Treating Immunotherapy-Resistant Colorectal Cancer With CRISPR-Enhanced TILs

A New Attack on the Immune System's Internal Brakes

Immunotherapieshave transformed cancer treatment in recent years. However, many advanced cancers, particularly tumors resistant to checkpoint inhibitors , do not respond to these treatments. This has brought a new target into focus: CISH (Cytokine-inducible SH2-containing protein).

CISH acts as an intracellular immune checkpoint and works like an "internal brake" that prevents excessive T-cell activation. To remove this brake, researchers used CRISPR-Cas9 gene-editing technology to create modified tumor-infiltrating lymphocytes (TILs) for the first time in a phase 1 clinical trial .

The results were published on April 29, 2025, in The Lancet Oncology and could open the door to a new era in cancer treatment.

Trial Details: Who Participated and How Was Treatment Given?

This phase 1 trial was conducted between May 2020 and September 2022 at the University of Minnesota Medical School. Participants:

• Had metastatic gastrointestinal cancers.

• Had disease progression despite at least one line of standard treatment.

• Had at least one surgically resectable tumor lesion from which TILs could be produced.

• Had another measurable tumor lesion for assessing treatment response.

Treatment Process:

1. TILs obtained from tumor biopsieswere expanded according to their response to tumor-specific neoantigens.

2. Using CRISPR-Cas9, the cells underwent CISH gene knockout (CISH knockout).

3. Patients received lymphodepleting chemotherapy with cyclophosphamide and fludarabine before the cells were infused.

4. This was followed by high-dose IL-2 (interleukin-2) treatment (720,000 IU/kg per dose, every 8 hours, up to 6 doses).

Results in Numbers: Safety and Efficacy

• 22 patients were enrolled, and in 19 (86%) a CISH-knockout TIL product was successfully manufactured.

• Of these 19 patients, 12 (63%) received a single infusion of CISH-knockout TILs.

• Median follow-up was 129 days (interquartile range: 15–283 days).

Safety Data:

• All patients developed treatment-related serious adverse effects .

• The most common grade 3/4 adverse effects:

  • Hematological toxicity (12 patients): Attributed to lymphodepleting treatment or IL-2

  • Fatigue (4 patients, 33%)

  • Loss of appetite (3 patients, 25%)

• Regarding cytokine release syndrome or neurotoxicity , no grade ≥3 events were identified.

• No treatment-related deaths or serious adverse events were observed.

Clinical Responses:

• On day 28, stable disease was found in 6 patients (50%), and in 4 (33%) on day 56 .

• A particularly notable case: One patient with microsatellite instability-high (MSI-high) colorectal cancer who was resistant to anti–PD-1/CTLA-4 therapies achieved a complete response lasting more than 21 months after treatment.

What Does This Mean? Another Step Toward Next-Generation Immunotherapies

These results indicate that CISH inhibition is safe and potentially has antitumor activity. This strategy opens a new treatment avenue, particularly for patients with metastatic cancer that does not respond to immune checkpoint inhibitors.

For the first time, this trial provided clinical evidence that an intracellular immune checkpoint (CISH) can be targeted through genetic engineering and that this can produce a therapeutic response . Integrating CRISPR-Cas9 technology into TIL therapy means redefining the immune system's natural limits.

Conclusion: New Horizons for Personalized, Genetically Based Immune Treatments

This phase 1 trial highlights the promise of genetically enhanced cellular therapies for patients who do not respond to conventional immunotherapies. Disabling "internal checkpoint" targets such as CISH may enable the immune system to recognize and eliminate cancer more effectively.

In the future, personalized immunotherapies using molecular modifications such as CISH knockout could become a central strategy in cancer treatment.