Immunomodulation by a unicellular green algae (Chlorella pyrenoidosa) in tumor-bearing mice

A unicellular algae, Chlorella pyrenoidosa, was used as a biological response modifier. In C57BL/6(B6), C3H/He and DDD/1 mice, both intraperitoneal or oral administrations of autoclaved Chlorella cells or heat-extracted substance were carried out every other day for 10 days before mouse mammary carcinoma (MM-2) or Ehrlich ascites cells were transplanted into the peritoneal cavity. In case of mouse leukemia cells (EL-4), subcutaneous transplantation was carried out. All control mice died within 20 days after each tumor cell transplantation, while 73.3-80% of the treated groups survived over 60 days in the combination of MM-2 vs. C3H/He and EL-4 vs. B6, respectively. The cytotoxic activities against tumor cells, that were abolished by treatment with anti-Thyl.2 monoclonal antibody plus complement, were evidenced in the experimental host. Since Chlorella cells and derivatives showed no indication of direct in vitro cytotoxicity to either tumor or mouse spleen cells, the antitumor effects documented may be mediated by host immune response.