During the past decade new insights have been gained into the role of T lym
phocytes in the host's immune response to cancer in general and to melanoma
in particular. Several melanoma-associated antigens (MAA) recognized by T
cells have been characterized, and a number of HLA class I- and class II-re
stricted peptides have been identified. These antigens can be divided into
three different groups: tumor-associated testis-specific antigens, melanocy
te differentiation antigens, and mutated or aberrantly expressed antigens.
These proteins give rise to several antigenic peptides. The number of known
melanoma-associated peptides that can induce killing by cytotoxic T-lympho
cytes (CTL) exceeds 30 and is still increasing. In line with these findings
, clinical data indicate that the immune system is essential in the control
of tumor growth. A brisk infiltration of lymphocytes is associated with a
favorable prognosis, and complete or partial regression of primary melanoma
occurs quite frequently. Furthermore, immunomodulatory therapies have acco
mplished complete or partial tumor regression in a number of patients. Howe
ver, the immune response is in most cases inadequate to control tumor growt
h as tumor progression often occurs. Hence, the coexistence of a cellular i
mmune response in melanoma lesions, demonstrated by the presence of clonall
y expanded T cells, remains a major paradox of tumor immunology. In the pre
sent paper we review current knowledge regarding tumor infiltrating lymphoc
ytes (TIL) in melanoma and discuss possible mechanisms of escape from immun
e surveillance.