IMMUNOBIOLOGY OF CUTANEOUS T CELL LYMPHOMA

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Cutaneous T cell lymphoma (CTCL) is a clonal malignancy of T cells with a marked propensity to infiltrate epidermis and a phenotype characteristic of the normal cells from which they are thought to be derived: CD4+ (helper/inducer), CD45RO+ (memory) and CLA+ (cutaneous lymphoid antigen). Observations made during the current funding period suggest that two other CTCL cell membrane molecules, capable of housing small peptides distinctive to malignant clones, are also of substantial importance. Class I bound peptides on the malignant T cells are strong candidates for tumor specific antigens, and the abundantly displayed glycoprotein BE2 is homologous with members of the heat shock protein 70(hsp70) family, thought to expedite transfer of peptide antigens to class I major histocompatibility complex (MHC) molecules. As in vivo anti-CTCL immune response directed against class I MHC-associated peptides is suggested by the large number of nonmalignant CD8+ T cells in early plaque stage CTCL lesions, by the capacity of CD8+ T cells to selectively lyse autologous CTCL cells and by CTCL cell display of distinctive peptides in the groove of class I MHC. Since CD8+ T cells recognize peptides in the context of class I MHC, it is noteworthy that photopheresis produces longstanding remissions in only those erythrodermic CTCL patients who retain normal levels of CD8+ T cells, supporting the possibility that a natural CD8+ T cell mediated anti-CTCL response can be therapeutically enhanced. In this project, class I- associated peptides which distinguish CTCL cells will be eluted and sequenced; the cytoplasmic proteins of origin of these peptides will be identified; and the capacity of the peptides to serve as targets for anti-tumor CD8+ T cell responses will be determined. First, purified populations of leukemic cell will be isolated on the basis of their already established binding of individual anti-Vbeta (T cell receptor or TCR) family specific monoclonal antibodies. These freshly obtained CTCL cells will serve as the principal source of peptides to be characterized. In addition, hybridoma cell lines will be derived in which CTCL cells contribute the expressed class I MHC and TCR membrane proteins, and lines of autologous CD8+ anti-CTCL cells, extracted form blood and lesions of patients, will be propagated. Second, from solubilized CTCL cells, distinctive class I MHC-associated peptides will be eluted, affinity column purified, analyzed by HPLC and compared to sequences of known proteins to determine their cytoplasmic molecules of origin. The capacity of these peptides to sensitize autologous B lymphoblasts to lysis by autologous anti-CTCL CD8+ T cells will also be examined. Third, the significance of the abundant expression of BE2 antigen on the surface of CTCL cells will be explored in the context of the homology between this molecule and hsp70, a family of proteins known to have important immunologic functions and to be capable of chaperoning tumor specific peptide antigens in experimental systems. The structure of CTCL-derived BE2, as well as of BE2-bound small peptides, will be more firmly delineated, and the capacity of these BE2-bound peptides to sensitize autologous target cells for specific anti-tumor lysis will also be determined. Together, these studies should facilitate an improved understanding of CTCL cell peptide processing and immunogenicity.