Tumor-associated dendritic cells: molecular mechanisms to suppress antitumor immunity

Drug Resistance in Cancers: A Free Pass for Bullying

The cancer burden continues to grow globally, and drug resistance remains a substantial challenge in cancer therapy. It is well established that cancerous cells with clonal dysplasia generate the same carcinogenic lesions. Tumor cells pass on genetic templates to subsequent generations in evolutionary terms and exhibit drug resistance simply by accumulating genetic alterations. However, recent evidence has implied that tumor cells accumulate genetic alterations by progressively adapting. As a result, intratumor heterogeneity (ITH) is generated due to genetically distinct subclonal populations of cells coexisting. The genetic adaptive mechanisms of action of ITH include activating "cellular plasticity", through which tumor cells create a tumor-supportive microenvironment in which they can proliferate and cause increased damage. These highly plastic cells are located in the tumor microenvironment (TME) and undergo extreme changes to resist therapeutic drugs. Accordingly, the underlying mechanisms involved in drug resistance have been re-evaluated. Herein, we will reveal new themes emerging from initial studies of drug resistance and outline the findings regarding drug resistance from the perspective of the TME; the themes include exosomes, metabolic reprogramming, protein glycosylation and autophagy, and the relates studies aim to provide new targets and strategies for reversing drug resistance in cancers.

Acquired resistance to cancer immunotherapy: Role of tumor-mediated immunosuppression

In the tumor microenvironment (TME), tumor cells are constantly evolving to reduce neoantigen generation and the mutational burden to escape the anti-tumor response. This will lower tumor reactivity to the adaptive immune response and give rise to tumor intrinsic factors, such as altered expression of immune regulatory molecules on tumor cells. Tumor-extrinsic factors, such as immunosuppressive cells, soluble suppressive molecules or inhibitory receptors expressed by immune cells will alter the composition and activity of tumor-infiltrating lymphocytes (TILs) (by increasing T regulatory cells:T effector cells ratio and inhibiting T effector cell function) and promote tumor growth and metastasis. Together, these factors limit the response rates and clinical outcomes to a particular cancer therapy. Within the TME, the cross-talks between immune and non-immune cells result in the generation of positive feedback loops, which augment immunosuppression and support tumor growth and survival (termed as tumor-mediated immunosuppression). Cancer immunotherapies, such as immune checkpoint inhibitors (ICIs) and adoptive cell transfer (ACT), have shown therapeutic efficacy in hematologic cancers and different types of solid tumors. However, achieving durable response rates in some cancer patients remains a challenge as a result of acquired resistance and tumor immune evasion. This could be driven by the cellular and molecular suppressive network within the TME or due to the loss of tumor antigens. In this review, we describe the contribution of the immunosuppressive cellular and molecular tumor network to the development of acquired resistance against cancer immunotherapies. We also discuss potential combined therapeutic strategies which could help to overcome such resistance against cancer immunotherapies, and to enhance anti-tumor immune responses and improve clinical outcomes in patients.

Mycobacterium indicus pranii induces dendritic cell activation, survival, and Th1/Th17 polarization potential in a TLR-dependent manner

MIP is a nonpathogenic, soil-borne predecessor of Mycobacterium avium. It has been reported previously that MIP possesses strong immunomodulatory properties and confers protection against experimental TB and tumor. DCs, by virtue of their unmatched antigen-presentation potential, play a critical role in activation of antitumor and antimycobacterial immune response. The effect of MIP on the behavior of DCs and the underlying mechanisms, however, have not been investigated so far. In the present study, we showed that MIP induces significant secretion of IL-6, IL-12p40, IL-10, and TNF-α by DCs and up-regulates the expression of costimulatory molecules CD40, CD80, and CD86. MIP(L) induced a significantly higher response compared with MIP(K). PI and Annexin V staining showed that MIP increases DC survival by inhibiting apoptosis. Consistently, higher expression of antiapoptotic proteins Bcl-2 and Bcl-xl was observed in MIP-stimulated DCs. Cytokines, produced by naïve T cells, cocultured with MIP-stimulated DCs, showed that MIP promotes Th1/Th17 polarization potential in DCs. Response to MIP was lost in MyD88(-/-)DCs, underscoring the critical role of TLRs in MIP-induced DC activation. Further studies revealed that TLR2 and TLR9 are involved in DC activation by MIP(L), whereas MIP(K) activates the DCs through TLR2. Our findings establish the DC activation by MIP, define the behavior of MIP-stimulated DCs, and highlight the role of TLRs in MIP-induced DC activation.

Dendritic cells in Barrett's esophagus carcinogenesis: an inadequate microenvironment for antitumor immunity?

Barrett's esophagus corresponds to the replacement of the normal esophageal squamous epithelium by a columnar epithelium through a metaplastic process. This tissue remodeling is associated with chronic gastroesophageal reflux and constitutes a premalignant lesion leading to a 30- to 60-fold increase in the risk to evolve into esophageal adenocarcinoma. The present study aimed to investigate a possible immune evasion in Barrett's esophagus favoring esophageal adenocarcinoma development. We demonstrated that myeloid and plasmacytoid dendritic cells are recruited during the esophageal metaplasia-dysplasia-carcinoma sequence, through the action of their chemoattractants, macrophage inflammatory protein 3α and chemerin. Next, we showed that, in contrast to plasmacytoid dendritic cells, myeloid dendritic cells, co-cultured with Barrett's esophagus and esophageal adenocarcinoma cell lines, display a tolerogenic phenotype. Accordingly, myeloid dendritic cells co-cultured with esophageal adenocarcinoma cell lines stimulated regulatory T cell differentiation from naïve CD4(+) T cells. In agreement with those results, we observed that both metaplastic areas and (pre)malignant lesions of the esophagus are infiltrated by regulatory T cells. In conclusion, soluble factors secreted by epithelial cells during the esophageal metaplasia-dysplasia-carcinoma sequence influence dendritic cell distribution and promote tumor progression by rendering them tolerogenic.