Janne Nestvold

A Second Prophylactic Mhc-mismatched Bone Marrow Transplantation Protects Against Rat Acute Myeloid Leukemia (bnml) Without Lethal Graft-versus-host Disease

Background. We have employed a rat model for human acute myeloid leukemia, a promyelocytic leukemia in the BN rat strain (BNML), to develop new protocols for immunotherapy in combination with allogeneic bone marrow transplantation (alloBMT). The status of mixed chimerism in allotransplanted rats provided an opportunity for immunotherapy using alloreactive donor cells. In addition to T or natural killer (NK) cells, we introduced a second infusion of bone marrow cells as prophylactic donor lymphocyte infusions (DLI) to test whether an effective graft-versus-leukemia (GVL) response could be obtained without clinical graft-versus-host disease (GVHD). Methods. BN rats were sublethally irradiated and transplanted with T-cell depleted bone marrow cells from either fully major histocompatibility complex (MHC)-mismatched (PVG) donor rats or MHC-matched (PVG.1N) as controls. Seven days after transplantation, rats were given 500 leukemic cells to mimic minimal residual disease. Additional cellular therapy was given at day +7. The efficiency of DLI was monitored by chimerism analysis in peripheral blood. Results. Rats receiving infusions of NK cells succumbed to leukemia. T-DLI induced complete donor T-cell chimerism and lethal GVHD. A second alloBMT protected against leukemia. This effect was dependent on an MHC incompatibility between the donor and host and also on the presence of alloreactive T cells in the second bone marrow inoculum, resulting in an increased, mixed donor T-cell chimerism. Conclusion. A second prophylactic transplantation influenced the degree of T-cell chimerism to balance favorably between GVL and GVHD. If applicable to humans, repeated alloBMT may provide a novel approach to leukemia therapy.

Phenotype and natural killer cell sensitivity of a radiation-induced acute T-cell leukaemia (Roser leukaemia) in PVG rats

A radiation‐induced T‐cell leukaemia [Roser leukaemia (RL)] in the rat was conditioned for growth in vitro by repeated in vivo–in vitro passages. This in vitro cell line, termed RL‐T, maintained its leukaemia‐inducing property when transferred to syngeneic PVG rats. It expresses several T‐cell markers and the T‐cell α/β receptor–CD3 complex. RL‐T, furthermore, expresses major histocompatibility complex (MHC) I antigens, both classical (RT1.A) and nonclassical (RT1.C), which makes it susceptible to killing by alloreactive natural killer cells in vitro.

Partial NK cell tolerance induced by radioresistant host cells in rats transplanted with MHC-mismatched bone marrow

We have studied the effect of radioresistant host cells in inducing tolerance and adaptation of the MHC recognition repertoire of donor-derived NK cells in stem cell allotransplanted (allo-SCT) rats. Sub-lethally irradiated PVG.1AV1 rats (RT1(av1)) were transplanted with bone marrow from fully MHC-mismatched allotype-marked PVG.7B (RT1(c)) rats; MHC-identical PVG (RT1(c)) controls were transplanted in parallel. In the PVG.7B → PVG.1AV1 allogeneic chimeras, NK cells were donor derived and showed partial tolerance toward host cells. Allogeneic chimeras failed to efficiently reject PVG.1AV1 cells by an NK-mediated mechanism in vivo (allogeneic lymphocyte cytotoxicity), and IL-2-cultured NK cells derived from these chimeras showed diminished cytolytic activity against PVG.1AV1 cells in vitro. There were corresponding changes in the phenotype and function of the highly alloreactive Ly49i2(+) NK cells, which are specifically inhibited by a donor MHC class I ligand, RT1-A1(c). The ligand-negative host MHC haplotype apparently induced expression of a second uncharacterized inhibitory MHC receptor responsible for the partial tolerance toward host-derived cells, along with a modest increase in Ly49i2 receptor levels. The host MHC haplotype did not induce a general hyporesponsiveness in Ly49i2(+) NK cells, which showed normal activation responses in a panel of MHC congenic strains. The data suggest that the MHC constitution of radiation-resistant host cells can have permanent, albeit not fully tolerogenic, effects on the development of a functional NK repertoire following allo-SCT.

A novel rat fibrosarcoma cell line from transformed bone marrow-derived mesenchymal stem cells with maintained in vitro and in vivo stemness properties

ABSTRACT Increasing evidence suggests a possible relationship between mesenchymal stem cells (MSCs) and sarcoma. MSCs are hypothesized to be the cells initiating sarcomagenesis, and cancer stem cells (CSCs) sharing features of MSCs have been identified in sarcomas. Here, we report on the characteristics of a bone marrow‐derived rat mesenchymal stem cell line that spontaneously transformed in long‐term culture. The rat transformed mesenchymal stem cells (rTMSCs) produced soft‐tissue fibrosarcomas in immunocompromised mice and immunocompetent rats. In vitro, the rTMSCs displayed increased proliferation capacity compared to the untransformed cell line. The transformed MSCs maintained the mesenchymal phenotype by expression of the stem cell marker CD 90 and the lack of hematopoietic and endothelial markers. Cytogenetic analysis detected trisomy 6 in the rTMSCs. Side population (SP) isolation and tumorsphere cultivation of the transformed cells confirmed the presence of CSCs among the rTMSCs. Importantly, the rTMSCs retained their differentiation capacity towards osteogenic and adipogenic lineages. This transformed MSC‐based cell line may be valuable in examining the balance in a mixed cell population between cancer stem cell properties and the ability to differentiate to specific non‐transformed cell populations. Moreover, it may also be a useful tool to evaluate the efficacy of novel targeted immunotherapies in vivo. HighlightsSpontaneously transformed rat MSCs (rTMSCs) share characteristics with normal MSCs.rTMSCs possess a side population, enriched with tumorigenic cells.rTMSCs model fibrosarcoma in vivo.

Oncolytic peptide LTX-315 induces an immune-mediated abscopal effect in a rat sarcoma model

ABSTRACT LTX 315 is an oncolytic peptide with potent immunological properties. In the present study, we demonstrate that intratumoral treatment with LTX-315 resulted in a complete regression and systemic immune response in a rat fibrosarcoma model. The treatment was T-cell dependent, and also resulted in an abscopal effect as demonstrated by the regression of distal non-treated lesions. Significant infiltration of CD8+ T cells was observed in both treated and non-treated lesions, as shown by immunohistochemical and flow cytometric analysis. LTX-315 rapidly killed the cells in vitro with a lytic mode of action followed by the subsequent release of Danger-Associated Molecular Pattern (DAMP) molecules such as HMGB1, ATP and Cytochrome c. Together, our data demonstrate that LTX-315 represents a new approach to cancer immunotherapy, which has the potential as a novel immunotherapeutic agent.

Abstract 11: The oncolytic peptide LTX-315 enhances T cell clonality and induces synergy with chemotherapy

LTX-315, a novel oncolytic peptide is effective against both drug-resistant and drug-sensitive cancer cells with lower toxicity towards normal cells. Intratumoral treatment with LTX-315 results in growth inhibition, complete regression and long lasting tumor-specific immune responses. The oncolytic effect of LTX-315 involves perturbation of the plasma membrane and distortion of intracellular organelles including the mitochondria with subsequent release of Damage-Associated Molecular Pattern molecules (DAMPs) such as ATP, cytochrome c and HMGB1. LTX-315 effectively induces necrosis within the tumor followed by the release of tumor antigens as demonstrated by a greater increase in tumor infiltrating CD8+ T cells, expansion of T cell clonality, and number of clones within the tumor microenvironment. LTX-315`s ability to modify the tumor microenvironment makes it ideal as a combination partner for other cancer therapies, including chemotherapy and immune checkpoint inhibitors. In preclinical tumor models, combination of LTX-315 and chemotherapeutic agents such as cyclophosphamide and doxorubicin demonstrates significant synergy. Citation Format: Ketil Andre Camilio, Meng Yu Wang, Janne Nestvold, Gunhild Maelandsmo, Baldur Sveinbjornsson, Oystein Rekdal. The oncolytic peptide LTX-315 enhances T cell clonality and induces synergy with chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 11. doi:10.1158/1538-7445.AM2017-11

Listeria monocytogenes infection differentially affects expression of ligands for NK cells and NK cell responses, depending on the cell type infected

The pivotal role of NK cells in viral infection is extensively studied, whereas the role of NK cells in bacterial infection has been poorly investigated. Here, we have examined how Listeria monocytogenes (LM) affects expression of ligands for NK cell receptors and subsequent NK cell responses, depending on the type of cell infected. LM infected rat cell lines derived from different tissues were coincubated with splenic NK cells, and NK cell proliferation and IFN‐γ production were measured. In addition, expression of ligands for the NK cell receptors Ly49 and NK cell receptor protein 1 (NKR‐P1), MHC class I and C‐type lectin‐related molecules, respectively, was assessed. Infected pleural R2 cells, but not epithelium‐derived colon carcinoma cell line CC531 cells, induced proliferation of NK cells. Reporter cells expressing the inhibitory NKR‐P1G receptor or the activating NKR‐P1F receptor were less stimulated under incubation with infected CC531 cells versus uninfected CC531 controls, suggesting that the ligand(s) in question were down‐regulated by infection. Conversely, LM infection of R2 cells did not affect reporter cell stimulation compared with uninfected R2 controls. We characterized a rat monocyte cell line, termed RmW cells. In contrast to LM infected R2 cells that up‐regulate MHC class I molecules, RmW cells displayed unchanged MHC class I expression following infection. In line with MHC class I expression, more NK cells produced a higher amount of IFN‐γ against infected R2 cells compared with RmW cells. Together, L. monocytogenes infection may variously regulate cellular ligands for NK cells, depending on the cell type infected, affecting the outcome of NK cell responses.

Irradiation and bone marrow reconstitution affect the functional Ly49 natural killer cell repertoire in rats

Total body irradiation (TBI) is part of the preconditioning regimen for allogeneic bone marrow transplantation (alloBMT) and the procedure is associated with treatment-related toxicity and delayed immune reconstitution. Natural killer (NK) cells develop and acquire functional competence in close interaction with stromal bone marrow cells that are considered relatively radioresistant compared to the hematopoietic compartment. We thus undertook a study to assess the effect of TBI on the reconstitution of class I MHC-specific Ly49 NK cell receptors in a rat model of alloBMT. In rats subjected to TBI alone or followed by MHC-matched BMT, the irradiation conditioning induced a skewing of the Ly49 repertoire. Specifically, the activating Ly49s3bright subset exhibited increased frequency and receptor density which correlated with augmented alloreactivity relative to untreated control rats. Our results highlight the plasticity of NK cells and indicate that ionizing radiation (IR) affects the stromal compartment and as a consequence the maturation and functional properties of bone marrow-derived NK cells. These changes lasted throughout the 6 months observation period, showing that irradiation induces long term effects on the generation of the NK cell receptor repertoire.

Intratumoral treatment of one tumor lesion with LTX-315 induces complete tumor regression and long-term specific protective immune responses in a metastatic rodent tumor model

Host defense peptides are naturally occurring peptides that have an important function in innate immune responses in almost every life form. Recently it has been documented that several host defense peptides have anticancer activity. Based on a naturally occurring host defense peptide, we have do novo designed the short chemically modified peptide LTX-315. We have demonstrated that LTX-315 induces an immunogenic type of cell death with subsequent release of danger signals (e.g. HMBG1, ATP and Cytochrome C) and tumor associated antigens (TAAs). In addition LTX-315 also has the ability to directly modulate immune-responses. In a novel rat mescenhymal sarcoma model (rTMSC) we demonstrate that LTX-315 induces a complete tumor regression by intratumoral (i.t.) injection. Studies on treated tumor tissue confirmed massive necrosis and infiltration of immune cells. Successfully treated animals were protected against re-challenge with the tumor cell type treated, but not against other types of tumor cells. Moreover, tumor resistance could be adoptively transferred by spleen cells from LTX-315-treated animals. The resistance was abrogated by depletion of T-lymphocytes. To clarify whether intratumoral injection of LTX-315 in one tumor lesion can have an effect on metastatic disease, intraperitoneal tumor and two subcutaneous tumors were established in the animals. Thereafter, LTX-315 was injected into one of the subcutaneous lesion and tumor growth assessed by living imaging. The results showed that LTX-315 eradicated all three lesions and the animal went into durable complete remission. We propose that by targeting tumor locally LTX-315 can be used for individualized therapeutic in situ vaccination against cancer.

Abstract 474: Complete regression and long-term specific protective immune responses obtained in rodent tumor models after intratumoral treatment with LTX-315 .

LTX-315 is a de novo designed peptide derived from a naturally occurring host defence peptide. LTX-315 has the potential to induce long-term specific protective immune responses by stimulating immune cells, inducing tumor cell lysis with subsequent release of danger signals (e.g. HMGB1) and tumor associated antigens (TAA`s). A complete tumor regression has been obtained in several syngenic rodent tumor models by intratumoral (i.t.) injection with LTX-315. The effect was T- cell- dependent since the intervention was inefficient in immune-deficient animals. Studies on treated tumor tissue confirmed infiltration of immune cells and a switch in the cytokine profile towards a Th1 response. Successfully treated animals were protected against re-challenge with the tumor cell type treated, but not against other types of tumor cells. Moreover, tumor resistance could be adoptively transferred by spleen cells from LTX-315-treated animals. The resistance was abrogated by depletion of T- lymphocytes. Additional studies also indicate that LTX-315`s potential to locally activate the innate immune system by the immunogenic stressing of cells, in addition to the subsequent release of endogenous adjuvants and natural danger signals, provides a strong rationale for using LTX-315 as an adjuvant for vaccines based on tumor-associated antigens (TAA) and for combination with other types of immune–modulatory therapies. LTX-315 is currently being tested in a Phase I dose escalation clinical study and may represents a novel strategy for personalized in situ vaccination against cancer. Citation Format: Oystein Rekdal, Gunnar Kvalheim, Pal-Dag Line, Bent Rolstad, Ketil Camilio, Gerd Berge, Janne Nestvold, Mengyu Wang, Jihua Shi, Ali Areffard, Baldur Sveinbjornsson. Complete regression and long-term specific protective immune responses obtained in rodent tumor models after intratumoral treatment with LTX-315 . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 474. doi:10.1158/1538-7445.AM2013-474