PPIA and infection: An augmentation of successful lentiviral infection of human HSPCs is seen with high multiplicity of infection (MOI) exposures and treatment of human stem cells with multiple cytokines such as interleukin-3 (IL-3), interleukin-6 (IL-6), interleukin-7 (IL-7), stem cell factor (SCF), Flt3 ligand (FLT3L), and thrombopoietin (TPO), with proteasome inhibitors, with targeted siRNA blockade of the cell cycle quiescent factor p21, or with cyclophilin A, rapamycin and cyclosporine [4, 5, 8, 14–21].