Cytotoxic Activity of CD4+ T Cells against Autologous Tumor Cells

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Abstract
The 51Cr‐release assay is mostly applied to detecting the cytotoxic activity of CD8+ T cells, and little is known about the activity of CD4+ T cells. Therefore, the correlation between the cytotoxic activity of CD4+ or CD8+ T cells and the incubation period with autologous tumor cells was analyzed by two methods. The incubation periods were 4 and 20 h (4 h and 20 h assay) for the 51Cr‐release assay. Eight pairs of tumor cells and T cells were assayed. T cells were fractionated into CD4+ and CD8+ T cells by using magnetic beads and panning methods, and those cells were activated by culture with recombinant interleukin‐2 and immobilized anti‐CD3 monoclonal antibody. In 6 out of 8 cases, no cytotoxic activity of CD4+ T cells was detected by the 4 h assay, whereas cytotoxic activity was detected in all cases in the 20 h assay. The cytotoxic activities in 20 h assay of CD4+ T cells were increased 67‐fold in comparison with the activities in 4 h assay (range: 5–197). In the case of CD8+ T cells, cytotoxic activities were detected in 6 out of 8 cases in the 4 h assay. The lytic unit ratio of CD4+ and CD8+ T cells was calculated as 1.5 in the 20 h assay (range: 0.2‐>7.2) versus 0.4 in the 4 h assay (range: < 0.1–1.3). Cytotoxic activities in colorimetric assay using Crystal Violet with a 24 h incubation were similar to those in the 20 h 51Cr‐release assay in all eight cases. These results indicate that CD4+ T cells have cytotoxic activity as strong as that of CD8+ T cells towards autologous tumor cells.

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