Ex vivo tetramer staining and cell surface phenotyping for early activation markers CD38 and HLA-DR to enumerate and characterize malaria antigen-specific CD8+ T-cells induced in human volunteers immunized with a Plasmodium falciparum adenovirus-vectored malaria vaccine expressing AMA1

• Published in: Malaria journal Vol. 12; no. 1; p. 376
• Main Authors: Schwenk, Robert, Banania, Glenna, Epstein, Judy, Kim, Yohan, Peters, Bjoern, Belmonte, Maria, Ganeshan, Harini, Huang, Jun, Reyes, Sharina, Stryhn, Anette, Ockenhouse, Christian F, Buus, Soren, Richie, Thomas L, Sedegah, Martha
• Format: Journal Article
• Language: English
• Published: London BioMed Central 29.10.2013; BioMed Central Ltd
• Subjects: Adenoviruses; ADP-ribosyl Cyclase 1 - analysis; Antigens, Protozoan - immunology; Biomedical and Life Sciences; Biomedicine; CD8-Positive T-Lymphocytes - chemistry; CD8-Positive T-Lymphocytes - immunology; Cytokines; Entomology; Evaluation; Genetic diversity; Genotype & phenotype; Growth hormones; Health aspects; Healthy Volunteers; Histocompatibility antigens; HLA histocompatibility antigens; HLA-DR Antigens - analysis; Humans; Immunology; Immunophenotyping - methods; Infectious Diseases; Labeling; Liver; Lymphocytes; Malaria; Malaria vaccine; Malaria Vaccines - administration & dosage; Malaria Vaccines - immunology; Malaria, Falciparum - immunology; Medical research; Medicine, Experimental; Membrane Glycoproteins - analysis; Membrane Proteins - immunology; Microbiology; Parasitology; Peptides; Plasmodium falciparum; Primates; Proteins; Protozoan Proteins - immunology; Public Health; Staining and Labeling - methods; Studies; T cell receptors; T-Lymphocyte Subsets - chemistry; T-Lymphocyte Subsets - immunology; Tropical diseases; Tropical Medicine; Vaccines; Vaccines, Synthetic - administration & dosage; Vaccines, Synthetic - immunology; United States; MHC-I tetramers; CD8+ T cells; Malaria; Activation markers
• ISSN: 1475-2875; 1475-2875
• DOI: 10.1186/1475-2875-12-376

Background Malaria is responsible for up to a 600,000 deaths per year; conveying an urgent need for the development of a malaria vaccine. Studies with whole sporozoite vaccines in mice and non-human primates have shown that sporozoite-induced CD8 + T cells targeting liver stage antigens can mediate sterile protection. There is a need for a direct method to identify and phenotype malaria vaccine-induced CD8 + T cells in humans. Methods Fluorochrome-labelled tetramers consisting of appropriate MHC class I molecules in complex with predicted binding peptides derived from Plasmodium falciparum AMA-1 were used to label ex vivo AMA-1 epitope specific CD8 + T cells from research subjects responding strongly to immunization with the NMRC-M3V-Ad-PfCA (adenovirus-vectored) malaria vaccine. The identification of these CD8 + T cells on the basis of their expression of early activation markers was also investigated. Results Analyses by flow cytometry demonstrated that two of the six tetramers tested: TLDEMRHFY: HLA-A*01:01 and NEVVVKEEY: HLA-B*18:01, labelled tetramer-specific CD8 + T cells from two HLA-A*01:01 volunteers and one HLA-B*18:01 volunteer, respectively. By contrast, post-immune CD8 + T cells from all six of the immunized volunteers exhibited enhanced expression of the CD38 and HLA-DR hi early activation markers. For the three volunteers with positive tetramer staining, the early activation phenotype positive cells included essentially all of the tetramer positive, malaria epitope- specific CD8 + T cells suggesting that the early activation phenotype could identify all malaria vaccine-induced CD8 + T cells without prior knowledge of their exact epitope specificity. Conclusions The results demonstrated that class I tetramers can identify ex vivo malaria vaccine antigen-specific CD8 + T cells and could therefore be used to determine their frequency, cell surface phenotype and transcription factor usage. The results also demonstrated that vaccine antigen-specific CD8 + T cells could be identified by activation markers without prior knowledge of their antigen-specificity, using a subunit vaccine for proof-of-concept. Whether, whole parasite or adjuvanted protein vaccines will also induce {CD38 and HLA-DR hi } + CD8 + T cell populations reflective of the antigen-specific response will the subject of future investigations.