Tumor size, leukocyte adherence inhibition and serum levels of tumor antigen in dogs with the canine transmissible venereal sarcoma

Tumor antigen (TA) associated with the canine transmissible venereal sarcoma (CTVS) was detected in the sera of dogs bearing the tumor. Rabbit antisera specific for tumor antigen and 3 M KCl extracts of CTVS cells were used in both a competitive enzyme-linked immunosorbent assay (ELISA) and antigen-capture ELISA to quantify levels of circulating TA. In a study of 29 dogs bearing the transplanted CTVS, levels of circulating TA correlated positively with tumor volume. In a longitudinal study of four dogs receiving a transplant of 10(8) viable CTVS cells, circulating CTVS antigen was detected transiently 2 days after transplantation, while persistent levels of TA associated with increasing tumor volume were demonstrable 19-34 days after transplantation. In three of four tumor-bearing dogs, levels of serum TA correlated inversely with values obtained with peripheral blood leukocytes in the leukocyte adherence inhibition (LAI) assay; elevated levels of circulating TA found in dogs with large (greater than 7 cm3) tumors were associated with decreased LAI reactivity of peripheral blood leukocytes. TA could not be detected in sera 48-72 h after surgical removal of CTVS whereas LAI reactivity of peripheral blood leukocytes to CTVS antigen rebounded 1-3 weeks following tumor excision. Results of this study support the use of the competitive ELISA and LAI techniques in assessing levels of circulating tumor antigen, tumor burden and tumor-specific immunity.