Pancreatic ductal carcinoma remains an extremely high-risk disease, with low five-year survival rates and available therapies are associated with severe side effects that can greatly reduce quality of life for patients undergoing treatment. Immunotherapies have demonstrated robust success in treating hematologic malignancies, and research is ongoing in solid tumors to harness the capability of these therapies to combat disease spread. In pancreas cancer, immunotherapy efforts have zeroed in on mesothelin, a glycoprotein highly expressed on tumor cells but not on healthy cells of the pancreas. Previous research efforts from Dr. Ingunn Stromnes, Dr. Sunil Hingorani, Dr. Philip Greenberg, a member of Fred Hutch’s Clinical Research Division, and colleagues engineered CD8+ T-cells to express a mesothelin receptor, causing them to effectively attack the mesothelin expressing tumor cells. Their initial experiments showed promising anti-tumor effects; however, the engineered T-cells soon became exhausted, a state that inhibits their effective clearing of the tumor. While repeated T-cell infusions are a viable option in mouse models of pancreas cancer, their translation into a clinical setting would be challenging and the authors sought to overcome this exhausted T-cell state. Their most recent study, published in Journal for Immunotherapy of Cancer, aimed to determine whether immune checkpoint blockade therapy would improve the long-term efficacy of engineered T-cell treatment in pancreas cancer. Detailing the background and premise for their study further, Dr. Stromnes said “we developed a novel engineered T cell therapy for pancreatic cancer that is now in early phase clinical trials. Based on our preclinical research in faithful mouse pancreatic cancer models, we identified that engineered T cells infiltrate pancreatic tumors and mediate substantial antitumor activity. However, the engineered T cells upregulate multiple inhibitory receptors, also known as immune checkpoints, in the suppressive tumor microenvironment that correlates with loss of engineered T cell antitumor function. This loss of T cell antitumor function, or exhaustion, likely limits the long-term durability of this approach. In this study, we tested the hypothesis that we could rescue engineered T cell function in pancreatic cancer by blocking multiple immune checkpoint pathways simultaneously in a preclinical animal model.”
The authors confirmed (in pancreas cancer mouse models) that a subset of their engineered T-cells express PD1, an immune checkpoint protein that acts as a go-to-sleep-switch for T cells potentially contributing their exhausted state. The authors tried to reinvigorate the exhausted PD1+ T-cells and reinstate their anti-tumor activity by treating their mice with PD1/PDL1 blockade therapy, but this approach did not impact the levels of circulating T-cells in the spleen or tumor after 28 days, nor did it rescue a reduction in the engineered T-cells’ cytokine production. To investigate this loss of function further, the authors performed transcriptomic analysis of their engineered T-cells and observed decreased expression of effector T-cell related genes and genes attributed to T-cell function and longevity in the intra-tumoral population. The authors note that this may reflect the exhausted state of the engineered T-cell population.
The authors performed a series of further characterization experiments, observing a “distinct differentiation program” in the engineered T-cells as compared to endogenous exhausted T-cells. Moreover, they noted that their engineered T-cells exhibited differential regulation of specific genes, including Ccl5, Ccr2 and Ifng, adding additional strength to their hypothesis that engineered T-cells have a contrasting transcriptomic profile to endogenous cells, one that may contribute to their exhausted state. Lastly, the authors treated the mice with multiple immune checkpoint blockade therapies (anti-PDL1, Tim-3 and Lag3) at once to determine whether the combination helped prolong the ability of the engineered T-cells. Unfortunately, even the combination treatment did not overcome the exhausted state of the T-cells, which was likely caused in-part by intra-tumoral suppression. “Our results showed that blocking multiple immune checkpoints fails to rescue engineered T cell function in pancreatic cancer and instead resulted in subclinical reactivity in the lung where the target tumor antigen mesothelin is expressed at low levels. Thus, there are suppressive factors in the pancreatic tumor microenvironment that surpass immune checkpoint pathways. Our results also suggest that the combination of engineered T cell therapy with immune checkpoint inhibitors may be more detrimental than beneficial,” summarized Dr. Stromnes.
The continuing goals of the authors are to improve the outcomes of immunotherapies for patients with pancreas cancer and to better our understanding of how to prolong the efficacy of engineered T-cell therapies. “Our study raises the question as to what are the dominant immunosuppressive pathways driving engineered T cell dysfunction in pancreatic cancer. Further, in other studies we performed, our results also suggest that engineered T cells may respond differently from endogenous T cells to immune checkpoint inhibitors in cancer. The Stromnes lab at the University of Minnesota has developed novel T cell receptor Trac knock-in mouse models to efficiently test how engineered vs. endogenous tumor-reactive [T-cells] specific to the same target antigen respond in the pancreatic tumor microenvironment, ultimately to identify novel strategies to overcome T cell dysfunction in pancreatic cancer. These novel models will be incredibly useful tools for the field to elucidate how to enhance engineered T cell functionality in mesothelin+ malignancies, which include many solid tumors. Since pancreatic cancer elicits a chronic inflammatory response, our studies are interrogating if interfering with this can overcome T cell dysfunction,” detailed Dr Stromnes.
The Fred Hutch and University of Washington Cancer Consortium contributed to this work by supporting the postdoctoral training of Dr. Stromnes as she developed the expertise that cumulated in the leadership of her own lab at the University of Minnesota. “The Cancer Consortium Collaboration provided seed funding for the Greenberg and Hingorani labs to support the work of myself as a postdoctoral fellow. This support provided a great training opportunity while I spearheaded the development of a novel cellular therapy for pancreatic cancer patient treatment,” said Dr. Stromnes.
This work was supported by funding from the National Institutes of Health, a Dennis W. Watson fellowship, an American Association of Immunologists (AAI) postdoctoral fellowship, the American Cancer Society, Randy Shaver Cancer Research Fund, the Masonic Cancer Center (University of Minnesota Medical School), the National Cancer Institute, the Pancreatic Cancer Action Network, a Stand up to Cancer Lustgarten grant and Juno Therapeutics, a Celgene company.
UW/Fred Hutch Cancer Consortium members Dr. Sunil R. Hingorani and Dr. Philip D. Greenberg contributed to this work.
Stromnes IM, Hulbert A, Rollins MR, Basom RS, Delrow J, Bonson P, Burrack AL, Hingorani SR, Greenberg PD. Insufficiency of compound immune checkpoint blockade to overcome engineered T cell exhaustion in pancreatic cancer. J Immunother Cancer. 2022 Feb;10(2):e003525. doi: 10.1136/jitc-2021-003525. PMID: 35210305; PMCID: PMC8883283.