P. falciparum and P. vivax Epitope-Focused VLPs Elicit Sterile Immunity to Blood Stage Infections.

In order to design P. falciparum preerythrocytic vaccine candidates, a library of circumsporozoite (CS) T and B cell epitopes displayed on the woodchuck hepatitis virus core antigen (WHcAg) VLP platform was produced. To test the protective efficacy of the WHcAg-CS VLPs, hybrid CS P. berghei/P. falciparum (Pb/Pf) sporozoites were used to challenge immunized mice. VLPs carrying 1 or 2 different CS repeat B cell epitopes and 3 VLPs carrying different CS non-repeat B cell epitopes elicited high levels of anti-insert antibodies (Abs). Whereas, VLPs carrying CS repeat B cell epitopes conferred 98% protection of the liver against a 10,000 Pb/Pf sporozoite challenge, VLPs carrying the CS non-repeat B cell eptiopes were minimally-to-non-protective. One-to-three CS-specific CD4/CD8 T cell sites were also fused to VLPs, which primed CS-specific as well as WHcAg-specific T cells. However, a VLP carrying only the 3 T cell domains failed to protect against a sporozoite challenge, indicating a requirement for anti-CS repeat Abs. A VLP carrying 2 CS repeat B cell epitopes and 3 CS T cell sites in alum adjuvant elicited high titer anti-CS Abs (endpoint dilution titer >1x10(6)) and provided 80-100% protection against blood stage malaria. Using a similar strategy, VLPs were constructed carrying P. vivax CS repeat B cell epitopes (WHc-Pv-78), which elicited high levels of anti-CS Abs and conferred 99% protection of the liver against a 10,000 Pb/Pv sporozoite challenge and elicited sterile immunity to blood stage infection. These results indicate that immunization with epitope-focused VLPs carrying selected B and T cell epitopes from the P. falciparum and P. vivax CS proteins can elicit sterile immunity against blood stage malaria. Hybrid WHcAg-CS VLPs could provide the basis for a bivalent P. falciparum/P. vivax malaria vaccine.

Palivizumab epitope-displaying virus-like particles protect rodents from RSV challenge.

Respiratory syncytial virus (RSV) is the most common cause of serious viral bronchiolitis in infants, young children, and the elderly. Currently, there is not an FDA-approved vaccine available for RSV, though the mAb palivizumab is licensed to reduce the incidence of RSV disease in premature or at-risk infants. The palivizumab epitope is a well-characterized, approximately 24-aa helix-loop-helix structure on the RSV fusion (F) protein (F254-277). Here, we genetically inserted this epitope and multiple site variants of this epitope within a versatile woodchuck hepadnavirus core-based virus-like particle (WHcAg-VLP) to generate hybrid VLPs that each bears 240 copies of the RSV epitope in a highly immunogenic arrayed format. A challenge of such an epitope-focused approach is that to be effective, the conformational F254-277 epitope must elicit antibodies that recognize the intact virus. A number of hybrid VLPs containing RSV F254-277 were recognized by palivizumab in vitro and elicited high-titer and protective neutralizing antibody in rodents. Together, the results from this proof-of-principle study suggest that the WHcAg-VLP technology may be an applicable approach to eliciting a response to other structural epitopes.

Use of hepadnavirus core proteins as vaccine platforms.

The first virus-like particle to be tested for use as a vaccine carrier was based on the hepatitis B virus nucleocapsid protein. This viral subunit, while not infectious on its own, is a 36-nm particle that is highly immunogenic during a natural infection. The self-assembly and high degree of immunogenicity is maintained when expressed as a recombinant protein and, moreover, can confer a high degree of immunogenicity on foreign antigens linked to the particle, either chemically or genetically. This review describes the current state of the hepadnaviral core protein as a vaccine carrier.

Androgen induction of in vitro prostate cell differentiation.

To better understand androgen action in normal prostate cells, we characterized the androgen growth response of an immortalized nontumorigenic rat prostate cell line called CA25 that had been stably transfected with androgen receptor (AR) cDNA. Surprisingly, we found that AR(+) CA25 cells grew slower in the presence of dihydrotestosterone (DHT), whereas the growth of AR(-) CA25 cells was not affected by the hormone. DHT-mediated growth inhibition of CA25 cells was not attributable to an increase in apoptosis but rather to a morphological conversion consistent with terminal differentiation. Specifically, we found that DHT treatment of CA25 cells resulted in a striking change in cell architecture, localization of desmoplakin to cell-cell boundaries, and an increase in alpha 6p integrin levels, a newly described marker of cell differentiation. Although no androgen-dependent changes were observed in the transcript levels of the mitochondrial aspartate aminotransferase or c-Myc genes by Northern blot analysis, RNA expression profiling of DHT-treated CA25 cells identified 282 genes of 1,018 that were continually expressed over a 48-h period. It was found that 63 of these genes were up-regulated >5-fold within the first 4 h of treatment and encoded functions involved in transport, signal transduction, and metabolism. These expression profile data are consistent with the striking morphological changes we observed in DHT-treated CA25 cells and provide a starting point for molecular analysis of in vitro prostate cell differentiation.