Problems persist with CAR T-Cell Therapy in pancreatic cancer

The success of chimeric antigen receptor (CAR) T-cell therapy observed in hematological malignancies has not yet been translated into a solid tumor; However, efforts are continuing to integrate this new modality into the paradigm of treating solid tumors, including pancreatic cancer.

Gregory L. Beatty, MD, Ph.D., discussed the barriers to the effectiveness of CAR cells in this context at the 2019 symposium of the American Society of Clinical Oncology and the Society of Medicine. cancer immunotherapy.¹

Several CAR targets have been developed, with CD19 being the most attractive for therapy. CD19 is largely expressed by normal tissue, which is important for the recognition of toxicities on the target but not on the tumor. Numerous clinical trials of T-cell-based therapy have been conducted with a range of targets on several solid malignancies, with observed dose-limiting toxicities.

"[CAR T-cell therapy] has been largely bearable, "said Beatty, director of translational research at the Pancreatic Cancer Research Center at the University of Pennsylvania (Penn) in Philadelphia. "Nevertheless, intratumoral activity has been little appreciated so far." Unlike malignant hemopathies, inserting T CAR cells into peripheral tissues and working in the microenvironment of solid malignant tumors is a challenge, according to Beatty.

The overall survival rate of patients with advanced pancreatic cancer in response to cytotoxic chemotherapy is <20% at 2 years and <5% at 5 years, and attempts at introduction of immunotherapy have had limited success. The response rate is 0% for anti – PD – 1 / L1 and anti – CTLA – 4 and <10% for the second and most recent lines with immunotherapy badociations.²

"The microenvironment of the tumor shows a desmoplastic reaction [and] is poorly vascularized, and there is significant infiltration of myeloid cells and often a shortage of T cells, "said Beatty, explaining some of the problems encountered.

RCA specific to mesothelin

At Penn, Beatty's lab has developed a specific CAR for mesothelin, a protein overexpressed by pancreatic ductal adenocarcinoma cells. In vitro, CAR T cells modified to express mesothelin "will react and kill mesothelin-positive tumor cells, but not those that are negative," he said. Even in autologous T cells, CAR T cells were effective at recognizing tumor cells positive for mesothelin.

A CAR T cell engineering strategy uses an RNA platform and electroporation to transiently express CAR in T cells. An alternative strategy is to use a lentiviral platform and transduction to express permanently the CAR. "Although permanent transduction leads to higher activity," said Beatty, both showed antitumor activity in a mesothelioma human tumor model; However, the transient expression of RCA induced through the RNA platform could appeal to safety.

Activity and security start phase

The safety, feasibility and activity of CAR T cells specific for RNA mesothelin (CARTmeso) were explored during a Phase I study in 6 patients with one Metastatic pancreatic ductal adenocarcinoma refractory to chemotherapy.³ All patients had received at least two previous treatment lines. CAR T RNA T cells were infused 3 times a week for a total of 9 doses. "We did not observe any dose-limiting toxicity, and we found no evidence of cytokine release syndrome," Beatty said. Fatigue and abdominal pain, possibly resulting from pancreatic cancer, were the most common side effects. The best overall response was stable in 2 patients with 3.8-month and 5.4-month progression-free survival.

18Fludeoxyglucose (18F-FDG) – PET / CT imaging was used to monitor the active metabolic volume of tumors. Total metabolic activity remained stable (for 1 month) in 3 patients and decreased by 69.2% after 1 month in 1 patient with biopsy-proven mesothelin expression and significant hepatic tumor burden at baseline. All liver lesions had a complete reduction in 18F-FDG uptake at 1 month from baseline, although the primary lesion was unaffected.

The study demonstrated that CAR T cells can have biological activity in patients with pancreatic cancer and that very different immune evasion mechanisms can function in the distinct anatomical region where the disease is present, said Beatty.
A trial of lentiviral T-T-T lymphocytes included 15 patients with mesothelioma (n = 5), ovarian cancer (n = 5) or pancreatic cancer (n = 5). Two doses (1-3 × 107 / m2 and 1-3 × 108 / m2) were infused (with or without prior cyclophosphamide) with a lymphoepithelial pattern. The average number of previous treatments was 5 (range: 1-11). Lymphodéplétion improved the expansion of CAR T cells in the peripheral blood at both doses. Lymphodépletion did not have an impact on the persistence of T-cells in CAR; CAR T cells became undetectable in peripheral blood after 2 months in almost all patients. The best overall response was a stable disease in 11 of the patients.

Mechanisms of potential resistance

Potential Resistance Mechanisms That Could Affect the CAR T cell therapy in solid malignant tumors is the ability and trafficking of cells, the expression of the CAR target in the tumor microenvironment and cell fate. Patients with pancreatic cancer screened in the Phase I study showed low T cell proliferation in vitro. Further badysis showed a reduced proliferative expansion of CD8 T cells in vitro, as well as a decrease in the number of naive T cells and an increase in the number of effector cells in the peripheral blood in patients with dementia. pancreatic cancer, as well as an alteration of cytokine secretion. capacity.

"We also found that CAR T cells were able to turn into tumors in some patients. The levels of CAR T cells detected in the tumors were actually low, "said Beatty. "CARTmeso cells were detectable in some tumor biopsies, but not in all tumor biopsies, so traffic was a challenge."

High heterogeneity has been observed in the tumor microenvironment, with some regions of the tumor lacking T cells and other regions with a high influx of T cells. PD-L1 is not expressed in pancreatic cancer and most T cells do not actively proliferate. The same biology exists in metastatic tumors, he said.

Multiple patterns of T cell infiltration have been identified: those in which T cells are not present, those in which T cells are present but do not engage tumor cells and those that do not. engage but do not destroy tumor cells.

"The profile of expression is quite important. Many of our patients have intracellular expression, and this will not work with CAR T cells, "said Beatty. "We noticed that mesothelin was expressed on the surface of the tumor cells in the patient who had an 18F-FDG-PET / CT response.