CD34 and neoplasm: Therefore, tolerance of mismatched or dangerous human tumour cell lines in humanized CD34+ NSG mice is because the outcome of the immune response is not determined by signal I or II, rather, it is determined by signal III, which is the expression of the AdRs on target cells engaging the AdLs on T cells to relay survival signals in target cells, as previously described by the adaptation model of immunity.59, 60