Involvement of both Tac and non-Tac interleukin 2-binding peptides in the interleukin 2-dependent proliferation of human tumor-infiltrating lymphocytes.

Interleukin 2 (IL-2) receptor expression was examined on recombinant IL-2 (rIL-2)-propagated tumor-infiltrating lymphocytes (TIL) from eight metastatic melanoma and three sarcoma samples. All 11 TIL expanded with similar growth rates. rIL-2 propagated TIL from five of eight metastatic melanoma specimens contained no Tac antigen-positive lymphocytes as determined by immunofluorescence and flow cytometry performed multiple times during the 4 to 8 week culture period. However, "Tac-negative" TIL did express the non-Tac IL-2-binding peptide, p70-75 as determined by [125I]IL-2 cross-linking and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. IL-2-binding assays revealed that these "Tac-negative" TIL expressed only an intermediate affinity IL-2 receptor. In contrast, TIL from the other three of eight melanoma and all three sarcoma contained one-third Tac-positive cells as assessed by flow cytometry analysis, and expressed surface non-Tac (p70-75) and Tac (p55) peptides by [125I]IL-2 cross-linking. These "Tac-positive" TIL displayed both the high and intermediate affinity IL-2 receptors. However, rIL-2-dependent growth of both "Tac-negative" and "Tac-positive" TIL was significantly inhibited by anti-Tac mAb, suggesting a transient Tac expression on the "Tac-negative" TIL. Additionally, due to the limits of our methodology, we cannot rule out the possibility of a constitutive expression of a low level of Tac, with an indicible expression of higher levels. Addition of culture supernatants from phytohemagglutinin- and phorbol myristate acetate-stimulated peripheral blood mononuclear cells to the "Tac-negative" TIL-induced detectable Tac expression within 48 h. These results indicate that both non-Tac and Tac IL-2 receptors play important roles during IL-2-dependent proliferation of TIL.