ORLANDO – Patients with advanced hematologic malignancies of B-cell lineage had robust immune responses following infusion of a chimeric antigen receptor (CAR)–T-cell construct designed to deliver a specific balance of antigens, investigators reported.
Adults with relapsed or refractory B-lineage acute myeloid leukemia (ALL), non–Hodgkin lymphoma (NHL), and chronic lymphocytic leukemia (CLL) who received a CAR-T cell construct consisting of autologous CD4-positive and CD-8-positive T cells that were transduced separately, recombined, and then delivered in a single infusion had comparatively high overall response and complete response rates, reported Cameron Turtle, MBBS, PhD, from the Fred Hutchinson Cancer Research Center in Seattle.
“We know that patients have a highly variable CD4 to CD8 ratio, so by actually controlling this and separately transducing, expanding, and then reformulating in this defined composition, we’re able to eliminate one source of variability in CAR-T cell products,” Dr. Turtle said at the ASCO-SITC Clinical Immuno-Oncology Symposium.
In preclinical studies, an even balance of CD4-positive and CD8-positive central memory T cells or naive T cells evoked more potent immune responses against B-cell malignancies in mice than CD19-positive cells, he explained
To see whether this would also hold true in humans, the investigators enrolled into a phase I/II trial adults with relapsed/refractory B-cell malignancies, including ALL (36 patients), NHL (41), and CLL (24). No patients were excluded on the basis of either absolute lymphocyte, circulating tumors cells, history of stem cell transplant, or results of in vitro test expansions.
All patients underwent leukapheresis for harvesting of T-cells, and populations of CD4- and CD8-positive cells were separated and transduced with a lentiviral vector to express a CD19 CAR and a truncated human epidermal growth factor receptor that allowed tracing of the transduced cells via flow cytometry. The patients underwent lymphodepleting chemotherapy with cyclophosphamide (for the earliest patients), or cyclophosphamide plus fludarabine. Fifteen days after leukapheresis, the separated, transduced, and expanded cells were combined and delivered back to patients in a single infusion at one of three dose levels: 2 x 105, 2 x 106, or 2 x 107 CAR-T cells/kg.
ALL results
Two of the 36 patients with ALL died from complications of the CAR-T cell infusion process prior to evaluation. The 34 remaining patients all had morphologic bone marrow complete responses (CR). Of this group, 32 also had bone marrow CR on flow cytometry.
Using immunoglobulin H (IgH) deep sequencing in a subset of 20 patients 3 weeks after CAR-T cell infusion, the investigators could not detect the malignant IgH index clone in 13 of the patients, and found fewer than 10 copies in the bone marrow of 5 patients.
Six of seven patients with extramedullary disease at baseline had a complete response. The remaining patient in this group had an equivocal PET scan result, and experienced a relapse 2 months after assessment.
The investigators also determined that the lymphodepletion regimen may affect overall results, based on the finding that 10 of 12 patients who received cyclophosphamide alone achieved a CR, but seven of these 10 patients had a relapse within a few months. Of these seven patients. five received a second T-cell infusion, but none had significant T-cell expansion. The investigators traced the failure of the second attempt to a CD8-mediated transgene immune response to a murine single-chain variable fragment used in the construct.
For subsequent patients, they altered the lymphodepletion regimen to include fludarabine to prevent priming of the anti-CAR transgenic immune response. This modification resulted in improved progression-free survival and overall survival for subsequent patients receiving a second infusion, Dr. Turtle said.
NHL results
Of the 41 patients with NHL, 30 (73%) had aggressive histologies, including diffuse large B-cell lymphoma, primary mediastinal large B-cell lymphoma, T-cell/histiocyte-rich large B-cell, and Burkitt lymphomas, and 11 (27%) had indolent histologies, including mantle cell and follicular lymphomas. Most of the patients had received multiple prior lines of therapy, and 19 (46%) had undergone either an autologous or allogeneic stem cell transplant.
Of the 39 evaluable patients who completed therapy, the overall response rate was 67%, including 13 (39%) with CR. Dr. Turtle noted that the CR rate was substantially higher among patients who received cyclophosphamide and fludarabine lymphodepletion, compared with cyclophosphamide alone.
There were also a few responses, including two CRs, among patients with indolent histologies, he said.
CLL, safety results
All 24 patients with CLL had previously received ibrutinib (Imbruvica). Of this group, 19 either had no significant responses to the drug, inactivating mutations, or intolerable toxicities. All but 1 of the 24 patients also had high-risk cytogenetics.
Of the 16 ibrutinib-refractory patients who were evaluable for restaging, 14 had no evidence of disease in bone marrow by flow cytometry at 4 weeks. The overall response rate in this group was 69%, which included four CRs.
Among a majority of all patients, toxicity with the CAR-T cell therapy was mild to moderate. Early cytokine changes appeared to be predictive of serious adverse events such as the cytokine release syndrome, a finding that may allow clinicians to intervene early to prevent complications, Dr. Turtle said.
In the CAR-T cell therapy, “multiple things affect the response and toxicity, including CAR T-cell dose, disease burden, the anti-CAR transgene immune response and the lymphodepletion regimen, not to mention other patient factors that we’re still sorting out,” he commented.
The trial was funded by the National Institutes of Health, Life Science Development Fund, Juno Therapeutics and the Bezos Family Foundation. Dr. Turtle disclosed consultancy, honoraria, and/or research funding from Juno Therapeutics and Seattle Genetics.