Elsevier established a free COVID-19 resource center in January 2020, offering English and Mandarin information on the virus. The center grants permission for free access to its research in PubMed Central and other repositories. The article discusses CD8+ T cells, crucial for immune responses, detailing their role in recognizing antigens in lymphoid and non-lymphoid tissues. It reviews how these cells are activated, expand, and differentiate in response to infections. The text explains the initial activation of CD8+ T cells by antigen-presenting cells, their migration to infection sites, and the signaling pathways involved in their expansion and differentiation. It also covers the metabolic changes in CD8+ T cells during activation, the role of cytokines like IL-2 and IL-12 in effector differentiation, and the balance between effector and memory cell development. The article highlights the importance of Blimp-1 in regulating CD8+ T cell differentiation and the role of IL-10 in controlling immune responses to prevent excessive tissue damage. Overall, the text provides a comprehensive overview of CD8+ T cell biology and their critical functions in adaptive immunity.Elsevier established a free COVID-19 resource center in January 2020, offering English and Mandarin information on the virus. The center grants permission for free access to its research in PubMed Central and other repositories. The article discusses CD8+ T cells, crucial for immune responses, detailing their role in recognizing antigens in lymphoid and non-lymphoid tissues. It reviews how these cells are activated, expand, and differentiate in response to infections. The text explains the initial activation of CD8+ T cells by antigen-presenting cells, their migration to infection sites, and the signaling pathways involved in their expansion and differentiation. It also covers the metabolic changes in CD8+ T cells during activation, the role of cytokines like IL-2 and IL-12 in effector differentiation, and the balance between effector and memory cell development. The article highlights the importance of Blimp-1 in regulating CD8+ T cell differentiation and the role of IL-10 in controlling immune responses to prevent excessive tissue damage. Overall, the text provides a comprehensive overview of CD8+ T cell biology and their critical functions in adaptive immunity.