Characterizing the germinal center response to electroporated DNA immunogens

Abstract

Most licensed vaccines rely on the production of antibodies that mediate protection from disease. The germinal center (GC) is a dynamic cellular substructure found in lymphoid organs where follicular helper T cells (T_FH) provide the necessary proliferation stimuli and cytokine signaling that promote antibody class-switching, somatic hypermutation, and affinity maturation of B cell receptors. Here, mature B cells differentiate into long-lived antibody-secreting cells and memory B cells, instituting the characteristic humoral memory response to vaccination. Although HIV-1 DNA vaccines have been shown to be highly immunogenic, leading to enhanced HIV-1 env epitope breadth and titers in pre-clinical and clinical studies, many questions remain regarding the quality of the humoral immune response and the ability of the DNA antigen/molecular adjuvant to induce long-lived anti-viral antibody that seeds mucosal secondary immune tissues. However, the magnitude and kinetics of the GC response to EP DNA has not been elucidated. Our results indicate that DNA antigens induce a GC response. Antigen-specific GC B cells (B220⁺CD138⁻IgM⁻IgD⁻PNA⁺CXCR5⁺gp120⁺) are successfully detected by flow cytometry using fluorophore-conjugated HIV-1 gp120 protein after two immunizations in the spleens and draining lymph nodes of vaccinated animals and by antigen-specific ELISpot assay. The presence of antigen-specific antibodies of multiple isotypes is successfully detected in the serum of vaccinated animals via ELISA. These results represent, to our knowledge, the first reports on the magnitude and kinetics of the germinal center response to EP DNA. This work is funded by a W.W. Smith Charitable Foundation grant to MK.