Therapies with novel mechanisms of action are needed for patients with multiple myeloma. T cells can be genetically modified to express chimeric antigen receptors (CARs), which are artificial proteins that target T cells to specific antigens. In collaboration with Dr. Kochenderfer, NCI, we have evaluated expression of B-cell maturation antigen (BCMA) as a potential target for CAR T-cell therapy. The results showed that BCMA was expressed in normal and malignant plasma cells, but not other normal cells. Surface BCMA expression is required for CAR T-cell binding and killing. We determined the incidence and intensity of expression of BCMA in bone marrow plasma cells of multiple myeloma (MM) patients using flow cytometry (FC) and immunohistochemistry (IHC). BCMA expression was assessed by FC in 70 patients and in 43 concurrent specimens by IHC. BCMA expression was detected in 94% of patients. FC could assess BCMA expression in all specimens and expression was quantifiable (QuantiBRITE system, BD Biosciences, San Jose, CA) in 89% of cases. BCMA expression was highly variable and could be classified as dim, moderate or bright. In the 43 specimens assessed successfully by both IHC and FC, FC showed higher positivity rate (97%) than IHC (72%) (p=0.002; McNemar's test). We conclude that FC is more sensitive than IHC and can be used to objectively quantify BCMA expression in myeloma cells. IHC is primarily useful when there is a significant infiltration of the bone marrow by myeloma and is less sensitive when percent of myeloma cells is low. The ability of FC to differentiate between normal and abnormal plasma cells and to quantify BCMA on these cells makes it a useful and sensitive tool in screening patients for CAR T-cell therapy and for follow-up post therapy. Dr. Kochenderfer group conducted first-in-humans clinical trial of CAR T-cell therapy targeting BCMA in relapsed multiple myeloma patients who tested positive for BCMA expression. Sixteen patients were treated at the highest dose level of the trial. The patients had a median of 9.5 prior lines of MM therapy. Sixty-three percent of patients had MM refractory to the last treatment regimen before protocol enrollment. T cells were transduced with a retroviral vector encoding CAR-BCMA. Patients received CAR-BCMA T cells after a conditioning chemotherapy regimen of cyclophosphamide and fludarabine. The overall response rate was 81%, with 63% very good partial response or complete response. Median event-free survival was 31 weeks. Responses included eradication of extensive bone marrow myeloma and resolution of soft-tissue plasmacytomas. All 11 patients who obtained an anti-MM response of partial response or better and had MM evaluable for minimal residual disease obtained bone marrow minimal residual disease-negative status. High peak blood CAR positive cell levels were associated with anti-MM responses. Cytokine-release syndrome toxicities were severe in some cases but were reversible. Blood CAR-BCMA T cells were predominantly highly differentiated CD8 positive T cells and BCMA antigen loss from MM was observed. These results should encourage additional development of CAR T-cell therapies for MM. Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of mature, autoreactive B cells in secondary lymphoid tissues, blood and bone marrow and progressive immune dysfunction. In collaboration with Dr. Wiestner, NHLBI, we have investigated bone marrow and peripheral blood findings in CLL patients treated with single-agent ibrutinib on an investigator-initiated phase 2 trial. The safety and efficacy of ibrutinib in CLL were evaluated in 51 patients who had TP53 aberration (TP53 cohort) and in 35 patients who were 65 years or older (elderly cohort). Both cohorts included patients with treatment-naive (TN) and relapsed/refractory (RR) CLL. With the median follow-up of 4.8 years, 49 (57.0%) of 86 patients remain on study. Treatment was discontinued for progressive disease in 20 (23.3%) patients and for adverse events in 5 (5.8%). Atrial fibrillation occurred in 18 (20.9%) patients for a rate of 6.4 per 100 patient-years. No serious bleeding occurred. The overall response rate at 6 months, the primary study endpoint, was 95.8% for the TP53 cohort (95% confidence interval, 85.7%-99.5%) and 93.9% for the elderly cohort (95% confidence interval, 79.8%-99.3%). Depth of response improved with time: at best response, 14 (29.2%) of 48 patients in the TP53 cohort and 9 (27.3%) of 33 in the elderly cohort achieved a complete response. Median minimal residual disease (MRD) in peripheral blood was 3.8 10-2 at 4 years, with MRD-negative (<10-4) remissions in 5 (10.2%) patients. In the TP53 cohort, the estimated 5-year progression-free survival (PFS) was 74.4% in TN-CLL compared with 19.4% in RR-CLL (P = .0002), and overall survival (OS) was 85.3% vs 53.7%, respectively (P = .023). In the elderly cohort, the estimated 5-year PFS and OS in RR-CLL were 64.8% and 71.6%, respectively, and no event occurred in TN-CLL. Long-term administration of ibrutinib was well tolerated and provided durable disease control for most patients. In patients with CLL, prior studies looking into global gene expression profiling of CD4+ and CD8+ cells revealed defects involving cell differentiation, cytotoxicity, and cytoskeletal pathways. Thus, restoration of T cell antitumor immunity represents an attractive treatment strategy to restore immune surveillance in these patients. Previous studies in CLL indicated that immunomodulatory drug lenalidomide can repair defective T cell function in vitro. We investigated changes in the immune microenvironment in patients with CLL treated with single-agent lenalidomide and associated the immunologic effects of lenalidomide with antitumor response. Within days of starting lenalidomide, T cells increased in the tumor microenvironment and showed Th1-type polarization. Gene expression profiling of pretreatment and on-treatment biopsy specimens revealed upregulation of IFN- and many of its target genes in response to lenalidomide. The IFN--mediated Th1 response was limited to patients achieving a clinical response defined by a reduction in lymphadenopathy. Deep sequencing of TCR genes revealed decreasing diversity of the T cell repertoire and an expansion of select clonotypes in responders. To validate our observations, T cells and CLL cells were stimulated with lenalidomide in culture. Results showed lenalidomide-dependent increases in T cell proliferation. Taken together, our data demonstrate that lenalidomide induced Th1 immunity that is associated with clinical response.
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