Cancer immunoediting from immune surveillance to immune escape

Immune Stress-induced Tumor Mutation Burden and Neoantigen Expression in 4T1 Mammary Cancer Cells: A Potential Mechanism for Long-term Survival in Patients Treated With Immune Checkpoint Inhibitors

BACKGROUND/AIM

The Kaplan-Meier curves for patients treated with immune checkpoint inhibitors (ICIs) display a small group of potentially-cured patients with long-term survival, creating a 'kangaroo-tail' shape of the survival curve. However, the mechanistic basis of this phenomenon and what occurs in patients whose cancer is resistant to ICIs remain unclear. The present study aimed to answer these questions.

MATERIALS AND METHODS

We analyzed mutations in mouse 4T1 mammary-gland-derived cancer cells expressing the hemagglutinin antigen (4T1-HA), which were grown in either wild-type mice or cytotoxic T-lymphocyte (CTL)-loaded immunocompromised mice (RAG-/- + ACT) under immune stress. These mutations were compared to those in 4T1-HA cells grown in RAG-/- mice without immune stress as a control.

RESULTS

The number of gene mutations, the tumor mutation burden (TMB) and microsatellite instability (MSI) scores were increased in the cancer cells under immune stress. The mutations in the antigen protein were such that the protein retained its immunogenicity and could still function as a neoantigen. Repeated immune recognition of additional neoantigens may lead to the kangaroo-tail survival phenomenon. The common genetic mutations of the analyzed 4T1-HA cells under immune stress included genes related to immune response. Analysis of alternative splicing of genes showed that are accumulated gene alterations under immune stress related to cancer-cell proliferation. Copy-number variation (CNV) analysis indicated that normal-antigen presentation and immune responses may be impaired under immune stress.

CONCLUSION

Cancer cells, under immune stress, may acquire both immune escape capabilities and increased immunogenicity. This dual effect could lead to either resistance or response to ICIs, respectively.

GM3-containing nanoparticles in immunosuppressed hosts: Effect on myeloid-derived suppressor cells

Cancer vaccines to date have not broadly achieved a significant impact on the overall survival of patients. The negative effect on the immune system of the tumor itself and conventional anti-tumor treatments such as chemotherapy is, undoubtedly, a key reason for these disappointing results. Myeloid-derived suppressor cells (MDSCs) are considered a central node of the immunosuppressive network associated with tumors. These cells inhibit the effector function of natural killer and CD8⁺ T cells, expand regulatory T cells and can differentiate into tumor-associated macrophages within the tumor microenvironment. Thus, overcoming the suppressive effects of MDSCs is likely to be critical for cancer immunotherapy to generate effective anti-tumor immune responses. However, the capacity of cancer vaccines and particularly their adjuvants to overcome this inhibitory population has not been well characterized. Very small size proteoliposomes (VSSP) is a nanoparticulated adjuvant specifically designed to be formulated with vaccines used in the treatment of immunocompromised patients. This adjuvant contains immunostimulatory bacterial signals together with GM3 ganglioside. VSSP promotes dendritic cell maturation, antigen cross-presentation to CD8⁺ T cells, Th1 polarization, and enhances CD8⁺ T cell response in tumor-free mice. Currently, four cancer vaccines using VSSP as the adjuvant are in Phase I and II clinical trials. In this review, we summarize our work characterizing the unique ability of VSSP to stimulate antigen-specific CD8⁺ T cell responses in two immunocompromised scenarios; in tumor-bearing mice and during chemotherapy-induced leukopenia. Particular emphasis has been placed on the interaction of these nanoparticles with MDSCs, as well as comparison with other cancer vaccine adjuvants currently in preclinical or clinical studies.