This data shows priming with gp120 DNA alone, without booster injections, already triggers more robust GC responses and antigen-specific IgG production than does gp120 protein. Figure2.Increased germinal center activity after gp120 DNA priming. vaccine, one of the common objectives has been the generation of high affinity, protective antibodies which, in the case of HIV, are cross-clade reactive and have neutralizing capacity.1,2While much focus has been placed on serum antibody analysis in the development of HIV vaccines, little research has been carried out on evaluating the robustness of germinal center (GC) development with different vaccination approaches. The GC reaction or GC response represents the quick clonal growth of antigen-specific B cells, and typically peaks 2 wk following initial exposure to antigen. Within the GC, activated antigen-specific B cells undergo quick proliferation, isotype class switching, somatic hypermutation and affinity maturation.3-5GC B cells express standard B cell markers such as B220, but also upregulate activation markers such as GL7 and glycoproteins that bind Peanut Agglutinin (PNA).3-5GC B cells express high levels of the transcription factor BCL6, and BCL6 is required Clofazimine for formation of GCs.3-5Additionally, GC B cells express high levels of Fas, since the majority of GC B cells die and are highly susceptible to apoptosis.3-5Follicular helper T (TFH) cells are a special subset of T helper Rabbit Polyclonal to TRIM16 (Th) cells that are indispensable for the GC reaction.6,7TFH cells are CD4+ T Clofazimine cells that express the chemokine receptor CXCR5, which allows for their localization within the GC.6,7TFH cells also express the T cell activation markers ICOS and PD-1, and like GC B cells, also require BCL6 for their development.6,7The GC prospects to the development of plasma cells, which secrete high affinity antibodies, and also promotes the formation of memory B cells.3-5The GC has been shown to peak earlier in a secondary response than after a primary immunization,8but nothing is known about the kinetics of the TFH response and the GC reaction with vaccines that require repeated immunizations. Since GC responses lead to high affinity antibody production and the formation of memory B cells, it is critical to study the development of TFH cells and GCs to gain insights into effective HIV vaccine strategies. Currently, heterologous prime-boost vaccination Clofazimine strategies employing a DNA priming component are making headways in different disease fields, such as HIV, influenza, malaria, and tuberculosis.9-12Previously, we have shown mice immunized with a DNA vector encoding the gp120 form of the HIV-1 envelope glycoprotein, followed by injection of recombinant gp120 protein, yield antibodies with higher specificity and avidity than either vaccine alone, and, more importantly, develop improved neutralizing antibodies against main viral isolates.13-15Because TFH cells are crucial for the Clofazimine development of plasma cells secreting mutated high affinity antibody from your GC, we hypothesized DNA priming causes more TFH cell differentiation, thereby triggering a more strong GC response. To test this, we utilized a gp120 DNA primary and gp120 protein boost vaccination plan. Compared with protein priming, DNA priming resulted in TFH cells which were elevated earlier in the immune response and GC B cells that were significantly increased across all time points, suggesting DNA priming preferentially affected the differentiation of GC B and memory B cells. Additionally, we utilized a novel conditional BCL6 knockout mouse system, where BCL6 can be deleted with Tamoxifen treatment after the start of the immunization regimen, to block GC formation. We found that loss of the ability to form GCs during the priming phase, paradoxically prospects to a greater antibody response. Together, our data show a complex role for the GC reaction in generating high titer antibodies after immunization with an HIV vaccine preparation. == Results == == Immunization with gp120-encoding DNA yields.