Previous studies demonstrated that both CD8+ and CD4+ T cells, derived from infiltrates in melanomas, colon carcinomas, breast carcinomas, and lymphomas can manifest MHC-restricted recognition of tumor-associated antigens (Ag). Current projects focus on identifying melanoma-associated proteins and peptides recognized by CD4+ T cells, as well as extending this work to prostate cancer. These studies are directly relevant to clinical efforts to develop cancer vaccines. 1. Characterize tyrosinase peptides recognized by CD4+ T cells. Two 15- mer peptides derived from tyrosinase, an enzyme expressed by cells of the melanocytic lineage, were found to stimulate CD4+ T cells from one melanoma patient. These bound to MHC class II molecules with intermediate to low affinities. Amino acid substitutions at the MHC binding anchor positions yielded peptides with high affinity binding and enhanced T cell stimulation. These modified peptides have been used to raise reactive CD4+ T cells from the PBL of other melanoma patients. Studies in progress will assess whether peptide-stimulated T cells also recognize melanomas. If so, modified tyrosinase peptides may provide useful immunogens. 2. Search for other melanoma-associated proteins recognized by CD4+ T cells. CD4+ T cells reacting to autologous melanoma cells seem to recognize unique Ag in 7 of 8 cases studied. In one system, sequential protein purifications have yielded a partially purified Ag from detergent lysates of melanoma cells. Definitive identification of the recognized protein is in progress. Also, model systems are being used to develop molecular cloning strategies for identifying MHC class II-restricted tumor Ag. These involve transient expression of cDNA libraries from tumor cells in eukaryotic or prokaryotic systems. 3. Defining immune responses against prostate cancer. Virtually no information is available on the human immune response to prostate cancer, in part owing to a scarcity of cultured prostate cancer lines for testing. We have developed an innovative method of generating immortal cultures from human prostatic epithelium which has proved uniformly successful in establishing over 20 different cell lines from benign and malignant prostatic tissue. Loss of allelic heterozygosity on chromosome 8p, the potential site of a suppressor gene related to prostate cancer, has been used to characterize these lines. Evaluations of their capacity to provoke specific immune recognition from autologous and MHC-matched allogeneic PBL from prostate cancer patients are in progress.
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