Recoverin is a photoreceptor-specific
calcium binding protein that is only expressed in the retina in normal tissues. Aberrant expression of
recoverin, however, has been observed in several
cancer tissues and may cause a very rare
autoimmune disease,
cancer-associated retinopathy (CAR). It has been suggested that CAR-positive
cancer patients have a more favorable prognosis than CAR-negative
cancer patients. To estimate the status of
recoverin-specific T cells in such
cancer patients, we generated an HLA-A24-recoverin
peptide tetramer. By use of the tetramer, we could directly assess the frequency of CTL precursors (CTLp) of 20
HLA-A24(+)
cancer patients with ten colon, six stomach and four breast
cancers, and seven healthy individuals. Four
cancer patients showed a CTLp frequency higher than 0.9%. Seven
cancer patients including the former four patients and two healthy individuals showed specific anti-
recoverin cytotoxic responses in an HLA-A24-restricted manner after in vitro stimulation with the
recoverin peptide. Moreover, five
cancer patients analyzed in an independent experiment using different peripheral blood mononuclear cells (PBMC) samples showed similar CTLp and cytotoxic T lymphocyte (CTL) frequencies and cytotoxic responses, suggesting that the CTLp frequency analyzed by the tetramer and the cytotoxic response may have a good correlation. Thus, we hypothesize that anti-
recoverin CTLp may exist in some
cancer patients, and that anti-
recoverin CTL may be readily induced.