Suppressor cell activity in cancer patients: a possible role for thymic hormones

We have identified the presence of suppressor cell activity in the peripheral blood of immunosuppressed stage IV cancer patients. The patients' cells had a diminished mitogenic response to phytohemagglutinin (PHA) and suppressed the PHA mitogenic response of a normal donor's peripheral blood lymphocytes (PBL). Thus, PBL from a cancer patient whose PHA mitogenic response was 3932 counts per minute (cpm), cultured together with a normal donor's PBL with a PHA mitogenic response of 82,865 net cpm, caused a greater than 50% reduction in the latter (37,651 net cpm). Suppressor cell activity was present in 12 of 14 patients tested. This effect was partially mitigated by irradiation with 4000 rads in nine of 14 patients. Preincubation of the patients' cells with thymosin followed by the addition of thymosin to the co-cultured cells mitigated the suppressor activity in five of ten patients and thymic humoral factor did the same in four of 11 patients. A radiosensitive and thymic hormone-responsive suppressor cell may be present in the peripheral blood of cancer patients. Confirmation of this preliminary observation and further characterization of the cell or cells is currently being undertaken.