Chimeric antigen receptor (CAR) T cell therapies have transformed the treatment of certain blood cancers, yet translating this success to solid tumors has remained a major challenge. One of the key obstacles has been T cell exhaustion, a state in which engineered immune cells lose their ability to sustain an effective anti-tumor response.
Now, early clinical data from a first-in-human Phase I trial suggest a new approach may help overcome this limitation. Presenting at the AACR annual meeting in San Diego, researchers from the Perelman School of Medicine at the University of Pennsylvania report that a novel “KIR-CAR” T cell therapy shows promising safety and early efficacy signals across multiple solid tumor types.
New design inspired by natural killer cells
The investigational therapy, SynKIR-110, represents a departure from traditional CAR T designs. Rather than using a single-chain receptor, the therapy is modeled after natural killer (NK) cell receptors and uses a “multi-chain” architecture.
This design separates tumor recognition from activation, effectively creating an intrinsic “on-off” mechanism. The T cell remains in a resting state until it encounters its target, at which point the receptor components assemble to trigger an immune attack.
“The KIR-CAR design provides a natural ‘on-off’ mechanism, which helps avoid the problem of T cell exhaustion,” said Janos L. Tanyi, MD, PhD, principal investigator of the study. “The CAR turns on when it finds its target, kills it, and then rests, rather than constantly burning energy.”
This contrasts with conventional CAR T cells, which remain continuously active and can become depleted over time, limiting their effectiveness—particularly in the more complex microenvironment of solid tumors.
Early clinical signals in difficult-to-treat cancers
The Phase I dose-escalation trial enrolled nine patients with advanced, mesothelin-expressing cancers, including ovarian cancer, mesothelioma, and cholangiocarcinoma. These patients had limited treatment options, having received an average of four prior lines of therapy.
Although the primary goal of the study was to assess safety, early signs of efficacy were observed. Disease stabilization was reported in four patients, and one patient in the highest dose cohort achieved an ongoing partial response.
“These are cancer types that have never had an approved cell therapy,” Tanyi said. “We’re seeing good efficacy signals, even at low doses, and limited toxicity.”
The results suggest that the therapy may be able to generate meaningful anti-tumor responses even in heavily pretreated populations.
Favorable safety profile
Safety has been another major barrier for CAR T therapies, particularly in solid tumors. However, the KIR-CAR approach appears to mitigate some of these concerns.
No dose-limiting toxicities were observed in the initial cohorts. Cytokine release syndrome (CRS), a common side effect of CAR T therapy, occurred in 33% of patients but was limited to low-grade events. Notably, there were no cases of immune effector cell-associated neurotoxicity syndrome (ICANS), a more severe complication sometimes seen with CAR T therapies.
The ability to limit toxicity while maintaining activity is a key step toward broader application of cell therapies in solid tumors.
Targeting mesothelin across tumor types
SynKIR-110 targets mesothelin, a protein expressed on the surface of several solid tumors but largely absent from normal tissues. This makes it an attractive target for immunotherapy, particularly in cancers such as ovarian cancer and mesothelioma, where treatment options are limited.
The trial results indicate that the therapy’s activity is not confined to a single tumor type, raising the possibility of broader applicability across mesothelin-expressing cancers.
Expanding CAR T into solid tumors
The findings come amid growing efforts to adapt CAR T technology for solid tumors. While the approach has revolutionized hematologic malignancies, solid tumors present additional challenges, including immunosuppressive microenvironments, physical barriers to T cell infiltration, and antigen heterogeneity.
Researchers are exploring multiple strategies to address these barriers, including improved targeting, combination therapies, and next-generation receptor designs such as KIR-CAR.
As noted by CAR T pioneer Carl June, MD, advancing cellular therapies into solid tumors remains a central goal for the field.
Looking ahead
The Phase I study is ongoing, with plans to enroll up to 42 patients and identify the maximum tolerated dose before advancing to a Phase II trial. Early data indicate that CAR T cell expansion in the blood increases with dose, suggesting that higher doses may further enhance efficacy.
While still preliminary, the results highlight the potential of multi-chain CAR designs to address one of the most persistent challenges in cell therapy: maintaining durable activity without excessive toxicity.
If confirmed in larger studies, KIR-CAR therapies could represent a new generation of engineered immune cells, ones that more closely mimic natural immune regulation while retaining the precision of targeted cancer therapy.
For now, the data offer an encouraging signal that the next wave of CAR T innovation may finally extend the reach of cell therapy into solid tumors, where the need remains greatest.
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