you have to use an overlapping peptide library for your protein of interest, probably HIV-1 Gag, for ex vivo stimulation. Such libraries are available for free in limited amounts at the NIH AIDS Reagent Program. Probably the most convenient read out would be the IFN-y ELISpot. See the link for a standard protocol. Another option would be to perform intracellular cytokine staining for IFN-y or granzyme B (you can also include a fluorescently labeled anti-CD107a antibody during stimulation).