Key words: HLA; immune escape; loss of heterozygosity; metastases; tumor antigen Acknowledgments: We thank Carmen Amezcua, Immaculada Delgado and Josefa Gil for expert technical assistance, and K. Shashok for help with manuscript preparation. This work was supported by the Fondo de Investigaciones Sanitarias, the Servicio Andaluz de Salud and the Plan Andaluz de Investigacio ´n. R. Mendez is supported by research grant MUTIS from the Agencia Espan ˜ola de Cooperacio ´n Internacional. Received 17 April 2000, revised, accepted for publication 21 February 2001 Copyright c Munksgaard 2001 Tissue Antigens . ISSN 0001-2815 Tissue Antigens 2001: 57: 508–519 Printed in Denmark . All rights reserved 508 R. Mendez Analysis of HLA class I expression in A. Serrano different metastases from two melanoma E. Jäger I. Maleno patients undergoing peptide immunotherapy F. Ruiz-Cabello A. Knuth F. Garrido Abstract: We characterized the HLA class I alterations in five metastases obtained from two patients with melanoma immunized with Melan A/ MART-1, tyrosinase and gp100 tumor peptides. All three metastases ana- lyzed in the first patient (NW145) showed a similar HLA class I alteration with a dual population of melanoma cells. One population was HLA class I antigen positive and the other had loss of heterozygosity (LOH) in the short arm of chromosome 6 leading to an HLA haplotype loss (A02011, B4007, Cw1). The absence of HLA-A2 antigen may explain why this patient did not develop HLA-A2 restricted, Melan A/MART-1 specificity immunization, since this HLA molecule is the restriction element for the tumor peptides used. However, this HLA-deficient population was not selected after peptide immunotherapy. The primary tumor in this patient presented LOH in region 6q, but only in the vertical growth phase of the lesion, whereas LOH at 6p was observed only in DNA from metastatic material. The second patient (NW16) also presented two metastatic lesions with an identical HLA mol- ecular defect, i.e. HLA B locus downregulation (HLA B51011: serological B51; B1503: serological B70). One lesion expressed the tumor antigen (Melan A/ MART-1), but the other did not. Interestingly, the antigen-positive metastasis regressed after peptide immunotherapy, whereas the other progressed rapidly. These findings provide the first indication that multiple metastases generated in the same host can have identically altered HLA class I pheno- types. Tumor cells can partially or totally lose the expression of major histocompatibility complex (MHC) class I antigens during tumor progression (1–3). These alterations in HLA class I molecules favor tumor cell escape from T-cell immunosurveillance (4–6). However, there is little information about the pattern of HLA class I alter- ations at different metastatic sites within the same patient (7), or whether HLA alterations found in different metastases are already present in the primary tumor (8). This information is important in order to identify patients as potentially eligible for peptide immuno- therapy. It can also contribute to our understanding of the induction Authors’ affiliations: R. Mendez 1 , A. Serrano 1 , E. Jäger 2 , I. Maleno 1 , F. Ruiz-Cabello 1 , A. Knuth 2 , F. Garrido 1 1 Departamento de. Analisis Clinicos, Hospital Universitario Virgen de las Nieves, Universidad de Granada, Spain, 2 II Medizinische Klinik, Krankenhaus Nordwest, Frankfurt am Main, Germany Correspondence to: Federico Garrido Departamento de Ana ´lisis Clinicos Hospital Universitario Virgen de las Nieves Avda. Fuerzas Armadas 2 Granada 18014 Spain Fax: π34 958283147 e-mail: fgarrido/HVN.SAS.CICA.ES