Live rubella vectors can express native HIV envelope glycoproteins targeted by broadly neutralizing antibodies and prime the immune response to an envelope protein boost

Live attenuated rubella vectors expressing Plasmodium falciparum circumsporozoite protein (Pf-CSP) provide a novel malaria vaccine platform in the rhesus macaque

There is an urgent need for a malaria vaccine that can prevent severe disease in young children and adults. Despite earlier work showing an immunological mechanism for preventing infection and reducing disease severity, there is currently no reliable vaccine that can provide durable protection. In part, this may reflect a limited number of ways that the host can respond to the NANP repeat sequences of circumsporozoite protein (CSP) in the parasite. In addition, it may reflect antigenic escape by the parasite from protective antibodies. To be successful, a vaccine must protect against repeated exposure to infected mosquitoes in endemic areas. We have created a series of live viral vectors based on the rubella vaccine strain that express multiple tandem repeats of NANP, and we demonstrate immunogenicity in a rhesus macaque model. We tested the vectors in a sequential immunization strategy. In the first step, the animals were primed with CSP-DNA vaccine and boosted with rubella/CSP vectors. In the second step, we gave rubella/CSP vectors again, followed by recombinant CSP protein. Following the second step, antibody titers were comparable to adult exposure to malaria in an endemic area. The antibodies were specific for native CSP protein on sporozoites, and they persisted for at least 1½ years in two out of three macaques. Given the safety profile of rubella vaccine in children, these vectors could be most useful in protecting young children, who are at greatest risk of severe malarial disease.

Viral Vectors for the Induction of Broadly Neutralizing Antibodies against HIV

Extensive research on generating an efficient HIV vaccine is ongoing. A major aim of HIV vaccines is the induction of long-lasting, broadly neutralizing antibodies (bnAbs) that can confer sterile immunity for a prolonged period of time. Several strategies have been explored to reach this goal, i.e. protein immunization, DNA, or viral vectors, or a combination thereof. In this review, we give an overview of approaches using viral vectors for the induction of HIV-specific bnAbs. Many pre-clinical studies were performed using various replication-competent and -incompetent vectors. Amongst them, poxviral and adenoviral vectors were the most prevalent ones. In many studies, viral vectors were combined with a DNA prime or a protein boost. However, neutralizing antibodies were mainly induced against the homologous HIV-1 vaccine strain or tier 1 viruses, and in rare cases, against tier 2 viruses, indicating the need for improved antigens and vaccination strategies. Furthermore, we also review next generation Env antigens that are currently being used in protein vaccination approaches and point out how they could be utilized in viral vectors.