Solid tumours are composed of tumour stromal cells, blood vessels, infiltrating immune cells and tumour cells themselves. Over the last decade, a growing body of literature has highlighted the importance of the tumour microenvironment for the prognosis of different types of cancer [
1]. The significance of tumour stroma for the overall prognosis may be in part due to the fact that several components of the tumour-microenvironment have been shown to compromise immune effector functions against tumour cells [
2]. Tumour invading immune cells are functionally impaired within tumours: NK cells, derived from non small cell lung tumours display a decreased cytotoxicity against cancer cells
in vitro and differ from NK cells from peripheral blood not only by a different cytokine secretion, but also by other functional alterations [
3]. In a comprehensive study, tumour-infiltrating lymphocytes were analysed and regulatory T cells could be identified in all tumour samples, which impair anti-tumour responses of immune effector cells [
4]. More evidence for the immunological activities of tumour stroma came from the elimination of cancer associated fibroblasts in a murine breast cancer model resulting in a shift from Th2 to Th1 polarization [
5]. Hence, tumour stromal cells (TStrC) may participate in regulation of immune effector functions at several levels [
6]. However, the exact mechanisms are poorly understood. The site of origin and recruitment of TStrC into the tumour have been identified as key issues in the elucidation of TStrC function in the microenvironment [
7]. TStrC resemble multipotent mesenchymal stromal cells (MSC) in morphological aspects and MSC might indeed be a source for these specialized stromal cells [
8]. MSC have been shown to suppress proliferation and alloreactivity of T cells [
9‐
11]. Furthermore, they modulate functions of B cells and of dendritic cells [
12] and, importantly, MSC do not only inhibit the proliferation of NK cells but also suppress their cytotoxic activity [
13‐
15]. These immunological properties may contribute to tumour spread as MSC can be found in human breast cancers and promote metastasis [
16]. Bioluminescence imaging of mice indicated a tropism of bone marrow-derived MSC to inflammatory microenvironments such as tumours [
17]. In this context, the inhibitory effects of MSC on virtually all cells of the immune system may be relevant [
12]. To investigate immunological features of stromal cells in neuroblastomas and other paediatric tumours, we isolated TStrC and hypothesized that immunomodulatory properties of these cells may contribute to the immune evasion of tumours. When we focused on NK cells, we found that the activating NK cell receptors NKp44 and NKp46 were downregulated while the inhibitory receptor NKG2A remained unaffected. This may be one mechanism to inhibit lysis of e. g. neuroblastoma cells, which are known to express only low densities of HLA molecules and represent good NK cell targets [
18].