Shawn M. Jensen

Signaling Through OX40 Enhances Antitumor Immunity

The existence of tumor-specific T cells, as well as their ability to be primed in cancer patients, confirms that the immune response can be deployed to combat cancer. However, there are obstacles that must be overcome to convert the ineffective immune response commonly found in the tumor environment to one that leads to sustained destruction of tumor. Members of the tumor necrosis factor (TNF) superfamily direct diverse immune functions. OX40 and its ligand, OX40L, are key TNF members that augment T-cell expansion, cytokine production, and survival. OX40 signaling also controls regulatory T-cell differentiation and suppressive function. Studies over the past decade have demonstrated that OX40 agonists enhance antitumor immunity in preclinical models using immunogenic tumors; however, treatment of poorly immunogenic tumors has been less successful. Combining strategies that prime tumor-specific T cells together with OX40 signaling could generate and maintain a therapeutic antitumor immune response.

Tumor-Derived Autophagosome Vaccine: Induction of Cross-Protective Immune Responses against Short-lived Proteins through a p62-Dependent Mechanism

Purpose: Tumor-specific antigens of 3-methylcholanthrene (MCA)-induced sarcomas were defined by the narrow immune responses they elicited, which uniquely rejected the homologous tumor, with no cross-reactions between independently derived syngeneic MCA-induced tumors. This study examines whether an autophagosome-enriched vaccine derived from bortezomib-treated sarcomas can elicit an immune response that cross-reacts with other unique sarcomas. Experimental Design: Mice were vaccinated with either MCA-induced sarcomas or autophagosomes derived from those tumors and later challenged with either homologous or nonhomologous sarcomas. In addition, 293 cells expressing a model antigen were used to understand the necessity of short-lived proteins (SLiP) in this novel vaccine. These findings were then tested in the sarcoma model. Autophagosomes were characterized by Western blotting and fluorescent microscopy, and their ability to generate immune responses was assessed in vitro by carboxyfluorescein succinimidyl ester dilution of antigen-specific T cells and in vivo by monitoring tumor growth. Results: In contrast to a whole-cell tumor vaccine, autophagosomes isolated from MCA-induced sarcomas treated with a proteasome inhibitor prime T cells that cross-react with different sarcomas and protect a significant proportion of vaccinated hosts from a nonhomologous tumor challenge. Ubiquitinated SLiPs, which are stabilized by proteasome blockade and delivered to autophagosomes in a p62/sequestosome-dependent fashion, are a critical component of the autophagosome vaccine, as their depletion limits vaccine efficacy. Conclusion: This work suggests that common short-lived tumor-specific antigens, not physiologically available for cross-presentation, can be sequestered in autophagosomes by p62 and used as a vaccine to elicit cross-protection against independently derived sarcomas. Clin Cancer Res; 17(20); 6467–81. ©2011 AACR.

Tumor‐specific CD4+ T cells maintain effector and memory tumor‐specific CD8+ T cells

Immunotherapies that augment antitumor T cells have had recent success for treating patients with cancer. Here we examined whether tumor‐specific CD4+ T cells enhance CD8+ T‐cell adoptive immunotherapy in a lymphopenic environment. Our model employed physiological doses of tyrosinase‐related protein 1‐specific CD4+ transgenic T cells‐CD4+ T cells and pmel‐CD8+ T cells that when transferred individually were subtherapeutic; however, when transferred together provided significant (p ≤ 0.001) therapeutic efficacy. Therapeutic efficacy correlated with increased numbers of effector and memory CD8+ T cells with tumor‐specific cytokine expression. When combined with CD4+ T cells, transfer of total (naïve and effector) or effector CD8+ T cells were highly effective, suggesting CD4+ T cells can help mediate therapeutic effects by maintaining function of activated CD8+ T cells. In addition, CD4+ T cells had a pronounced effect in the early posttransfer period, as their elimination within the first 3 days significantly (p < 0.001) reduced therapeutic efficacy. The CD8+ T cells recovered from mice treated with both CD8+ and CD4+ T cells had decreased expression of PD‐1 and PD‐1‐blockade enhanced the therapeutic efficacy of pmel‐CD8 alone, suggesting that CD4+ T cells help reduce CD8+ T‐cell exhaustion. These data support combining immunotherapies that elicit both tumor‐specific CD4+ and CD8+ T cells for treatment of patients with cancer.

Treatment of malignant pleural mesothelioma by fibroblast activation protein-specific re-directed T cells

IntroductionMalignant pleural mesothelioma (MPM) is an incurable malignant disease, which results from chronic exposition to asbestos in at least 70% of the cases. Fibroblast activation protein (FAP) is predominantly expressed on the surface of reactive tumor-associated fibroblasts as well as on particular cancer types. Because of its expression on the cell surface, FAP is an attractive target for adoptive T cell therapy. T cells can be re-directed by retroviral transfer of chimeric antigen receptors (CAR) against tumor-associated antigens (TAA) and therefore represent a therapeutic strategy of adoptive immunotherapy.MethodsTo evaluate FAP expression immunohistochemistry was performed in tumor tissue from MPM patients. CD8+ human T cells were retrovirally transduced with an anti-FAP-F19-∆CD28/CD3ζ-CAR. T cell function was evaluated in vitro by cytokine release and cytotoxicity assays. In vivo function was tested with an intraperitoneal xenograft tumor model in immunodeficient mice.ResultsFAP was found to be expressed in all subtypes of MPM. Additionally, FAP expression was evaluated in healthy adult tissue samples and was only detected in specific areas in the pancreas, the placenta and very weakly for cervix and uterus. Expression of the anti-FAP-F19-∆CD28/CD3ζ-CAR in CD8+ T cells resulted in antigen-specific IFNγ release. Additionally, FAP-specific re-directed T cells lysed FAP positive mesothelioma cells and inflammatory fibroblasts in an antigen-specific manner in vitro. Furthermore, FAP-specific re-directed T cells inhibited the growth of FAP positive human tumor cells in the peritoneal cavity of mice and significantly prolonged survival of mice.ConclusionFAP re-directed CD8+ T cells showed antigen-specific functionality in vitro and in vivo. Furthermore, FAP expression was verified in all MPM histotypes. Therefore, our data support performing a phase I clinical trial in which MPM patients are treated with adoptively transferred FAP-specific re-directed T cells.

Partial CD4 Depletion Reduces Regulatory T Cells Induced by Multiple Vaccinations and Restores Therapeutic Efficacy

Purpose: A single vaccination of intact or reconstituted-lymphopenic mice (RLM) with a granulocyte macrophage colony-stimulating factorsecreting B16BL6-D5 melanoma cell line induces protective antitumor immunity and T cells that mediate the regression of established melanoma in adoptive immunotherapy studies. We wanted to study if multiple vaccinations during immune reconstitution of the lymphopenic host would maintain a potent antitumor immune response. Experimental Design: RLM were vaccinated multiple times over a 40-day period. Spleens were isolated from these mice, activated in vitro, and adoptively transferred into mice bearing 3-day experimental pulmonary metastases. Results: Multiple vaccinations, rather than boosting the immune response, significantly reduced therapeutic efficacy of adoptive immunotherapy and were associated with an increased frequency and absolute number of CD3+CD4+Foxp3+ T regulatory (Treg) cells. Anti-CD4 administration reduced the absolute number of Treg cells 9-fold. Effector T-cells generated from anti-CD4treated mice were significantly (P < 0.0001) more therapeutic in adoptive transfer studies than T cells from multiply vaccinated animals with a full complement of CD4+ cells. Conclusion: These results suggest that CD4+ Treg cells limit the efficacy of multiple vaccinations and that timed partial depletion of CD4+ T cells may reduce suppression and tip-the-balance in favor of therapeutic antitumor immunity. The recent failure of large phase III cancer vaccine clinical trials, wherein patients received multiple vaccines, underscores the potential clinical relevance of these findings. (Clin Cancer Res 2009;15(22):688190)

Disruption of TGF-β Signaling Prevents the Generation of Tumor-Sensitized Regulatory T Cells and Facilitates Therapeutic Antitumor Immunity

Regulatory T (Treg) cells represent a major roadblock to the induction of antitumor immunity through vaccine approaches. TGF-β is a cytokine implicated in the generation and maintenance of Treg cells, as well as in their suppressive function. These experiments examined whether the generation of tumor-sensitized Treg cells was TGF-β dependent and evaluated whether TGF-β produced by Treg cells blocked the priming of tumor-specific T cells in vaccinated reconstituted lymphopenic mice. We show that tumor-sensitized Treg cells (CD25+/FoxP3+) obtained from tumor-bearing mice block the generation of tumor-specific T cells in reconstituted lymphopenic mice. Strikingly, this suppression is absent if tumor-sensitized Treg cells are acquired from tumor-bearing mice expressing the dominant-negative TGFβRII in T cells. This loss of suppression was a result of the crucial role of TGF-β in generating tumor-sensitized Treg cells, and not due to the insensitivity of naive or tumor-primed effector T cells to the direct suppressive influence of TGF-β. We conclude that blocking TGF-β in a tumor-bearing host can inhibit the induction of highly suppressive tumor-sensitized Treg cells. These data suggest that an integrative strategy combining “up-front” Treg cell ablation followed by vaccination and TGF-β blockade may limit generation of new tumor-sensitized Treg cells and improve the generation of therapeutic immune responses in patients with cancer.

Increased Frequency of Suppressive Regulatory T Cells and T Cell-Mediated Antigen Loss Results in Murine Melanoma Recurrence

Therapeutic treatment of large established tumors using immunotherapy has yielded few promising results. We investigated whether adoptive transfer of tumor-specific CD8+ T cells, together with tumor-specific CD4+ T cells, would mediate regression of large established B16BL6-D5 melanomas in lymphopenic Rag1−/− recipients devoid of regulatory T cells. The combined adoptive transfer of subtherapeutic doses of both TRP1-specific TCR transgenic Rag1−/− CD4+ T cells and gp100-specific TCR transgenic Rag1−/− CD8+ T cells into lymphopenic recipients, who received vaccination, led to regression of large (100–400 mm2) melanomas. The same treatment strategy was ineffective in lymphoreplete wild-type mice. Twenty-five percent of mice (15/59) had tumors recur (15–180 d postregression). Recurrent tumors were depigmented and had decreased expression of gp100, the epitope targeted by the CD8+ T cells. Mice with recurrent melanoma had increased CD4+Foxp3+ TRP1-specific T cells compared with mice that did not show evidence of disease. Importantly, splenocytes from mice with recurrent tumor were able to suppress the in vivo therapeutic efficacy of splenocytes from tumor-free mice. These data demonstrate that large established tumors can be treated by a combination of tumor-specific CD8+ and CD4+ T cells. Additionally, recurrent tumors exhibited decreased Ag expression, which was accompanied by conversion of the therapeutic tumor-specific CD4+ T cell population to a Foxp3+CD4+ regulatory T cell population.

Cancer Immunotherapy: The Role Regulatory T Cells Play and What Can be Done to Overcome their Inhibitory Effects

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.

Timing of PD-1 Blockade Is Critical to Effective Combination Immunotherapy with Anti-OX40.

Purpose: Antibodies specific for inhibitory checkpoints PD-1 and CTLA-4 have shown impressive results against solid tumors. This has fueled interest in novel immunotherapy combinations to affect patients who remain refractory to checkpoint blockade monotherapy. However, how to optimally combine checkpoint blockade with agents targeting T-cell costimulatory receptors, such as OX40, remains a critical question. Experimental Design: We utilized an anti-PD-1–refractory, orthotopically transplanted MMTV-PyMT mammary cancer model to investigate the antitumor effect of an agonist anti-OX40 antibody combined with anti-PD-1. As PD-1 naturally aids in immune contraction after T-cell activation, we treated mice with concurrent combination treatment versus sequentially administering anti-OX40 followed by anti-PD-1. Results: The concurrent addition of anti-PD-1 significantly attenuated the therapeutic effect of anti-OX40 alone. Combination-treated mice had considerable increases in type I and type II serum cytokines and significantly augmented expression of inhibitory receptors or exhaustion markers CTLA-4 and TIM-3 on T cells. Combination treatment increased intratumoral CD4+ T-cell proliferation at day 13, but at day 19, both CD4+ and CD8+ T-cell proliferation was significantly reduced compared with untreated mice. In two tumor models, sequential combination of anti-OX40 followed by anti-PD-1 (but not the reverse order) resulted in significant increases in therapeutic efficacy. Against MMTV-PyMT tumors, sequential combination was dependent on both CD4+ and CD8+ T cells and completely regressed tumors in approximately 30% of treated animals. Conclusions: These results highlight the importance of timing for optimized therapeutic effect with combination immunotherapies and suggest the testing of sequencing in combination immunotherapy clinical trials. Clin Cancer Res; 23(20); 6165–77. ©2017 AACR. See related commentary by Colombo, p. 5999

Induction of Circulating Tumor-reactive Cd8+ T Cells After Vaccination of Melanoma Patients With the gp100209-2m Peptide

Patients with stage I-III melanoma were vaccinated with the modified HLA-A2–binding gp100209-2M-peptide after complete surgical resection of their primary lesion and sentinel node biopsy. Cytoplasmic interferon-γ production by freshly thawed peripheral blood mononuclear cells (direct ex vivo analysis) or by peripheral blood mononuclear cells subjected to 1 cycle of in vitro sensitization with peptide, interleukin-2, and interleukin-15 was measured following restimulation with the modified and native gp100 peptides, and also A2+gp100+ melanoma cell lines. Peptide-reactive and tumor-reactive T cells were detected in 79% and 66% of selected patients, respectively. Patients could be classified into 3 groups according to their vaccine-elicited T-cell responses. One group of patients responded only to the modified peptide used for immunization, whereas another group of patients reacted to both the modified and native gp100 peptides, but not to naturally processed gp100 antigen on melanoma cells. In the third group of patients, circulating CD8+ T cells recognized A2+gp100+ melanoma cell lines and also both the modified and native peptides. T cells with a low functional avidity, which were capable of lysing tumor cells only if tumor cells were first pulsed by the exogenous administration of native gp100209-217 peptide were identified in most patients. These results indicate that vaccination with a modified gp100 peptide induced a heterogeneous group of gp100-specific T cells with a spectrum of functional avidities; however, high avidity, tumor-reactive T cells were detected in the majority of patients.