Depending on their phenotype IL-7 or IL-15 will help survival. If you want to keep them for weeks they should be put on irradiated feeders cells (such as PBMCs).
I briefly wanted to reach out concerning your inquiry. Assuming that you are working with Trypanosoma cruzi infected mice, please try blocking the Fas/FasL pathway with a blocking antibody to overcome the apoptotic program and improve the survival of your CD8 T cells as per the attached publication.