Direct mTORC1 inhibition by short-term low-dose rapamycin treatment has recently been

Direct mTORC1 inhibition by short-term low-dose rapamycin treatment has recently been shown to improve CD8 T cell immunological memory. of low-dose rapamycin treatment. Mechanistically the CD8 defect was linked to impaired glycolytic switch in stimulated na?ve cells and the reduced formation of short-lived effector cells (SLEC). Therefore more than one cell type required for a protective effector immune response are impaired by rapamycin in both mice and humans at the dose shown to improve immune memory and extend lifespan. This urges caution with regard to the relative therapeutic costs and benefits of rapamycin treatment as means to improve immune memory. Introduction Rapamycin (rapa) is a specific inhibitor of the mTORC1 signaling complex the central regulator of cell nutrient sensing and energy metabolism (1). Applied in high doses (typical suppressive dose – 750 μg/kg) rapa is a well-known immune suppressant used to prevent organ rejection (2). However recent seminal studies highlighted the importance of nutrient sensing pathways during an immune response by showing that short-term mTORC1 inhibition using low-dose rapa (75μg/kg) enhanced the development of antigen-specific memory CD8 T cells during acute infection (3 4 Subsequent studies suggested that the low-dose rapa used in the above studies did not adversely affect primary immune responses (5). Of note these conclusions were based on limited data examining the presence but not the function of antigen-specific CD8 T cells. Recently mTORC1 signaling has been shown to be required for Th1 differentiation (6 7 likely by inducing Tbet expression (8). We therefore sought to reexamine whether mTORC1 inhibition by low-dose rapa treatment during CD8 T cell priming may have deleterious consequences to the functional CD8 T cell immune response during acute infection. Here we report that low-dose NVP-BGT226 rapa treatment inhibits CD8 T cell effector (CD8eff) accumulation and function during infections with both viral (lymphocytic NVP-BGT226 choriomeningitis virus – LCMV) and bacterial (expressing the ovalbumin protein – Lm-OVA) microbial pathogens. This was likely due to a rapa-induced block in metabolic switch to glycolysis in stimulated CD8eff cells which exhibited curtailed differentiation into short-lived effector cells (SLEC); by contrast memory-precursor effector cells (MPEC) were unaffected or increased in the course of rapa treatment. Moreover the same dose of rapa led to poor viral control in the NVP-BGT226 brain and higher mortality of the West Nile Virus (WNV)-infected mice. Finally the same dose of rapa inhibited human CD8 T cell cytokine secretion in vitro and reduced intracellular acidification of vesicles following the uptake of Lm-OVA in both human and mouse macrophages. Our data shows that acute low-dose rapa treatment is deleterious to both innate and adaptive acute immunity against primary infection. Because the favorable effect on memory formation by rapa treatment likely comes at the expense of developing a robust primary effector response rapa treatment/ mTORC1 modulation strategies to improve vaccine-mediated immune memory formation should consider the downside of increasing susceptibility to acute infections which could be of particular importance in partially immunosuppressed and/or vulnerable individuals. Materials and Methods Mice C57BL/6J (8-12 weeks old) were purchased from Jackson Labs (Bar Rabbit Polyclonal to HSP60. Harbor ME). Mice were housed under specific pathogen-free conditions at the University of Arizona. All experimental procedures were conducted with approval from the University of Arizona Institutional Animal Care and Use Committee. Human subjects sample collection and PBMC isolation Written informed consent was obtained and whole venous blood was collected into heparinized tubes from healthy volunteers. Subject inclusion criteria were limited to males aged 20-30 years old at time of blood draw who tested negative for both cytomegalovirus and flaviviruses. NVP-BGT226 Exclusion criteria included any immune-compromising disease heart disease organ transplant cancer or stroke. Study was approved by the University of Arizona Institutional Review Board. PBMCs were isolated using Histopaque (Sigma-Aldrich St. Louis MO) and cryopreserved in DMSO/FBS (10%/90%) until use. Rapamycin treatment Rapamycin (Calbiochem Darmstadt Germany) was administered by daily i.p. injection beginning 2 days prior to infection and lasting through day 7 post-infection. Rapa was administered at a dose of 75μg/kg in 200μL of PBS. Control groups were given PBS + 1%DMSO (vehicle) injections. For in vitro assays rapa was added at.