First-in-Human Data Support CISH Knockout Strategy to Enhance TIL Activity, Circumvent ICI Resistance in Metastatic GI Cancers

Emil Lou, MD, PhD, FACP

Early-phase data have provided proof of concept that disrupting cytokine-inducible SH2-containing protein (CISH) through CRISPR-Cas9–mediated CISH gene knockout can be done safely and may enhance the antitumor activity of tumor-infiltrating lymphocytes (TILs) in patients with drug-refractory forms of metastatic gastrointestinal epithelial cancers, including colorectal cancer (CRC), according to Emil Lou, MD, PhD, FACP.

Data from a first-in-human, single-center phase 1 trial (NCT04426669), published in Lancet Oncology, demonstrated that the neoantigen-reactive TIL therapy was well tolerated and produced early signs of efficacy. Although severe treatment-related adverse effects (AEs) were reported in all evaluable patients (n = 12), none were attributed to TIL therapy. The maximum tolerated dose was not reached, as all administered doses of TIL therapy were tolerated by all patients. At a median follow-up of 129 days (interquartile range, 15–283), 50% of patients achieved stable disease (SD) by day 28, with 33% maintaining ongoing SD at day 56.

“In the last 10 to 15 years, we've seen a virtual revolution of immuno-oncology, [but] it has not yet extended to all cancer types,” Lou, an associate professor of medicine in the Division of Hematology, Oncology and Transplantation at the University of Minnesota Medical School and a medical oncologist at M Health Fairview Masonic Cancer Clinic in Minneapolis, said in an interview with OncLive®. “To have an essentially incurable form of disease in 1 of these 12 patients, and to see that durable response for more than 2 years [was exciting], as a complete form of cure in a patient with CRC following TILs that were not engineered has not been seen [before]. Obviously, we want to replicate this.”

In the interview, Lou expanded on the rationale for developing CRISPR-Cas9–mediated CISH gene knockout TIL therapy; reported preliminary efficacy and safety data with this novel immunotherapeutic strategy; and outlined future directions for clinical exploration, including efforts to develop small molecule CISH inhibitors to broaden accessibility and reduce cost.

OncLive: What was the mechanistic rationale for targeting the intracellular checkpoint CISH using CRISPR-Cas9 gene editing in metastatic GI cancers? How does this approach aim to overcome the limitations of conventional checkpoint inhibitors?

Lou: There are approximately 150,000 cases of CRC annually in the US, and what has become increasingly concerning over the past 1–2 decades is the rising incidence of early-onset, or young adult, CRC. This is defined as under the age of 50 by the American Cancer Society, and other societies sometimes define it as under age 55. Regardless, that represents about 20% of all cases of CRC.

There's a growing need in that population and for anyone with metastatic stage IV forms of CRC. In that form, this cancer is invariably incurable with very few exceptions involving limited disease. For the patients with incurable forms of CRC, standard-of-care [SOC] chemotherapies have not changed much in the past few decades. They might have good palliative intent for patients and patients might have better quality of life, but we know that this is not a set of treatments with the ability to cure. Since the average lifespan of someone with stage IV CRC is anywhere between 20 and 30 months, we need to do better.

Enter our innovative strategy, in which we looked at an intracellular form checkpoint [called] CISH. [This treatment is] essentially a form of cellular immunotherapy. We’ve seen an explosion of immunotherapy in the last decade, with the greatest success in stage IV forms of melanoma or NSCLC. [However], that success has not yet reached GI cancers.

In those cases where immunotherapy is most talked about, it's referring to the class of immune checkpoint inhibitors that are antibodies regulating and targeting cell surface receptors. However, they do not have the ability to go inside the cell. CISH is a novel form of intracellular immune checkpoint that's located inside the cell, and so it's not targetable by the antibodies that are traditionally used for immunotherapy in the last few years.

What we did was use CRISPR-Cas9–based gene editing as a tool to delete that gene from inside the cell and therefore offset the checkpoint, to allow the immune system to be retrained—rebooted, in essence—to go against the cancer in patients with metastatic GI cancer.

What was unique about the design, patient population, and manufacturing process employed in this first-in-human study?

There were 22 patients enrolled [onto the study], and we ultimately were able to move forward with treatment in 12 of them. Eligible [patients] were adults with CRC who were refractory to many forms of SOC therapy. [The number of prior therapies] may have varied, but these were patients for whom the chemotherapies we use had already been administered and had not been successful in terms of inducing a meaningful response over [many] years.

When the trial was underway, it was probably the most complicated cancer clinical trial in the country. It was intricate and novel in several respects. The process after enrollment was complex, because this was essentially a designer treatment tailored to each individual patient’s tumor and the composition of the tumor with the immune cells. Patients were enrolled and underwent a biopsy or surgery to remove a portion of the tumor—enough from which we could extract the tumor-infiltrating lymphocytes [TILs]. Although TILs have been used for many years, in this case, we were engineering them. [It] took weeks to months to grow enough of the T cells from the patient’s own tumor to perform the CRISPR-Cas9 gene editing, retrain [the T cells], reactivate the immune system, and then grow enough of the product for the patient to receive treatment.

Patients who received treatment were admitted to our hospital under the auspices of our bone marrow transplant service, because the process very much mirrors—but is not identical to—what patients undergo during a bone marrow transplant for leukemia or other blood-based malignancies. They received high-dose forms of chemotherapy that are often used to remove the intact immune system, to allow it to rebuild, and to accept the engineered T cells. Then, the patients were infused with a single infusion of the engineered cell therapy product targeting CIS. After that, they received high doses of interleukin-2 [IL-2], a cytokine that helps increase the probability that the T cells will persist in the weeks and months that followed.

Once they recovered enough to be discharged from the hospital, they followed up very closely in our clinic. They had CT scans for assessment at months 1, 2, 3, and 6, and then at the appropriate intervals thereafter as outlined by the study protocol.

What efficacy signals were reported in this study?

Almost all patients that we enrolled were patients with CRC, at least in strong part because it is the most prevalent type of GI cancer. The efficacy for patients with refractory forms of GI cancer was notable. Half of those with CRC achieved stable disease for at least 1 month, if not several months.

This is quite significant because these patients basically had the worst-of-the-worst types of CRC. They were progressing at the time they entered the trial and by the time they received this treatment. The study drug was successful in halting disease in approximately half of those patients, at least for a few months before progression.

Most remarkably, we had a young woman [with] early-onset CRC who had tried every form of chemotherapy, and even immunotherapies, and they no longer worked for her. More than 2 years after she received a single infusion of the CISH knockout TILs, she is cancer free, with her first few scans showing elimination of cancer following the study treatment.

What should be known about the safety of this novel approach?

The study of safety is paramount. Especially when you enter the elements of CRISPR-Cas9 gene editing, which has certainly been in the news for many years, [safety is] something we had to be especially mindful of.

[We administered] a novel engineered cell therapy product and all of the combination therapy sandwiched in between high-dose chemotherapy and the IL-2 that came after it. [Taking this into account, alongside] the natural state of aggressive forms of cancer and the AEsof having aggressively growing cancer, [those 3 disease aspects] have known toxicities and constellations of AEs that largely accounted for [those observed] on the study. High-dose chemotherapy, in particular, can cause a lot of difficulties and challenges for patients, and that doesn't go away after the chemotherapy has been given or after the TILs were given.

In general, as we carefully parsed that out, we found that there were no severe AEs that we could specifically attribute to the principle of knocking out CISH in this case, but rather AEs that would have been expected going into the study from the chemotherapy, the IL-2, and just the eventual progression of aggressive cancers.

What are the broader implications of this study for the future of CISH-targeted strategies and leveraging of immunotherapy in GI cancers?

Those of us in GI oncology have been desperate to make immunotherapy work and to achieve what cannot be achieved with chemotherapy and other forms of targeted therapy, and we definitely want to build upon this work. To have an essentially incurable form of disease in one of these 12 patients, but, remarkably, to see that durable response for more than 2 years [was exciting]. A complete form of cure in a patient with CRC following TILs that were not engineered had not been seen [before]. We believe that there is a signal in which deletion of CISH was able to reactivate the immune system in [the] particular patient [who was cured following treatment].

At this point, some of the interesting research and development that is ongoing is to be able to make this in a way that we can democratize and make it more accessible. Using the solid tumor cell therapy as a vehicle in the trial was an expensive process, but we are transitioning to a small molecule approach to delete CISH in that manner—so, same strategy but a different tactic.

Research studies using that tactic of small molecule inhibition are well underway, and we want to open up a clinical trial at the University of Minnesota and potentially other centers in the next year or so to try and replicate the extraordinary response that we saw in that young adult woman [who was] cured [after 2 years]. We hope to do that and be able to do that with more patients and make it a more cost-effective process as well.

In the last 10 to 15 years, we've seen a virtual revolution of immuno-oncology, [but] it has not yet extended to all cancer types. Those of us in GI oncology have been desperate to make immunotherapy work and to achieve what cannot be achieved with chemotherapy and other forms of targeted therapy. We want cures where the cancers have previously been incurable. To achieve a cure [we need to look] outside the box. Investigating [intracellular] checkpoints like CISH, devising tactics that can work, and then trying to make [the treatment] more accessible, requires research funding and partnerships between academia and the private sector. This trial serves as a great example of that. I hope other groups will be able to build upon that [model] with similarly promising strategies.

Reference

Lou E, Choudhry MS, Starr TK, et al. Targeting the intracellular immune checkpoint CISH with CRISPR-Cas9-edited T cells in patients with metastatic colorectal cancer: a first-in-human, single-centre, phase 1 trial. Lancet Oncol. 2025;26(5):559-570. doi:10.1016/S1470-2045(25)00083-X