The parasite Theileria parva claims the life of approximately 1 million cattle every year. Immune animals to the parasite develop a lifelong immunity based on a cytotoxic T lymphocyte (CTL) response with a strong immunodominance restricted by the bovine leukocyte antigen (BoLA) class I molecules.
In our goal of developing a next-generation vaccine against T. parva, we have undertaken to identify new CTL inducing antigens that can be included in a recombinant vaccine. A peptide library of 18-mer peptides overlapping by 12 amino acids and covering 500 genes of the whole parasite genome was synthesized; giving approximately 40,000 peptides aliquoted in pools of 50 peptides.
Genes were selected based on the presence of a signal peptide, abundance, and divergence to the related parasite T. annulata, as well as by a selection using immuno-informatic tools predicting, by artificial neural network, peptides binding with strong affinity to the BoLA class I molecules present in cattle of Africa.
A bank of ten CTL lines from cattle immunized with the live parasite expressing different BoLA class I specificities were screened by IFN-g ELISpot assay. Among these cells, four secreted IFN-g in the presence of a different peptide library pool. Peptides from these pools were synthesized and positive individual 18-mer peptides were identified. Dissection of the minimal epitope is underway using IFN-g ELISpot, cytotoxicity as well as peptide-BoLA class I flow cytometry assays. These newly identified antigens will hopefully allow us to develop a vaccine towards T. parva giving wide coverage in cattle population with diverse BoLA class I molecules.
See a poster presented at the recent Keystone Symposia meeting: New approaches to vaccines for human and veterinary tropical diseases:
Download the poster:
Svitek, N., Saya, R., Awino, E., Nielsen, M., MacHugh, N., Silva, J.C. da, Nene, V. and Steinaa, L. 2016. Discovery of novel CTL epitopes by peptide library screening of CTL lines from Theileria parva immune animals. Poster prepared for the Keystone Symposium on New Approaches to Vaccines for Human and Veterinary Tropical Diseases, Cape Town, 22-26 May 2016. Nairobi, Kenya: ILRI.