The dependence of successful immunotherapy on adequate tumor burden as shown by the treatment of AKR leukemia with poly A-poly U.

The therapeutic efficacy of polyadenlyic-polyuridylic acid (poly A-poly U) on the transplantable AKR leukemia varied with the dose of tumor cells implanted. The greater the number of AKR tumor cells injected into 8-week-old AKR mice free of clinical evidence of cancer, the greater the effect of poly A-poly U in mediating host immunologic control of the tumor. Poly A-poly U was either ineffective or could enhance tumor growth when smaller doses of tumor cells were transferred. The efficacy of an immune adjuvant depended on a tumor burden affording optimum host responsiveness. This does not necessarily arise in the host bearing minimal tumor burden.