Expression of CD45 Isoforms in Fresh and IL-2-cultured Tumor-Infiltrating Lymphocytes from Basal Cell Carcinoma

Immunohistochemistry and flow cytometry analyses were performed to characterize the specific T cell subpopulations infiltrating basal cell carcinomas (BCC) and to determine their phenotypic response to in vitro expansion with IL-2. Tumor-infiltrating lymphocytes (TIL) within BCC predominantly expressed the CD45RO (activated or "memory") phenotype (65 ± 3%) and the percentage of TIL expressing CD45RO consistently increased when cultured in vitro with IL-2 (85 ± 5%). In comparison, fresh normal peripheral blood lymphocytes predominantly expressed the CD45RA (naive) phenotype (79 ± 4%), but shifted to the expression of CD45RO following in vitro expansion in IL-2 (86 ± 6%). To determine whether IL-2 alone, in the absence of antigen or mitogen, can promote naive lymphocytes to convert from the expression of the CD45RA isoform to the CD45RO isoform, we cultured purified CD45RA + lymphocytes in IL-2. After three weeks in culture, 90% of the lymphocytes expressed exclusively CD45RO. We conclude that tumor-infiltrating lymphocytes from BCC predominantly express CD45RO and that this expression may represent specific antigen stimulation and/or in situ activation by cytokines.