Cancer Immunity 12:6 (2012)

Introduction In the second half of the 1970s, Lloyd J. Old and his group at Memorial Sloan-Kettering Cancer Center (MSKCC) discovered the first human cancer antigens by establishing an approach called “autologous typing.” The key preconditions of these discoveries were improvements in establishing human cancer cell lines from fresh tissue specimens and cultures from autologous healthy tissues, including fibroblasts and epithelial cells from different organs, as well as Epstein-Barr virus (EBV)transformed B lymphocytes. Based on the assumption that cancer cells are recognized by the immune system and thus elicit a cellular and humoral immune response, we postulated that serum and T cells from cancer patients may be used as tools to identify immunogenic tumor-associated antigens. Because methods to generate T cell lines and clones in vitro were not established yet, the first experiments to discover tumor-associated antigens were performed with patients’ sera that were pre-absorbed extensively with autologous, allogeneic, and xenogeneic healthy cells. Subsequently, such sera were incubated with autologous cancer cells, which resulted in the discovery of a larger series of new human cancer antigens in different types of cancer like melanoma, leukemia, renal cell, brain, and others (1). As antibodies against these newly discovered cell surface antigens of human cancer generally were present in a rather low concentration, attempts to boost humoral immune responses in vivo were undertaken by vaccination with in vitro-expanded and lethally irradiated autologous cancer cells. In the midst of these studies, a new era was ushered in when Georges Köhler and César Milstein developed a method to immortalize antibody-producing B cells (hybridomas) for which they were awarded the Nobel Prize in 1984 together with Niels Jerne (2). This new technique enabled the production of an unlimited amount of antibodies with a known and single specificity and opened a Pandora’s Box for the discovery of multiple cell surface antigens in cancer and other tissues. The hope for antibodies as therapeutic reagents dominated the decade to follow. In the late 1970s, methods to expand cytotoxic T lymphocytes (CTLs) after antigenic stimulation in vitro were developed (3, 4), which enabled the search for tumor-associated antigens that are recognized by T cells. One major advantage of T cells over antibodies as a discovery tool is that T cells also recognize antigens that are not expressed on the cell surface. We initially focused on melanoma because we had established autologous sets of tumor cells and T cells mainly from this group of patients. At MSKCC, we started with a patient named A.V. who had stage IV disease (SK-MEL-29) and had been subjected to multiple surgical interventions without ever achieving tumorfree surgical margins. From the blood of this patient, we established T cell cultures that were reactive to autologous SKMEL-29 melanoma cells in vitro. With the tools available at the time, an extensive specificity analysis was done showing tumorrestricted reactivity at the clonal level (5). Because A.V. had the strongest autologous T cell reactivity of a total of 13 melanoma patients, whom we extensively studied over the following years, we interpreted the fact that he was alive and free of disease for more than 30 years after his initial diagnosis by cancer immune surveillance.