title: Genetically attenuated parasite vaccines induce contact-dependent CD8+ T cell killing of Plasmodium yoelii liver stage-infected hepatocytes.
abstract: The production of IFN-gamma by CD8(+) T cells is an important hallmark of protective immunity induced by irradiation-attenuated sporozoites against malaria. Here, we demonstrate that protracted sterile protection conferred by a Plasmodium yoelii genetically attenuated parasite (PyGAP) vaccine was completely dependent on CD8(+) T lymphocytes but only partially dependent on IFN-gamma. We used live cell imaging to document that CD8(+) CTL from PyGAP-immunized mice directly killed hepatocyte infected with a liver stage parasite. Immunization studies with perforin and IFN-gamma knockout mice also indicated that the protection was largely dependent on perforin-mediated effector mechanisms rather than on IFN-gamma. This was further supported by our observation that both liver and spleen CD8(+) T cells from PyGAP-immunized mice induced massive apoptosis of liver stage-infected hepatocytes in vitro without the release of detectable IFN-gamma and TNF-alpha. Conversely, CD8(+) T cells isolated from naive mice that had survived wild-type P. yoelii sporozoite infection targeted mainly sporozoite-traversed and uninfected hepatocytes, revealing an immune evasion strategy that might be used by wild-type parasites to subvert host immune responses during natural infection. However, CTLs from wild-type sporozoite-challenged mice could recognize and kill infected hepatocytes that were pulsed with circumsporozoite protein. Additionally, protection in PyGAP-immunized mice directly correlated with the magnitude of effector memory CD8(+) T cells. Our findings implicate CTLs as key immune effectors in a highly protective PyGAP vaccine for malaria and emphasize the critical need to define surrogate markers for correlates of protection, apart from IFN-gamma.
authors.affiliation: Seattle Biomedical Research Institute, Seattle, WA 98109, USA.
authors.forename: Adama
authors.initials: A
authors.lastname: Trimnell
authors.forename: Akihide
authors.initials: A
authors.lastname: Takagi
authors.forename: Megha
authors.initials: M
authors.lastname: Gupta
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Richie
authors.forename: Stefan H
authors.initials: SH
authors.lastname: Kappe
authors.forename: Ruobing
authors.initials: R
authors.lastname: Wang
mesh_terms: D000818:Animals; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology* / Q000469:parasitology / Q000473:pathology; D002450:Cell Communication / Q000235:genetics / Q000276:immunology*; D003602:Cytotoxicity, Immunologic / Q000235:genetics*; D005260:Female; D022781:Hepatocytes / Q000276:immunology* / Q000469:parasitology* / Q000473:pathology; D007156:Immunologic Memory / Q000235:genetics; D007371:Interferon-gamma / Q000172:deficiency / Q000235:genetics; D008109:Liver Diseases, Parasitic / Q000276:immunology / Q000469:parasitology / Q000517:prevention & control*; D008288:Malaria / Q000276:immunology / Q000469:parasitology / Q000517:prevention & control; D017780:Malaria Vaccines / Q000008:administration & dosage / Q000235:genetics* / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D008822:Mice, Transgenic; D054353:Perforin / Q000172:deficiency / Q000235:genetics; D010967:Plasmodium yoelii / Q000235:genetics* / Q000276:immunology; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology
chemical_list: D017780:Malaria Vaccines; D014613:Vaccines, Attenuated; D054353:Perforin; D007371:Interferon-gamma