Virus-specific memory T cells populate tumors and can be repurposed as a tumor immunotherapy

The immunosuppressive tumor microenvironment limits the success of current immunotherapies. The host retains memory T cells specific for previous infections throughout the entire body that are capable of executing potent and immediate immunostimulatory functions. Here we show that virus-specific memory T cells extend their surveillance to mouse and human tumors. Reactivating these antiviral T cells can arrest growth of checkpoint blockade-resistant and poorly immunogenic tumors in mice after injecting adjuvant-free non-replicating viral peptides into tumors. Peptide mimics a viral reinfection event to memory CD8+ T cells, triggering antigen presentation and cytotoxic pathways within the tumor, activating dendritic cells and natural killer cells, and recruiting the adaptive immune system. Viral peptide treatment of ex vivo human tumors recapitulates immune activation gene expression profiles observed in mice. Lastly, peptide therapy renders resistant mouse tumors susceptible to PD-L1 blockade. Thus, re-stimulating known antiviral immunity may provide a unique therapeutic approach for cancer immunotherapy.

Abstract B182: Repurposing antiviral T-cells to fight tumors

Overcoming the immunosuppressive tumor microenvironment and localizing adoptive cell and checkpoint blockade therapies to solid tumors remain major impediments to successful cancer immunotherapy. Humans experience many viral infections. Once controlled, the host retains memory T-cells throughout the entire body to sense reinfection or recrudescence. Mouse models have demonstrated that when that same virus is reencountered, these T-cells sound an alarm that induces a local immunostimulatory environment that activates and recruits many arms of the immune system. We observed that, like healthy tissue, human tumors are commonly surveyed by memory T-cells specific for previously encountered viral infections. Antiviral T-cell immune surveillance of tumors was recapitulated in mouse cancer models. We tested and discovered that local delivery of adjuvant-free peptide, derived from previously encountered mouse viral infections, recapitulated the sensing and alarm T-cell function within the tumor: recruiting and activating both the innate and adaptive immune system. This approach induced intratumoral accumulation of granzyme B+ CD8+ T and NK cells, and activated dendritic cells within the tumor and subsequently within the tumor draining lymph node. In addition to stimulating the tumor microenvironment, preliminary data suggest activated antiviral T-cells directly killed peptide coated tumor cells. Viral peptide administration arrested rapidly growing and poorly immunogenic B16 melanomas in vivo and this treatment synergized with anti-PD-L1 checkpoint blockade to eliminate measurable tumors, and prevented recurrence in 34% of mice. Most cured mice rejected subsequent B16 tumor challenges at distant sites, indicating that effective systemic tumor-specific immunity was established. In support of the hypothesis that this approach could translate to human cancer immunotherapy, we found that viral peptide alarm therapy of freshly isolated human tumors drove similar immune activation to that observed in mice. This study demonstrates that natural and existing antiviral immunity can be repurposed to fight tumors without the need for adjuvant, vaccination, or personalized identification of immunogenic tumor neoantigens.

Citation Format: Pamela C. Rosato, Sathi Wijeyesinghe, J. Michael Stolley, Christine Nelson, Rachel L. Davis, Luke S. Manlove, Christopher A. Pennell, Bruce R. Blazar, Clark C. Chen, Melissa A. Geller, Vaiva Vezys, David Masopust. Repurposing antiviral T-cells to fight tumors [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B182.

Abstract 1789: CD30+T regulatory cells, but not CD30+CD8 T cells, are impaired following brentuximab vedotin treatment in vitro and in vivo

Brentuximab vedotin (BV) is an antibody-drug conjugate (ADC) directed against CD30, a TNF receptor superfamily (TNFRSF) member highly expressed on Reed Sternberg cells in Hodgkin lymphoma (HL) and also commonly expressed in a number of other lymphoid malignancies such as ALCL and CTCL. BV consists of a monoclonal antibody conjugated to monomethyl auristatin E (MMAE), a highly potent microtubule-disrupting agent. MMAE-based ADC antitumor activity primarily results from intracellular payload release, leading to mitotic arrest and apoptotic cell death, although secondary MOAs may exist. CD30 is mostly absent on resting peripheral lymphocytes, but is known to be transiently upregulated on both CD4+ and CD8+ T cells following activation. Recently, CD30 was identified, by separate research groups, as a marker differentially upregulated by human intratumoral T regulatory cells (Tregs). This recent observation raises the possibility that BV could target and eliminate intratumoral CD30+ Tregs. Abundant evidence shows that tumor-specific CD8+ T cells are paramount to antitumor immunity. In contrast, tumor-resident T regulatory cells have been shown to counteract immunosurveillance and promote tumor escape. Given that CD30 may be expressed on both activated CD8+ T cells and intratumoral Tregs, we explored the outcome of BV treatment on each cell type. In this work, we show that BV directly depleted inducible and primary CD30+ Tregs in vitro, in a dose-dependent manner, while CD30+ CD8+ T cells were unaffected. Moreover, BV selectively depleted Tregs in a Treg:CD8 T cell co-culture suppression assay, resulting in expansion of proliferating CD8+ T cells. In vivo, using a humanized mouse model of graft-versus-host disease (xeno-GVHD), treatment of mice with BV significantly reduced splenic Treg numbers, while amplifying total xeno-reactive CD8+ cytotoxic T cells. In an effort to understand BV's selective impairment of Tregs, we evaluated CD30 expression following in vitro activation with CD3/CD28. Freshly isolated Tregs showed notably accelerated CD30 expression kinetics along with significantly higher peak receptor number compared to CD8+ T cells. Furthermore, assays confirmed that the heightened receptor expression on Tregs translated into increased BV internalization and drug-linker cleavage. Finally, CD8+ T cells were much more efficient at effluxing rhodamine than Tregs, suggesting lowered drug accumulation and exposure over time. Together, these data raise the novel possibility that brentuximab vedotin may be able to positively impact the Treg:CD8 T cell balance in the tumor microenvironment through selective depletion of CD30+ Tregs, but not activated CD8+ T cells.

Citation Format: Ryan A. Heiser, Bryan M. Grogan, Luke S. Manlove, Shyra J. Gardai. CD30+T regulatory cells, but not CD30+CD8 T cells, are impaired following brentuximab vedotin treatment in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1789.

Abstract B056: Harnessing tissue resident memory T cells to combat solid tumors

The immunosuppressive tumor microenvironment is a major hurdle to overcome in the development of successful cancer therapies. Newly discovered tissue resident memory CD8+ T cells (TRM) function to create a potent immunostimulatory environment to protect against local reinfection. As TRM are present in abundance in nearly every tissue and can be triggered by cognate peptide alone, without adjuvant, we tested whether we could hijack infection-specific TRM in tumors to reverse the immunosuppressive tumor microenvironment and enhance existing immunotherapies. Mice with established vesicular stomatitis virus (VSV)-specific skin TRM were challenged with the transplantable B16 melanoma cell line. We find VSV-specific CD8+ T cells within established tumors and within 12 hours of cognate peptide delivery, these cells upregulate IFNγ, CD25, and Granzyme B. This led to 1) tumor NK cell activation through Granzyme B upregulation, 2) NK cell recruitment to the tumor, and 3) CD8+ T cell recruitment to the tumor. Ongoing studies are testing whether TRM immunotherapy synergizes with CAR T cell and checkpoint blockade immunotherapies for eradication of recalcitrant tumors. These results demonstrate proof of principal efficacy for exploiting infection-specific TRM as a tumor immunotherapy.

Citation Format: Pamela C. Rosato, Luke S. Manlove, Christine E. Nelson, Christopher A. Pennell, Vaiva Vezys, David Masopust. Harnessing tissue resident memory T cells to combat solid tumors [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B056.

Quantifying Memory CD8 T Cells Reveals Regionalization of Immunosurveillance

Memory CD8 T cells protect against intracellular pathogens by scanning host cell surfaces; thus, infection detection rates depend on memory cell number and distribution. Population analyses rely on cell isolation from whole organs, and interpretation is predicated on presumptions of near complete cell recovery. Paradigmatically, memory is parsed into central, effector, and resident subsets, ostensibly defined by immunosurveillance patterns but in practice identified by phenotypic markers. Because isolation methods ultimately inform models of memory T cell differentiation, protection, and vaccine translation, we tested their validity via parabiosis and quantitative immunofluorescence microscopy of a mouse memory CD8 T cell population. We report three major findings: lymphocyte isolation fails to recover most cells and biases against certain subsets, residents greatly outnumber recirculating cells within non-lymphoid tissues, and memory subset homing to inflammation does not conform to previously hypothesized migration patterns. These results indicate that most host cells are surveyed for reinfection by segregated residents rather than by recirculating cells that migrate throughout the blood and body.

Heterologous Vaccination and Checkpoint Blockade Synergize To Induce Antileukemia Immunity

Checkpoint blockade-based immunotherapies are effective in cancers with high numbers of nonsynonymous mutations. In contrast, current paradigms suggest that such approaches will be ineffective in cancers with few nonsynonymous mutations. To examine this issue, we made use of a murine model of BCR-ABL(+) B-lineage acute lymphoblastic leukemia. Using a principal component analysis, we found that robust MHC class II expression, coupled with appropriate costimulation, correlated with lower leukemic burden. We next assessed whether checkpoint blockade or therapeutic vaccination could improve survival in mice with pre-established leukemia. Consistent with the low mutation load in our leukemia model, we found that checkpoint blockade alone had only modest effects on survival. In contrast, robust heterologous vaccination with a peptide derived from the BCR-ABL fusion (BAp), a key driver mutation, generated a small population of mice that survived long-term. Checkpoint blockade strongly synergized with heterologous vaccination to enhance overall survival in mice with leukemia. Enhanced survival did not correlate with numbers of BAp:I-A(b)-specific T cells, but rather with increased expression of IL-10, IL-17, and granzyme B and decreased expression of programmed death 1 on these cells. Our findings demonstrate that vaccination to key driver mutations cooperates with checkpoint blockade and allows for immune control of cancers with low nonsynonymous mutation loads.

Adaptive Immunity to Leukemia Is Inhibited by Cross-Reactive Induced Regulatory T Cells

BCR-ABL(+) acute lymphoblastic leukemia patients have transient responses to current therapies. However, the fusion of BCR to ABL generates a potential leukemia-specific Ag that could be a target for immunotherapy. We demonstrate that the immune system can limit BCR-ABL(+) leukemia progression although ultimately this immune response fails. To address how BCR-ABL(+) leukemia escapes immune surveillance, we developed a peptide: MHC class II tetramer that labels endogenous BCR-ABL-specific CD4(+) T cells. Naive mice harbored a small population of BCR-ABL-specific T cells that proliferated modestly upon immunization. The small number of naive BCR-ABL-specific T cells was due to negative selection in the thymus, which depleted BCR-ABL-specific T cells. Consistent with this observation, we saw that BCR-ABL-specific T cells were cross-reactive with an endogenous peptide derived from ABL. Despite this cross-reactivity, the remaining population of BCR-ABL reactive T cells proliferated upon immunization with the BCR-ABL fusion peptide and adjuvant. In response to BCR-ABL(+) leukemia, BCR-ABL-specific T cells proliferated and converted into regulatory T (Treg) cells, a process that was dependent on cross-reactivity with self-antigen, TGF-β1, and MHC class II Ag presentation by leukemic cells. Treg cells were critical for leukemia progression in C57BL/6 mice, as transient Treg cell ablation led to extended survival of leukemic mice. Thus, BCR-ABL(+) leukemia actively suppresses antileukemia immune responses by converting cross-reactive leukemia-specific T cells into Treg cells.

Interleukin-2 and STAT5 in regulatory T cell development and function

Interleukin-2 and its downstream target STAT5 have effects on many aspects of immune function. This has been perhaps best documented in regulatory T cells. In this review we summarize the initial findings supporting a role for IL2 and STAT5 in regulatory T cell development and outline more recent studies describing how this critical signaling pathway entrains regulatory T cell differentiation and affects regulatory T cell function.

Modular assembly of transposon integratable multigene vectors using RecWay assembly

Studying complex biological processes such as cancer development, stem cell induction and transdifferentiation requires the modulation of multiple genes or pathways at one time in a single cell. Herein, we describe straightforward methods for rapid and efficient assembly of bacterial marker free multigene cassettes containing up to six complementary DNAs/short hairpin RNAs. We have termed this method RecWay assembly, as it makes use of both Cre recombinase and the commercially available Gateway cloning system. Further, because RecWay assembly uses truly modular components, it allows for the generation of randomly assembled multigene vector libraries. These multigene vectors are integratable, and later excisable, using the highly efficient piggyBac (PB) DNA transposon system. Moreover, we have dramatically improved the expression of stably integrated multigene vectors by incorporation of insulator elements to prevent promoter interference seen with multigene vectors. We demonstrate that insulated multigene PB transposons can stably integrate and faithfully express up to five fluorescent proteins and the puromycin-thymidine kinase resistance gene in vitro, with up to 70-fold higher gene expression compared with analogous uninsulated vectors. RecWay assembly of multigene transposon vectors allows for widely applicable modelling of highly complex biological processes and can be easily performed by other research laboratories.