T cell receptor gene therapy targeting WT1 prevents acute myeloid leukemia relapse post-transplant

Relapse after allogeneic hematopoietic cell transplantation (HCT) is the leading cause of death in patients with acute myeloid leukemia (AML) entering HCT with poor-risk features^1-3. When HCT does produce prolonged relapse-free survival, it commonly reflects graft-versus-leukemia effects mediated by donor T cells reactive with antigens on leukemic cells⁴. As graft T cells have not been selected for leukemia specificity and frequently recognize proteins expressed by many normal host tissues, graft-versus-leukemia effects are often accompanied by morbidity and mortality from graft-versus-host disease⁵. Thus, AML relapse risk might be more effectively reduced with T cells expressing receptors (TCRs) that target selected AML antigens⁶. We therefore isolated a high-affinity Wilms' Tumor Antigen 1-specific TCR (TCR_C4) from HLA-A2⁺ normal donor repertoires, inserted TCR_C4 into Epstein-Bar virus-specific donor CD8⁺ T cells (T_TCR-C4) to minimize graft-versus-host disease risk and enhance transferred T cell survival^7,8, and infused these cells prophylactically post-HCT into 12 patients ( NCT01640301 ). Relapse-free survival was 100% at a median of 44 months following infusion, while a concurrent comparative group of 88 patients with similar risk AML had 54% relapse-free survival (P = 0.002). T_TCR-C4 maintained TCR_C4 expression, persisted long-term and were polyfunctional. This strategy appears promising for preventing AML recurrence in individuals at increased risk of post-HCT relapse.

T-Cell Therapy Using Interleukin-21-Primed Cytotoxic T-Cell Lymphocytes Combined With Cytotoxic T-Cell Lymphocyte Antigen-4 Blockade Results in Long-Term Cell Persistence and Durable Tumor Regression

Purpose Peripheral blood-derived antigen-specific cytotoxic T cells (CTLs) provide a readily available source of effector cells that can be administered with minimal toxicity in an outpatient setting. In metastatic melanoma, this approach results in measurable albeit modest clinical responses in patients resistant to conventional therapy. We reasoned that concurrent cytotoxic T-cell lymphocyte antigen-4 (CTLA-4) checkpoint blockade might enhance the antitumor activity of adoptively transferred CTLs. Patients and Methods Autologous MART1-specific CTLs were generated by priming with peptide-pulsed dendritic cells in the presence of interleukin-21 and enriched by peptide-major histocompatibility complex multimer-guided cell sorting. This expeditiously yielded polyclonal CTL lines uniformly expressing markers associated with an enhanced survival potential. In this first-in-human strategy, 10 patients with stage IV melanoma received the MART1-specific CTLs followed by a standard course of anti-CTLA-4 (ipilimumab). Results The toxicity profile of the combined treatment was comparable to that of ipilimumab monotherapy. Evaluation of best responses at 12 weeks yielded two continuous complete remissions, one partial response (PR) using RECIST criteria (two PRs using immune-related response criteria), and three instances of stable disease. Infused CTLs persisted with frequencies up to 2.9% of CD8⁺ T cells for as long as the patients were monitored (up to 40 weeks). In patients who experienced complete remissions, PRs, or stable disease, the persisting CTLs acquired phenotypic and functional characteristics of long-lived memory cells. Moreover, these patients also developed responses to nontargeted tumor antigens (epitope spreading). Conclusion We demonstrate that combining antigen-specific CTLs with CTLA-4 blockade is safe and produces durable clinical responses, likely reflecting both enhanced activity of transferred cells and improved recruitment of new responses, highlighting the promise of this strategy.

Augmentation of adoptive T-cell therapy for Merkel cell carcinoma with avelumab

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Background: 80% of Merkel cell carcinomas (MCCs) are caused by Merkel cell polyomavirus (MCPyV) oncoproteins. Although absent in most cases, abundant MCPyV-specific CD8+ TIL are associated with good MCC outcomes, implying tumor susceptibility to immune attack. Indeed, anti-PD-1 axis blockade has a response rate of 32-56%. However, half of patients do not respond, suggesting a lack of adequate MCPyV-specific T cells and/or tumor evasion from MCC-related reduced HLA expression. We hypothesized the combination of adoptive transfer of MCPyV-specific T cells with HLA upregulation and PD1 axis blockade would be more effective than either approach alone. Methods: 8 adult patients with MCPyV-associated metastatic MCC without pre-existing immune deficiencies were enrolled. The safety and efficacy of ex vivo expanded MCPyV-specific T-cells plus HLA-upregulation (radiation or interferon) with (triple therapy) and without (double therapy) avelumab (mAb against PD-L1, dose 10 mg/kg IV q2weeks) were compared in 2 related phase I/II studies. Results: All 4 patients who received triple therapy (100%) are alive (median follow-up 10 months), and experienced objective responses (RECIST 1.1) with 3 of 4 sustained complete responses (CRs) at last follow-up (longest 13 mo). This compared favorably to outcomes among the 4 patients who received double therapy (3 with progression and 1 CR (25%) for 14 months before progression) and published data for avelumab monotherapy – response rate 32% and CR rate 9% in patients who had failed chemotherapy (Kaufman et al, Lancet Oncol, 2016). Grade 3-4 T cell-related adverse events were similar and anticipated in both groups, including transient lymphopenia (n = 7) and modest cytokine release syndrome lasting < 24 hours, manageable on the general ward (n = 4). No grade 3-4 toxicities were attributed to avelumab. Among patients receiving triple therapy, transferred T cells persisted, and peak frequencies correlated with rate of tumor regression. Conclusions: The combination of MCPyV-specific T cells, avelumab and HLA upregulation is safe and correlative studies suggest avelumab enhances the T cell responses to MCC. This strategy has potential for MCC treatment, and can be readily applied to other solid tumors. Clinical trial information: NCT01758458 and NCT02584829.

Tracking the Fate and Origin of Clinically Relevant Adoptively Transferred CD8+ T Cells In Vivo

Adoptively transferred tumor-specific cells can mediate tumor regression in cancers refractory to conventional therapy. Autologous polyclonal tumor-specific cytotoxic T cells (CTL) generated from peripheral blood and infused into patients with metastatic melanoma show enhanced persistence, compared to equivalent numbers of more extensively expanded monoclonal CTL, and are associated with complete remissions (CR) in select patients. We applied high-throughput T cell receptor Vβ sequencing (HTTCS) to identify individual clonotypes within CTL products, track them in vivo post-infusion and then deduce the pre-adoptive transfer (endogenous) frequencies of cells ultimately responsible for tumor regression. The summed in vivo post-transfer frequencies of the top 25 HTTCS-defined clonotypes originally detected in the infused CTL population were comparable to enumeration by binding of antigen peptide-HLA multimers, revealing quantitative HTTCS is a reliable, multimer-independent alternative. Surprisingly, the polyclonal CTL products were composed predominantly of clonotypes that were of very low frequency (VLF) in the endogenous samples, often below the limit of HTTCS detection (0.001%). In patients who achieved durable CRs, the composition of transferred CTLs was dominated (57-90%) by cells derived from a single VLF clonotype. Thus, HTTCS now reveals that tumor-specific CTL enabling long-term tumor control originate from endogenous VLF populations that exhibit proliferative/survival advantages. Along with results indicating that naïve cell populations are most likely to contain cells that exist at VLF within the repertoire, our results provide a strong rationale for favoring T cells arising from VLF populations and with early-differentiation phenotypes when selecting subset populations for adoptive transfer.

Combined IL-21-primed polyclonal CTL plus CTLA4 blockade controls refractory metastatic melanoma in a patient

Chapuis et al. demonstrate that the combination of adoptive cellular therapy with CTLA4 blockade induces long-term remission in a melanoma patient resistant to both modalities administered serially and individually.

Adoptive transfer of peripheral blood–derived, melanoma-reactive CD8⁺ cytotoxic T lymphocytes (CTLs) alone is generally insufficient to eliminate bulky tumors. Similarly, monotherapy with anti-CTLA4 infrequently yields sustained remissions in patients with metastatic melanoma. We postulated that a bolus of enhanced IL-21–primed polyclonal antigen-specific CTL combined with CTLA4 blockade might boost antitumor efficacy. In this first-in-human case study, the combination successfully led to a durable complete remission (CR) in a patient whose disease was refractory to both monoclonal CTL and anti-CTLA4. Long-term persistence and sustained anti-tumor activity of transferred CTL, as well as responses to nontargeted antigens, confirmed mutually beneficial effects of the combined treatment. In this first-in-human study, Chapuis et al. demonstrate that the combination of adoptive cellular therapy with CTLA4 blockade induces long-term remission in a melanoma patient resistant to both modalities administered serially and individually.

Interleukin-21 enhances rituximab activity in a cynomolgus monkey model of B cell depletion and in mouse B cell lymphoma models

Rituximab, a monoclonal antibody targeting CD20 on B cells, is currently used to treat many subtypes of B cell lymphomas. However, treatment is not curative and response rates are variable. Recombinant interleukin-21 (rIL-21) is a cytokine that enhances immune effector function and affects both primary and transformed B cell differentiation. We hypothesized that the combination of rIL-21 plus rituximab would be a more efficacious treatment for B cell malignancies than rituximab alone. We cultured human and cynomolgus monkey NK cells with rIL-21 and found that their activity was increased and proteins associated with antibody dependent cytotoxicity were up-regulated. Studies in cynomolgus monkeys modeled the effects of rIL-21 on rituximab activity against CD20 B cells. In these studies, rIL-21 activated innate immune effectors, increased ADCC and mobilized B cells into peripheral blood. When rIL-21 was combined with rituximab, deeper and more durable B cell depletion was observed. In another series of experiments, IL-21 was shown to have direct antiproliferative activity against a subset of human lymphoma cell lines, and combination of murine IL-21 with rituximab yielded significant survival benefits over either agent alone in xenogeneic mouse tumor models of disseminated lymphoma. Therefore, our results do suggest that the therapeutic efficacy of rituximab may be improved when used in combination with rIL-21.

Abstract B71: Protective immunizations using cultured peripheral blood cells

Murine models of Autologous Cellular Immunotherapy (ACI) have been useful tools for understanding the mechanisms by which human immunotherapy may work. Sipuleucel-T is an FDA approved therapeutic for the treatment of asymptomatic or minimally symptomatic, metastatic castration-resistant metastatic prostate cancer; Phase 3 studies demonstrated a statistically significant prolongation in overall survival when compared to a control group. Sipuleucel-T is manufactured by activating peripheral blood mononuclear cells (PBMC), including antigen presenting cells, with a recombinant protein fusion of prostatic acid phosphatase and granulocyte macrophage colony-stimulating factor (GM-CSF). We have previously reported a method for the use of cultured PBMC in a pre-clinical setting to elicit a T cell response against a tumor associated antigen, and to protect mice from tumors expressing that antigen. The model antigen we used was human Carbonic Anhydrase IX (hCA9). Mouse PBMCs were cultured with the antigen fused to murine GM-CSF (hCA9-GM) or with GM-CSF alone. Mice were immunized 3 times with these cells at 2 week intervals. Satellite mice were then harvested for evaluation of in vitro T cell response (antigen recall assay) and the remaining mice were inoculated with hCA9-expressing tumor cells, and tumor growth followed over time. Immunized mice mounted a robust T cell response in vitro to hCA9 in a dose dependent manner, a result that correlated with protection from tumor challenge in mice immunized with PBMC cultured in hCA9-GM.

Herein, we investigate the cellular requirements for protection against tumor challenge and ability of a selective Toll-like receptor (TLR) 9 agonist to enhance the potency of this cellular immunotherapy. To investigate the importance of T cells for anti-tumor responses, we demonstrate that selective depletion of either CD4 or CD8 T cells results in a diminution or loss of protection toward tumor challenge; indicating T cells are necessary in vivo to prevent tumor growth. Next, to stimulate antigen specific T cell activity in the ACI therapy, relative to hCA9 antigen alone, cells were cultured with hCA9-GM antigen in combination with the TLR9 agonist CpG1826. Addition of CpG1826 resulted in significant accumulation of pro-inflammatory cytokines (IL-1b, IL-6, IL-10, TNFa, KC and IFNg) in the culture medium, and to higher surface expression of activation and co-stimulatory markers (CD25, CD69, CD80, CD86, and MHC Class II) on cultured cells. Moreover, inclusion of CpG1826 to cultures enhanced protection against tumor cell challenge. Interestingly, this enhancement in potency was not associated with increased antigen specific T cell responses, as measured in the in vitro antigen recall assay.

In conclusion, we show that, in mice, unfractionated white blood cells collected from peripheral blood can be harnessed to mount effective anti-tumor immune responses and that TLR9 agonists complement this approach. Furthermore, this active immunotherapy triggers a balanced immune response relying on the activity of both CD4 and CD8 T cells. Future studies will be aimed at evaluating the role of various PBMC subsets (T cell, B cell and myeloid cell) in protecting mice from tumor cell challenge.

Citation Format: Kenneth A. Brasel, Craig Meagher, Marykay Ligocki, Lauren Cerretti, Felecia Wagener, Sam Li, James Trager. Protective immunizations using cultured peripheral blood cells. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr B71.

Abstract B18: Combining selective toll-like receptor 9 (TLR9) agonists and GM-CSF activity for potentiating cellular activation in active cell immunotherapy (ACI)

Sipuleucel-T (Provenge®), indicated for the treatment of asymptomatic or minimally symptomatic metastatic castration resistant prostate cancer, is the first FDA-approved Active Cellular Immunotherapy (ACI). Here we describe the development of a therapeutic ACI for the treatment of renal, lung, colon, and cervical cancer. Like PROVENGE®, this new ACI utilizes a recombinant antigen consisting of carbonic anhydrase IX (CA9) linked to GM-CSF (CA9:GM-CSF). In these studies, we investigated the effects of incorporating selective TLR9 agonists on in vitro measures of ACI potency.

Initially, employing a panel of proprietary TLR9 agonists, we compared the phenotype of antigen presenting cells (APC) following culture of PBMC from normal healthy donors with either CA9:GM-CSF or CA9:GM-CSF plus TLR9 agonist. While antigen derived GM-CSF activity matured APC, characterized by elevated cell surface expression of CD40, CD54, CD80 and CD86, proprietary agonists for TLR9 further enhanced expression of CD40, CD80, and CD86. By extension, stimulation via TLR9 elicited increased costimulatory capacity of CD14+ large APC in allogeneic mixed lymphocyte response assays. Elevated levels of MCP1-3 in culture supernatant were consistent with APC activation, and notably, viability of CD14+ large APC was unaffected following TLR9 stimulation within the ACI product. Interestingly, using an HLA class II restricted CA9-specific T cell hybridoma reporter assay, staggering the addition of CA9:GM-CSF prior to TLR9 agonist was important to maximize antigen uptake and peptide presentation. Collectively, antigen derived GM-CSF activity is robust at activating APC and certain TLR9 agonists strengthen this effect.

Next, as determined by cell surface expression of activation markers (CD27, CD38, CD40, CD54, CD86, IgD), the potential for TLR9 agonists to activate B cells was examined. Relative to cultures supplemented with only CA9:GM-CSF, TLR9 agonists were sufficient to produce a generalized B cell activation pattern consisting of enhanced cell surface expression of CD38, CD40, CD86, and CD54; while expression of CD27 was decreased. Expression of IgD remained unchanged. Associated with the prominent pattern of B cell activation was a marked increase in the accumulation of proinflammatory Type-1 like growth factors (IFN-α, IFN-γ, CXCL9, CXCL10, CCL3, and CCL4) in response to each TLR9 agonist. Despite the degree of B cell activation, this phenotype did not correlate with cellular activation of any T cell subset; suggesting the inflammatory signature resulting from TLR9 stimulation is primarily driven by B cells and/or APC in the ACI setting. Importantly, IL-10 levels were significantly enhanced following TLR9 stimulation, raising the possibility for enhanced regulatory cell activity, but changes in the frequency of regulatory CD4+ T cells were not observed. However, continuing studies are aimed at examining whether regulatory B cell numbers may be enhanced. Thus, in the ACI product, TLR9 agonists potentiate B cell activation and represent powerful polarizers of predominantly Type 1-like cytokine responses.

Overall, agonists of TLR9 are compatible with the ACI platform for potentially enhancing antigen specific immunotherapy of cancer. In current experiments, the capacity of TLR9 agonists to enhance cross-priming and generate cytotoxic T cell responses is under investigation.

Citation Format: Jason Chinn, Crystal Cummings, Felecia Wagener, Shaarwari Sridhar, Kien Khuu-Duong, Xinhui Ge, Karen Yoshino, Sam Li, Lisa Martel, Chris Ramsborg, Ken Brasel, James Trager, Craig Meagher. Combining selective toll-like receptor 9 (TLR9) agonists and GM-CSF activity for potentiating cellular activation in active cell immunotherapy (ACI). [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr B18.

Diversity of the CD8+ T-cell response to herpes simplex virus type 2 proteins among persons with genital herpes

Cytolytic T cells play a major role in controlling herpes simplex virus type 2 (HSV-2) infections in humans. In an effort to more thoroughly evaluate the response to HSV-2 directly, ex vivo, we developed an enzyme-linked immunospot (ELISPOT) assay that utilized pools of overlapping synthetic peptides presented by autologous dendritic cells to purified CD8(+) T cells. Donor response rates to individual open reading frames (ORFs) ranged from fewer than 5% responding to as many as 70% responding, with the greatest frequency of responses (by ORF) being directed against UL39, UL25, UL27, ICP0, UL46, and UL47 in descending order of frequency. HSV-2-seropositive subjects responded to as few as 3 or as many as 46 of the 48 ORFs tested, with a median of 11 ORFs recognized. HLA-B*07 expression correlated with stronger responses overall that were directed primarily against UL49 and UL46. Cumulative precursor frequencies in the blood ranged from 500 to almost 6,000 HSV-2 spot-forming units/10(6) CD8(+) T cells. The magnitude and breadth of the response in the infected population were greater than previously appreciated. Whether this variability in the CD8(+) T-cell response within individuals is associated with the frequency of viral reactivation warrants further study.

Phosphoinositid-3-Kinase- (PI3-K) Expression

Phosphoinositide 3-kinase (PI3-K) is a heterodimeric enzyme involved in the regulation of mitogenesis, apoptosis, cell adhesion, and motility. PI3-K was suggested as a protooncogene in human cancer. To determine the expression of PI3-K during cancerogenesis and tumor invasion of HNSCC, we investigated normal and dysplastic epithelium of the oral cavity, squamous cell carcinoma and lymph node metastasis by immunohistochemistry. The strongest immunoreactivity for p85alpha and p110alpha was found in invasive tumors and their metastases. Carcinomas in situ showed a focal positivity. Dysplasias and normal epithelium reacted predominantly negatively. The PI3-K inhibitor LY294002 inhibited proliferation and invasion of the HNSCC cell line CAL-27 and induced apoptosis in vitro. Our data suggest PI3-K as a marker of malignancy and tumor invasion. We suggest including PI3-K in the multistep carcinogenesis model of HNSCC. In addition, PI3-K is a potential target for pharmacological intervention.

The Epstein-Barr virus BARF1 gene encodes a novel, soluble colony-stimulating factor-1 receptor

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus associated with infectious mononucleosis and several tumors. The BARF1 gene is transcribed early after EBV infection from the BamHI A fragment of the EBV genome. Evidence shown here indicates that the BARF1 protein is secreted into the medium of transfected cells and from EBV-carrying B cells induced to allow lytic replication of the virus. Expression cloning identified colony-stimulating factor-1 (CSF-1) as a ligand for BARF1. Computer-assisted analyses indicated that subtle amino acid sequence homology exists between BARF1 and c-fins, the cellular proto-oncogene that is the receptor for CSF-1. Recombinant BARF1 protein was found to be biologically active, and it neutralized the proliferative effects of human CSF-1 in a dose-dependent fashion when assayed in vitro. Since CSF-1 is a pleiotropic cytokine best known for its differentiating effects on macrophages, these data suggest that BARF1 may function to modulate the host immune response to EBV infection.