CD8+ T cells treated with a combination of IL-15 and MCP-1 showed the highest level of p-STAT3 (Fig. 3A), suggesting that in addition to direct effects of STAT3 mutations, increased levels of IL-6, IL-15, or MCP-1 (Fig. 1A, B) may further hyperactivate STAT3, DNMT1, and MYC signaling in LGLL. Here, IL6 is linked to T-cell large granular lymphocyte leukemia.