Jan Peter Dutz

Vaccination is a cost-effective method to prevent diseases. Yet, vaccine effectivenessremains lower than anticipated and infectious disease is still a leading cause of illness and death.Immunostimulatory oligodeoxynucleotides containing CpG motifs (CpG ODNs) activate Tolllikereceptor 9 (TLR9), bridging innate and adaptive immune responses. CpG ODNs have beenstudied as adjuvants, agents to improve vaccine efficacy. However, split administration of topicalTLR9 agonists with parenteral vaccines has been less explored. I hypothesized that topical CpGODN 1826 activates the skin immune system in a unique fashion, increasing the efficacy oflocally administered protein-based vaccines. I found that an effective strategy to administer CpGODN was single dose topically at time of local parenteral vaccine delivery. The generation ofantigen-specific antibodies, CD4⁺ T helper 1 cells and CD8⁺ T cells were augmented. In murineListeria monocytogenes and influenza A infection models, application of topical CpG ODN attime of parenteral protein immunization reduced bacterial and viral burden.The mechanisms whereby topical CpG adjuvant improves vaccine outcomes wereinvestigated. Using bone marrow chimeric mice, I found that TLR9 expression in thehematopoietic compartment was necessary while expression in the stromal compartment alsocontributed to the enhancement of specific CD8⁺ T cell generation. Keratinocytes responded totopical CpG ODN partly by up-regulating TLR9 expression. Topical CpG ODNs wereinternalized by CD11c⁺ cells and were detected within the skin draining lymph nodes (SLNs).Topical compared to subcutaneous administration of CpG ODN differentially modulatedcytokine and chemokine gene expressions in the SLNs and induced a higher proportion of specific CD4⁺ T cells to express tissue-homing molecules. In the influenza model, topical CpGadjuvant increased the proportion of specific CD8⁺ memory T cells at the site of infection.This work demonstrates the effectiveness of a novel immunization strategy that separates topicalCpG adjuvant from a protein-based vaccine in enhancing rapid and long-lasting protectivehumoral and cellular vaccine responses. These improved responses are the consequences of theactivation of stromal and hematopoietic cells in the skin, which subsequently modulate themicroenvironment of the SLNs and alter the migratory ability of the T cells to tissues.

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