**4.1.4 Dendritic cells and mast cells**

218 Breast Cancer – Focusing Tumor Microenvironment, Stem Cells and Metastasis

c-Myc, MMP, and VEGF, which are all involved in promoting tumourigenesis. In BCA, NOS2 expression within tumour cells themselves is correlated with increased tumour grade

T cells orient their cytoskeleton and migrate towards sites of inflammation, such as those present in a tumour microenvironment (TME), in a PKC-dependent manner as a direct result of CD44 crosslinking by HA (Fanning *et al*., 2005). In BCA, CD8+ T cells are most predominant in advanced cancer stages where their presence in proliferating tumours is a good prognostic indicator. T cells are able to participate in either a Th1 or Th2 polarized immune response and, when polarized to a Th1 response, they express and secrete IFNγ, TGFβ, TNFα, IL-2, resulting in cytotoxic cooperation (T cells and M1). Th2 polarized CD4+ T cells secrete IL-4,5,6,10,13 which leads to an increase in B cell mediated immunity (DeNardo and Coussens, 2007). Because of the anti-tumour effects of T cells, the activation of cytotoxic T cells against HA receptors as immunotherapy in leukemias is currently undergoing clinical trials and will be discussed later in this chapter. On the other hand, the presence of CD4+ T cells correlates with disease progression and metastasis; however, it has been shown by different groups that CD4+ T cells are crucial for mounting an immune response against cancer. For example, tumour growth of EL4 lymphoma cells inoculated into mice is inhibited by the presence of dendritic cells primed against RHAMM protein. This interaction, however, is dependent on CD4+ T cells, as the effect of DC killing of the tumour is significantly reduced with a reduced CD4+ T cell population (Fukui *et al*., 2006). Furthermore, Rakhra *et al.* (2010) showed that in ALL and B-cell leukemia, CD4+ cells were necessary for sustained tumour regression. In mouse models, inhibition of MYC or BCR-ABL rescues tumours from oncogene addiction; however, tumours regress in the presence of TSP-1 induced CD4+ T cells, and knockdown of TSP-1 impairs this ability (Rakhra *et al*.,

Regulatory T cells (Treg; CD4+/CD25+/FOXP3+) play controversial roles in tumour progression and can have both anti- and pro-tumourigenic effects, depending on the chemokines or cytokines produced and the type of solid tumour. Treg cells may be activated in an immunosuppressive manner, preventing cytotoxic immune responses, and allowing the tumours to evade immune attack. For example, in CLL, a large Treg population dampens specific CD8+ T cell responses against tumour associated antigens (Giannopoulos *et al*., 2010). The same may be true for solid tumours. When coordinated, however, with a high T cell density, they may indicate good prognosis and inhibition of metastasis (Camus *et* 

Immunoglobulin deposition by B cells in BCA stroma can be detrimental to disease progression and the accumulation of autoantibodies produced by B cells and deposited in the stroma correlates with poor prognosis (Fernandez Madrid *et al*., 2005). An increase in serum IgG correlates with an increase in TAM numbers which, in turn, promotes angiogenesis in mouse mammary carcinoma, a process associated with poor clinical outcome. A proposed mechanism for the involvement of TAMs in B cell processes is the phagocytosis of IgG by macrophages. IgG engages Fcγ receptors, which stimulates VEGF secretion, increases angiogenesis and promotes tumour growth rate (Barbera-Guillem *et al*.,

and angiogenesis (Ambs and Glynn, 2011).

**4.1.2 T Cells** 

2010).

*al*., 2009, Carreras *et al*., 2006).

**4.1.3 B Cells** 

Dendritic cells (DC) can also exhibit HA dependent characteristics that either promote or inhibit tumourigenesis. HA or chondroitin sulphate, in conjunction with CSF-1, activate DC from an immature to differentiated state via an NFκB regulated process, illustrating the importance of HA in eliciting an immune response (Yang *et al*., 2002). Pedroza-Gonzalez *et al* (2011) recently showed that human BCA produces thymic stromal lymphopoietin (TSLP) which induces expression of OX40L on DCs, polarizing them towards a Th2 inflammatory response. *In vitro* this drives the production of IL-13 and TNF by Th2 polarized T cells (Pedroza-Gonzalez *et al*., 2011). DC also become tumour insensitive and, as a result, do not mature and differentiate into cytotoxic cells. Furthermore, HA fragment build ups are at least partly responsible for preventing DC maturation in tumour bearing animals (Kuang *et al*., 2008).

In BCA, c-kit expression by mast cells, a protein which is usually only present in specific tissue types, such as germ cells, predicts primary tumour recurrence (Khazaie *et al*., 2011). However, an abundance of stromal mast cells in invasive BCA is associated with good prognosis (Rajput *et al*., 2008). The mast cell line HMC-1 expresses high levels of CD44s and, through an interaction with HA, adheres to stromal tissue (Fukui *et al*., 2000). Therefore, in both mast cells and DC, a CD44-HA interaction may result in anti-tumour responses.
