Neuropsychiatric toxicity
Another problem is the possibility of neuropsychiatric toxicity. Past studies have reported a wide range of such toxicities associated with CAR T-cell therapy, including seizures and hallucinations. Most have occurred early in the course of treatment and appear to be short-lived and reversible. However, there remain questions about long-term neuropsychiatric problems.
In a long-term study of 40 patients with relapsed/refractory CLL, non-Hodgkin lymphoma, and ALL, nearly half of patients (47.5%, 19/40) self-reported at least one clinically meaningful negative neuropsychiatric outcome (anxiety, depression, or cognitive difficulty) 1 to 5 years after anti-CD19 CAR T-cell therapy. In addition, 37.5% (15/40) self-reported cognitive difficulties.
“Patients with more severe neurotoxicity showed a trend for more cognitive difficulties afterwards,» said Bar, senior author of the study.
However, teasing out the role that CAR T-cell therapy plays in these problems poses a challenge. All of these patients had been heavily pretreated with previous cancer therapy, which has also been associated with neuropsychiatric problems.
“So far, we don’t know what caused it,” Bar said. “Nevertheless, people need to pay attention to neuropsychiatric symptoms in CAR T-cell therapy. It is important to continue to monitor these patients for these issues.”
Graft-vs-host disease
Another potential problem is graft-vs-host disease (GVHD). This is not uncommon after hematopoietic stem cell transplants. It develops when the donor T cells view antigens on healthy recipient cells as foreign and attack them.
For patients who are treated with CAR T cells, GVHD is mostly a concern among individuals who have previously had a transplant and who are already at increased risk for it.
In a study of late effects among 86 adults treated with anti-CD19 CAR T cells for relapsed/refractory non-Hodgkin lymphoma, Bar and colleagues found that GVHD occurred only among patients who had received a previous donor stem cell transplant. Of these, 20% (3/15) developed GVHD about 28 months after CAR-T therapy.
“The data for CAR T cells causing GVHD really hasn’t shown that it’s a huge problem, although we have seen it and are continuing to monitor for it,” the NCI’s Shah commented to Medscape Medical News.
Other Long-term Adverse Effects
A range of other long-term adverse effects have been reported with CAR-T therapy, including prolonged cytopenias (reduced mature blood cells), myelodysplasia (bone marrow failure), and second malignancies.
In the study with the longest follow-up to date, 16% (7/43) of patients developed second malignancies, which is comparable to data from Bar’s study in Seattle (15%, 13/86). The researchers in this study consider this rate to be no higher than expected: these patients had already received extensive chemotherapy, which increases the risk for other cancers, they point out.
However, this brings up theoretical concerns about the long-term effects of gene modification. CAR T cells are engineered using retroviruses (mainly lentiviruses), which randomly insert the CAR genes into the host genome. Doing so may cause mutations that could promote cancer. These lentiviruses also carry the theoretical risk of becoming capable of viral replication once inside the body.
To address these concerns, viruses used to engineer CAR T cells go through comprehensive safety testing. After therapy, patients are checked every few months during the first year and annually after that.
So far, there have been no reports of cancers associated with CAR T-cell therapy.
“Any type of cancer is a very theoretical risk,” Bar told Medscape Medical News. «Most likely the malignancies in our study were related to prior treatment that the patients received. None of them had any evidence of replication-competent lentivirus, or any other evidence that the malignancies were related to the CAR T cells.»
Another theoretical concern is the possibility of new-onset autoimmune disease, although, once again, no cases have been reported so far.
“We think of it as a theoretic possibility. Whenever you jack up the immune system, autoimmune disease is a potential risk,” said Carl June, MD, director of the Center for Cellular Immunotherapies at the University of Pennsylvania.
June was the co–principal investigator of the trial in which Olson participated. He is also the inventor on patents for CAR T cells licensed by the University of Pennsylvania to Novartis and Tmunity and is a scientific founder with equity in Tmunity.
Still, autoimmunity could occur, and scientists are looking out for it.
“We are continuing to be vigilant in our monitoring for autoimmune disease,” Shah added. “We’ve been doing CAR T-cell therapy since 2012, and I think we have yet to see true autoimmunity beyond GVHD.”