Previously we showed that IL2 expanded tumor-infiltrating lymphocytes (TILs) from renal cell carcinoma mediated non-major histocompatibility complex-restricted cytotoxicity. Phenotypic analysis showed that cultured TILs were composed mostly of T-lymphocytes with varying numbers of CD4+, CD8+, and CD56+ (Leu19+) populations. Here we compared the cytolytic activity of the two predominant TIL subsets, CD3+CD4+ and CD3+CD8+, to that of the CD56+ populations. Using magnetic beads coated with antibodies to either CD4 or CD8, CD3+CD4+, and CD3+CD8+ TILs were isolated in a highly enriched form (>92%) and could be expanded for over 40 days in vitro with 1000 units/ml IL2. In a 4-h 51Cr release assay the CD4+ and CD8+ TILs showed minimal lytic activity, whereas unseparated cells exhibited significant levels of non-major histocompatibility complex-restricted cytotoxicity. The lytic activity seen in the 4-h assay with unseparated TILs appeared to be related to the presence of CD56+ populations. With one exception none of the purified CD4+ or CD8+ TILs expressed any significant levels of CD56, while the unseparated TILs contained varying numbers of CD3+CD56+ and CD3-CD56+ populations. Cell-sorting experiments verified that the CD56+ populations were responsible for most of the lytic activity in 4 h even though CD3+CD56- cells represented the predominant cell type. Although CD3+CD56- TILs were minimally lytic in 4 h, we show here that both CD3+CD4+ and CD3+CD8+ subsets displayed substantial cytotoxicity in long-term assays. In the 18-h 51Cr release assay 5 of 6 CD4+ and 2 of 3 CD8+ TILs were lytic for the autologous tumor. In two cases, restimulation with the autologous tumor induced augmented cytolytic activity of TIL subsets and in one case induced lytic activity in 4 h. The cytotoxic activity of TIL subsets was further examined using a 72-h assay in which TILs were cocultured with a confluent layer of tumor cells. The degree of cytotoxicity was quantitated by measuring the amount of crystal violet dye that was incorporated by tumor cells which remained after the incubation period. CD4+ and CD8+ TILs typically caused greater than a 50% reduction of tumor cells in 3 days and the level of reduction was increased when IL2 was added to the cultures. All the CD4+ and CD8+ subset preparations were cytotoxic in the 3-day assay even though some were not lytic for certain targets in the 18-h 51Cr release assay. The lytic activity mediated by the CD4+ and CD8+ TILs in the long-term assay was not restricted to the autologous tumor, although in many cases the TIL subsets displayed greater activity toward autologous tumor when compared to allogeneic targets. These results demonstrate that the TIL subsets, CD3+CD4+ and CD3+CD8+ which were devoid of CD56+ expression, had substantial antitumor activity and that their mechanism of tumor cell destruction appears to be distinct from that used by CD56+ lymphokine-activated killer cell populations.

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This study was supported by a National Cancer Institute contract (CM47673-03) and a grant from The Cleveland Foundation.

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