064 A murine model to understand the efficacy of smallpox vaccination

No viral infection has shaped human history more profoundly than smallpox, caused by Variola major infection. Smallpox was eradicated by a world-wide vaccination program by 1980, using the orthopox virus Vaccinia (VACV). Two features of smallpox vaccination are unique. First, infection of disrupted epidermis (“skin scarification”, or ss) was required for optimal protection, while intramuscular injection was ineffective. Second, T cells rather than antibodies, are responsible for protective immunity. Smallpox is transmitted through respiratory droplets, and while skin immunization yields skin TRM, lung TRM are necessary for protective immunity. Using a murine model of VACV vaccination, we compared infection with VACV via ss, intramuscular (im), subcutaneous (sc), and intradermal (id) routes. At 60 hours, CD8 T cells in draining lymph node were sorted and analyzed by transcriptional profiling. Immunization by ss generated a gene expression pattern that differed significantly from ss, im, and sc. As predicted, ss was superior in generating CD8 skin TRM, but ss also generated abundant lung TRM, better than all other routes of vaccination. We hypothesized that similar gene expression patterns might emerge in activated CD8 T cells after ss infection and direct intratracheal (it) infection. We infected mice with VACV via ss and it, and used gut infection as a control. At 60 hours, we profiled cells having in draining lymph nodes (inguinal, mediastinal and mesenteric). By PCA, skin and lung infection generated T cells with strikingly similar gene expression patterns, quite distinct from gut infection. Not only was skin infection an efficient way of generating lung TRM, but it/lung infection efficiently generated skin TRM. Gut infection generated neither skin nor lung TRM. These observations suggest significant overlap between skin and lung homing of T cells. This helps explain puzzling phenomena such as the atopic march and the TB skin test.