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B-cell maturation antigen (BCMA) expression has been proposed as a marker for the identification of malignant plasma cells in patients with multiple myeloma (MM). Nearly all MM tumor cells express BCMA, while normal tissue expression is restricted to plasma cells and a subset of mature B cells. Consistent BCMA expression was confirmed on MM biopsies (29/29 BCMA+), and it was further demonstrated that BCMA is expressed in a substantial number of lymphoma samples, as well as primary chronic lymphocytic leukemia B cells. To target BCMA using redirected autologous T cells, lentiviral vectors (LVV) encoding chimeric antigen receptors (CARs) were constructed with four unique anti-BCMA single-chain variable fragments, fused to the CD137 (4-1BB) co-stimulatory and CD3ζ signaling domains. One LVV, BB2121, was studied in detail, and BB2121 CAR-transduced T cells (bb2121) exhibited a high frequency of CAR + T cells and robust in vitro activity against MM cell lines, lymphoma cell lines, and primary chronic lymphocytic leukemia peripheral blood. Based on receptor quantification, bb2121 recognized tumor cells expressing as little as 222 BCMA molecules per cell. The in vivo pharmacology of anti-BCMA CAR T cells was studied in NSG mouse models of human MM, Burkitt lymphoma, and mantle cell lymphoma, where mice received a single intravenous administration of vehicle, control vector-transduced T cells, or anti-BCMA CAR-transduced T cells. In all models, the vehicle and control CAR T cells failed to inhibit tumor growth. In contrast, treatment with bb2121 resulted in rapid and sustained elimination of the tumors and 100% survival in all treatment models. Together, these data support the further development of anti-BCMA CAR T cells as a potential treatment for not only MM but also some lymphomas.

Despite the strides that immunotherapy has made in mediating tumor regression, the clinical effects are often transient, and therefore more durable responses still are needed. The temporary nature of the therapy-induced immune response can be attributed to tumor immune evasion mechanisms, mainly the effect of suppressive immune cells and, in particular, T regulatory cells (Treg). Although the depletion of Treg has been shown to be effective in enhancing immune responses, selective depletion of these suppressive cells without affecting other immune cells has not been very successful, and new agents are sought. We found that PI3K-Akt pathway inhibitors selectively inhibit Treg with minimal effect on conventional T cells (Tconv). Our results clearly show selective in vitro inhibition of activation (as represented by a decrease in downstream signaling) and proliferation of Treg in comparison to Tconv when treated with different Akt and PI3K inhibitors. This effect has been observed in both human and murine CD4 T cells. In vivo treatment with these inhibitors resulted in a significant and selective reduction in Treg both in naïve and tumor-bearing mice. Furthermore, these PI3K-Akt inhibitors led to a significant therapeutic antitumor effect, which was shown to be Treg-dependent. Here, we report the use of PI3K-Akt pathway inhibitors as potent agents for the selective depletion of suppressive Treg. We show that these inhibitors are able to enhance the antitumor immune response and are therefore promising clinical reagents for Treg-depletion.

Adoptive cell therapy using tumor-infiltrating lymphocytes (TIL) can mediate objective and durable tumor regressions in patients with metastatic melanoma. CD8+ tumor-reactive TIL are well studied in humans and animals, yet the function of tumor-infiltrating CD4+ T lymphocytes in patient treatments remains controversial. We recently demonstrated that CD4+ TILs are not necessary for objective responses in patients. Coinfusion with tumor-specific CD4 TIL may enhance or increase the durability of tumor regressions, but the number of patients with tumor-reactive CD4 TIL is unknown. We screened 44 CD8+-depleted TIL for in vitro reactivity against autologous tumor. Nine (20%) showed specific reactivity by interferon-γ release assay, of which 8 were specifically blocked by an anti-HLA-DR antibody. Flow-cytometric analysis of these reactive TIL confirmed a high CD4+ composition (median 89%). Highlighting the contribution of CD4+ TIL to tumor regression, a patient with widespread metastatic disease was administered TIL containing HLA class II-restricted tumor activity with high-dose interleukin-2 therapy after lymphodepletion that mediated regression of extensive metastatic disease in the liver and spleen. These results demonstrate that at least 20% of metastatic melanomas contain CD4+ lymphocytes with specific tumor recognition and suggest a possible role for CD4+ cells in the effectiveness of adoptive cell therapy.

The Skp2 oncoprotein belongs to the family of F-box proteins that function as substrate recognition factors for SCF (Skp1, cullin, F-box protein) E3 ubiquitin-ligase complexes. Binding of the substrate to the SCF Skp2 complex catalyzes the conjugation of ubiquitin molecules to the bound substrate, resulting in multi-ubiquitination and rapid degradation by the 26 S proteasome. Using Skp2 as bait in a yeast two-hybrid screen, we have identified UBP43 as a novel substrate for Skp2. UBP43 belongs to the family of ubiquitin isopeptidases and specifically cleaves ISG15, a ubiquitin-like molecule that is induced by cellular stresses, such as type 1 interferons (IFN), nephrotoxic damage, and bacterial infection. UBP43 was originally identified as an up-regulated gene in knock-in mice expressing an acute myelogenous leukemia fusion protein, AML1-ETO, as well as in melanoma cell lines treated with IFN-␤. The phenotype of UBP43 knockout mice includes shortened life span, hypersensitivity to IFN, and neuronal damage, suggesting that tight regulation of ISG15 conjugation is critical for normal cellular function. In this study, we demonstrate that UBP43 is ubiquitinated in vivo and accumulates in cells treated with proteasome inhibitors. We also show that Skp2 promotes UBP43 ubiquitination and degradation, resulting in higher levels of ISG15 conjugates. In Skp2؊/؊ mouse cells, levels of UBP43 are consistently up-regulated, whereas levels of ISG15 conjugates are reduced. Our results demonstrate that the SCF Skp2 is involved in controlling UBP43 protein levels and may therefore play an important role in modulating type 1 IFN signaling.Modification of proteins by ubiquitin and ubiquitin-like (Ubl) 1 molecules, including SUMO, Nedd8, and ISG15, has emerged as a critical regulatory process in eukaryotes, controlling pathways such as the cell cycle, cellular stress response, intracellular signaling, development, and the immune response (1-5). Deregulation of ubiquitin or Ubl modification can cause autoimmune and neurodegenerative diseases, developmental abnormalities, and cancer.Conjugation of ubiquitin and Ubls involves a three-step mechanism initially demonstrated for ubiquitin as follows. A single E1 ubiquitin-activating enzyme activates the Ubl molecule via formation of a thioester bond. Activated Ubl is then transferred to one of a large family of E2 ubiquitin-conjugating enzymes. In most cases, E2 enzymes are targeted to appropriate substrates by a class of substrate receptor complexes termed E3 ubiquitin ligases. Together, the E2 and E3 enzymes catalyze the formation of isopeptide bonds between ubiquitin and lysine residues on the target proteins. In the case of multiubiquitination, additional ubiquitin molecules are added to form ubiquitin chains. The multiubiquitinated proteins are then recognized and rapidly degraded into short peptides by the 26 S proteasome (3, 6). Modification by ubiquitin and Ubl molecules is a reversible process mediated by a large family of isopeptidases that exist to remove these molecules from the...

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Patients treated with chimeric antigen receptor (CAR) T cells targeting CD19 for B cell malignancies have experienced rapid and durable tumor regressions. Manufacture of CAR T cells is challenged by the necessity to produce a unique drug product for each patient. Each treatment requires ex vivo culture of patient T cells to facilitate CAR gene transfer and to achieve therapeutic amounts of T cells. Paradoxically, ex vivo culture with IL-2 also decreases CAR T cell activity. Some investigators have proposed isolating central memory T cells (thought to be enriched for therapeutic T cells), yet isolation techniques are cumbersome and costly to scale commercially. Culture of T cells in IL-7 and IL-15 has also been shown by several investigators to improve therapeutic activity. Here we explored the potential for culture modifications to improve the therapeutic potential of CAR T cells without adding complexity to manufacturing. We tested this hypothesis using CAR T cells specific to B cell maturation antigen (BCMA) manufactured using standard IL-2 culture with an inhibitor of PI3K added to the media, or with IL-7 and IL-15 in place of IL-2. The in vivo activity was studied in NSG mouse models of human Burkitt's lymphoma (Daudi), and multiple myeloma (RPMI-8226), both of which express BCMA. In the lymphoma model, NSG mice were injected intravenously (IV) with 2 x 106 Daudi cells and allowed to accumulate a large tumor burden before being treated with 4 x 106 CAR+ T cells on day 18 post-tumor injection. At this late time point post implantation, mice had highly disseminated Daudi tumor (our goal was to model late stage disease observed in relapsed and refractory lymphoma). In this model of advanced disease, IL-2 cultured anti-BCMA CAR T cells had no effect on tumor growth (p = 0.22) and all mice succumbed to the tumors within two weeks after treatment. Anti-BCMA CAR T cells grown in IL-7 and IL-15 also failed to control tumor growth (p = 0.23). In sharp contrast, all animals treated with anti-BCMA CAR T cells cultured with the PI3K inhibitor survived and experienced complete long-term tumor regression (p=0.003). The same anti-BCMA CAR T cells were used in a model of multiple myeloma. NSG mice were injected subcutaneously (SC) with 107 RPMI-8226 MM cells, and at 22 days post-implantation mice received a single IV administration of anti-BCMA CAR T cells (4 x 105 CAR+ T cells/mouse) cultured under various conditions. In this model, all treatment groups demonstrated tumor regression, regardless of the in vitro culture conditions. To evaluate CAR T cell durability, two weeks after initial tumor clearance, surviving animals were then re-challenged with RPMI-8226 cells on the opposite flank to model tumor relapse. We found that only animals that had been treated with anti-BCMA CAR T cells cultured with PI3K inhibition were immune to subsequent tumor challenge (p=0.005). Given the superior in vivo efficacy of anti-BCMA CAR T cells cultured with PI3K inhibition, we sought to identify phenotypic characteristics associated with the improved therapeutic activity. Anti-BCMA CAR T cells cultured with PI3K inhibition contained an increased frequency of CD62L+ CD8 T cells in the final product (p < 0.001) suggesting improved expansion of a distinct CD8 T cell subset. These data suggest that inhibition of PI3K during ex vivo expansion with IL-2 may generate a superior anti-BCMA CAR T cell product for clinical use. Furthermore, this approach could potentially be used in the manufacture of other T cell therapies. Disclosures Perkins: bluebird bio: Employment, Equity Ownership. Grande:bluebird bio: Employment, Equity Ownership. Hamel:bluebird bio: Employment, Equity Ownership. Horton:bluebird bio: Employment, Equity Ownership. Garrett:bluebird bio: Employment, Equity Ownership. Miller:bluebird bio: Employment, Equity Ownership. Latimer:bluebird bio: Employment, Equity Ownership. Horvath:bluebird bio: Employment, Equity Ownership. Kuczewski:bluebird bio: Employment, Equity Ownership. Friedman:bluebird bio: Employment, Equity Ownership. Morgan:bluebird bio: Employment, Equity Ownership.

Since multiple lines of experimental and clinical data clearly identified regulatory T cells as an integral part of the immune response, these cells have become a major focus of investigation in tumor immunology. Regulatory T cells are in place to dampen ongoing immune responses and to prevent autoimmunity, but they also have profound effects in blocking therapeutic anti-tumor activity. Therefore regulatory T cells are seen as a major hurdle that must be overcome in order for cancer immunotherapy to reach its therapeutic potential. Regulatory T cells are heterogeneous with sub-populations that exhibit distinct functional features. Here we will review the individual sub-populations in regards to their mode of action and their potential impact on blocking anti-tumor immunity. Approaches to measure function and frequency of regulatory T cells in model systems and clinical trails will be discussed. Finally, we will describe possible ways to interfere with regulatory T cell-mediated immune suppression with the focus on recent pre-clinical and clinical findings.