1. ¹ICFS, Departments of Surgery and Research, Basel University Hospital, Hebelstrasse 20, CH-4031 Basel, Switzerland
2. ²Department of Pathology, Basel University Hospital, Hebelstrasse 20, CH-4031 Basel, Switzerland

Correspondence: Dr C Feder-Mengus, E-mail: cfeder@uhbs.ch

³These two authors contributed equally to this work

Received 20 November 2006; Revised 31 January 2007; Accepted 1 February 2007; Published online 6 March 2007.

Abstract

Cancer cells' growth in three-dimensional (3D) architectures promotes resistance to drugs, cytokines, or irradiation. We investigated effects of 3D culture as compared to monolayers (2D) on melanoma cells' recognition by tumour-associated antigen (TAA)-specific HLA-A^*0201-restricted cytotoxic T-lymphocytes (CTL). Culture of HBL, D10 (both HLA-A^*0201+, TAA+) and NA8 (HLA-A^*0201+, TAA-) melanoma cells on polyHEMA-coated plates, resulted in generation of 3D multicellular tumour spheroids (MCTS). Interferon-gamma (IFN-) production by HLA-A^*0201-restricted Melan-A/MART-1_27–35 or gp100_280–288-specific CTL clones served as immunorecognition marker. Co-culture with melanoma MCTS, resulted in defective TAA recognition by CTL as compared to 2D as witnessed by decreased IFN- production and decreased Fas Ligand, perforin and granzyme B gene expression. A multiplicity of mechanisms were potentially involved. First, MCTS per se limit CTL capacity of recognising HLA class I restricted antigens by reducing exposed cell surfaces. Second, expression of melanoma differentiation antigens is downregulated in MCTS. Third, expression of HLA class I molecules can be downregulated in melanoma MCTS, possibly due to decreased interferon-regulating factor-1 gene expression. Fourth, lactic acid production is increased in MCTS, as compared to 2D. These data suggest that melanoma cells growing in 3D, even in the absence of immune selection, feature characteristics capable of dramatically inhibiting TAA recognition by specific CTL.