The immunogenicity of tumour cells

Immune Checkpoint Inhibition Followed by Tumor Infiltration of Dendritic Cells in Murine Neuro-2a Neuroblastoma

BACKGROUND

Most tumors responding to immunotherapy with monoclonal antibodies targeting programmed cell death protein1 (PD1) and programmed death ligand-1 (PD-L1) show surface expression of PD-L1. Neuroblastoma has been reported to show low PD-L1 surface expression.

METHODS

The effect of immune checkpoint inhibitor on mouse neuroblastoma was investigated, and host immune cells were analyzed in the tumor microenvironment. Expression of co-stimulatory molecules by Neuro-2a mouse neuroblastoma cells was analyzed using flow cytometer. Neuro-2a cells were inoculated subcutaneously into A/J mice, followed by intraperitoneal injection of antibodies targeting PD-1 and PD-L1. Mice were sacrificed for the measurement of tumor weights on day 14 following tumor inoculation, and tumor-infiltrating cells were analyzed using a flow cytometer.

RESULTS

Dim expression of PD-L1 was observed on the cell surface of cultured Neuro-2a cells. Growth of subcutaneous tumors was significantly suppressed, and PD-L1-expressing tumor cells were depleted by the antibody treatment. We confirmed that Neuro-2a cells opsonized by the anti-PD-L1 antibody were phagocytosed in the in vitro setting. In the treated tumor microenvironments, CD8α⁺ lymphocyte and CD11c⁺ MHC II⁺ cells were significantly accumulated in comparison with the control group. These CD11c⁺ MHC II⁺ cells expressed CD80, CD86, CD14, and CD40, but not CD205, PD-L1, or CTLA4. PD-1 expression was detected dimly. Immune suppressive effects of CD11b⁺Gr-1⁺ myeloid-derived suppressor cells by the administration of anti-PD-1 and PD-L1 antibodies were not observed in spleen, regional lymph nodes, or tumor microenvironment.

CONCLUSIONS

Our findings raise the possibility that co-administration of anti-PD-1 and anti-PD-L1 antibodies have a synergistic effect on inhibition of tumor growth and could be an effective therapy against neuroblastoma with dim expression of PD-L1.

Improved Anti-Tumour Adaptive Immunity Can Overcome the Melanoma Immunosuppressive Tumour Microenvironment

Clinical benefits obtained from checkpoint blockade regimens demonstrate the importance of overcoming the immunosuppressive tumour microenvironment (TME) in cancer immunotherapy. Intravenous (i.v.) injection of B16 melanoma cells (H-2K^b) leads to lethal disseminated pulmonary metastasis in Balb/c recipients (H-2K^d). This lack of immune control is related to low major histocompatibility complex (MHC) expression on B16 cells which is associated with delayed and decreased anti-tumour adaptive immune responses (e.g., alloantibody formation) as: (i) other tumour types with normal H-2K^b expression are rejected with concomitant antibody production; (ii) preincubation of B16 with IFN-gamma to upregulate H-2K^b expression resulted in improved antibody production and anti-tumour activity. The delayed/decreased anti-tumour adaptive immune responses induced by B16 inoculation is not able to interrupt progression of primary metastases, while it is able to effectively eliminate secondary inoculated subcutaneously (s.c.) B16 cells from progression. This is due to the presence of an immunosuppressive TME within the primary metastases characterized by increased regulatory T cells (Tregs) and an increased T helper cells (Th) 2/1 profile. These tumour-induced immunosuppressive T cell populations are counteracted by improved adaptive immunity via active and passive immunization, resulting in effective elimination of the TME, destruction of the metastatic tumour and a reversal of Th2/1 profile in a time-sensitive manner. Thus, we here demonstrate that the TME is not irreversible and adaptive immunity is able to eradicate established solid tumour and its immunosuppressive TME. This study will help design treatments to overcome the immunosuppressive effect of the TME and improve efficacy of cancer immunotherapy.

Combination immunotherapy strategies in advanced non-small cell lung cancer (NSCLC): Does biological rationale meet clinical needs?

Immune checkpoint inhibitors (ICIs) have emerged as one of the main new therapeutic options for advanced non-small cell lung cancer (NSCLC) patients. Even though they demonstrated superiority towards standard chemotherapy in different disease settings, the response rates do not exceed 45% in highly molecularly selected patients. This is related to known limitations of the available biomarkers, as well to the complex and dynamic nature of tumor microenvironment. The study of the different strategies adopted by tumor cells to escape the immune system lays the basis of the new combination strategies. This review focuses on analyzing the biological rationale and early clinical data available concerning therapeutic strategies combining ICIs together, ICIs with different regimens and schedules of standard chemotherapy, ICIs with tyrosine kinase inhibitors, ICIs with antiangiogenic agents and ICs with radiotherapy.

Ex vivo induction of antitumor DEC-205+ CD11c+ cells in a murine neuroblastoma model by co-stimulation with doxorubicin, lipopolysaccharide and interleukin-4

The antigen-presenting capacity of specific cells and tumor immunogenicity involved in innate cellular immunity are important for initiating an antitumor response to advanced neuroblastoma. The present study was performed to establish a method of producing antigen-presenting cells that induced an immune response to murine neuroblastoma cells through culture with neuroblastoma cells that had undergone immunogenic cell death. Immunogenic death of neuro-2a murine neuroblastoma cells was induced by exposure to doxorubicin. Mouse bone marrow cells were cultured in medium containing granulocyte-macrophage colony-stimulating factor, followed by the addition of doxorubicin-treated neuro-2a cells to the culture with or without lipopolysaccharide (LPS) and/or interleukin-4. Subsequently, cluster of differentiation (CD) 8α⁺ lymphocytes were co-cultured with neuro-2a cells and the adherent bone marrow cells obtained by the above procedure to evaluate CD8α⁺ lymphocyte proliferation and interferon-γ production. Furthermore, the surface antigen profile of adherent bone marrow cells was analyzed by flow cytometry. When adherent bone marrow cells were treated with LPS and/or interleukin-4, followed by co-culture with CD8α⁺ lymphocytes and neuro-2a cells, interferon-γ production by the CD8α⁺ cells increased in response to anti-CD3/CD28 antibody stimulation. CD11c major histocompatibility complex II (MHC II) double-positive cells were increased among adherent cells derived from cultured bone marrow cells. These cells were positive for DEC-205, but not CD8α. These findings suggest that co-culture of bone marrow-derived cells with tumor cells (that have undergone immunogenic death by exposure to doxorubicin) plus stimulation by LPS and interleukin-4 induces antigen-presenting cells that can evoke an immune response to neuroblastoma. Bone marrow-derived DEC-205⁺ CD11c⁺ MHC II⁺ dendritic cells are key antigen-presenting cells in the induction of an immune response following phagocytosis of doxorubicin-treated neuroblastoma cells.

Antigen delivery to CD11c+CD8- dendritic cells induces protective immune responses against experimental melanoma in mice in vivo

Dendritic cells (DCs) are central modulators of immune responses and, therefore, interesting target cells for the induction of antitumor immune responses. Ag delivery to select DC subpopulations via targeting Abs to DC inhibitory receptor 2 (DCIR2, clone 33D1) or to DEC205 was shown to direct Ags specifically to CD11c(+)CD8(-) or CD11c(+)CD8(+) DCs, respectively, in vivo. In contrast to the increasing knowledge about the induction of immune responses by efficiently cross-presenting CD11c(+)CD8(+) DCs, little is known about the functional role of Ag-presenting CD11c(+)CD8(-) DCs with regard to the initiation of protective immune responses. In this study, we demonstrate that Ag targeting to the CD11c(+)CD8(-) DC subpopulation in the presence of stimulating anti-CD40 Ab and TLR3 ligand polyinosinic-polycytidylic acid induces protective responses against rapidly growing tumor cells in naive animals under preventive and therapeutic treatment regimens in vivo. Of note, this immunization protocol induced a mixed Th1/Th2-driven immune response, irrespective of which DC subpopulation initially presented the Ag. Our results provide important information about the role of CD11c(+)CD8(-) DCs, which have been considered to be less efficient at cross-presenting Ags, in the induction of protective antitumor immune responses.

HL-60 myeloid leukaemia cells acquire immunostimulatory capability upon treatment with retinoic acid: analysis of the responding population and mechanism of cytotoxic lymphocyte activation

HL-60 myeloid leukaemia cells are ineffective as stimulators of allogeneic lymphocytes in mixed leucocyte culture (MLC). These cells can be induced to differentiate along the monocytic or granulocytic pathways with or without acquisition of major histocompatibility complex (MHC) class II antigen by various agents. Surprisingly, treatment of HL-60 cells with 10 nM all-trans retinoic acid (RA) for 7 days (HL-60-R7) resulted in a marked increase in MLC stimulation although the cells lacked detectable MHC class II antigen expression at the initiation of the MLC. In contrast, treatment with interferon-gamma (IFN-gamma), with or without RA, induced MHC class II antigen expression but failed to enhance MLC stimulation. Lymphocytes responding to HL-60-R7 were predominantly CD8+ and/or CD16+ and displayed enhanced cytolytic capacity for HL-60 and HL-60-R7 cells as well as natural killer (NK)-sensitive K562 cells. Nevertheless, monoclonal antibodies (mAb) to MHC class II antigens substantially inhibited the MLC and some CD4+ lymphocytes in the responding population were required, although this requirement could be replaced by the addition of interleukin-2 (IL-2). HL-60-R7 (and HL-60) cells were shown to acquire detectable MHC class II antigen expression during the first 3 days of the MLC. Thus a low level of activation by MHC class II+ stimulator cells appears to be required for the response. Analysis of the role of cytokines with costimulatory activity for T cells and/or NK cells indicated that tumour necrosis factor-alpha (TNF-alpha) was important in the proliferative response, while interleukins-1, -6 and -12 and stem cell factor did not seem to be involved. Cell interaction molecules lymphocyte function-associated antigen-1 (LFA-1) (CD11a), intracellular adhesion molecule-1 (ICAM-1) (CD54), ICAM-3 (CD50) and B7.2 (CD86) were up-regulated on HL-60-R7. Blocking mAb to LFA-1 and B7.2 potently inhibited the proliferative response indicating a key role for these molecules in the enhanced immunostimulation by HL-60-R7 cells. The results may have implications for the mechanism of the therapeutic effect of RA in acute promyelocytic leukaemia and may also provide valuable information in regard to the immunogenicity of tumour cells in general.