ATLANTA – Intrapleurally administered, mesothelin-targeted chimeric antigen receptor (CAR) T cells combined with programmed death 1 (PD-1) inhibition showed CAR T-cell antitumor activity without toxicity in a phase 1 clinical trial of patients with malignant pleural disease.
The findings are encouraging, particularly given the aggressive nature of such tumors and the poor prognosis associated with mesothelin – a cell-surface antigen expressed on them,, reported during a press briefing at the annual meeting of the American Association for Cancer Research.
In 21 patients, including 19 with malignant pleural mesothelioma and 1 each with metastatic lung cancer and metastatic breast cancer, a single dose of a second-generation, CD28-costimulated mesothelin CAR T-cell therapy (iCasM28z) was administered intrapleurally either with or without cyclophosphamide preconditioning.
Antitumor activity, as evidenced by the presence of CAR T cells in the blood for several months, was noted in 13 patients, and the presence of the cells was associated with a reduction in a mesothelin-related peptide in the blood, as well as with evidence of tumor regression on imaging studies, said Dr. Adusumilli, deputy chief of the thoracic service at Memorial Sloan Kettering Cancer Center, New York, and lead study author.
Intense clinical, laboratory, and radiological monitoring along with electrocardiography showed no evidence of toxicity.
“Most importantly, the neurotoxicity, serious cytokine release syndrome, and on-target off-target tumor toxicity that has been seen in other CAR T-cell trials, we did not notice in our trial,” he said.
Additionally, one patient successfully underwent curative-intent surgical resection 6 weeks after CAR T-cell infusion, followed by radiation therapy to the chest, said Dr. Adusumilli, who also is director of the mesothelioma program and head of solid tumor cell therapy at the at Memorial Sloan Kettering Cellular Therapeutic Center.
That patient is doing well at 20 months without further treatment, he noted.
Of a subset of 14 patients who received off-protocol anti-PD-1 checkpoint blockade once lack of toxicity was established for the CAR T-cell therapy, 2 achieved a complete metabolic response at 38 and 60 weeks following checkpoint blockade, 5 had a partial response, and 4 had stable disease.
The anti-PD-1 therapy was initiated in those patients based on prior preclinical data, showing that CAR T cells can become functionally exhausted in large tumors and that anti-PD-1 therapy can reactivate the exhausted cells and eradicate the tumors, he explained.
The findings are notable because malignant pleural disease from primary malignant pleural mesothelioma or secondary metastatic disease affects more than 150,000 patients a year in the United States alone, and effective therapies are lacking.
“[Our finding] strongly supports pursuing a CAR T-cell therapy combined with anti-PD-1 strategies is in solid tumors,” Dr. Adusumilli said, adding that such a trial is being planned for 2019, and another, with CAR T-cell intrinsic PD-1 dominant negative receptor (a decoy receptor) is planned for 2020.
Press briefing moderator, of the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University, Baltimore, said the findings represent “potentially the most compelling CAR T data that we’ve ever seen in solid tumors at this point,” and noted that a “vast number of patients” could potentially benefit from the approach.
Dr. Adusumilli agreed, suggesting that, with a system of regional factories and distribution centers and development of “some clever strategies,” it is possible the technology and treatment approach could be scaled up to the level necessary to help increasing numbers of patients.
Dr. Adusumilli reported receiving federal grant support from the National Cancer Institute and Department of Defense; peer-reviewed grant support from the Mesothelioma Applied Research Foundation, Experimental Therapeutics Center, Baker Street Foundation, Batishwa Fellowship, Dallepezze Foundation, Derfner Foundation, Emerson Collective Foundation, and MSK Technology Development Fund; and research grant support from OSE Immunotherapeutics, ACEA Biosciences, and Atara Biotherapeutics. He also has a licensing/royalty agreement for Mesothelin CAR and PD-1 DNR (licensed to Atara Biotherapeutics).
SOURCE: Adusumilli PS et al. AACR 2019, .