A limiting dilution analysis (LDA) was used to assess the functional profiles of tumor-infiltrating lymphocytes (TIL) recovered from 15 human solid tumors. The microculture system applied in this study has been shown to allow virtually all normal peripheral blood T lymphocytes (PBL-T) to undergo clonal proliferation and was applied to obtain estimates of the frequency of both proliferating and cytolytic cells among the TIL population. A total of 624 microcultures proliferating in the presence of irradiated allogeneic spleen cells and interleukin 2 (IL 2) were expanded for clonal analysis. These TIL microcultures were assessed for surface antigen phenotype, IL 2 production (helper function) and for their cytolytic capabilities against the human erythroleukemic line K562 (natural killer (NK)-like activity) and P815, a mouse mastocytoma line, in the presence of phytohemagglutinin (PHA), i.e., lectin-dependent cell cytotoxicity (LDCC) which allows the detection of cytolytic activity irrespective of the antigenic specificity of the effector cells. Whenever feasible, cytolytic activity against autologous and allogeneic tumor cells was tested. LDA first demonstrated that the proliferative potential was decreased in T lymphocytes infiltrating human solid tumors (approximately 1 in 50 to 1 in 2 proliferating T lymphocyte precursors (PTL-P) in this series) as compared to normal PBL-T (1 in 2 to 1 in 1 PTL-P). The growth pattern in the titration cultures showed a remarkable agreement with the single-hit Poisson model implying that third party cells are unlikely to be involved in the reduced proliferative potential. Quantitative estimates of functional precursors showed that, in spite of reduced proliferative potential, cytolytic T lymphocyte precursors (CTL-P) against unknown antigens (LDCC-reactive) accounted for a considerable part of the microcultures in many cases. The precursor frequency of T lymphocytes with NK-like activity was usually low in situ (with the exception of glioma), whereas it was in the normal range in the patient's autologous PBL-T. In four evaluable cases, quantitative assessment showed that 1 in 200 to 1 in 1000 T lymphocytes from TIL was cytolytic against allogeneic tumor cells, which is in the range of alloreactive cytolytic T lymphocytes (CTL) generated in the mixed lymphocyte culture from normal PBL. Cytolytic activity against autologous target cells could not be quantitatively estimated but out of 88 clones from 4 patients, 3 clones originating from 2 glioma patients showed high lytic values against autologous tumor. Clonal analysis of the 624 microcultures showed a heterogeneous pattern of functional activities but unexpectedly disclosed a high number of T4+ CTL-clones, which also produced IL 2 in certain tumors; T4+ CTL is a rare functional subset of normal PBL-T, suggesting that this type of cell is selectively accumulated in situ. When simultaneously tested, most of the NK-like activity was mediated by specific CTL against unknown antigens (i.e., those reactive in the LDCC). Our quantitative approach shows that a significant cytolytic potential is latently present among TIL. However, the impaired proliferative potential of T lymphocytes may play an important role in the immunological escape of tumors.
|Number of pages||8|
|Journal||Journal of Immunology|
|Publication status||Published - 1987|
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