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Traditionally, vaccines have helped eradication of several infectious diseases and also saved millions of lives in the human history. Those prophylactic vaccines have acted through inducing immune responses against a live attenuated, killed organism or antigenic subunits to protect the recipient against a real infection caused by the pathogenic microorganism. Nevertheless, development of anticancer vaccines as valuable targets in human health has faced challenges and requires further optimizations. Dendritic cells (DCs) are the most potent antigen presenting cells (APCs) that play essential roles in tumor immunotherapies through induction of CD8+ T cell immunity. Accordingly, various strategies have been tested to employ DCs as therapeutic vaccines for exploiting their activity against tumor cells. Application of whole tumor cells or purified/recombinant antigen peptides are the most common approaches for pulsing DCs, which then are injected back into the patients. Although some hopeful results are reported for a number of DC vaccines tested in animal and clinical trials of cancer patients, such approaches are still inefficient and require optimization. Failure of DC vaccination is postulated due to immunosuppressive tumor microenvironment (TME), overexpression of checkpoint proteins, suboptimal avidity of tumor-associated antigen (TAA)-specific T lymphocytes, and lack of appropriate adjuvants. In this review, we have an overview of the current experiments and trials evaluated the anticancer efficacy of DC vaccination as well as focusing on strategies to improve their potential including combination therapy with immune checkpoint inhibitors (ICIs). • DC vaccination is the current focus in cancer therapy. • DC vaccination acts through enhancement of antitumor immune responses. • Clinical efficacy of DC vaccination is not satisfactory. • Combination with ICIs increases antitumor efficacy of DC vaccination. [ABSTRACT FROM AUTHOR]

B7 homolog 3 (B7-H3, also called CD276) is a checkpoint of B7 family that is aberrantly and consistently expressed in several human cancers, and its overexpression correlates with weak prognosis. B7-H3 is expressed on a number of cells, and it acts as a driver of immune evasion. This is mediated through hampering T cell infiltration and promoting exhaustion of CD8+ T cells. Increased B7-H3 activity also promotes macrophage polarity toward pro-tumor type 2 (M2) phenotype. In addition, high B7-H3 activity induces aberrant angiogenesis to promote hypoxia, a result of which is resistance to common immune checkpoint inhibitor (ICI) therapy. This is mediated through the impact of hypoxia on dampening CD8+ T cell recruitment into tumor area. The immunosuppressive property of B7-H3 offers insights into targeting this checkpoint as a desired approach in cancer immunotherapy. B7-H3 can be a target in blocking monoclonal antibodies (mAbs), combination therapies, chimeric antigen receptor-modified T (CAR-T) cells and bispecific antibodies. • B7-H3 is overexpressed in tumor vs. normal tissue. • B7-H3 hampers CD8+ T cell infiltration and promotes their exhaustion. • B7-H3 poorly co-expresses with PD-L1. • B7-H3 can provide an alternative mechanism for bypassing ICI therapy. • Anti-B7-H3 biAbs act more selectively compared with monotherapy. [ABSTRACT FROM AUTHOR]

Extending the durability of response is the current focus in cancer immunotherapy with immune checkpoint inhibitors (ICIs). However, factors like non-immunogenic tumor microenvironment (TME) along with aberrant angiogenesis and dysregulated metabolic systems are negative contributors. Hypoxia is a key TME condition and a critical promoter of tumor hallmarks. It acts on immune and non-immune cells within TME in order for promoting immune evasion and therapy resistance. Extreme hypoxia is a major promoter of resistance to the programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) inhibitor therapy. Hypoxia inducible factor-1 (HIF-1) acts as a key mediator of hypoxia and a critical promoter of resistance to the anti-PD-(L)1. Targeting hypoxia or HIF-1 can thus be an effective strategy for reinvigoration of cellular immunity against cancer. Among various strategies presented so far, the key focus is over vascular normalization, which is an approach highly effective for reducing the rate of hypoxia, increasing drug delivery into the tumor area, and boosting the efficacy of anti-PD-(L)1. • Hypoxic TME is a key promoter of ICI resistance/refractory. • High PD-L1 level is a marker of poor prognosis but higher response to ICIs. • Aberrant angiogenesis/hypoxia/dysregulated metabolism promote T cell exclusion/exhaustion. • Vascular normalization dampens tumor hypoxia and promotes ICI sensitization. • Low-dose anti-angiogenic therapy increases ICI sensitivity. [ABSTRACT FROM AUTHOR]

Immune checkpoint inhibitor (ICI) resistance demands for acquisition of novel strategies in order to broaden the therapeutic repertoire of advanced cancers. Bispecific antibodies can be utilized as an emerging therapeutic paradigm and a step forward in cancer immunotherapy. Synchronous inhibition of programmed death-1 (PD-1), programmed death-ligand 1 (PD-L1) or cytotoxic T lymphocyte associated antigen-4 (CTLA-4), or with other agents can expand antibody selectivity and improve therapeutic window through tightening cell-to-cell bridge (a process called immunological synapse) within tumor immune microenvironment (TIME). There is evidence of higher potency of this co-targeting approach over combined single-agent monoclonal antibodies in reinvigorating anti-tumor immune responses, retarding tumor growth, and improving patient survival. In fact, immunological synapses formed by interactions of such bispecific agents with TIME cells directly mediate cytotoxicity against tumor cells, and durable anti-tumor immune responses are predictable after application of such agents. Besides, lower adverse events are reported for bispecific antibodies compared with individual checkpoint inhibitors. These are all indicative of the importance of exploiting novel bispecific approach as a replacement for conventional combo checkpoint inhibitor therapy particularly for tumors with immunosuppressive or cold immunity. Study in this area is still continued, and in the future more will be known about the importance of this bispecific approach in cancer immunotherapy. • Bispecific inhibitors are more effective compared with combination of single-agent mAbs. • Lower adverse events are reported for bispecific (vs. monospecific) antibodies. • Bispecific inhibitors reactivate anti-cancer T cells more selectively. [ABSTRACT FROM AUTHOR]

Resistance to immune checkpoint inhibitors (ICIs) is a major issue of the current era in cancer immunotherapy. Immune evasion is a multi-factorial event, which occurs generally at a base of cold immunity. Despite advances in the field, there are still unsolved challenges about how to combat checkpoint hijacked by tumor cells and what are complementary treatment strategies to render durable anti-tumor outcomes. A point is that anti-programed death-1 receptor (PD-1)/anti-programmed death-ligand 1 (PD-L1) is not the solo path of immune escape, and responses in many types of solid tumors to the PD-1/PD-L1 inhibitors are not satisfactory. Thus, seeking mechanisms inter-connecting tumor with its immune ecosystem nearby unravel more about resistance mechanisms so as to develop methods for sustained reinvigoration of immune activity against cancer. In this review, we aimed to discuss about common and specific paths taken by tumor cells to evade immune surveillance, describing novel detection strategies, as well as suggesting some approaches to recover tumor sensitivity to the anti-PD-(L)1 therapy based on the current knowledge. • Resistance to anti-PD-(L)1 is multi-factorial. • Defective infiltration and effector CD8+ T cells is a critical driver of ICI resistance. • PD-L1 high MHC-I low tumor cell signature is a reliable biomarker of ICI resistance. [ABSTRACT FROM AUTHOR]

Immunotherapy has revolutionized treatment of cancer during the last decades. Oncolytic virotherapy has also emerged as a strategy to fight against cancer cells both via lysis of malignant cells and activating immune responses. Accepted as a logical strategy, combination of monoclonal antibodies particularly against the programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) is introduced to improve clinical responses to immune checkpoint inhibitors (ICIs). Accordingly, Talimogene laherparepvec (T-VEC) has received approval for clinical use, while a number of oncolytic Adenoviruses (Ads) are being investigated in clinical trials of malignancies. Combination of oncolytic Ads with PD-1/PD-L1 inhibitors have shown potentials in promoting responses to ICIs, changing the tumor microenvironment, inducing long-term protection against tumor, and promoting survival among mice models of malignancies. Regarding the increasing importance of oncolytic Ads in combination therapy of cancers, in this review we decide to outline recent studies in this field. [ABSTRACT FROM AUTHOR]

Tumor microenvironment (TME) takes critical roles in tumor resistance to immune checkpoint inhibitors (ICIs) including anti-programmed death-1 (PD-1) or anti-programmed death-ligand 1 (PD-L1). Cancer stem cells (CSCs) are one of the key components of TME that play important roles in immunoregulation and therapy resistance. CSCs suppress CD8+ T cell infiltration, and promote recruitment of type 2 macrophages (M2) and the activity of type 2 neutrophils (N2). There is a positive association between CSC expansion with high PD-L1 expression in TME, and the expression of PD-L1 is higher in CSCs than cancer cells. PD-L1 expression in metastatic cancer cells induces a dedifferentiation program through stimulating an epithelial-mesenchymal transition (EMT) profile, thereby replenishing CSC proportion inside tumor. Conversion from EMT to mesenchymal-epithelial transition (MET) downregulates PD-L1 expression on CSCs and non-CSCs and increases ICI efficacy. There is an evidence of CSC replenishment secondary to the anti-PD-1 therapy. Targeting CSCs is, in fact, a key step in effective tumor breakdown and reducing tumor recurrence after immunotherapy. A number of signaling are involved in CSC enrichment within tumor area, among them a key focus is over transforming growth factor-β (TGF-β). TGF-β induces a dedifferentiation program, and its activity as a bridge between EMT with increased PD-L1 level rationalizes application of dual TGF-β/anti-PD-L1 inhibitors as an effective strategy for reinvigorating immunoactivities in patients under ICI therapy. In this review, we aimed to discuss about connections between CSCs with immune ecosystem of tumor and the impact of such interactions on cancer responses to ICI therapy. • The impact of CSCs on tumor immune ecosystem is necessary for hampering ICI efficacy. • EMT is strongly associated with increased expression of immune checkpoints. • MET conversion can be an approach for tumor sensitization to the ICI therapy. • TGF-β is a key CSC inducer that links EMT with increased PD-L1 level in tumor area. • CSCs can be targeted to boost ICI efficacy. • Tumor heterogeneity is linked positively with CSC characteristics and affects ICI responses. [ABSTRACT FROM AUTHOR]