Listeria monocytogenes infection enhances the interaction between rat non-classical MHC-Ib molecule and Ly49 receptors

Murine NK cell Ly49 receptors, functionally analogous to KIRs in humans recognize MHC class I molecules and play a key role in controlling NK cell function. We have previously shown that the paired activating Ly49s4 and inhibitory Ly49i4 receptors recognize undefined non-classical MHC-Ib ligands from the RT1-CE region in rats. Here, the RT1-CE16 gene of the RT1^d haplotype was stably transfected into the mouse RAW macrophage cell line, termed RAW-CE16^d cells. Combining RAW-CE16^d cells with Ly49 expressing reporter cells demonstrated Ly49i4 and Ly49s4 specificity for CE16^d. The Ly49s4/i4:CE16^d interaction was confirmed by specific MHC-I blocking monoclonal Abs. Further, we used our in vitro model to study the effect of Listeria monocytogenes (LM) on CE16^d after infection. LM infection and IFN-γ stimulation both led to enhanced CE16^d expression on the surface of transfected RAW-CE16^d cells. Interestingly, the reporter cells displayed increased response to LM-infected RAW-CE16^d cells compared with IFN-γ-treated RAW-CE16^d cells, suggesting a fundamental difference between these stimuli in supporting enhanced Ly49 recognition of CE16^d. Collectively, our data show that Ly49s4 and Ly49i4 recognize the non-classical RT1-CE16^d molecule, which in turn is up-regulated during LM infection and thereby may contribute to NK-mediated responses against infected cells.

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.

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 André Camilio, Meng Yu Wang, Janne Nestvold, Gunhild Mælandsmo, Baldur Sveinbjørnsson, Øystein 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

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

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 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: Øystein Rekdal, Gunnar Kvalheim, Pål-Dag Line, Bent Rolstad, Ketil Camilio, Gerd Berge, Janne Nestvold, Mengyu Wang, Jihua Shi, Ali Areffard, Baldur Sveinbjørnsson. 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

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.

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 alpha/beta 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.