Modulation of Immune Responses to DNA-based Vaccine Antigens Following Co-delivery of Mucosal Chemokine Molecular Adjuvants CCL28 and CCL25
Authors:   , Kathuria Noshin , Kutzler Michele A 
Published: July 2024

The ability of DNA vaccines to elicit robust immune responses against pathogens is well established. The DNA vaccine platform allows for specific modulation of immune responses using plasmid-encoded molecular adjuvants such as chemokines to target unique components of the immune system. A vaccine approach that drives B cell responses to mucosal surfaces is critical for protection against mucosal pathogens including HIV. Trafficking of IgA secreting B cells to various mucosal effector sites depends on the expression of CCR10 that enables them to migrate towards CCL28 expressed by mucosal epithelial cells. We hypothesized that co-immunization with plasmids encoding HIV-1 envelop antigens with CCL28 as an adjuvant would augment B cell responses at mucosal surfaces. We demonstrate that CCL28 when administered with HIV antigens in mice significantly enhances HIV-1 envelope specific serum IgG levels without changing the type and breadth of the antibody response induced by the antigen. More importantly, CCL28 administration increases antigen-specific IgA levels in mucosal secretions with a corresponding increase in the number of CCR10 expressing HIV-1 envelope-specific B cells within the intestinal mucosal epithelium. We also demonstrate the validity of CCL28 as a mucosal adjuvant in non-human primate model of HIV infection. CCL28 mediated increase in antigen-specific antibody response is associated with a decrease in peak viral load and a faster control of viremia in infected animals. Attenuation of both the serum IgG and mucosal IgA levels in immunized CCR10 knock out animals support the role of CCL28 as an important regulator of the antibody response. The ability of plasmid encoded immune mediators to suppress pathogenic immune responses in a DNA vaccine setting is a novel approach. Here, we demonstrate that systemic co-administration of mucosal chemokine CCL25 can suppress antigen specific CD8+ T cell responses. Intramuscular administration of CCL25 with electroporation results in the recruitment of a distinct subset of plasmacytoid dendritic cells (pDCs) characterized by the expression of CCR9, the only receptor for CCL25. Co-immunization with CCL25 results in global attenuation of antigen-specific CD8+ T cell responses by suppressing their proliferation. The primary CD8+ T cell response generated upon co-immunization with CCL25 displays weakened secondary expansion, leading to a significantly reduced pool of antigen-specific memory CD8+ T cells. Moreover, when sorted CCR9+ pDCs are co-cultured with purified CD8+ T cells, a significant decrease in the proliferation and increased apoptosis of CD8+ T cells is observed relative to the CD8+ T cells cultured with CCR9- DCs. These data suggest a direct role of CCR9+ pDCs in a profound attenuation of antigen-specific CD8+ T cell response after immunization with CCL25. The memory CD8+ T cells generated upon immunization with CCL25 also fail to respond to antigenic challenge as seen by decreased footpad swelling compared to the memory CD8+ T cell response generated by immunizing with antigen alone. Our findings propose a novel way to functionally attenuate potentially pathogenic CD8+ T cell responses by recruiting CCR9+pDCs upon co-immunization with pCCL25. Taken together we demonstrate distinct ways by which closely related mucosal chemokines can differently modulate immune responses when administered systemically as expression plasmids in a DNA vaccine platform.