Establishing an in-vitro assay to test immunogenicity of baboon iPSCs
Induced pluripotent stem cells (iPSCs) are somatic cells that have been reprogrammed into a pluripotent state. This allows them to form all three embryonic layers of tissue and can be directed to differentiate into any cell type of the body. They were created to replace the use of embryonic stem cells and all their current uses in regenerative medicine. iPSCs were believed to be immunologically tolerated in a syngeneic host but current evidence is inconclusive of this due to some reports showing that autologous iPSCs are immunogenic whereas others report no immunogenicity of in-vitro differentiated syngeneic iPSC-derived cells. Some common issues that can lead to immune recognition include mutations, viral vector transgene expression, and early transcription factors not commonly seen in adult tissues. Typically, T lymphocytes are not undergoing thymic tolerance (negative selection) for early transcription factors, while common tissue proteins get expressed to provide tolerance. These issues have been highlighted in studies showing rejection of teratomas derived from iPSCs while embryonic stem cell teratomas remained viable. Another lab showed the specific immunogenicity of the transcription factor Oct4 that is necessary for pluripotency. The purpose of our study was to develop an in-vitro assay to investigate the immunogenicity of autologous baboon iPSCs. Our preliminary work focused on testing MHC-mismatched baboon splenocytes in a mixed lymphocyte reaction (MLR) to detect the levels of alloreactive cells using the Enzyme-linked ImmunoSpot (ELISPOT) assay. We also wanted to determine the minimal number of stimulator cells that would be needed to elicit an allogeneic response.