Tumor vaccines and beyond

Therapeutic targets and biomarkers of tumor immunotherapy: response versus non-response

Cancers are highly complex diseases that are characterized by not only the overgrowth of malignant cells but also an altered immune response. The inhibition and reprogramming of the immune system play critical roles in tumor initiation and progression. Immunotherapy aims to reactivate antitumor immune cells and overcome the immune escape mechanisms of tumors. Represented by immune checkpoint blockade and adoptive cell transfer, tumor immunotherapy has seen tremendous success in the clinic, with the capability to induce long-term regression of some tumors that are refractory to all other treatments. Among them, immune checkpoint blocking therapy, represented by PD-1/PD-L1 inhibitors (nivolumab) and CTLA-4 inhibitors (ipilimumab), has shown encouraging therapeutic effects in the treatment of various malignant tumors, such as non-small cell lung cancer (NSCLC) and melanoma. In addition, with the advent of CAR-T, CAR-M and other novel immunotherapy methods, immunotherapy has entered a new era. At present, evidence indicates that the combination of multiple immunotherapy methods may be one way to improve the therapeutic effect. However, the overall clinical response rate of tumor immunotherapy still needs improvement, which warrants the development of novel therapeutic designs as well as the discovery of biomarkers that can guide the prescription of these agents. Learning from the past success and failure of both clinical and basic research is critical for the rational design of studies in the future. In this article, we describe the efforts to manipulate the immune system against cancer and discuss different targets and cell types that can be exploited to promote the antitumor immune response.

Clinically feasible approaches to potentiating cancer cell-based immunotherapies

The immune system exerts both tumor-destructive and tumor-protective functions. Mature dendritic cells (DCs), classically activated macrophages (M1), granulocytes, B lymphocytes, aβ and ɣδ T lymphocytes, natural killer T (NKT) cells, and natural killer (NK) cells may be implicated in antitumor immunoprotection. Conversely, tolerogenic DCs, alternatively activated macrophages (M2), myeloid-derived suppressor cells (MDSCs), and regulatory T (Tregs) and B cells (Bregs) are capable of suppressing antitumor immune responses. Anti-cancer vaccination is a useful strategy to elicit antitumor immune responses, while overcoming immunosuppressive mechanisms. Whole tumor cells or lysates derived thereof hold more promise as cancer vaccines than individual tumor-associated antigens (TAAs), because vaccinal cells can elicit immune responses to multiple TAAs. Cancer cell-based vaccines can be autologous, allogeneic or xenogeneic. Clinical use of xenogeneic vaccines is advantageous in that they can be most effective in breaking the preexisting immune tolerance to TAAs. To potentiate immunotherapy, vaccinations can be combined with other modalities that target different immune pathways. These modalities include 1) genetic or chemical modification of cell-based vaccines; 2) cross-priming TAAs to T cells by engaging dendritic cells; 3) T-cell adoptive therapy; 4) stimulation of cytotoxic inflammation by non-specific immunomodulators, toll-like receptor (TLR) agonists, cytokines, chemokines or hormones; 5) reduction of immunosuppression and/or stimulation of antitumor effector cells using antibodies, small molecules; and 6) various cytoreductive modalities. The authors envisage that combined immunotherapeutic strategies will allow for substantial improvements in clinical outcomes in the near future.

Timing and intensity of exposure to interferon-γ critically determines the function of monocyte-derived dendritic cells

A growing body of evidence suggests that inflammatory cytokines have a dualistic role in immunity. In this study, we sought to determine the direct effects of interferon-γ (IFN-γ) on the differentiation and maturation of human peripheral blood monocyte-derived dendritic cells (moDC). Here, we report that following differentiation of monocytes into moDC with granulocyte-macrophage colony-stimulating factor and interleukin-4, IFN-γ induces moDC maturation and up-regulates the co-stimulatory markers CD80/CD86/CD95 and MHC Class I, enabling moDC to effectively generate antigen-specific CD4(+) and CD8(+) T-cell responses for multiple viral and tumour antigens. Early exposure of monocytes to high concentrations of IFN-γ during differentiation promotes the formation of macrophages. However, under low concentrations of IFN-γ, monocytes continue to differentiate into dendritic cells possessing a unique gene-expression profile, resulting in impairments in subsequent maturation by IFN-γ or lipopolysaccharide and an inability to generate effective antigen-specific CD4(+) and CD8(+) T-cell responses. These findings demonstrate that IFN-γ imparts differential programmes on moDC that shape the antigen-specific T-cell responses they induce. Timing and intensity of exposure to IFN-γ can therefore determine the functional capacity of moDC.

Expression of the brother of the regulator of imprinted sites gene in the sputum of patients with lung cancer

Background

Brother of the regulator of imprinted sites (BORIS) is a putative new oncogene that is classified as a cancer germline gene; however, its role in the development of cancer is unclear. This study investigated the expression of BORIS in lung cancer and its clinical implications.

Methods

The expression of BORIS messenger ribonucleic acid (mRNA) in the sputum of 100 patients with lung cancer (50 with squamous cell carcinoma, 36 with adenocarcinoma, and 14 with small-cell carcinoma) was evaluated by reverse transcription polymerase chain reaction.

Results

The overall expression rate of BORIS in patients with lung cancer was 36.0%: 19 of 50 squamous cell carcinomas (38.0%), 13 of 36 adenocarcinomas (36.1%), and 4 of 14 (28.6%) small-cell carcinomas. There was no significant difference in the BORIS expression according to age, gender, or histologic type. However, the mRNA expression of BORIS was significantly related to the pathologic cancer stage (p=0.004) and lymph node metastasis (p=0.001). The expression of the melanoma antigen gene family A1–6 was not associated with the expression of BORIS.

Conclusion

Our results suggest that the expression of BORIS might be a negative prognostic factor in lung cancers and implicate BORIS as a molecular target for immunotherapy.

Cancer vaccines: harnessing the potential of anti-tumor immunity

Although the presence of cancer suggests failure of the immune system to protect against development of tumors, the possibility that immunity can be redirected and focused to generate an anti-tumor response offers great translational possibility. The key to this is identifying antigens likely to be present in any given tumor and functionally critical to tumor survival and growth. Such tumor-associated antigens (TAAs) are varied and optimally should be absent from normal tissue. Of particular interest are TAAs associated with the tumor stroma, as immunity directed against the stroma may restrict the ability of the tumor to grow and metastasize. Important to directing the immune system toward an effect anti-tumor response is the understanding of how TAAs are processed and how the tumor is able to evade immune elimination. The process of immunoediting happens in response to the selective pressure that the immune system places upon tumor cell populations and allows for emergence of tumor cells capable of escaping immune destruction. Efforts to harness the immune system for clinical application has been aided by vaccines based on purified recombinant protein or nucleic acid TAAs. For example, a vaccine for canine melanoma has been developed and approved based on immunization with DNA components of tyrosinase, a glycoprotein essential to melanin synthesis. The performance of cancer vaccines has been aided in some cases when supplemented with immunostimulatory molecules such as interleukin 2 or a novel extracellular matrix vaccine adjuvant. Vaccines with the broadest menu of antigenic targets may be those most likely to succeed against cancer. For this reason, tissue vaccines produced from harvested tumor material may offer significant benefit. With several cancer vaccines on the veterinary and human markets, efforts to understand basic tumor immunology are soon to yield great dividends.

Examining T cells at vaccine sites of tumor-bearing hosts provides insights to dysfunctional T-cell immunity

When tumor vaccines are administered as cancer immunotherapy, cellular interactions at the vaccine site are crucial to the generation of antitumor immunity. Examining interactions at the vaccine site could provide important insights to the success or failure of vaccination. Our laboratory previously showed that while administration of a cell-based vaccine to tumor-free mice leads to productive antineuroblastoma immunity, vaccination of tumor-bearing mice does not. The goal of this study was to examine immune effectors at the vaccine site to identify mechanisms responsible for the generation of ineffective antitumor immunity in tumor-bearing mice. The results of this study show that vaccine sites of tumor-bearing mice contained significantly fewer T cells than vaccine sites of tumor-free mice. Similar migration and proliferation of T cells was observed in the vaccine sites of tumor-bearing and tumor-free mice, but T cells in the sites of tumor-bearing mice were more apoptotic. T cells at the vaccine sites of both tumor-free and tumor-bearing mice had an effector-memory phenotype and expressed activation markers. Despite the activated phenotype, T cells from tumor-bearing mice elicited defective antitumor immune responses. Although T cells from vaccine sites of tumor-bearing mice were capable of producing inflammatory cytokines, the T cells from tumor-bearing mice produced lower levels of cytokines compared with T cells from the tumor-free mice. Remarkably, this defect seems to be systemic, affecting distal T cells in tumor-bearing mice. This study demonstrates that the defective vaccine-induced immune response to neuroblastoma in tumor-bearing hosts originates as a result of tumor burden, resulting in poor antitumor immunity.

Innovation and opportunity for chimeric antigen receptor targeted T cells

Adoptive cell therapy truly began with the introduction of hematopoietic stem cell transplantation. The ability to manipulate genes through cloning and expression methodologies have allowed for the development of novel chimeric receptors to selectively target cancer when introduced into immune cells. Over the past decade, gene engineered cells have been tested in clinical trials throughout the world. Recent data and striking clinical responses demonstrate the power of this new type of therapy. Current challenges include managing a potent therapy that is a dividing, rather than a static drug, safeguarding against potential toxicity, and further development to enable access to a greater number of patients.