Using molecular chemokine adjuvants to target the germinal center reaction and enhance HIV-specific humoral responses to DNA immunogens in the mucosa or the periphery

Abstract

Abstract The germinal center (GC) is a dynamic cellular substructure found in lymphoid organs where follicular helper T cells (TFH) provide the necessary proliferation stimuli and cytokine signaling that promote antibody classs-witching and affinity maturation of B cell receptors. DNA vaccines have demonstrated great potential as vaccine immunogens and in vivo electroporation (EP) has enhanced this immunogenicity. The ability to deliver plasmid encoded molecular adjuvants to direct immune responses is an advantage of the DNA platform. Mucosa-associated epithelial chemokine (MEC, or CCL28) is secreted by epithelial cells that line mucosal surfaces, it signals through CC-chemokine receptors 10 and 3 (CCR10 and CCR3) which are expressed on IgA+ plasma cells, TH17 cells, and mucosa-resident antigen presenting cells. IL-12 is a T cell stimulating cytokine that promotes a helper-T cell phenotype. Mice were vaccinated twice intramuscularly with either consensus HIV-1 env DNA alone or DNA plus molecular MEC or IL-12 delivered by in vivo EP. Fourteen days post vaccination, animals were sacrificed and spleens and draining lymph nodes were harvested for flow cytometric analysis. Both MEC and IL-12 significantly increased antigen-specific GC B cells (B220+CD138−Igm−IgD−PNA+CXCR5+gp120+) (11.1% and 8.91% respectively, compared to 6% with DNA alone). Antigen specific isotype- ELISA confirmed that MEC increases IgA in serum (900ng/ml compare to 600ng/ml with DNA alone) and fecal extracts (27ng/ml compared to 22ng/ml), while IL-12 increases IgG in serum alone (2200ng/ml compared to 1300ng/ml with DNA alone). These data indicate that molecular adjuvants can be used to specifically direct immune responses to the mucosa or the periphery.