Souped-Up T Cells
The University of Pennsylvania team that reported the stunning results in leukemia this month seem to have overcome some of the challenges previous TIL therapies faced, such as persistence in patients as Dr. Rosenberg pointed out. The Penn investigators reported that in their trial, which included three advanced chronic lymphocytic leukemia (CLL) patients, genetically modified versions of their own T cells behaved like “serial killers” and hunted down and obliterated tumors, resulting in sustained remissions of up to a year.
“Within three weeks the tumors had been blown away in a way that was much more violent that we expected,” said senior author Carl June, M.D., director of Translation Research and a professor at Penn’s Abramson Cancer Center. His team published their results in simultaneously in The New England Journal of Medicine and Science Translational Medicine.
The treatment protocol involved removing patients’ cells, genetically modifying them in Penn’s vaccine production facility, and then infusing the new cells back into the patient’s body following chemotherapy. T cells extracted from patients were genetically customized to trigger an attack on cancer cells. Of the three patients treated with the T cells, two remained free of leukemia for more than a year, and the third patient remained in remission for seven months.
Investigators said that the treatment may potentially offer a replacement for risky bone marrow transplants as well as allow a personalized approach useful in other cancers. For the three patients in the study, the only potential curative therapy would have involved a bone marrow transplant. The procedure carries at least a 20% mortality risk and has only about a 50% chance of a cure.
Key hurdles that had to be overcome, according to the Penn scientists, included robust expansion of the cells after delivery to the patient, prolonged persistence of the cells in the patient, and ongoing functional expression of the chimeric antigen receptors (CARs) post-infusion.
Their technique for producing the CAR cells and the combination of genetic elements introduced into the cells overcame these problems. The scientists genetically modified patient T cells to express desired proteins, introducing genes into the cells via a nonreplicating lentivirus. The T cells were engineered to express CARs on their surfaces, recognizing a protein, CD19, expressed on the surface of normal and cancerous B cells.
Particularly ingenious was engineering cells that could provoke a T-cell response to CD19 antigen in the absence of a major histocompatibility (MHC) restriction, allowing for much broader cellular targeting than can be obtained with normal T cells. The CAR T cells also expanded over 1,000-fold in the patients and persisted for over six months.
It takes between 10 and 12 days to produce the genetically engineered T cells, including isolation of cells from the patient, selection of the appropriate cells, transfection with the lentiviral construct, and expansion in culture. Each infused CAR-expressing T cell, the investigators said, eradicates about 1,000 CLL cells and, they said, some of the infused cells persist as memory CAR T cells, retaining anti-CD19 functionality.
Also reporting encouraging results with TIL therapy, Alena Chekmasova, Ph.D., and Renier Brentjens, M.D., Ph.D., investigators at the Department of Medicine at Memorial Sloan-Kettering Cancer Center, reported the generation of several CARs targeted to the retained extracellular domain of MUC16, termed MUC-CD, an antigen expressed on most ovarian carcinomas.
“Our approach doesn’t differ particularly from the Penn group’s approach. Only the target is different,” Dr. Brentjens told GEN. “However, the dynamics of how a therapy works in a liquid tumor like leukemia may differ from how it works against a solid tumor.” He explained that his laboratory is using “mouse models to study how the cells will function when we translate the therapy to a clinical setting.” Dr. Brentjens noted that his group’s research with engineering T cells from leukemia patients will appear online in the journal Blood later this month.
In his ovarian cancer work, Dr. Brentjens’ team studied the in vitro biology of human T cells retrovirally transduced to express CARs by co-culture assays on artificial antigen-presenting cells as well as by cytotoxicity and cytokine-release assays using human MUC-CD(+) ovarian tumor cell lines and primary patient tumor cells. They also assessed the in vivo antitumor efficacy of MUC-CD-targeted T cells in SCID-Beige mice bearing peritoneal human MUC-CD(+) tumor cell lines.
They reported that the CAR-modified, MUC-CD-targeted T cells showed efficient MUC-CD-specific antitumor cell activity against both human ovarian cell lines and primary ovarian carcinoma cells in vitro. In mice bearing human MUC-CD(+) tumors, infusion of the engineered cells either delayed progression or eradicated the disease. The authors concluded that the preclinical study results justify further clinical investigation in patients with high-risk, MC16-bearing ovarian cancers.
Dr. Brentjens said that his laboratory collaborates with Dr. June’s group at Penn and also runs CD19 trials. “Going forward we have a collaboration with Carl June at Penn wherein we will treat patients with a 50-50 mix of T cells modified to express either our receptor or their receptor. While both receptors target CD19, we use a different co-signaling domain, CD28, and they use 4-1BB. The question, he says, for the field in general, centers on which type of receptor design works best so we can move forward on how to further optimize this technology.”
GEN asked Dr. Brentjens whether and how this cell-based therapy will be marketed. “It depends on what the product is,” he said. “Will it be the virus that contains the artificial receptor gene or will the modified T cells themselves be the product?” If the cells are the product, it requires GMP facilities where they can generate the cells. Each patient will be an individual customer, similar to the Dendreon model.
Tumors have evolved many different multiple strategies to evade the immune system, including reduced antigen presentation and inhibition of effector lymphocyte function as well as the maintenance of tumor microenvironments hostile to immune function.
Scientists however continue to hope that genetic modifications of adoptively transferred cells may eventually overcome these challenges and improve clinical outcomes for intractable cancers. As researchers translate basic research into clinical results, all eyes are on proving safety and efficacy in patients in Phase II and III studies.