CYBB and chronic granulomatous disease: This strategy can produce retroviral SIN vectors with titers in the range of 105–106 infectious particles/mL and proof-of-concept has been demonstrated as for the clinically relevant vectors expressing collagen 7 (epidermolysis bullosa; [88]) as well as IL2γc (severe combined immunodeficiency) and gp91phox (chronic granulomatous disease) [134].