Modulation of antigen-presenting cell function as a potential regulatory mechanism in tumor-host immune reactions

A growing body of information suggests that immunological defense mechanisms against newly emerging tumors may exist within the skin. In this regard, the recognition and presentation of tumor-associated antigens by cutaneous antigen presenting cells is a prerequisite for the establishment of specific tumor immunity. However, despite the recently demonstrated ability of normal I-A+ epidermal cells (Langerhans cells) to effectively present tumor-associated antigens in vivo, even tumors with recognizable antigenic epitopes can grow progressively in situ. Therefore, regulatory mechanisms within the local microenvironment may exist that control the ability of resident epidermal APC to initiate and to elicit protective immunity against incipient cutaneous neoplasms. This report reviews the role of APC in tumor immunity and the effects of cytokines and ultraviolet radiation (UVR) on tumor antigen presentation by epidermal APC. Our data suggest that these agents can significantly modify the ability of epidermal cells to present tumor-associated antigens and may therefore control the type and effectiveness of tumor immune responses in situ. Furthermore, the induction of primary tumor immunity and the elicitation of secondary immune responses are independently regulated and respond differently to cytokine application.