New approaches to vaccines are urgently needed for many viruses including HIV and herpes simplex. Dermal vaccination appears increasingly promising as the dense network of immune cells in the skin, especially dendritic cells (DC), allows for enhanced immune responses and the opportunity to tailor vaccine responses by targeting specific subsets for activation.
A macaque model for skin vaccination will be valuable for dissecting the immune response to novel vaccines, incorporating both resident and migratory immune cells and may be critical for HIV challenge studies, where no small animal model of infection is available. In order to adapt delivery devices and vaccine formulations for such trials, we need to understand the immune cell composition of macaque skin. Macaque blood DCs are similar in phenotype and function to humans but we know very little about their skin.
We are comparing biopsies of healthy skin from pigtail macaques and humans and enumerating immune cell populations using fluorescence microscopy. We found that the epidermis of macaque skin was thinner than human abdominal skin but there were equivalent numbers of Langerhans cells. In the macaque dermis we can identify two of three human myeloid DC subsets - CD1a+, CD14+ but not CD141+. While the macaque equivalent of CD141+ cross-presenting DCs has been identified in blood using XCR1 and CADM1, we found expression of these molecules in human skin was not restricted to CD141+ cells. We found rare langerin+ CD11c+ myeloid cells in the dermis of humans but marked numbers in macaques. Further investigation will confirm whether these are the equivalent of dermal resident langerin+ DCs recently confirmed in humans although the functional features of this subset are unknown
These results will help inform design of delivery devices targeting vaccines to the dermo-epidermal junction and specific DC subsets in the skin, for testing in macaque models.