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High objective response rate, OS seen with ATA129 in PTLD



– An allogeneic off-the-shelf Epstein-Barr virus–targeted cytotoxic T lymphocyte–cell product known as ATA129 (tabelecleucel), is associated with a high response rate and a low rate of serious adverse events in patients with posttransplant lymphoproliferative disorder (PTLD), according to interim findings from an ongoing multicenter study.

The objective response rate at a median of 3.3 months among patients who were treated with ATA129 and who had sufficient follow-up to assess response was 80% in six patients treated following hematopoietic cell transplantation (HCT), and 83% in six who were treated after solid organ transplant (SOT), Susan E. Prockop, MD, reported at the combined annual meetings of the Center for International Blood & Marrow Transplant Research and the American Society for Blood and Marrow Transplantation.

Dr. Susan E. Prockop Sharon Worcester/Frontline Medical News

Dr. Susan E. Prockop

Overall survival at 1 year among all patients in the study, which in addition to the 12 transplant recipients also included 11 nontransplant PTLD patients, was 90.3%, demonstrating the durability of response, said Dr. Prockop of Memorial Sloan Kettering Cancer Center, New York.

Study participants included those with or without underlying immune deficiency with Epstein-Barr virus (EBV)–positive PTLD, EBV-positive lymphoma, EBV-positive hemophagocytic lymphohistiocytosis, or EBV viremia, and they had to have measurable disease. All had adequate organ function and performance status. The overall median age of the cohort was 41 years, and among the transplant recipients the median age was 24.5 years. They received a median of 5 weeks of therapy (2.1 months among post-HCT patients and 12.9 months among post-SOT patients), she said.

Patients in the trial underwent the adoptive T cell therapy with partially human leukocyte antigen (HLA)–matched ATA129 that shared at least 2 of 10 HLA alleles at high resolution, including at least 1 through which ATA129 exerted cytotoxicity, or “HLA restriction,” Dr. Prockop said, noting that the product was licensed and obtained breakthrough designation in February 2015.

The ATA129 dose was 1.6-2 million T cells/kg infused on days 1, 8, and 15 of every 35-day cycle. Those without toxicity were eligible to receive additional cycles, and patients with progressive disease after one cycle were allowed to switch to an ATA129 product with a different HLA restriction, she noted.

Treatment-emergent adverse events occurred in 21 patients, including 17 who experienced grade 3 or greater adverse events or serious adverse events. Six were treatment related; one of those was grade 3 or greater, and five were considered serious adverse events. One patient had a grade 5 treatment-emergent adverse event (disease progression); two in the post-HCT group experienced graft-versus-host disease (GVHD), including one with grade 3 skin GVHD after sun exposure, which resolved with topical therapy; and one had grade 4 GVHD of the gastrointestinal tract and liver. One patient had a tumor flare that resolved, Dr. Prockop said.

“The most common safety events were GI disorders in seven patients, infections and infestations in five patients, and general disorders and administration site conditions in four,” she said. “No events have been categorized as drug reactions.”

PTLD, an EBV-driven lymphoproliferative disorder, is a life-threatening condition typically involving aggressive, clonal, diffuse large B cell lymphomas. Survival without therapy is a median of 31 days, she explained. Patients at high risk have a mortality rate of 72%, and these included those over age 30 years, those with GVHD at the time of diagnosis, and those with extranodal disease, three or more sites of disease involved, or central nervous system disease.

Although some patients respond to single-agent rituximab (Rituxan) therapy, those with rituximab-refractory disease have a median overall survival of 16-56 days, she said.

SOT recipients who develop indolent PTLD may respond to reduction of immunosuppression. Two-year risk-based survival in these patients is 88% with zero or one risk factors, and 0% with three or more risk factors, which include older age, poor performance status at diagnosis, high lactate dehydrogenase, CNS involvement, and short time from transplant to development of PTLD.

Rituximab monotherapy response rates are 76% in those with early lesions, and 47% in those with high-grade lesions, she said.

“Two-year overall survival in this patient population is 33%, reflecting their eligibility for multiagent chemotherapy, although this approach comes with significant morbidity,” she added, noting that patients failing rituximab experience increased chemotherapy-induced treatment-related mortality, compared with other lymphoma patients.

The benefit-risk profile observed in this multicenter trial is favorable with maximum response rates being reached after two cycles of therapy, and the findings confirm those from prior single-center studies, she said, noting that based on those earlier findings in patients treated with both primary and third-party donor EBV-cytotoxic T lymphocytes, the therapy is now an established National Comprehensive Cancer Network guideline therapeutic alternative for PTLD.

“Further evaluation in rituximab-refractory PTLD is ongoing in phase 3 registration trials,” she said.

Atara Biotherapeutics sponsored the trial. Dr. Prockop reported having no disclosures.

SOURCE: Prockop S et al. BMT Tandem Meetings Abstract 21.

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