FV infection was monitored by palpation of the spleens (A) and by analysis of FV loads in plasma on day 10 p.c. viral antigens only. Improved protection correlated with enhanced virus-specific CD4+T cell responses and higher neutralizing antibody titers. To apply these results to an HIV vaccine, mice were immunized with adenoviral vectors encoding the HIV antigens Env and Gag-Pol and coadministered vectors encoding CCL3. Again, this combination vaccine induced higher virus-specific antibody titers and CD4+T cell responses than did the HIV antigens alone. These results indicate that coexpression of the chemokine CCL3 by adenovirus-based vectors may be a promising tool to improve antiretroviral vaccination strategies. == INTRODUCTION == Dendritic cells (DCs) are specialized antigen-presenting cells (APCs) that play a central role in the induction of primary cellular immune responses (reviewed in references1and42). After antigen uptake and activation, DCs LIFR mature and migrate to lymphoid tissues, where they present antigen-derived peptides on major histocompatibility complex type II (MHC-II) molecules and provide stimulatory signals for maslinic acid antigen-specific T cells. Because of the important role of DCs in the induction of protective immunity, DC targeting of antigens has been a much-pursued strategy in the development of genetic and protein-based vaccines. For this, vaccine antigens were fused to antibodies or ligands of DC surface molecules and delivered directly as a protein vaccine or through encoding DNA in a genetic plasmid- or viral vector-based vaccine regimen (4,33,37,43,44). A different approach is the coexpression of chemoattractant molecules by a genetic vaccine to recruit APCs to the site of vaccine delivery. This approach has been studied in immunotherapy of tumors (16,19,34,46) and also for vaccination against virus infections maslinic acid (5,13,26,47), but it has not yet been tested in a retrovirus challenge model. In this vaccination study we sought to increase the presence of DCs at the site of vaccine delivery. For this, we coadministered adenovirus vectors encoding different chemokines along with viral antigens. Chemokines are a group of proinflammatory proteins of 6 to 14 maslinic acid kDa that act as ligands of G-protein-coupled receptors (reviewed in reference31) expressed on leukocytes. Chemokines induce the migration of these cells and play an important role in both homeostasis and inflammation. For these different processes, some chemokines are expressed continuously in certain tissues, while others are only expressed in response to inflammatory stimuli. Depending on the expression of their respective receptors, chemokines can stimulate multiple cell types. In the present study we studied the effects of the chemokines CCL3, CCL20, CCL21, and CXCL14 on immune responses induced by an adenovirus-based vaccine. All four tested chemokines, while acting on differing ranges of target cells, are known to be chemoattractants for DCs (reviewed in reference48). We analyzed the adjuvant effect of chemokines for retroviral immunity using an HIV vaccination mouse model and the Friend retrovirus (FV) model. FV is an immunosuppressive retroviral complex, consisting of the apathogenic Friend murine leukemia virus (F-MuLV) and the replication-defective but pathogenic spleen focus-forming virus, that causes splenomegaly and lethal erythroleukemia in susceptible mice (15). In contrast to the vaccination against HIV proteins, the FV model allows for challenging immunized mice with a pathogenic retrovirus. The FV infection model has offered valuable insights into the role of particular cell types in the immune response to a retroviral infection and into the basic requirements for immune protection. Using attenuated F-MuLV helper virus, it was demonstrated that complete protection from lethal maslinic acid FV challenge requires both humoral and cellular responses, comprising antibodies and CD4+and CD8+T cells (10). Although the correlates of immune protection from HIV infection are still unclear, it is now widely assumed that complex immunity is required to protect against retroviruses in general. The delivery of vaccine antigens by adenoviral vectors is a much-pursued strategy in HIV vaccine research. In studies in nonhuman primates, this vaccine approach has resulted in strong immune responses that were shown to confer partial protection from challenge infections (25,39,40). In a large phase IIb study, however, no protective effect was seen in vaccinated individuals (9). Thus, it is urgently necessary to further improve these vaccine approaches, and a promising strategy is the enhancement and modulation of vaccine-induced immune responses with genetic adjuvants..