Placental stem cells have not been thymized and do not provoke an immune reaction when administered to any recipient.
"Another thing is that the cells from the placenta haven't developed—they haven't been thymized yet. They haven't developed an "us versus them" characteristic, so you can give placental cells to anybody, because the placenta doesn't generate an immune reaction against cells and your cells don't generate an immune reaction against placental cells." (said at 0:09:06)
The claim is contradicted on multiple biological and immunological grounds. First, 'thymization' (thymic education and selection) is a process specific to T lymphocytes, not stem cells or stromal cells. Second, while placental-derived stem cells and mesenchymal stromal cells (MSCs) possess immunomodulatory and hypoimmunogenic properties (such as lower baseline HLA expression), they are immune-evasive rather than completely immune-privileged. Published evidence demonstrates that allogeneic placental and mesenchymal cells can elicit host alloimmune responses, induce donor-specific anti-HLA antibodies, and undergo immune clearance/rejection upon administration to immunocompetent recipients.
- contradicts: Mesenchymal stem cells: immune evasive, not immune privileged. (Nature biotechnology 2014)
"MSCs have long been reported to be hypoimmunogenic or 'immune privileged'... However, recent studies describing generation of antibodies against and immune rejection of allogeneic donor MSCs suggest that MSCs may not actually be immune privileged." (abstract, results)
pubmedfull study (doi) - contradicts: Immunogenicity of decidual stromal cells in an epidermolysis bullosa patient and in alloge… (Stem cells and development 2015)
"After two infusions of DSCs, the JEB patient had developed multispecific anti-HLA class-I antibodies... AM and DSC infusions may have improved the healing process in the JEB patient, but DSCs appeared to induce anti-HLA antibodies." (abstract, results)
pubmedfull study (doi) - context: Allogenic Use of Human Placenta-Derived Stromal Cells as a Highly Active Subtype of Mesenc… (International journal of molecular sciences 2021)
"The low expression of HLA class I and II on f-hPSCs reduces the risk of rejection in allogeneic or xenogeneic applications in normal immunocompetent hosts." (abstract, results, passage verified)
pubmedfull study (doi)