T-Cell Fuel Source, Chemotherapy Exposure Reduce Potential to Develop CAR-T Therapy

David M. Barrett, MD, PhD

Both prior chemotherapy and a dependence on glycolysis appear to reduce the potential to develop T cells into chimeric antigen receptor (CAR) T-cell therapy.

Researchers working at Children’s Hospital of Philadelphia (CHOP) found that solid tumors are especially likely to produce T cells with poor potential.

“Many of our solid tumors, osteosarcoma and Ewing sarcoma, have very poor T cell performance,” said David M. Barrett, MD, PhD, assistant professor of pediatrics at CHOP. “This gives me great concern as we try to make cell therapies for these cancers in the future.”

In results presented on a presscast ahead of the 2018 AACR Annual Meeting, Barnett added that chemotherapy, especially cyclophosphamide- and doxorubicin-containing regimens, exacerbates the problem but that these T cells are poor starting material, even before treatment.

“This is an outgrowth of the work we were doing at Children’s Hospital on chimeric antigen-receptor T cells for pediatric cancer,” he said. “We treated a number of children between 2012 and 2014 and one of the things that became very clear was that it was quite challenging to make an effective CAR T-cell product.

Researchers realized there were patients who could not be treated because their T cells died in the lab prior to processing. In order to develop CAR T cells, the patient’s T cells must be healthy enough to survive processing in the lab, then retain enough energy to kill tumor cells after reintroduction to the body, Barrett added. He and his team wanted to determine why some children have poor quality T cells and establish what qualities make for viable starting material for CAR manufacture.

“What is the quality of the T cells that we collect from patients with cancer before they’ve gotten chemotherapy? I think everybody knows that chemotherapy is really bad for your T cells and the more chemo you get, the less likely you are to have healthy T cells, but I really wanted to know what is the potential at diagnosis. As we think about expanding CAR T-cell therapy to other cancers besides leukemia and lymphoma, we really want to know what are our challenges.”

Investigators at CHOP collected peripheral blood samples from 157 pediatric patients with acute lymphoblastic leukemia (ALL), chronic myelogenous leukemia, non-Hodgkin lymphoma, Hodgkin lymphoma, neuroblastoma, osteosarcoma, rhabdomyosarcoma, Wilms tumor, or Ewing sarcoma, at diagnosis and after each cycle of chemotherapy. They then depleted the adherent cells from this collection, quantified the CD3+ population using flow cytometry, and expanded these T cells using CD3/CD28 stimulatory beads as in CAR T cell manufacturing.

They determined that the CAR T-cell potential of the T cells was very poor in all tumor types except ALL and Wilms tumor in the prechemotherapy samples. Barnett said that more than 90% of patients with standard- and high-risk ALL had very high-quality T cells at diagnosis, which may explain why this CAR T-cell therapy has been so successful in pediatric ALL. Patients with Wilms tumor, the only other class to show good performance, produced potentially successful cells more than 50% of the time.

Researchers observed a decline in CAR T-cell potential with cumulative chemotherapy in all cancer types, but the effect was particularly significant in children aged less than 3 years.

Certain types of chemotherapy were especially harmful to the T cell’s SRC, a measure of energy reserve. Cyclophosphamide- and doxorubicin-containing regimens were strongly associated with severely depleted CAR T cell potential. Cyclophosphamide and doxorubicin were associated with mitochondrial dysfunction after chemotherapy both in vitro and in patient T cells after in vivo chemotherapy.

“These T cells seem to be exhausted, probably by the tumor or the chemo. We can now predict who is going to do well and not do well [on CAR T-cell therapy],” said Michael Caligiuri, MD, AACR president and president and physician-in-chief of City of Hope National Medical Center.

“If you think about subjecting people to these clinical trials, the cost involved, the notion now—which we will pursue, I’m sure—is creating alternate strategies, different chemotherapies, different preparatory regimens that decrease the injury to the T cells’ metabolic pathway—if not reversing that metabolic pathway—and seeing if that predicts for a great outcome with the immune therapy,” added Caligiuri.

Barnett suggested that the T cells from solid tumor patients may need different manufacturing protocols to be successful. Results from preliminary experiments showed that it was possible to force T cells to use fatty acids, such as palmitate, to restore SRC in chemotherapy-exposed T cells.

Das RK, Storm J, Barrett DM. T cell dysfunction in pediatric cancer patients at diagnosis and after chemotherapy can limit chimeric antigen receptor potential. Presented at: 2018 AACR Annual Meeting; April 14-18, 2018; Chicago, IL.

Oxygen consumption rate (OCR) analysis revealed a poor spare respiratory capacity (SRC) in the T cell samples that go on to perform poorly as CAR T cells. Nanostring RNA profiling of metabolic pathways showed that the poor performing samples were more likely to use glycolysis as a fuel source, rather than fatty acids.