Topical Adjuvant Application during Subcutaneous Vaccination Promotes Resident Memory T Cell Generation.

Skin tissue resident memory T cells (TRM) provide superior protection to a second infection. In this study, we evaluated the use of topical CpG oligodeoxynucleotide (ODN) as adjuvant to generate skin TRM in mice. Topical or s.c. CpG ODN adjuvant administration at the time of a s.c. Ag injection led to an accumulation of CD103- CD8 T cells in the epidermis. However, only mice with CpG ODN administered topically had significant numbers of CD103+ Ag-specific CD8 T cells persisting in the local epidermal skin, enhanced circulating memory cells in the blood, and showed protection from intradermal challenge with melanoma cells. Generation of Ag-specific CD8 T cells was dependent on TLR9 expression on hematopoietic cells and partially dependent on receptor expression on stromal cells. Topical challenge of immunized mice at a distal site led to significant expansion of Ag-specific T cells in the blood and accumulation in the challenged skin. We demonstrate that local and systemic T cell memory can be generated with topical CpG ODN at the time of s.c. immunization, suggesting a new method of enhancing current vaccine formulations to generate tissue TRM.