Lentiviral transfer of the perforin gene into haematopoietic progenitors in a Prf−/− murine model led to the recovery of NK cell function, CD8 T-lymphocyte cytotoxicity and reduced IFN-ɤ secretion in vitro alongside improvement in cytopaenias and cytokine hypersecretion when gene corrected mice were challenged with lymphocytic choriomeningitis virus (LCMV) to induce an HLH phenotype (49). Here, CD8A is linked to hemophagocytic syndrome.