While there is good clinical and experimental evidence for immunological tumor control in some tumors – malignant melanomas, for instance – the immunogenicity of colorectal carcinoma (CRC) still remains unsettled. We examined surgical specimens from 4 CRC patients for T cell clones among tumor-infiltrating lymphocytes (TIL). The growth of specific lymphocyte clones in a tumor indicates an immunological response in vivo. We used a T cell receptor Vβ family-specific semiquantitative PCR with additional sequencing to examine TIL for clonal expansion. In CRC, specific T cell clones could not be demonstrated. However, we observed a predominance of Vβ9 in 3 of 4 tumors.

The expression of Fas ligand (FasL) by malignant cells might be a mechanism for tumor immune escape. We investigated FasL expression by LS 174T colon carcinoma cells. Furthermore, the effects of in vitro stimulation with rIL-2, rIFN-γ and rTNF-α were investigated with regard to a possible regulation of the FasL expression by cytokines. FasL expression was detected by flow cytometry and RT-PCR. We observed a spontaneous expression of FasL by LS 174T cells. Incubation with high-dose rTNF-α induced an upregulation of FasL of 23%. rIL-2 and rIFN-γ did not significantly affect FasL expression. To control whether our cytokine stimulation experiments were suitable to prove an upregulation of membrane proteins by tumor cells, we investigated the expression of ICAM-1, N-CAM, CD44s, CD44v6 and CD44v10. These adhesion molecules were spontaneously expressed by LS 174T cells. Only ICAM-1 and CD44v10 were significantly upregulated by rIFN-γ and rTNF-α, respectively. These results could indicate that cytokines, released by tumor-infiltrating leukocytes, may induce the FasL-dependent apoptotic signal by which tumors downregulate an immunological host response.

Tumor-infiltrating lymphocytes (TILs) from colorectal cancers were separated from tumor cells by enzymatic and mechanical tissue disaggregation and discontinuous density gradients. Peripheral blood lymphocytes (PBLs) were isolated using the same procedure. The freshly separated TILs and PBLs were analyzed phenotypically by flow cytometry. The CD4+/ CD8+ ratios of the freshly isolated TILs and PBLs were comparable ( > 1 in both lymphocyte populations). CD25+, HLA-DR+ and CD56+ cells were significantly more frequent in the TIL than in the PBL population. However, the number of CD45RA+ cells was lower in the TILs as compared to PBLs, while CD29+ accumulated by about 90% in TILs. TILs and autologous PBLs were expanded in vitro with rIL-2. The mean rate of proliferation after 4 weeks was 642-fold in TIL cultures and 335-fold in PBLs. More than 90% of the rIL-2-expanded lymphocytes expressed CD2 and the great majority was CD29+. Stimulation with rIL-2 in vitro induced an outgrowth of CD56+ cells mainly in the TILs. Accordingly the expression of CD3+ and α/β receptor in the TILs was low. Those cells which phenotypically represented lymphokine-activated killer cells displayed a lytic activity against the autologous tumor as well as against allogeneic K562 and Daudi targets. In accordance with the better proliferative response of TILs in long-term cultures with rIL-2, the lytic activity of TILs against autologous and allogeneic tumor targets was significantly higher as compared to PBLs.

Objective: The Fas and Fas iigand (FasL) play an important role in maintaining immune privilege on malignant tumors. In present study, we investigated the expression of FasL in SW480 and LS174 human colon carcinoma cell lines and twenty primary colon carcinoma specimens. Methods: The expression of FasL in human colon carcinoma cell lines and primary colon carcinomas specimens was detected by immunohistochemistry and Reverse Transcription-PCR (RT-PCR). Results: We found that all of detected human colon carcinoma cell lines and primary colon carcinoma specimens constitutively expressed FasL at the mRNA and protein level. However, the expression of FasL was not found in normal colon epithelial cells. Conclusion: The expression of FasL may occur during malignant transformation from normal colon epithelial cells to colon carcinoma cells. Our results suggest that tumor cells kill cytotoxic T iymphocytes (CTLS) and natural killer (NK) cells by expression of FasL. It may be a new mechanism for tumor cells to escape the host's immune surveillance. The expression of FasL may contribute to the formation of colon carcinomas.Fas and FasL are the members of the tumor necrosis

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