During infection, CD8+ T cells initially increase then contract, leaving a small memory space pool providing long lasting immunity. explanation for poor CD8+ T cell memory space in the elderly and potentially gives 5-Iodotubercidin novel immune modulators to improve aged immunity. DOI: http://dx.doi.org/10.7554/eLife.03706.001 specifically in T cells, we find peripheral T cell lymphopenia, leading to proliferation and an activated phenotype within the CD8+ T cell compartment. While T cells respond normally during the early stages of live viral challenge, a seriously jeopardized memory space CD8+ T cell compartment was found in response to influenza and murine cytomegalovirus (MCMV). Using bone marrow (BM) chimeras, we excluded that this is due the effects of lymphopenia; poor CD4+ T cell help; exhaustion, or modified cytokine receptor manifestation. Moreover, autophagy was found to be highest in antigen-specific CD8+ T cells when compared to na?ve cells. Antigen-specific CD8+ T cells also underwent more cell death at the time of memory space formation, display jeopardized mitochondrial health, and increased manifestation of the glucose receptor GLUT1, a marker for glycolysis. Furthermore, recall CD8+ T cell reactions to repeat immunizations and vaccination protocols were greatly diminished. This being reminiscent of the human being ageing immune system (Haq and McElhaney, 2014), we confirmed reduced autophagy in the transcriptional and practical level in murine T cells from older mice. Importantly, we were able to restore the CD8+ T cell memory response in aged mice with the autophagy-inducing 5-Iodotubercidin compound spermidine, but not in autophagy-deficient mice. Finally, we found that spermidine induces autophagy independently of mTOR in T cells. Enhancing autophagy in an mTOR-independent manner may provide a safe way to improve vaccine responses in the elderly. Results Autophagy controls T cell figures in na?ve Tmice mice were bred with mice to generate mice with defective Cdh15 autophagy in both CD4+ and CD8+ T lymphocytes (TmRNA and Atg7 protein was confirmed in purified T cells (Physique 1figure product 1A and B, respectively). Using the imaging circulation cytometer (ImageStream) to count LC3 puncta in CD4+ and CD8+ T cells (Phadwal et al., 2012), we exhibited that functional autophagy was significantly diminished in CD8+ T cells 5-Iodotubercidin (Physique 1figure product 1C with examples of ImageStream images in right panel). In addition, using a classical technique to detect lipidated LC3, we confirmed that basal autophagy was diminished in the presence and absence of the autophagy flux inhibitor Bafilomycin A (Physique 1figure product 1D). Previous reports have noted a number of changes to the na?ve CD8+ T cell compartment in the absence of autophagy, with T cell lymphopenia, a consistent observation (Pua et al., 2007; Puleston and Simon, 2014). We set out to 5-Iodotubercidin investigate if an altered na?ve CD8+ T cell compartment exists in Tmice. We confirmed observations from previous reports using comparable autophagy-deficient mouse models (Pua et al., 2007, 2009) that thymic development of CD4+ and CD8+ T cells was normal in 6-week aged Tmice (Physique 1A). However, mice were lymphopenic for both CD4+ and CD8+ T cells in the lymph nodes and blood (Physique 1B,C). Moreover, CD8+ T cells exhibited an activated phenotype with increased CD44 expression (Physique 1D) and decreased CD62L expression (Physique 1E), resembling a virtual memory compartment (Akue et al., 2012). We observed comparable frequencies of central effector memory CD62L+CD44hi, however, T-specific (Physique 1figure product 2A and B). Next, we established that proliferation was increased in the activated CD44hi CD8+ T cell compartment by Ki-67 staining (Physique 1F). The observed activated phenotype and increased cell turnover in CD8+ T cells are likely driven by homeostatic proliferation in an attempt to fill the depleted T cell niche. Indeed, the expression of the homeostatic proliferation marker CD24 (Li et al., 2006) was found to be significantly increased on CD8+ T cells (Physique 1G). To investigate whether lymphopenia drives this activated phenotype in the CD8+ T cell compartment, we generated 1:1 mixed.