The ultimate goal of curative anti-cancer therapies: inducing an adaptive anti-tumor immune response

Development of GPC3 and EGFR-dual-targeting chimeric antigen receptor-T cells for adoptive T cell therapy

Adoptive transfer of T cells expressing specific anti-glypican-3 (GPC3) chimeric antigen receptors (CARs) has demonstrated therapeutic potential against hepatocellular carcinoma (HCC). However, normal tissues with low expression of neoplasm-associated antigens often show on-target, off-tumor toxicity. Previous studies have revealed that the development of HCC xenografts in mice could be inhibited effectively by GPC3-targeting CAR-T cells. However, these studies did not provide information regarding on-target, off-tumor toxicity. We hypothesized that on-target, off-tumor toxicity may decrease in dual-targeting CAR-T cells that co-express GPC3 with epidermal growth factor receptor (EGFR)-targeted CARs characterized by CD3ζ and 28BB expression. Our research confirmed that dual-targeting CAR-T (CARgpc3-egfr) cells exhibited similar proliferative ability and cytotoxicity to CARgpc3 T cells against GPC3+EGFR+ HCC in vitro. However, EGFR-targeting CAR-T (CARegfr) cells showed poor proliferation activity and cytotoxicity against GPC3+EGFR+ HCC cells, similar to mock CAR-T cells. CARgpc3 and CARgpc3-egfr T cells showed enhanced cytokine secretion compared to CARegfr and mock CAR-T cells in vitro. In vivo, tumor growth suppression was better for CARgpc3-egfr T cells than for CARgpc3 T cells in GPC3+EGFR+ HCC, while it was not observed for CARegfr or mock CAR-T cells. Taken together, our data indicated that dual-targeting CAR-T cells with two CARs against GPC3 and EGFR may maintain relatively effective anti-neoplasm functions in GPC3+EGFR+ HCC in vitro and in vivo, a strategy that may reduce off-tumor toxicity.

Cancer stem cell plasticity in glioblastoma multiforme: a perspective on future directions in oncolytic virotherapy

The cancer stem cell (CSC) hypothesis suggests that a rare population of stem-like cells underpin tumorigenesis. Oncolytic viruses (OVs) demonstrate novel mechanisms of targeting the elusive CSCs with greater selectivity - promising therapeutic potential against solid tumors such as glioblastoma (GBM) that are resistant to conventional treatment. In general, OVs have failed to translate the efficacy from bench to bedside. The success of OVs rely on the hypothesis that eliminating CSCs is key to preventing recurrence. However, newly emerging evidence of CSC plasticity challenge this hypothesis by proposing that the CSC pool can be regenerated from non-CSCs post-treatment. We review this evidence surrounding the CSC hypothesis to propose an original perspective on why several advanced OVs may be failing to reflect their true potential in clinical trials. We argue that preventing non-CSC to CSC dedifferentiation may be critical to achieving long-term treatment efficacy in future OV clinical trials.

The immune microenvironment: a major player in human cancers

Cancer is a major public health issue and figures among the leading causes of death in the world. Cancer development is a long process, involving the mutation, amplification or deletion of genes and chromosomal rearrangements. The transformed cells change morphologically, enlarge, become invasive and finally detach from the primary tumor to metastasize in other organs through the blood and/or lymph. During this process, the tumor cells interact with their microenvironment, which is complex and composed of stromal and immune cells that penetrate the tumor site via blood vessels and lymphoid capillaries. All subsets of immune cells can be found in tumors, but their respective density, functionality and organization vary from one type of tumor to another. Whereas inflammatory cells play a protumoral role, there is a large body of evidence of effector memory T cells controlling tumor invasion and metastasis. Thus, high densities of memory Th1/CD8 cytotoxic T cells in the primary tumors correlate with good prognosis in most tumor types. Tertiary lymphoid structures, which contain mature dendritic cells (DC) in a T cell zone, proliferating B cells and follicular DC, are found in the tumor stroma and they correlate with intratumoral Th1/CD8 T cell and B cell infiltration. Eventually, tumors undergo genetic and epigenetic modifications that allow them to escape being controlled by the immune system. This comprehensive review describes the immune contexture of human primary and metastatic tumors, how it impacts on patient outcomes and how it could be used as a predictive biomarker and guide immunotherapies.

Cancer stem cell immunology: key to understanding tumorigenesis and tumor immune escape?

Cancer stem cell (CSC) biology and tumor immunology have shaped our understanding of tumorigenesis. However, we still do not fully understand why tumors can be contained but not eliminated by the immune system and whether rare CSCs are required for tumor propagation.

Long latency or recurrence periods have been described for most tumors. Conceptually, this requires a subset of malignant cells which is capable of initiating tumors, but is neither eliminated by immune cells nor able to grow straight into overt tumors. These criteria would be fulfilled by CSCs. Stem cells are pluripotent, immune-privileged, and long-living, but depend on specialized niches. Thus, latent tumors may be maintained by a niche-constrained reservoir of long-living CSCs that are exempt from immunosurveillance while niche-independent and more immunogenic daughter cells are constantly eliminated.

The small subpopulation of CSCs is often held responsible for tumor initiation, metastasis, and recurrence. Experimentally, this hypothesis was supported by the observation that only this subset can propagate tumors in non-obese diabetic/scid mice, which lack T and B cells. Yet, the concept was challenged when an unexpectedly large proportion of melanoma cells were found to be capable of seeding complex tumors in mice which further lack NK cells. Moreover, the link between stem cell-like properties and tumorigenicity was not sustained in these highly immunodeficient animals. In humans, however, tumor-propagating cells must also escape from immune-mediated destruction. The ability to persist and to initiate neoplastic growth in the presence of immunosurveillance – which would be lost in a maximally immunodeficient animal model – could hence be a decisive criterion for CSCs.

Consequently, integrating scientific insight from stem cell biology and tumor immunology to build a new concept of “CSC immunology” may help to reconcile the outlined contradictions and to improve our understanding of tumorigenesis.

Enhancement of the anti-melanoma response of Hu14.18K322A by αCD40 + CpG

Targeted monoclonal antibodies (mAb) can be used therapeutically for tumors with identifiable antigens such as disialoganglioside GD2, expressed on neuroblastoma and melanoma tumors. Anti-GD2 mAbs (αGD2) can provide clinical benefit in patients with neuroblastoma. An important mechanism of mAb therapy is antibody-dependent cellular cytotoxicity (ADCC). Combinatorial therapeutic strategies can dramatically increase the anti-tumor response elicited by mAbs. We combined a novel αGD2 mAb, hu14.18K322A, with an immunostimulatory regimen of agonist CD40 mAb and class B CpG-ODN 1826 (CpG). Combination immunotherapy was more effective than the single therapeutic components in a syngeneic model of GD2-expressing B16 melanoma with minimal tumor burden. NK cell depletion in B6 mice showed that NK cells were required for the anti-tumor effect; however, anti-tumor responses were also observed in tumor-bearing SCID/beige mice. Thus, NK cell cytotoxicity did not appear to be essential. Peritoneal macrophages from anti-CD40 + CpG-treated mice inhibited tumor cells in vitro in an hu14.18K322A antibody-dependent manner. These data highlight the importance of myeloid cells as potential effectors in immunotherapy regimens utilizing tumor-specific mAb and suggest that further studies are needed to investigate the therapeutic potential of activated myeloid cells and their interaction with NK cells.

The immune microenvironment of human tumors: general significance and clinical impact

Human cancers grow in a microenvironment of stromal, inflammatory and immunocompetent cells which is variable from tumor to tumor. The characterization of the immune contexture, i.e. the type, density and functional orientation of immunocompetent cells, the presence or absence of tertiary lymphoid structures is a major prognostic factor for patients survival and represent a guide and a target for innovative cancer therapies.