ALBERT

Description: Plasmacytoid dendritic cell precursors (pDCs) are professional type I interferon-producing cells, a critical cell type in regulating innate and adaptive immune responses. By microarray gene expression analysis, we found that pDCs activated by virus or CpG-ODN preferentially express the ligand for the glucocorticoid-induced tumor necrosis factor receptor (GITRL), which was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) and flow cytometry analysis. Using the same approaches, we found GITR is expressed by activated natural killer (NK) cells and T cells. We show that pDCs activated by CpG-ODN promote NK cell cytotoxicity and interferon (IFN)-γ production through type I IFNs and GITRL. Using a GITRL-transfected cell line, we further demonstrate that GITRL promotes NK cell cytotoxicity and IFN-γ production in synergy with interleukin-2 (IL-2), IFN-α, and NKG2D triggering. We also demonstrated that pDCs localized in close contact to NK cells in T-cell areas of the tonsils, and a subpopulation of the pDCs expressed GITRL. This study reveals a novel function of GITR/GITRL in pDC-mediated coactivation of NK cells.

Description: The ability of plasmacytoid dendritic cells (pDCs) to promote plasma cell differentiation and immunoglobulin (Ig) secretion through the production of type I interferon and interleukin-6 has been well documented, although the role of additional factors, including tumor necrosis factor receptor-ligand interactions, has not been addressed. On stimulation with the Toll-like receptor ligand CpG (B type, 2006) we found that pDCs exhibit strong and stable expression of CD70, a tumor necrosis factor family ligand that binds to its receptor CD27 expressed on memory B cells and promotes plasma cell differentiation and Ig secretion. Using a pDC/B-cell coculture system, we found that CpG-stimulated pDCs can induce the proliferation of CD40L-activated human peripheral B cells and Ig secretion. This occurs independently of interferon and residual CpG, and requires physical contact between pDCs and B cells. CpG-stimulated pDCs can induce the proliferation of both naive and memory B cells, although Ig secretion is restricted to the memory subset. Blocking the interaction of CD70 with CD27 using an antagonist anti-CD70 antibody reduces the induction of B-cell proliferation and IgG secretion by CpG-stimulated pDCs. We have therefore identified CD70 as an important factor in the regulation of B-cell growth and differentiation by pDCs.

Description: Introduction: Adoptive transfer of T cells, genetically engineered to express chimeric antigen receptors (CARs) containing costimulatory domains, such as CD28 or 4-1BB, has yielded impressive clinical results in some blood cancers, but severe toxicities have been observed due to unchecked T cell activation. In contrast, CAR-T cells have demonstrated limited clinical efficacy, associated with poor engraftment, survival and proliferation of adoptively transferred cells when used to target a variety of solid tumors. Thus, technologies that can regulate T cell activation and proliferation in vivo should both mitigate toxicities and maximize anti-tumor efficacy, expanding their clinical utility to a wider range of indications. Here, we describe a novel T cell costimulation switch, inducible MyD88/CD40 (iMC), activated by a small molecule chemical inducer of dimerization, rimiducid, to enhance survival and drive T cell proliferation. Methods: T cells were activated with anti-CD3/28 and transduced with a retrovirus encoding tandem rimiducid-binding domains (FKBP12v36),cloned in-frame with MyD88 and CD40 signaling elements, and first generation CARs (CAR.ζ) targeting CD19 or PSCA (SFG-iMC-2A-CD19.ζ or SFG-iMC-2A-PSCA.ζ, respectively). iMC activation was measured by treating T cells with and without rimiducid and measuring cytokine production by ELISA and T cell activation markers by flow cytometry. Coactivation through iMC and CAR was tested in coculture assays with or without rimiducid using various tumor cells (CD19+, Raji and Daudi lymphoma; PSCA+, Capan-1 and HPAC pancreatic adenocarcinoma). Efficacy of iMC-modified CAR-T cells were assessed using an immune-deficient NSG mouse tumor model. For CD19-targeted CARs, 1x105 Raji tumor cells were injected i.v. followed on day 7 by a single i.v. injection at various doses of iMC-CD19.ζ-modified T cells. For PSCA-targeted CARs, 2x106 HPAC tumor cells were injected s.c. followed by iMC-PSCA.ζ-modified T cells on day 10. In both models, iMC was activated in vivo by weekly i.p. injections of rimiducid (5 mg/kg). In some experiments, iMC-CAR-modified T cells were engrafted into tumor-free mice. Tumor burden and CAR-T cell expansion in vivo was assessed using luciferase bioluminescent imaging and flow cytometry. Results: T cells transduced with either iMC-CD19.ζ or iMC-PSCA.ζ produce cytokines (e.g., IFN-γ and IL-6) in response to rimiducid; however, the key growth and survival cytokine, IL-2, was only produced when both iMC and CAR were activated simultaneously by rimiducid and tumor antigen, respectively. CD19+ Raji tumor-bearing mice treated with iMC-CD19.ζ-modified T cells with or without rimiducid administration increased survival compared to non-transduced T cells (p = 0.01). However, rimiducid treatment induced a 7.3-fold CAR-T cell expansion compared to mice infused with iMC-CD19.ζ, but untreated with dimer drug (p = 0.02). Additionally, treatment of NSG mice bearing large (〉200 mm3) HPAC tumors with a single dose iMC-PSCA.ζ, resulted in complete elimination in 10/10 mice (100%) of tumors both with and without rimiducid treatment compared to mice receiving non-transduced T cells (p = 0.0003). Rimiducid administration again dramatically increased CAR-T cell levels, resulting in a 23-fold expansion of iMC-PSCA.ζ-modified T cells compared to mice not receiving rimiducid (p = 0.02), justifying ongoing experiments using larger tumors at baseline with fewer T cells. In addition, in tumor-free mice, rimiducid prolonged iMC-PSCA.ζ-modified T cell engraftment and survival for 28 days compared to those mice not treated with dimerizer (p = 0.03). Importantly, following rimiducid withdrawal, CAR-T cell numbers declined, consistent with the requirement of MC-mediated costimulation in combination with CAR activation. Summary: Inducible MyD88/CD40 represents a novel activation switch that can be used to provide a controllable costimulatory signal to T cells transduced with a first generation CAR. The separation of the cytolytic signal 1 (CD3ζ) domain from a potent, regulatable, signal 2 costimulation (iMC) in the novel platform, called "GoCAR-T", allows the expansion of T cells only in response to both rimiducid and tumor antigen, and their decrease in number by withdrawal of rimiducid-induced iMC costimulation. The "GoCAR-T" platform may allow the development of a new generation of more effective CAR-T cell therapies. Disclosures Foster: Bellicum Pharmaceuticals: Employment. Mahendravada:Bellicum Pharmaceuticals: Employment. Shinners:Bellicum Pharmaceuticals: Employment. Chang:Bellicum Pharmaceuticals: Employment. Lu:Bellicum Pharmaceuticals: Employment. Morschl:Bellicum Pharmaceuticals: Employment. Shaw:Bellicum Pharmaceuticals: Employment. Saha:Bellicum Pharmaceuticals: Employment. Slawin:Bellicum Pharmaceuticals: Employment, Equity Ownership. Spencer:Bellicum Pharmaceuticals: Employment, Equity Ownership.

Description: Background: Adoptive transfer of allogeneic donor T cells can be an effective treatment for hematological malignancies through recognition of leukemia-associated antigens (LAAs) on tumor cells or through alloreactivity. However, alloreactive T cells can also cause graft-versus-host disease (GvHD) limiting their use as an immunotherapy. To leverage the anti-tumor effects of allogeneic polyclonal T cells while minimizing GvHD, we have genetically modified donor T cells with the inducible caspase-9 (iC9) safety switch, which induces apoptosis following exposure to the small molecule ligand rimiducid. Here we show that iC9-modified allogeneic T cells (BPX-501) persist, expand and contain functional LAA-specific T cells in children receiving an alpha/beta TCR and CD19-depleted HLA-haploidentical hematopoietic stem cell transplant (haplo-HSCT) for the treatment of myeloid malignancies. Methods: Pre-infusion products (BPX-501: donor T cells modified with the bicistronic retroviral vector encoding iC9 and truncated CD19 (ΔCD19)) and patient peripheral blood mononuclear cells (PBMCs) were analyzed from twelve patients (AML (10), MDS (1), JMML (1)) receiving BPX-501 (1x106 cells/kg) following an alpha/beta T cell and CD19 B cell-depleted haplo-HSCT (BP-004U: NCT03301168). Engraftment and persistence were measured by coexpression of CD3 and CD19 by flow-cytometry. Endogenous and gene-modified T cells were also phenotyped for CD4:CD8 ratios, memory cell composition (TN, TCM, TEM, TEMRA; CD45RA and CD62L) and T cell receptor Vβ diversity. BPX-501 products and post-treatment samples were characterized for LAA-specific T cells using IFN-γ ELISpot against peptide pools (15 aa overlapping by 5 aa) derived from WT1, PRAME, MAGE (A1, C1, C3), NE and PR3, with and without exposure to 10 nM rimiducid to determine the anti-leukemic contribution of BPX-501. Results: BPX-501 was infused at a median time of 22.5 days after HSCT (range 12-34, one patient was infused at day 89 and one patient was infused at day 147). BPX-501 cells (CD3+CD19+) were detectable in the peripheral blood at 1-2 weeks after infusion in all 12 patients, reaching a peak expansion frequency of a median of 24% ± 17% of total CD3+ T cells, and an absolute cell number of 66.9 ± 112 cells/µl at 2 months post-infusion and could be detected for up to 24 months. BPX-501 T cells showed a CD8-skewed phenotype whereas endogenous T cells exhibited a more balanced CD4:CD8 ratio. BPX-501 were predominantly CD45RA-CD62L+ and CD45RA-CD62L- central and effector memory T cells, respectively. In BPX-501 products, we detected LAA-specific T cells by ELISpot using overlapping peptide pools to WT1, PRAME, MAGE, NE and PR3, and in peripheral blood samples obtained 2 to 5 months post-T cell infusion. Importantly, LAA-reactivity was greatly diminished with exposure to iC9-activating rimiducid. Further, we measured the TCR Vβ usage and observed highly-skewed TCR repertoire in BPX-501 T cells compared to endogenous T cells in 6 months after HSCT indicating selection and expansion of TCR clones. Three patients engrafted BPX-501 were treated with rimiducid to control GvHD resulting in a rapid decrease (62% ± 12%) of CD3+CD19+ T cells in the peripheral blood. In patients treated with rimiducid, CD3+CD19+ T cells recover without further instances of GvHD suggestive of in vivo depletion of alloreactive T cell clones using iC9. Summary: Allogeneic T cells engineered with the iC9 safety switch engraft, expand and demonstrate long-term persistence following adoptive transfer into patients receiving a haplo-HSCT. LAA-specific T cells and alloreactive T cells within the BPX-501 product are detectable in the peripheral blood following infusion and likely contribute to elimination of myeloid malignancies. Disclosures Shaw: Bellicum Pharmaceuticals: Employment, Equity Ownership. Zhou:Bellicum Pharmaceuticals: Employment, Equity Ownership. Lu:Bellicum Pharmaceuticals: Employment, Equity Ownership. Aldinger:Bellicum Pharmaceuticals, Inc.: Employment. Spencer:Bellicum Pharmaceuticals: Employment, Equity Ownership. Locatelli:Bellicum: Consultancy, Membership on an entity's Board of Directors or advisory committees; bluebird bio: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Miltenyi: Honoraria; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Foster:Bellicum: Employment, Equity Ownership.

Description: Introduction: BPX-501 is an allogeneic product consisting of T cells modified to express the inducible caspase-9 (iC9) safety switch, which can provide virus and tumor-specific immunity following stem cell transplant. In instances of graft-versus-host disease (GvHD), activation of iC9 with rimiducid leads to rapid killing of alloreactive T cells and resolution of GvHD. However, gene-modified T cells re-expand in the host. Here we evaluate the relationship between transgene expression and sensitivity to rimiducid to understand differential apoptosis in patients treated with allogeneic, iC9-modified T cells. Methods: The safety switch system consists of a bicistronic vector encoding a mutated FKBP12 binding protein linked to caspase-9 and truncated CD19 (ΔCD19) to allow selection of gene-modified T cells (SFG-iC9-ΔCD19). Exposure to rimiducid dimerizes iC9 resulting in apoptosis of gene-modified T cells. To evaluate the effect of transgene expression levels to the sensitivity of rimiducid-induced apoptosis, BPX-501 T cells were sorted into 3 equal populations based on the intensity of CD19 staining (CD19high, CD19med and CD19low). Phenotyping and functional assays (i.e., apoptosis) were performed by flow cytometry, qPCR and Western blot before and after T cell reactivation using anti-CD3/anti-CD28 antibodies. In vivo studies were performed by i.v. injection of control or gene-modified T cells co-expressing luciferase into NSG mice, followed by i.p. injection of a titrated dose of rimiducid (0.001 to 1 mg/kg), control drug (temsirolimus; 1 mg/kg) or vehicle. Bioluminescent imaging and flow cytometry were subsequently performed to assess in vivo depletion following iC9 activation. Results: Purity of BPX-501 cells after transduction and CD19 selection was 95%. Sorting BPX-501 cells based on CD19 mean fluorescence intensity (MFI) resulted in a CD19 MFI of 73, 46 and 22 for CD19 high, medium and low sorted populations, respectively. There was no significant difference in the percentage of CD8 and CD4 compartments among these cells, however, iC9-ΔCD19low expressing cells contained less terminal effector memory cells and more naïve-like cells than iC9-ΔCD19high (28±6% vs 39±8% (TEMRA), and 57±9% vs 42±12% (Naïve), respectively, P

Description: After transplant the immune system is reconstituted by cells derived from both hematopoietic stem cells and peripheral expansion of differentiated donor T cells. Immune function is poor despite transplantation of mature lymphocytes from immune competent donors. We tested the hypothesis that early antigen encounter at the time of cell transplant would enhance desired donor T cell responses in the post-transplant repertoire. 2 independent models of peptide-specific T cell responses were studied. Model 1 : The model for CD4 cells employed T cells from transgenic DO11.11 mice that constitutively express the T cell receptor for the class II restricted ovalbumin (OVA) peptide 323–339. Fig 1: Early exposure to OVA antigen enhances clonal expansion of OVA specific transgenic T-cells following syngeneic BMT. Lethally irradiated BALB/c mice were injected with 300 μg of OVA peptide in CFA or CFA alone subcutaneously one day before transplantation (D-1). The transplanted mice received 2x106 transgenic OVA specific T-cells and 6x106 non-transgenic naive BALB/c bone marrow cells. At 2 days (A) and 7weeks (B) following BMT, draining lymph nodes were isolated and examined for the presence of OVA-specific T-cells using FITC-labeled KJ-126 antibody and PE-labeled anti mouse CD4 antibody. Naïve BALB/c animals were used as negative controls (C). The absolute number of antigen-specific T-cells was determined by multiplying the total cells recovered with the percentage of OVA-specific CD4+ T-cells identified by flow. Figure Figure Model 2: The model for CD8 cells employed nontransgenic H2-Db-restricted T cell responses to the influenza nucleoprotein peptide 366–374. Fig 2: Antigen specific CD8+ cells in antigen-exposed animals are functionally active. Donor SW mice were immunized three times by ip injection of virus-infected spleen cells. Recipient C57BL/6 animals underwent BMT using influenza-immune donors spleen cells and bone marrow (10x106 and 4x106 respectively). Some transplant recipients were exposed to influenza virus on D-1. Ten days following BMT, the animals were sacrificed and spleens were isolated and stimulated in vitro with 2 μg of NP peptide. After two rounds of stimulation, the splenocytes were assayed by intracellular cytokine assay for the secretion of IFNg by staining with PE-anti IFNγ and FITC-anti-CD8 antibodies. The results are representative of three experiments (total number n=4/experimental group). Figure Figure Encounter with specific antigen at the time of T cell transplantation led to clonal expansion of donor T cells and preservation of donor T cell function in the post-transplant immune environment. Antigen-specific donor T cell function was poor if antigen encounter was delayed or omitted. Severe parent〉F1 graft versus host reactions blocked the effect of early antigen exposure.

Description: Introduction: Efficacy of chimeric antigen receptor (CAR)-modified T cells is dependent on their in vivo survival and expansion following infusion. The addition of accessory molecules (e.g., costimulatory and cytokine genes) may improve CAR-T proliferation and potency, but may also increase toxicity of these next generation CAR-T cell therapies, suggesting that the incorporation of a built in "safety switch" would balance safety and efficacy in a single, controllable therapy. Here, we demonstrate that cytosolic coexpression of a MyD88/CD40-derived fusion protein dramatically enhances CAR-T activation, cytokine production, and proliferation in vivo, resulting in improved antitumor efficacy. Importantly, CAR-T cell numbers, elevated cytokine levels, and observed CAR-T-related toxicity could be controlled by titratable rimiducid administration to reduce or eliminate CAR-T cells by activating the inducible caspase-9 (iC9) suicide gene. Methods: Human T cells were activated with anti-CD3/CD28 and transduced with retrovirus encoding, iC9, a first generation CAR (with CD3ζ) targeting CD19, Her2 or PSCA, and a detached, fusion protein comprising signaling domains from MyD88 and CD40 (MC). For comparison, additional CARs were constructed without MC, with MyD88 or CD40 elements only, or with conventional CARs coexpressing CD28 within the CAR molecule (CAR.28.ζ). Transduced T cells were assessed in vitro for cytotoxicity, cytokine production and proliferation against tumor cell lines (CD19+: Daudi, Raji; Her2+: SK-BR-3; PSCA+: Capan-1, HPAC). In vivo antitumor efficacy of CAR-modified T cells was assessed using immunodeficient NSG mice engrafted with antigen-matched tumor cell lines (5x105 Raji, i.v.; 1x106 SK-BR-3, s.c; 2x106 HPAC, s.c.) followed by i.t. or i.v. injection of variable doses of T cells. Reduction or elimination of CAR-T cells was performed by i.p. injection of rimiducid (0 - 5 mg/kg). Tumor cell lines expressing luciferase or T cells co-transduced with luciferase-encoding vectors were used for bioluminescence imaging (BLI) to measure tumor growth or T cell expansion/elimination, respectively. Serum cytokine levels were assessed by blood draws and CAR-T cell frequency was measured by flow cytometry. Results: All CAR constructs were stably expressed in T cells (30-90%). CAR vectors coexpressing MC induced high IL-2 levels in vitro when exposed to target antigen+ tumor cells (CD19 = 4246 ± 52, Her2 = 2613 ± 1298, and PSCA = 3263 ± 1393 pg/ml per 1x105 T cells over 48 hrs) and corresponded to improved CAR-T cell proliferation and tumor elimination compared to control vectors. In NSG mice, MC costimulation resulted in 〉2,000-fold expansion of CD19-targeted CAR-T cells and complete tumor control for 〉100 days in 100% of mice engrafted with CD19+ Raji cells (p = 0.0002) following injection of 5x106 CAR-T cells, followed on day 7 with a single i.p. dose of rimiducid (5 mg/kg) to control toxicity. MC-enabled CAR-T cells were eliminated or partially reduced by rimiducid titrations, which corresponded to decreased cytokine (IL-6, IFN-γ, TNF-α) levels and restoration of health in animals showing signs of toxicity (e.g., ≥15% weight loss). For solid tumors, Her2-targeted, MC-enabled CAR-T cells showed a 150-fold in vivo expansion and compared favorably to first (Her2.ζ; p = 0.01) and second generation (Her2.28.ζ; p = 0.01) CARs, causing 100% elimination of SK-BR-3 tumors and enhanced survival for 〉60 days following i.t. injection (p = 0.0015). PSCA-targeted CARs expressing MC also drove complete and durable (〉42 days) elimination of large (200 mm3) HPAC tumors in 100% of mice, after a single i.v. injection of 1x107 CAR-T cells followed on day 14 with a single 5 mg/kg i.p. rimiducid dose to reverse toxicity. Summary: Coexpression of MC, and the cell therapy safety switch "CaspaCIDe", in combination with a first generation CAR, together comprising the novel "CIDeCAR" platform technology, dramatically increases efficacy against a number of tumor targets by enhancing T cell engraftment and proliferation following infusion, while incorporating an effective, built-in safety mechanism. In three distinct tumor models, rimiducid administration promptly eliminated signs and symptoms of CAR toxicity without subsequent loss of tumor control. CIDeCAR technology may allow the development of safer and more effective CAR-T cell therapies for a range of difficult-to-treat liquid and solid tumors. Disclosures Foster: Bellicum Pharmaceuticals: Employment. Chang:Bellicum Pharmaceuticals: Employment. Lin:Bellicum Pharmaceuticals: Employment. Crisostomo:Bellicum Pharmaceuticals: Employment. Mahendravada:Bellicum Pharmaceuticals: Employment. Lu:Bellicum Pharmaceuticals: Employment. Khalil:Bellicum Pharmaceuticals: Employment. Saha:Bellicum Pharmaceuticals: Employment. Shaw:Bellicum Pharmaceuticals: Employment. Morschl:Bellicum Pharmaceuticals: Employment. Slawin:Bellicum Pharmaceuticals: Employment, Equity Ownership. Spencer:Bellicum Pharmaceuticals: Employment, Equity Ownership.