Human
T-cell leukemia virus type 1 (HTLV-1) has infected as many as 10 million people worldwide. While 90% are asymptomatic, 5% develop severe diseases including
adult T-cell leukemia/lymphoka (
ATLL) and
HTLV-1-associated myelopathy/
tropical spastic paraparesis (HAM/TSP). No
vaccine against HTLV-1 exists, and screening programs are not universal. However, patients with chronic HTLV-1
infection have high frequencies of HTLV-1-activated CD8+ T cells, and the two main HLA alleles (A2, A24) are present in 88% of infected individuals. We thus utilized an immunoproteomics approach to characterize MHC-I restricted
epitopes presented by HLA-A2+, A24+ MT-2 and SLB-1 cell lines. Unlike traditional motif prediction algorithms, this approach identifies
epitopes associated with cytotoxic T-cell responses in their naturally processed forms, minimizing differences in antigen processing and
protein expression levels. Out of nine identified
peptides, we confirmed six novel MHC-I restricted
epitopes that were capable of binding
HLA-A2 and
HLA-A24 alleles and used in vitro and in vivo methods to generate CD8+ T cells specific for each of these
peptides. MagPix MILLIPLEX data showed that in vitro generated
epitope-specific CD8+ T cells secreted IFN-ɣ,
granzyme B, MIP-1α, TNF-α,
perforin and
IL-10 when cultured in the presence of MT-2 cell line. Degranulation assay confirmed cytotoxic response through surface expression of CD107 on CD8+ T cells when cultured with MT-2 cells. A CD8+ T-cell killing assay indicated significant
antiviral activity of CD8+ T cells specific against all identified
peptides. In vivo generated CD8+ T cells similarly demonstrated immunogenicity on ELISpot, CD107 degranulation assay, and MagPix MILLIPLEX analysis. These
epitopes are thus candidates for a therapeutic
peptide-based
vaccine against HTLV-1, and our results provide preclinical data for the advancement of such a
vaccine.