IL7 (interleukin-7) is a hematopoietic cytokine produced by stromal cells in thymus, bone marrow, and lymphoid organs that plays an essential role in lymphocyte development, expansion, and survival 1. IL7 exerts its biological effects through a heterodimeric receptor composed of IL7RA (CD127) and the common gamma chain (γc/CSF2RG) 1, activating JAK1/JAK3 kinases and downstream signaling through STAT5, PI3K/Akt/mTOR, and MEK/ERK pathways 1. IL7 is required for survival of naïve and memory T cells, pro-B cells, and innate lymphocytes, while downregulating its own receptor expression to enable equitable resource sharing among T cells competing for limited cytokine 2. Notably, IL7 enhances protein translation in T cells, improving mRNA-based therapeutic delivery in vivo 3. Deficiencies in the IL7 pathway cause severe combined immunodeficiency with lymphopenia, while excessive signaling drives autoimmunity including multiple sclerosis, type 1 diabetes, and rheumatoid arthritis 1. IL7 accumulation in aged tissues increases ACE2 expression, contributing to age-related SARS-CoV-2 susceptibility 4. IL7 signaling via CD127+ monocytes restrains inflammatory responses in COVID-19 and rheumatoid arthritis 5. Clinically, IL7 treatment expands lymphocytes in cancer and AIDS patients and accelerates recovery after hematopoietic stem cell transplantation 1, with IL7-expressing CAR-T cells demonstrating enhanced efficacy against solid tumors 6.