Wayne R. Godfrey

BACKGROUND: Phosphatidylinositol-3-kinase delta (PI3Kδ) mediates B-cell receptor signaling and microenvironmental support signals that promote the growth and survival of malignant B lymphocytes. In a phase 1 study, idelalisib, an orally active selective PI3Kδ inhibitor, showed antitumor activity in patients with previously treated indolent non-Hodgkin's lymphomas. METHODS: In this single-group, open-label, phase 2 study, 125 patients with indolent non-Hodgkin's lymphomas who had not had a response to rituximab and an alkylating agent or had had a relapse within 6 months after receipt of those therapies were administered idelalisib, 150 mg twice daily, until the disease progressed or the patient withdrew from the study. The primary end point was the overall rate of response; secondary end points included the duration of response, progression-free survival, and safety. RESULTS: The median age of the patients was 64 years (range, 33 to 87); patients had received a median of four prior therapies (range, 2 to 12). Subtypes of indolent non-Hodgkin's lymphoma included follicular lymphoma (72 patients), small lymphocytic lymphoma (28), marginal-zone lymphoma (15), and lymphoplasmacytic lymphoma with or without Waldenström's macroglobulinemia (10). The response rate was 57% (71 of 125 patients), with 6% meeting the criteria for a complete response. The median time to a response was 1.9 months, the median duration of response was 12.5 months, and the median progression-free survival was 11 months. Similar response rates were observed across all subtypes of indolent non-Hodgkin's lymphoma, though the numbers were small for some categories. The most common adverse events of grade 3 or higher were neutropenia (in 27% of the patients), elevations in aminotransferase levels (in 13%), diarrhea (in 13%), and pneumonia (in 7%). CONCLUSIONS: In this single-group study, idelalisib showed antitumor activity with an acceptable safety profile in patients with indolent non-Hodgkin's lymphoma who had received extensive prior treatment. (Funded by Gilead Sciences and others; ClinicalTrials.gov number, NCT01282424.).

PURPOSE: Therapeutic prostate-specific antigen (PSA) -targeted poxviral vaccines for prostate cancer have been well tolerated. PROSTVAC-VF treatment was evaluated for safety and for prolongation of progression-free survival (PFS) and overall survival (OS) in a randomized, controlled, and blinded phase II study. PATIENTS AND METHODS: In total, 125 patients were randomly assigned in a multicenter trial of vaccination series. Eligible patients had minimally symptomatic castration-resistant metastatic prostate cancer (mCRPC). PROSTVAC-VF comprises two recombinant viral vectors, each encoding transgenes for PSA, and three immune costimulatory molecules (B7.1, ICAM-1, and LFA-3). Vaccinia-based vector was used for priming followed by six planned fowlpox-based vector boosts. Patients were allocated (2:1) to PROSTVAC-VF plus granulocyte-macrophage colony-stimulating factor or to control empty vectors plus saline injections. RESULTS: Eighty-two patients received PROSTVAC-VF and 40 received control vectors. Patient characteristics were similar in both groups. The primary end point was PFS, which was similar in the two groups (P = .6). However, at 3 years post study, PROSTVAC-VF patients had a better OS with 25 (30%) of 82 alive versus 7 (17%) of 40 controls, longer median survival by 8.5 months (25.1 v 16.6 months for controls), an estimated hazard ratio of 0.56 (95% CI, 0.37 to 0.85), and stratified log-rank P = .0061. CONCLUSION: PROSTVAC-VF immunotherapy was well tolerated and associated with a 44% reduction in the death rate and an 8.5-month improvement in median OS in men with mCRPC. These provocative data provide preliminary evidence of clinically meaningful benefit but need to be confirmed in a larger phase III study.

Phenotypic analysis of hematopoietic stem and progenitor cells (HSCs) has been an invaluable tool in defining the biology of stem cell populations. We have recently described the production of AC133, a monoclonal antibody (MoAb) that binds to a novel cell surface antigen present on a CD34(bright) subset of human HSCs. This antigen is a glycosylated protein with a molecular weight of 120 kD. Here, we report the molecular cloning of a cDNA encoding this antigen and show that it does not share homology with any previously described hematopoietic or other cell surface antigen(s). The AC133 polypeptide has a predicted size of 97 kD and contains five-transmembrane (5-TM) domains with an extracellular N-terminus and a cytoplasmic C-terminus. Whereas the expression of tetraspan (4-TM) and 7-TM molecules is well documented on mature and immature hematopoietic cells and leukocytes, this 5-TM type of structure containing two large (255-amino acid [aa] and 290-aa) extracellular loops is unique and does not share sequence homology with any known multi-TM family members. Expression of this protein appears limited to bone marrow in normal tissue by immunohistochemical staining; however, Northern analysis suggests that the mRNA transcript is present in a variety of tissues such as the kidney, pancreas, placenta, and fetal liver. The AC133 antigen is also expressed on subsets of CD34+ leukemias, suggesting that it may be an important early marker for HSCs, as well as the first described member of a new class of TM receptors.

CD4(+)CD25+ T regulatory (Treg) cells have been shown to critically regulate self and allograft tolerance in mice. Studies of human Treg cells have been hindered by low numbers present in peripheral blood and difficult purification. We found that cord blood was a superior source for Treg-cell isolation and cell line generation compared with adult blood. Cord blood CD4(+)CD25+ cells were readily purified and generated cell lines that consistently exhibited potent suppressor activity, with more than 95% suppression of allogeneic mixed lymphocyte reactions (MLRs) (29 of 30 donors). Cultured Treg cells blocked cytokine accumulation in MLRs, with a less robust inhibition of chemokine production. These cell lines uniformly expressed CD25, CD62L, CCR7, CD27, and intracellular cytotoxic T-lymphocyte antigen-4 (CTLA4). FoxP3 protein, but not mRNA, was specifically expressed. Upon restimulation with anti-CD3/CD28 beads, the cultured Treg cells produced minimal cytokines (interleukin-2 [IL-2], interferon-gamma [IFN-gamma], and IL-10) and preferentially expressed tumor growth factor-beta (TGF-beta) latency associated protein. Cytokine production, however, was restored to normal levels by restimulation with phorbol myristate acetate (PMA)/ionomycin. Cord blood-derived cultured suppressor cell function was predominantly independent of IL-10 and TGF-beta. These results demonstrate cord blood contains a significant number of Treg precursor cells capable of potent suppressor function after culture activation. Banked cord blood specimens may serve as a readily available source of Treg cells for immunotherapy.

CD4(+)CD25(+) T-regulatory (Treg) cells have been shown to critically regulate self- and allograft tolerance in several model systems. Studies of human Treg cells have been restricted by the small number present in peripheral blood and their naturally hypoproliferative state. To better characterize Treg suppressor cell function, we determined methods for the isolation and expansion of these cells. Stringent magnetic microbead-based purification was required for potent suppressor cell line generation. Culture stimulation with cell-sized Dynabeads coated with anti-CD3 and anti-CD28 monoclonal antibodies, CD4(+) feeder cells, and interleukin 2, provided for marked expansion in cell number (100-fold), with retention and enhancement of suppressor function. The potent Treg cell lines suppressed proliferation in dendritic cell-driven allo-mixed lymphocyte reaction (MLR) cultures by more than 90%. The Treg-derived suppressor cells functioned early in allo-MLR because expression of activation antigens and accumulation of cytokines was nearly completely prevented. Importantly, cultured Treg cells also suppressed activated and matured dendritic cell-driven responses. These results demonstrate that short-term suppressor cell lines can be generated, and they can express a very potent suppressive activity. This approach will enable more detailed biologic studies of Treg cells and facilitate the evaluation of cultured Treg cells as a novel form of immunosuppressive therapy.