Tropism-modified AAV vectors overcome barriers to successful cutaneous therapy.

Autologous human keratinocytes (HK) forming sheet grafts are approved as skin substitutes. Genetic engineering of HK represents a promising technique to improve engraftment and survival of transplants. Although efficacious in keratinocyte-directed gene transfer, retro-/lentiviral vectors may raise safety concerns when applied in regenerative medicine. We therefore optimized adeno-associated viral (AAV) vectors of the serotype 2, characterized by an excellent safety profile, but lacking natural tropism for HK, through capsid engineering. Peptides, selected by AAV peptide display, engaged novel receptors that increased cell entry efficiency by up to 2,500-fold. The novel targeting vectors transduced HK with high efficiency and a remarkable specificity even in mixed cultures of HK and feeder cells. Moreover, differentiated keratinocytes in organotypic airlifted three-dimensional cultures were transduced following topical vector application. By exploiting comparative gene analysis we further succeeded in identifying αvß8 integrin as a target receptor thus solving a major challenge of directed evolution approaches and describing a promising candidate receptor for cutaneous gene therapy.

PECAM1(+)/Sca1(+)/CD38(+) vascular cells transform into myofibroblast-like cells in skin wound repair.

Skin injury induces the formation of new blood vessels by activating the vasculature in order to restore tissue homeostasis. Vascular cells may also differentiate into matrix-secreting contractile myofibroblasts to promote wound closure. Here, we characterize a PECAM1(+)/Sca1(+) vascular cell population in mouse skin, which is highly enriched in wounds at the peak of neoangiogenesis and myofibroblast formation. These cells express endothelial and perivascular markers and present the receptor CD38 on their surface. PECAM1(+)/Sca1(+)/CD38(+) cells proliferate upon wounding and could give rise to α-SMA(+) myofibroblast-like cells. CD38 stimulation in immunodeficient mice reduced the wound size at the peak of neoangiogenesis and myofibroblast formation. In humans a corresponding cell population was identified, which was enriched in sprouting vessels of basal cell carcinoma biopsies. The results indicate that PECAM1(+)/Sca1(+)/CD38(+) vascular cells could proliferate and differentiate into myofibroblast-like cells in wound repair. Moreover, CD38 signaling modulates PECAM1(+)/Sca1(+)/CD38(+) cell activation in the healing process implying CD38 as a target for anti-angiogenic therapies in human basal cell carcinoma.