Prolongation of concomitant antitumor immunity in mice treated with Z-100, an arabinomannan extracted from Mycobacterium tuberculosis

The effect of Z-100, a natural immunomodulator extracted from Mycobacterium tuberculosis strain Aoyama B, on concomitant antitumor immunity (CAI) was investigated in mice immunized with Meth-A tumor cells (primary inoculation) in combination with Corynebacterium parvum. CAI, which was observed in mice 10 days after immunization (I10 mice), disappeared in mice 20 days after immunization (I20 mice). However, no growth of secondarily inoculated Meth-A tumors was demonstrated in I20 mice treated with Z-100 (IZ20 mice). CAI was demonstrated in tumor-bearing recipients when splenic mononuclear cells (SMNC) from I10 mice or IZ20 mice were transferred to recipients intralesionally. However, CAI was not detected when recipients received SMNC from I20 mice or a SMNC mixture from I10 and I20 mice. The SMNC mixture from I10 and IZ20 mice inhibited the growth of Meth-A solid tumors in the recipients. The activity of nonspecific suppressor cells, which were characterized as CD8+ T cells, was demonstrated in SMNC from I20 mice, while SMNC from I10 and IZ20 mice did not show any suppressor cell activities. In addition, clear inhibition of tumor growth was demonstrated in recipient mice which received a SMNC mixture from I20 mice, previously treated with anti-Lyt-2+ MAb plus complement, and I10 mice. These results suggest that Z-100 might be able to prolong CAI observed in I10 mice through the inhibition of Lyt-2+ T suppressor cells detected in SMNC from I20 mice.