The ultimate goal of this project is to develop a sterilizing vaccine against malaria. The specific hypothesis tested in this proposal is that sterilizing immunity against malaria can be achieved by induction of a lasting effector memory T cell (TEM) response targeting the liver stage of Plasmodium parasites. Repeated immunizations with live or irradiated sporozoites are known to protect vaccinated individuals against malaria challenge. Recent evidence suggests that this protection correlated with the presence of frequent pluripotent TEM, suggesting that permanent sterilizing immunity against malaria requires the induction of high levels of long-lived TEM by vaccination. To test this hypothesis, we propose to use recombinant cytomegalovirus (CMV) as a vaccine vector because CMV is the prototypical virus inducing long-lived TEM that do not show signs of T cell exhaustion. This unique capability of CMV-vectors was recently applied to induce long-lived TEM against simian immunodeficiency virus, resulting in protection against SIV-challenge that was by far superior to conventional heterologous prime/boost vaccines with respect to efficacy and duration. Since sterilizing protection against Plasmodium knowlesi parasites was only partial and shortlived when heterologous prime/boost vaccines were used, we will examine whether CMV-derived vaccine vectors will similarly confer lasting and efficacious immunity against challenge with Plasmodium knowlesi (Pk) sporozoites. We propose to generate recombinant RhCMV expressing four Pk antigens previously used for heterologous prime boost vaccination: the circumsporozoite protein (CSP), the sporozoite surface protein 2 or thrombospondin-related adhesion protein (SSP2 or TRAP), the apical merozoite antigen-1 (AMA1) and the C-terminus of the merozoite surface protein 1 (MSP1c). We will inoculate animals with this panel of four recombinant RhCMV/Pk vectors and monitor the development of TEM in blood, lung and liver. To determine whether the RhCMV/Pk4 vaccine is protective we will challenge with P. knowlesi sporozoites. Upon completion of this exploratory project, we will thus know whether a TEM-inducing vaccine can improve the level and duration of sterilizing immunity induced by subunit vaccines against malaria parasites.
Malaria is a mosquito-borne parasitic disease that afflicts hundreds of millions individuals worldwide and many parasites are resistant to drug treatment. Thus, there is an urgent need to develop a malaria vaccine, ideally a vaccine that would completely prevent infection. We propose to use cytomegalovirus as a novel tool to immediately intersect incoming parasites at the liver stage, thus preventing blood infection and disease.