Decreased tumor surveillance after adoptive T-cell therapy

A replicating LCMV-based vaccine for the treatment of solid tumors

Harnessing the immune system to eradicate tumors requires identification and targeting of tumor antigens, including tumor-specific neoantigens and tumor-associated self-antigens. Tumor-associated antigens are subject to existing immune tolerance, which must be overcome by immunotherapies. Despite many novel immunotherapies reaching clinical trials, inducing self-antigen-specific immune responses remains challenging. Here, we systematically investigate viral-vector-based cancer vaccines encoding a tumor-associated self-antigen (TRP2) for the treatment of established melanomas in preclinical mouse models, alone or in combination with adoptive T cell therapy. We reveal that, unlike foreign antigens, tumor-associated antigens require replication of lymphocytic choriomeningitis virus (LCMV)-based vectors to break tolerance and induce effective antigen-specific CD8+ T cell responses. Immunization with a replicating LCMV vector leads to complete tumor rejection when combined with adoptive TRP2-specific T cell transfer. Importantly, immunization with replicating vectors leads to extended antigen persistence in secondary lymphoid organs, resulting in efficient T cell priming, which renders previously "cold" tumors open to immune infiltration and reprograms the tumor microenvironment to "hot." Our findings have important implications for the design of next-generation immunotherapies targeting solid cancers utilizing viral vectors and adoptive cell transfer.

Viral vector-mediated reprogramming of the fibroblastic tumor stroma sustains curative melanoma treatment

The tumor microenvironment (TME) is a complex amalgam of tumor cells, immune cells, endothelial cells and fibroblastic stromal cells (FSC). Cancer-associated fibroblasts are generally seen as tumor-promoting entity. However, it is conceivable that particular FSC populations within the TME contribute to immune-mediated tumor control. Here, we show that intratumoral treatment of mice with a recombinant lymphocytic choriomeningitis virus-based vaccine vector expressing a melanocyte differentiation antigen resulted in T cell-dependent long-term control of melanomas. Using single-cell RNA-seq analysis, we demonstrate that viral vector-mediated transduction reprogrammed and activated a Cxcl13-expressing FSC subset that show a pronounced immunostimulatory signature and increased expression of the inflammatory cytokine IL-33. Ablation of Il33 gene expression in Cxcl13-Cre-positive FSCs reduces the functionality of intratumoral T cells and unleashes tumor growth. Thus, reprogramming of FSCs by a self-antigen-expressing viral vector in the TME is critical for curative melanoma treatment by locally sustaining the activity of tumor-specific T cells.

Lymphocytic choriomeningitis virus (LCMV)-based viral vectors have been shown to induce potent antitumor immune responses. Here the authors show that a LCMV-based vaccine vector remodels the tumor-associated fibroblastic stroma, sustaining CD8+ T cell activation and reducing tumor growth in a preclinical model of melanoma.

Inefficient boosting of antitumor CD8(+) T cells by dendritic-cell vaccines is rescued by restricting T-cell cytotoxic functions

Dendritic cells (DCs) are powerful activators of primary and secondary immune responses and have promising activity as anticancer vaccines. However, various populations of immune cells, including natural killer cells, regulatory T cells and especially cytotoxic T lymphocytes (CTLs), can inhibit DC function through cytotoxic clearance. Spontaneous tumor-specific CTL responses are frequently observed in patients before immunotherapy, and it is unclear how such pre-existing responses may affect DC vaccines. We used an adoptive transfer model to show that DC vaccination fail to induce the expansion of pre-existing CTLs or increase their production of interferon γ (IFNγ). The expansion and effector differentiation of naïve host CD8⁺ T cells was also suppressed in the presence of CTLs of the same specificity. Suppression was caused by the cytotoxic functions of the adoptively transferred CTLs, as perforin-deficient CTLs could respond to DC vaccination by expanding and increasing IFNγ production. Proliferation and effector differentiation of host CD8⁺ T cells as well as resistance to tumor challenge were also significantly increased. Expression of perforin by antitumor CTLs was critical in regulating the survival of vaccine DCs, while FAS/FASL and TRAIL/DR5 had a significant, but comparatively smaller, effect. We conclude that perforin-expressing CTLs can suppress the activity of DC-based vaccines and prevent the expansion of naïve and memory CD8⁺ T cells as well as antitumor immune responses. We suggest that, paradoxically, temporarily blocking the cytotoxic functions of CTLs at the time of DC vaccination should result in improved vaccine efficiency and enhanced antitumor immunity.

Immunological tolerance to LCMV antigens differently affects control of acute and chronic virus infection in mice

Cytotoxic T lymphocytes (CTLs) play a key role in the control of lymphocytic choriomeningitis virus (LCMV) infection. In C57BL/6 mice (H-2^b ), the CTL response is mainly directed against epitopes from the LCMV glycoprotein (GP) and the nucleoprotein (NP) which represent the two major viral proteins. The role of GP- versus NP-derived epitopes for viral clearance was examined using transgenic (tg) mice ubiquitously expressing LCMV GP and NP, respectively. These mice lack GP- or NP-specific CTLs and show decreased levels of GP- or NP-specific antibodies as a result of tolerance induction. During acute LCMV infection, CTLs specific for GP- and NP-derived epitopes are generated with similar frequencies. Nonetheless, we found that lack of GP- but not of NP-specific CTLs abolished control of acute LCMV infection. In contrast, after high-dose or chronic LCMV infection, virus elimination was delayed to a similar extent in GP- and NP-tg mice. Thus, immunological tolerance to LCMV antigens differently affects virus clearance in acute and chronic infection settings. In addition, our data reveal that immunodominance of H-2^b -restricted LCMV-specific CTL epitopes and their antiviral activity do not strictly correlate.

CD70 reverse signaling enhances NK cell function and immunosurveillance in CD27-expressing B-cell malignancies

CD27 expression on malignant B cells triggers CD70 reverse signaling in NK cells and improves lymphoma immunosurveillance. CD70 reverse signaling in NK cells is mediated via the AKT signaling pathway and enhances survival and effector function.

Generation of Lymphocytic Choriomeningitis Virus Based Vaccine Vectors

Vaccination with a recombinant LCMV based vector expressing tumor-associated or viral antigens is a safe and versatile method to induce an immune response against tumors or viral infections. Here, we describe the generation of recombinant LCMV vectors in which the gene encoding the viral LCMV-GP was substituted with a gene of interest (vaccine antigen). This renders the vaccine vector propagation-incompetent while it preserves the property of eliciting a strong cytotoxic T cell response.

Artificial antigen-presenting cells plus IL-15 and IL-21 efficiently induce melanoma-specific cytotoxic CD8+ CD28+ T lymphocyte responses

OBJECTIVE

To develop a novel artificial antigen-presenting system for efficiently inducing melanoma-specific CD8(+) CD28(+) cytotoxic T lymphocyte (CTL) responses.

METHODS

Cell-sized Dynabeads® M-450 Epoxy beads coated with H-2K(b): Ig-TRP2180-188 and anti-CD28 antibody were used as artificial antigen-presenting cells (aAPCs) to induce melanoma-specific CD8(+)CD28(+) CTL responses with the help of IL-21 and IL-15. Dimer staining, proliferation, ELISPOT, and cytotoxicity experiments were conducted to evaluate the frequency and activity of induced CTLs.

RESULTS

Dimer staining demonstrated that the new artificial antigen-presenting system efficiently induced melanoma TRP2-specific CD8(+)CD28(+)CTLs. Proliferation and ELISPOT assays indicated that the induced CTLs rapidly proliferate and produce increased IFN- γ under the stimulation of H-2K(b): Ig-TRP2-aAPCs, IL-15, and IL-21. In addition, cytotoxicity experiments showed that induced CTLs have specific killing activity of target cells.

CONCLUSIONS

The new artificial antigen-presenting system including aAPCs plus IL-21 and IL-15 can induce a large number of antigen-specific CD8(+) CD28(+) CTLs against the melanoma. Our study provides evidence for a novel adoptive immunotherapy against tumors.

Ex vivo generation of highly purified and activated natural killer cells from human peripheral blood

Adoptive immunotherapy using natural killer (NK) cells has been a promising treatment for intractable malignancies; however, there remain a number of difficulties with respect to the shortage and limited anticancer potency of the effector cells. We here established a simple feeder-free method to generate purified (>90%) and highly activated NK cells from human peripheral blood-derived mononuclear cells (PBMCs). Among the several parameters, we found that CD3 depletion, high-dose interleukin (IL)-2, and use of a specific culture medium were sufficient to obtain highly purified, expanded (∼200-fold) and activated CD3(-)/CD56(+) NK cells from PBMCs, which we designated zenithal-NK (Z-NK) cells. Almost all Z-NK cells expressed the lymphocyte-activated marker CD69 and showed dramatically high expression of activation receptors (i.e., NKG2D), interferon-γ, perforin, and granzyme B. Importantly, only 2 hours of reaction at an effector/target ratio of 1:1 was sufficient to kill almost all K562 cells, and the antitumor activity was also replicated in tumor-bearing mice in vivo. Cytolysis was specific for various tumor cells, but not for normal cells, irrespective of MHC class I expression. These findings strongly indicate that Z-NK cells are purified, expanded, and near-fully activated human NK cells and warrant further investigation in a clinical setting.

A constructed HLA-A2-restricted pMAGE-A1(278-286) tetramer detects specific cytotoxic T lymphocytes in tumour tissues in situ

OBJECTIVE

To construct a human leucocyte antigen (HLA)-A2-restricted peptide 278-286 of melanoma-associated antigen family A, 1 (pMAGE-A1(278-286)) tetramer to analyse the distribution of cytotoxic T lymphocytes (CTLs) in tumour tissue and tumour-adjacent normal tissue.

METHODS

A HLA-A2-pMAGE-A1(278-286) tetramer was constructed. The distribution of pMAGE-A1(278-286)-specific CTLs was investigated in tumour tissues and tumour-adjacent normal tissues from patients with hepatocellular carcinoma using in situ HLA-A2-pMAGE-A1(278-286) tetramer staining.

RESULTS

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis indicated that HLA-A2 heavy and light chain proteins were successfully obtained. The successful construction of the HLA-A2-pMAGE-A1(278-286) monomer was confirmed with Western blot analysis using W6/32 antibody. Flow cytometry confirmed the specific binding of HLA-A2-pMAGE-A1(278-286) tetramer to pMAGE-A1(278-286)-specific CTLs. In situ HLA-A2-pMAGE-A1(278-286) tetramer staining demonstrated that the number of pMAGE-A1(278-286)-specific CTLs in tumour tissues was significantly higher than in tumour-adjacent normal tissues.

CONCLUSIONS

The HLA-A2-pMAGE-A1(278-286) tetramer was useful for the detection of pMAGE-A1(278-286)-specific CTLs in both tumour tissues and tumour-adjacent normal tissues. In situ tetramer staining is a powerful tool for investigating the distribution of pMAGE-A1278-286-specific CTLs in the tumour microenvironment.

CD27 signaling increases the frequency of regulatory T cells and promotes tumor growth

Signaling of the TNF receptor superfamily member CD27 activates costimulatory pathways to elicit T- and B-cell responses. CD27 signaling is regulated by the expression of its ligand CD70 on subsets of dendritic cells and lymphocytes. Here, we analyzed the role of the CD27-CD70 interaction in the immunologic control of solid tumors in Cd27-deficient mice. In tumor-bearing wild-type mice, the CD27-CD70 interaction increased the frequency of regulatory T cells (Tregs), reduced tumor-specific T-cell responses, increased angiogenesis, and promoted tumor growth. CD27 signaling reduced apoptosis of Tregs in vivo and induced CD4(+) effector T cells (Teffs) to produce interleukin-2, a key survival factor for Tregs. Consequently, the frequency of Tregs and growth of solid tumors were reduced in Cd27-deficient mice or in wild-type mice treated with monoclonal antibody to block CD27 signaling. Our findings, therefore, provide a novel mechanism by which the adaptive immune system enhances tumor growth and may offer an attractive strategy to treat solid tumors.

Safety analysis of ex vivo-expanded NK and NK-like T cells administered to cancer patients: a phase I clinical study

The chimeric state after allogeneic hematopoietic stem cell transplantation provides a platform for adoptive immunotherapy using donor-derived immune cells. The major risk with donor lymphocyte infusions (DLIs) is the development of graft-versus-host disease (GvHD). Development of new DLI products with antitumor reactivity and reduced GvHD risk represents a challenging task in cancer immunotherapy. Although natural killer (NK) and NK-like T cells are promising owing to their antitumor activity, their low concentrations in peripheral blood mononuclear cells reduces their utility in DLIs. We have recently developed a system that allows expansion of clinical-grade NK and NK-like T cells in large numbers. In this study, the safety of donor-derived long-term ex vivo-expanded human NK and NK-like T cells given as DLIs was investigated as immunotherapy for cancer in five patients following allogeneic stem cell infusion. Infusion of the cells was safe whether administered alone or with IL-2 subcutaneously. No signs of acute GvHD were observed. One patient with hepatocellular carcinoma showed markedly decreased serum alpha-fetoprotein levels following cell infusions. These findings suggest that the use of ex vivo-expanded NK and NK-like T cells is safe and appears an attractive approach for further clinical evaluation in cancer patients.

Development of replication-defective lymphocytic choriomeningitis virus vectors for the induction of potent CD8+ T cell immunity

Lymphocytic choriomeningitis virus (LCMV) exhibits natural tropism for dendritic cells and represents the prototypic infection that elicits protective CD8(+) T cell (cytotoxic T lymphocyte (CTL)) immunity. Here we have harnessed the immunobiology of this arenavirus for vaccine delivery. By using producer cells constitutively synthesizing the viral glycoprotein (GP), it was possible to replace the gene encoding LCMV GP with vaccine antigens to create replication-defective vaccine vectors. These rLCMV vaccines elicited CTL responses that were equivalent to or greater than those elicited by recombinant adenovirus 5 or recombinant vaccinia virus in their magnitude and cytokine profiles, and they exhibited more effective protection in several models. In contrast to recombinant adenovirus 5, rLCMV failed to elicit vector-specific antibody immunity, which facilitated re-administration of the same vector for booster vaccination. In addition, rLCMV elicited T helper type 1 CD4+ T cell responses and protective neutralizing antibodies to vaccine antigens. These features, together with low seroprevalence in humans, suggest that rLCMV may show utility as a vaccine platform against infectious diseases and cancer.

CTL induction by cross-priming is restricted to immunodominant epitopes

CTL are induced by two pathways, i.e. direct priming, where tumor cells present tumor antigens to naïve specific CTL, and cross-priming, where professional APC cross-present captured tumor antigens to CTL. Here, we examined direct priming versus cross-priming after immunizing (H-2(b) x H-2(d)) F1 mice with either H-2(b) or H-2(d) positive tumor cells transfected with the GP or nucleoprotein (NP) of lymphocytic choriomeningitis virus (LCMV). Cross-priming was observed for the immunodominant epitopes LCMV-gp33 and -np118, although direct induction resulted in higher CTL frequencies. In contrast, CTL specific for the subdominant epitopes LCMV-gp283 or -np396 were induced only if epitopes were presented directly on MHC class I molecules of the immunizing cell. The broader repertoire and the higher CTL frequencies induced after vaccination with haplotype-matched tumor cells resulted in more efficient anti-tumor and antiviral protection. Firstly, our results indicate that certain virus and tumor antigens may not be detected by CD8(+) T cells because of impaired cross-priming. Secondly, efficient cross-priming contributes to the immunodominant nature of a tumor-specific CTL epitope. Thirdly, vaccine strategies using autologous or syngenic antigen-expressing cells induce a broader repertoire of tumor-specific CTL and higher CTL frequencies.

Carbon nanosyringe array as a platform for intracellular delivery

We report a novel platform for intracellular delivery of genetic material and nanoparticles, based on vertically aligned carbon nanosyringe arrays (CNSAs) of controllable height. Using this technology, we have shown that plasmid and quantum dots can be efficiently delivered to the cytoplasm of cancer cells and human mesenchymal stem cells. The CNSA platform holds great promise for a myriad of applications including cell-based therapy, imaging, and tracking in vivo, and in biological studies aimed at understanding cellular function.