Targeting tumor-specific T cells with LAG3-directed interleukin-2 prevents T cell exhaustion and reinvigorates antitumor immunity

LAG3 is a critical inhibitory receptor that is highly enriched on exhausted T cells within the tumor microenvironment (TME), where it functions as a key driver of T cell exhaustion-an archetypal barrier to robust antitumor immunity. In a colon cancer model, we identified that LAG3+CD8+ tumor-infiltrating lymphocytes (TILs) constitute the predominant tumor-specific T cells but exhibit defective IL2 signaling. To address whether exogenous IL2 replenishment unpins their dysfunction, we engineered LAG3-LaIL2 (low-affinity IL2), a fusion protein delivering IL2 selectively to LAG3+CD8+ TILs. LAG3-LaIL2 expanded pre-exhausted tumor-specific CD8+ T cells, reprogrammed their exhaustion trajectory toward an intermediate effector state, and prevented terminal exhaustion, leading to tumor regression and prolonged survival in mice. Mechanistically, LAG3-LaIL2 restored IL2R-JAK3-STAT5 signaling by upregulating the high-affinity IL2 receptor subunit CD122, thereby rejuvenating TIL functionality. Furthermore, LAG3-LaIL2 amplified tumor-specific effector and memory T cells in draining lymph nodes, enabling systemic antitumor immunity against distal tumors and preventing tumor recurrence. Collectively, our findings validate LAG3-LaIL2 as a precision immunotherapeutic agent that specifically targets exhausted TILs, concomitantly enhancing therapeutic efficacy and safety by restricting IL2 exposure to non-target cells. This strategy provides a translatable approach to overcoming T cell exhaustion in solid tumors, offering a promising avenue to improve clinical outcomes for cancer patients Overall design: MC38 tumors were isolated at day 15 post-5 days treatment. Tumor tissues were minced and digested with MACS tumor dissociation kit (Miltenyi Biotec) according to the manufacturer's instruction. Following mechanical dissociation, cells were stained with anti-CD3 antibodies and sorted by BD FACSAria. scRNA-seq was conducted using the Chromium Next GEM Single Cell 3' Kit (10x Genomics). All subsequent steps were performed according to the manufacturer's protocol. The resulting libraries were purified and sequenced on a NextSeq sequencing system (Illumina).