HIV-1 p17 Gag (77-85), also called SL9, is a short part of the Human Immunodeficiency Virus 1 especially a short peptide of matrix composed of the viral protein p17 ensuring the integrity of the virion particle. HIV-1 p17 Gag (77-85) HLA-A*02:01-restricted was one of the first cytotoxic T lymphocytes epitope identified for HIV-1. It produces a specific cytotoxic T cells response in 75% of chronically infected adults but a rare activity in acute infection. Therefore, HIV-1 p17 Gag (77-85) may serve as target for anticancer immunotherapeutic strategies especially for vaccine development.Applications of HIV-1 p17 Gag (77-85):HIV-1 p17 Gag (77-85) is used to stimulate CTL responses in peripheral blood mononuclear cells (PBMCs). Then, ELISPOT assay is used to quantify peptide epitope specificity and IFN-γ releasing effector cells.Potential cross-reactivities with FluM1 (58-66) and HCV NS5B (2594-2602):Moreover, HIV-1 p17 Gag (77-85) share similarities with FluM1 (58-66) which can potentially show a cross-reactivity between these epitopes. It has been demonstrated a cross-reactivity and results suggest that immunity following infection by Influenza virus causes specific immune response to HIV-1 p17 Gag (77-85).Similarities between two others HLA-A2-restricted epitopes of two viruses have been demonstrated too: the amino acid sequence of HIV-1 p17 Gag (77-85) (SLYNTVATL) and of HCV NS5B (2594-2602) (ALYDVVTKL). Therefore, researches are conducted to know if during HCV/HIV co-infection it could be exist a T cell cross reactivity.