Tissue-specific homing of immune cells in malignant skin tumors

Tissue-specific migration of immune cells involved both in physiological and pathological immune responses is a current research subject for medical science. Several homing molecules have been identified orchestrating extravasation of immune cells to certain peripheral non-lymphoid tissues such as gut, lung and skin. Regarding lymphocyte homing to skin, the first-line defense of human body cutaneous lymphocyte associated antigen (CLA) and a group of chemokine-chemokine receptor pairs are considered to be of crucial importance. The aim of the present review is to summarize existing knowledge about skin- and tumor-specific migration of immune cells playing a major pathogenetic role in host immune responses induced by non-lymphoid malignant skin tumors as well as in the development of primary cutaneous T-cell lymphomas (CTCL). Melanoma malignum, squamous and basal cell carcinoma evoke host immune responses and consequently a subset of reactive immune cells is recruited to site of the tumor. Regarding migratory process and exact functional role of these cells a growing number of data is available in literature. On the other hand tissue-specific immune cell homing is regarded as a key process in the pathogenesis of CTCL where malignant T-lymphocytes can be found in circulation and symptomatic skin. Hereby homing mechanism of malignant T-cells in mycosis fungoides and Sézary-syndrome as separate clinical entities of CTCL is discussed. A precise insight into the molecular background of skin- and tumor-specific immune cell migration can contribute to developing efficient vaccine therapies in non-lymphoid malignant skin tumors and beneficial treatment modalities in CTCL.