Molecular determinants governing CD8+ T cell mediated anti-tumor immunity

Despite the ability of CD8+ T-cells to recognize and kill cancer cells, tumors manage to evade immune control through multiple mechanisms. Immunotherapeutic strategies have shown clinical benefit in some but not all cancer types or patients. Hence, a better understanding of the key parameters governing the complex relationship between CD8+ T-cells and tumors is necessary to ensure the success of immunotherapy in most cancer patients. Anti-tumor T-cell responses mostly involve CD8+ T-cells with high affinity for mutated self-antigens and of low affinity for tumor-associated antigens. Therefore, the first part of my thesis project addressed the impact of the recognition strength between the TCR and its antigen in CD8+ T-cell mediated anti-tumor responses. We found that CD8+ T-cell peripheral priming with a high affinity peptide vaccine was necessary to control low affinity antigen expressing B16 melanoma tumors. In addition, despite a high affinity peripheral priming, the affinity for the antigen that CD8+ T-cells encountered later in the tumor influenced on the CD8+ T-cell response: low affinity antigen recognition led to decreased CD8+ T-cell expansion and tumor control while induced lower expression levels of inhibitory receptors and increased cytokine production upon ex vivo restimulation. Interestingly, tumor infiltrating CD8+ T-cells regardless of their affinity for the tumor antigen, responded equally to PD-1 blocking monoclonal antibodies. Moreover, when tumor infiltrating CD8+ T-cells were re-transferred to tumor-free hosts, they showed similar in vivo re-expansion capacity irrespectively of the affinity for the tumor antigen. Interestingly, the re-expansion capacity of these T-cells was similar to that of their counterparts isolated from secondary lymphoid organs, suggesting that CD8+ T-cells in tumors may be rekindled upon relief of tumor immunosuppression. Our group had previously shown the importance of micro-RNA-155 (miR-155) for CD8+ T cells anti-tumor responses, as its overexpression enhanced tumor control by CD8+ T cells. However, the quantitative aspects of the regulation of miR-155 expression levels were poorly characterized. Thus, the second part of my thesis addressed miR-155 expression regulation in mouse and human CD8+ T cells from healthy tissues and melanoma tumors. I demonstrated that T cell affinity and antigen dose are two important factors determining miR-155 expression levels in CD8+ T cells. Interestingly, high miR-155 expression levels correlated with increased tumor control in low affinity antigen expressing B16 tumors and anti-PD-1 treatment increased CD8+ T cells miR-155 expression levels. Moreover, CD8+ T cells overexpressing miR-155 showed enhanced persistence in chronic infections. In line with these observations in mouse model systems, miR-155 expression levels in human effector memory CD8+ T cells positively correlated with their frequencies in tumor infiltrated lymph nodes. Thus, we propose that miR-155 expression levels reflect responsiveness and affinity for the antigen and may be used as an overall marker of tumor infiltrating CD8+ T cells fitness. Altogether, we suggest that combination of high affinity peripheral priming by altered peptide ligands and checkpoint blockade may enable tumor control of even low affinity antigen expressing tumors, which can be revealed by miR-155 upregulation in tumor infiltrating CD8+ T cells

Prophylactic vs. Therapeutic Treatment With P2Et Polyphenol-Rich Extract Has Opposite Effects on Tumor Growth.

Polyphenols have tumoricidal effects via anti-proliferative, anti-angiogenic and cytotoxic mechanisms and have recently been demonstrated to modulate the immune response through their anti- or pro- oxidant activity. Nevertheless, it remains controversial whether antioxidant-rich supplements have real beneficial effects on health, especially in complex diseases such as cancer. We previously identified a polyphenol-rich extract obtained from <i>Caesalpinia spinosa</i> (P2Et) with anti-tumor activity in both breast carcinoma and melanoma. The present work evaluated the ability of P2Et extract to modulate the immune system in either the steady state or following tumor challenge. We found that the prophylactic treatment of healthy mice increased the number of CD4 <sup>+</sup> and CD8 <sup>+</sup> activated T, NK, regulatory T, dendritic and myeloid-derived suppressor cells in lymphoid organs together with a significant increase in plasma IL-6. Interestingly, this pre-conditioning of the host immune system with P2Et did not involve a protective effect against the control of tumor growth and metastasis in transplantable models of melanoma (B16) and breast cancer (4T1), but in contrast, a detrimental effect was observed in both models. We further demonstrated that this effect was at least partly due to an increase in regulatory T cells, myeloid-derived suppressor cells, and proinflammatory cytokines, with a concomitant decrease in CD4 <sup>+</sup> and CD8 <sup>+</sup> T cells. Taken together, these results suggest that the anti-tumor and immunomodulation properties of the P2Et extract critically depend on the presence of the tumor and might be mediated by the complex interactions between the tumor cells and the other components of the tumor microenvironment

Dendritic cell cross‐dressing and tumor immunity

In addition to direct and cross‐presentation, dendritic cells (DCs) can present tumor antigens (TAs) to T cells via a hitherto poorly understood mechanism called “cross‐dressing.” DC cross‐dressing involves the acquisition of preformed peptide‐major histocompatibility class I/II (p‐MHC) complexes from cancer cells. This process has been documented both in cell culture and in tumor models; may occur via the uptake of tumor‐derived extracellular vesicles or the horizontal transfer of plasma membrane fragments from cancer cells to DCs; and can be enhanced through DC engineering for therapeutic applications. In some experimental contexts, DC cross‐dressing may be essential for productive anti‐tumor immunity, possibly owing to the fact that tumor‐derived p‐MHC complexes encompass the full repertoire of immunologically relevant TAs against which primed cytotoxic T cells can exert their tumoricidal activity

Overcoming microenvironmental resistance to PD-1 blockade in genetically engineered lung cancer models

Lung cancer resistance to PD-1 inhibition can be overcome by targeting tumor-associated macrophages in mouse models.info:eu-repo/semantics/publishe

Cytokine-armed dendritic cell progenitors for antigen-agnostic cancer immunotherapy

Dendritic cells (DCs) are antigen-presenting myeloid cells that regulate T cell activation, trafficking and function. Monocyte-derived DCs pulsed with tumor antigens have been tested extensively for therapeutic vaccination in cancer, with mixed clinical results. Here, we present a cell-therapy platform based on mouse or human DC progenitors (DCPs) engineered to produce two immunostimulatory cytokines, IL-12 and FLT3L. Cytokine-armed DCPs differentiated into conventional type-I DCs (cDC1) and suppressed tumor growth, including melanoma and autochthonous liver models, without the need for antigen loading or myeloablative host conditioning. Tumor response involved synergy between IL-12 and FLT3L and was associated with natural killer and T cell infiltration and activation, M1-like macrophage programming and ischemic tumor necrosis. Antitumor immunity was dependent on endogenous cDC1 expansion and interferon-γ signaling but did not require CD8+T cell cytotoxicity. Cytokine-armed DCPs synergized effectively with anti-GD2 chimeric-antigen receptor (CAR) T cells in eradicating intracranial gliomas in mice, illustrating their potential in combination therapies

Tumour-derived PGD2 and NKp30-B7H6 engagement drives an immunosuppressive ILC2-MDSC axis

Group 2 innate lymphoid cells (ILC2s) are involved in human diseases, such as allergy, atopic dermatitis and nasal polyposis, but their function in human cancer remains unclear. Here we show that, in acute promyelocytic leukaemia (APL), ILC2s are increased and hyper-activated through the interaction of CRTH2 and NKp30 with elevated tumour-derived PGD2 and B7H6, respectively. ILC2s, in turn, activate monocytic myeloid-derived suppressor cells (M-MDSCs) via IL-13 secretion. Upon treating APL with all-trans retinoic acid and achieving complete remission, the levels of PGD2, NKp30, ILC2s, IL-13 and M-MDSCs are restored. Similarly, disruption of this tumour immunosuppressive axis by specifically blocking PGD2, IL-13 and NKp30 partially restores ILC2 and M-MDSC levels and results in increased survival. Thus, using APL as a model, we uncover a tolerogenic pathway that may represent a relevant immunosuppressive, therapeutic targetable, mechanism operating in various human tumour types, as supported by our observations in prostate cancer.Group 2 innate lymphoid cells (ILC2s) modulate inflammatory and allergic responses, but their function in cancer immunity is still unclear. Here the authors show that, in acute promyelocytic leukaemia, tumour-activated ILC2s secrete IL-13 to induce myeloid-derived suppressor cells and support tumour growth

Tumour-derived PGD2 and NKp30-B7H6 engagement drives an immunosuppressive ILC2-MDSC axis

Group 2 innate lymphoid cells (ILC2s) are involved in human diseases, such as allergy, atopic dermatitis and nasal polyposis, but their function in human cancer remains unclear. Here we show that, in acute promyelocytic leukaemia (APL), ILC2s are increased and hyper-activated through the interaction of CRTH2 and NKp30 with elevated tumour-derived PGD2 and B7H6, respectively. ILC2s, in turn, activate monocytic myeloid-derived suppressor cells (M-MDSCs) via IL-13 secretion. Upon treating APL with all-trans retinoic acid and achieving complete remission, the levels of PGD2, NKp30, ILC2s, IL-13 and M-MDSCs are restored. Similarly, disruption of this tumour immunosuppressive axis by specifically blocking PGD2, IL-13 and NKp30 partially restores ILC2 and M-MDSC levels and results in increased survival. Thus, using APL as a model, we uncover a tolerogenic pathway that may represent a relevant immunosuppressive, therapeutic targetable, mechanism operating in various human tumour types, as supported by our observations in prostate cancer