Background:  Dendritic cell (DC) and B-cell activation by CpG-C ISS-ODN represents a promising strategy to boost immune responses and enhance vaccine efficacy. We have shown that in vitro macaque blood-derived DC respond to CpG-C stimulation and augment SIV-specific IFN-g responses. To gain more insight into the potential of CpG-C ISS-ODN as vaccine adjuvant, we assessed the effect of CpG-C ISS-ODN stimulation on macaque DC and B cells in vivo. 

Methods:  Superficial lymph nodes in naïve and SHIV162P-infected (healthy) macaques were directly injected with 500 mg of the CpG-C ISS-ODN C274; the inactive control ODN C661 was injected in the contralateral lymph nodes; 24 hours later, the lymph nodes were removed and the DC and B-cell surface immunophenotypes were evaluated by flow cytometry on freshly prepared suspensions. LNMC were also cultured in the presence of CD40L, AT-2 SIV, C274, or C661 or combinations of the stimuli and the surface immunophenotypes monitored. The release of cytokines and chemokines upon culture was measured by ELISA and Luminex fluorescent bead assays. For SHIV-infected monkeys, viral antigen-specific responses were monitored in the blood and lymph nodes before and after lymph node ODN injection.

Results:  Increased CD80 and CD86 expression by DC and B cells was evident in some (but not all) samples upon examination of the cell suspensions directly from the C274-injected lymph nodes. However, cells from the C274-injected lymph nodes reproducibly exhibited heightened responsiveness to stimuli upon in vitro culture (compared with cells from the C661-injected lymph nodes). This was reflected in changes in DC and B-cell surface immunophenotypes as well as in IFN-a and IL-12 production. C274-stimulated lymph node cells also secreted several other cytokines (IL-6, IL-10, TNF-a, GM-CSF) and chemokines (MCP-1, RANTES, MIP-1a). C274 better promoted plasmacytoid DC (PDC) survival during 24-hour culture compared with other stimuli, especially for cells from the C274-injected lymph nodes. These responses were seen in naïve and SHIV-infected macaques. SIV-specific responses in the blood did not change significantly upon intranodal injection of C274.

Conclusions:  C274 effectively activates macaque PDC and B cells within the lymphoid tissues in vivo. This has important implications for the use of CpG-C ISS-ODN to directly boost the cellular functions of resident DC and B cells in vivo to enhance anti-HIV vaccine immunogenicity.

Keywords: CpG-C ISS-ODN; dendritic cells/B cells; lymphoid