW, Mostoslavsky G, et al. Lack of immune response to differentiated cells derived from syngeneic induced pluripotent stem cells. Cell Stem Cell 2013;12:407-412.
  4. Lu Q, Yu M, Shen C, et al. Negligible immunogenicity of induced pluripotent stem cells derived from human skin fibroblasts. PLoS One 2014;9:e114949.
  5. Liu P, Chen S, Li X, et al. Low immunogenicity of neural progenitor cells differentiated from induced pluripotent stem cells derived from less immunogenic somatic cells. PLoS One 2013;8:e69617.
  6. Maynard KM, Arvindam U, Cross M, et al. Potentially immunogenic proteins expressed similarly in human embryonic stem cells and induced pluripotent stem cells. Exp Biol Med (Maywood) 2014;239:484-488.
  7. Awe JP, Gschweng EH, Vega-Crespo A, et al. Putative immunogenicity expression profiling using human pluripotent stem cells and derivatives. Stem Cells Translational Medicine 2015;4:136-145.