TREATMENT OF LYMPHOMA WITH RADIOLABELED ANTIBODY - ELIMINATION OF TUMOR-CELLS LACKING TARGET ANTIGEN

We have previously shown that 131I-labeled monoclonal antibodies against the Thy1.1 differentiation antigen can induce the regression of Thy1.1 antigen-positive (Thy1.1+) AKR/J SL2T cell lymphoma nodules in AKR/Cum (Thy1.2+) mice. In this study, we examined the ability of 131I-labled anti-thy1.1 antibodies to eliminate tumor nodules containing vairant lymphoma cells that do not express the Thy1.1 antigen (Thy1.1-). AKR/Cum mice were sc inoculated with mixtures of 1-2 × 107 AKR/J SL2 cells and varying amounts (0.3%-10%) of Lsp3, a Thy1.1 antigen-negative (Thy1.1-) subclone of the SL2. One week later, when an established tumor nodule was present, mice were treated with 1,500-1,700 μCi of 131I-labled anti-thy1.1 antibody. Complete regression of tumor was observed in 11 of 12(92%) mice inoculated with tumor containing 0.3%-1% antigen-negative cells. In contrast, nocomplete regressions were observed in mice with only antigen-negative tumor cells treated with 131I-labled anti-thy1.1 antibody or in mice inoculated with antigen-positive tumor and treated with an 131I-labled control antibody. Of the mice receiving mixtures containing 3%-10% antigen-negative cells, five of seven showed complete regression. These results demonstrate that radiolabled antibodies can eliminate small numbers of antigen-negative tumor cells present within a tumor mass. [J Natl Cancer Inst 82:47-50, 1990] © 1990 Oxford University Press.