Adoptive cell therapy using tumor-infiltrating lymphocytes (TILs) has shown promise for solid tumors, but its broader application is limited by reliance on high-dose interleukin-2 (IL-2), which drives T-cell exhaustion and causes severe toxicity. A new preclinical study published in Cancer Biology & Medicine introduces a feeder-free TIL expansion protocol that significantly reduces IL-2 dependence while preserving robust anti-tumor activity. The study also demonstrates that combining TIL therapy with low-dose PD-1 blockade enhances tumor control and treatment tolerability, offering a potential pathway toward safer TIL-based immunotherapies.
Conventional TIL therapy, recently validated by FDA approval of lifileucel for advanced melanoma, relies on high-concentration IL-2 (3,000–6,000 IU/mL) and feeder cells like irradiated peripheral blood mononuclear cells. This process complicates manufacturing, promotes T-cell exhaustion, and requires post-infusion high-dose IL-2 with significant toxicity. Tumor immune evasion, including MHC-I downregulation, further limits efficacy. The joint team from Chinese PLA General Hospital and Shanghai Juncell Therapeutics developed a feeder-free system using low-concentration IL-2, IL-7, and IL-15 in pre-REP, and CD3/CD28 co-stimulation with only 300 IU/mL IL-2 in REP. This protocol achieved expansion success rates of at least 90% across melanoma, pancreatic, gastric, cervical, and colorectal cancers, with melanoma TILs expanding ~2,500-fold. The resulting TILs showed high purity (CD45+CD3+ cells >93%), potent cytotoxicity, and a less exhausted phenotype with minimal PD-1 expression (<0.5%).
In a colorectal cancer PDX model, adding low-dose PD-1 blockade (2 mg/kg) to TIL therapy significantly reduced tumor volume (P = 0.002) and maintained body weights, completely preventing tumor ulceration seen in TIL-only and control groups. The researchers also explored hydroxychloroquine (HCQ) to upregulate MHC-I, which enhanced early TCR-T killing in vitro but showed limited in vivo benefit. The authors stated: "By creating a feeder-free system with carefully calibrated cytokine support, we've shown that we can generate functional, less exhausted TILs from multiple tumor types. The addition of low-dose PD-1 blockade not only boosted anti-tumor efficacy but also improved treatment tolerability." This IL-2-independent strategy has already been explored in a clinical trial for advanced gynecologic cancers with early favorable safety signals.
The findings simplify manufacturing and may lower costs, making TIL therapy more accessible. Low-dose PD-1 blockade, already clinically used, could replace high-dose IL-2 support, addressing a major safety concern. Future studies will validate these results in larger models and diverse tumors. If confirmed, this approach could expand TIL therapy to more patients with solid tumors. The study was supported by the Science and Technology Commission of Shanghai Municipality (Grant No. 22XD1432200).
