An overlooked tumor promoting immunoregulation by non-hematopoietic stromal cells

Mesenchymal and Vascular Dissemination Markers, Erythroblastosis Virus E26 Oncogene Homolog (ERG) and Alpha Smooth Muscle Actin (α-SMA), in Colorectal Cancer and Adjacent Tissue, Pericytes or Microvascular Density

The harmony between malignant cells and the adjacent microenvironment is a sophisticated subject; however, it seems to play an important role in cancer evolution. This study aimed to assess the microvascular density (MVD) and the mean pericyte number in the tumor and adjacent tissue, and to correlate the results with special histopathological prognostic variables of the tumor. The study included 48 colorectal cancer (CRC) cases diagnosed in the central lab of Duhok. The immunohistochemical (IHC) expressions of the mesenchymal and vascular dissemination markers, erythroblastosis virus E26 oncogene homolog (ERG, a member of the ETS family of transcription factors) and alpha smooth muscle actin (α-SMA) for microvascular density and pericytes, were assessed in tumor cells and in adjacent tissue around the tumor and then correlated to clinicopathological variables with a special concentration on inflammatory reaction, tumor budding, tumor deposition, and lymphovascular invasion. The results showed that the MVD was significantly higher outside the tumor in T1 and T2 compared with T3 and T4. Moreover, it was significantly higher in grade I when compared to grades II and III within the tumor. However, no correlation was found between the MVD and the special histopathological variables that had been studied. On the other hand, the low mean pericyte showed multiple significant associations outside tumor areas, with special histopathological features including a severe inflammatory reaction, a positive tumor deposit, and a negative lymphovascular invasion. These findings may indicate that defective or transformed pericytes around the tumor can participate in the development of the tumor and, subsequently, the outcome and prognosis.

TGF-β-induced IGFBP-3 is a key paracrine factor from activated pericytes that promotes colorectal cancer cell migration and invasion

The crosstalk between cancer cells and the tumor microenvironment has been implicated in cancer progression and metastasis. Fibroblasts and immune cells are widely known to be attracted to and modified by cancer cells. However, the role of pericytes in the tumor microenvironment beyond endothelium stabilization is poorly understood. Here, we report that pericytes promoted colorectal cancer (CRC) cell proliferation, migration, invasion, stemness, and chemoresistance in vitro, as well as tumor growth in a xenograft CRC model. We demonstrate that coculture with human CRC cells induced broad transcriptomic changes in pericytes, mostly associated with TGF-β receptor activation. The prognostic value of a TGF-β response signature in pericytes was analyzed in CRC patient data sets. This signature was found to be a good predictor of CRC relapse. Moreover, in response to stimulation by CRC cells, pericytes expressed high levels of TGF-β1, initiating an autocrine activation loop. Investigation of secreted mediators and underlying molecular mechanisms revealed that IGFBP-3 is a key paracrine factor from activated pericytes affecting CRC cell migration and invasion. In summary, we demonstrate that the interplay between pericytes and CRC cells triggers a vicious cycle that stimulates pericyte cytokine secretion, in turn increasing CRC cell tumorigenic properties. Overall, we provide another example of how cancer cells can manipulate the tumor microenvironment.

Immune Regulation by Pericytes: Modulating Innate and Adaptive Immunity

Pericytes (PC) are mural cells that surround endothelial cells in small blood vessels. PC have traditionally been credited with structural functions, being essential for vessel maturation and stabilization. However, an accumulating body of evidence suggests that PC also display immune properties. They can respond to a series of pro-inflammatory stimuli and are able to sense different types of danger due to their expression of functional pattern-recognition receptors, contributing to the onset of innate immune responses. In this context, PC not only secrete a variety of chemokines but also overexpress adhesion molecules such as ICAM-1 and VCAM-1 involved in the control of immune cell trafficking across vessel walls. In addition to their role in innate immunity, PC are involved in adaptive immunity. It has been reported that interaction with PC anergizes T cells, which is attributed, at least in part, to the expression of PD-L1. As components of the tumor microenvironment, PC can also modulate the antitumor immune response. However, their role is complex, and further studies will be required to better understand the crosstalk of PC with immune cells in order to consider them as potential therapeutic targets. In any case, PC will be looked at with new eyes by immunologists from now on.