Model forIn VivoAssessment of Humoral Protection against Malaria Sporozoite Challenge by Passive Transfer of Monoclonal Antibodies and Immune Serum

Abstract

fEvidence from clinical trials of malaria vaccine candidates suggests that both cell-mediated and humoral immunity to pre-erythrocytic parasite stages can provide protection against infection. Novel pre-erythrocytic antibody (Ab) targets could be key to improving vaccine formulations, which are currently based on targeting antigens such as the circumsporozoite protein (CSP). However, methods to assess the effects of sporozoite-specific Abs on pre-erythrocytic infection in vivo remain underdeveloped. Here, we combined passive transfer of monoclonal Abs (MAbs) or immune serum with a luciferase-expressing Plasmodium yoelii sporozoite challenge to assess Ab-mediated inhibition of liver infection in mice. Passive transfer of a P. yoelii CSP MAb showed inhibition of liver infection when mice were challenged with sporozoites either intravenously or by infectious mosquito bite. However, inhibition was most potent for the mosquito bite challenge, leading to a more significant reduction of liver-stage burden and even a lack of progression to blood-stage parasitemia. This suggests that Abs provide effective protection against a natural infection. Inhibition of liver infection was also achieved by passive transfer of immune serum from whole-parasite-immunized mice. Furthermore, we demonstrated that passive transfer of a MAb against P. falciparum CSP inhibited liver-stage infection in a humanized mouse/P. falciparum challenge model. Together, these models constitute unique and sensitive in vivo methods to assess serum-transferable protection against Plasmodium sporozoite challenge.

Artesunate versus Chloroquine Infection–Treatment–Vaccination Defines Stage-Specific Immune Responses Associated with Prolonged Sterile Protection against Both Pre-erythrocytic and Erythrocytic Plasmodium yoelii Infection

“…The difference observed between in vitro and in vivo assays could be because of the route of challenge used in our experiments, as it was recently shown that challenge by mosquito bite instead of i.v. not only allows Abs to act against the skin traversal phase of parasite infection, but also gives them sufficient time to block hepatocyte invasion (26).…”

“…For the MSP1 and schizont lysate ELISAs, Immulon 4 HBX 96-well plates were coated with 100 ml of 0.5 mg/ml yP.y. MSP1-19(XL)/VQ1 (MRA-48, deposited by D.C. Kaslow) or with 50 ml schizont lysate (5 mg/ml in PBS) prepared as previously described (26). Plates were incubated in blocking buffer (5% milk in PBS with 0.05% Tween 20; Fisher) for 1 h at room temperature.…”

“…with 300 ml pooled serum and challenged i.v. with 10,000 P. yoelii spz or 20,000 P. yoelii iRBCs 24 h postinjection, as described previously (26). Parasitemia was examined daily by thin blood smear and Giemsa staining, starting on day 3 postvaccination.…”

“…Twenty-four hours after receiving 300 ml donor sera by i.v. injection (26), mice were challenged with either 10,000 P. yoelii spz or 20,000 iRBC by i.v. injection.…”

An Expanding Toolkit for Preclinical Pre-Erythrocytic Malaria Vaccine Development: Bridging Traditional Mouse Malaria Models and Human Trials

“…These approaches are mutually exclusive in the same animal, though, as qPCR analysis requires animal euthanasia and liver extraction prior to blood-stage infection -resulting in a doubling of animal numbers if both liver burden and time to patency are to be measured. Recently, measurement of liver-stage burden without animal sacrifice has become possible through live bioluminescent imaging techniques and the generation of parasites expressing the firefly luciferase gene [34,[66][67][68][69][70]. This approach strikes a balance between sensitivity of measuring liver-stage burden while keeping the animal alive to measure parasite progression to bloodstage patency, thus reducing animal use and also enabling recurrent challenge for investigation of duration of protection and immunological memory.…”