A patient with malignant melanoma (RL) received a course of 28 immunizations with autologous, irradiated cultured melanoma cells plus Bacillus Calmette-Guérin. The postimmune serum and the preimmune plasma were tested for their reactivity in mixed hemadsorption microassays against five allogeneic melanoma cell lines and five non-melanoma lines. No reactivity was detected in the preimmune plasma against any of the cell lines tested, while strong reactivity against 5 of 5 melanoma lines (1:2,560 to 1:40,960) and 2 of 5 non-melanoma lines (1:320 and 1:1,280) were found in the unabsorbed postimmune serum. After absorption with human AB erythrocytes, pooled peripheral blood leukocytes, and spleen homogenate of normal adults, reactivity against these cell lines did not alter. Further absorption with cells of a human laryngeal carcinoma (KB) line resulted in 4- to 16-fold reduction in antibody titer and yet retained reactivity (1:160 to 1:5,120) directed against all five melanoma lines. The same absorbed serum no longer reacted with any of the five non-melanoma lines. Removal of reactivity against fetal calf serum by absorption with insolubilized fetal calf serum reduced the reactivity against melanoma cell lines to the same extent as did absorption with KB cells, but failed to remove reactivity against non-melanoma cell lines completely. Further absorption of the postimmune serum with human fetal homogenate or Bacillus Calmette-Guérin had no effect on the reactivity against melanoma lines. Blood group isoantigens, HLA antigens, and fetal calf serum were ruled out as causes of the observed seropositivity against melanoma cell lines in the final two stages of sequential absorptions. These data provide further evidence for the existence of common melanoma-associated antigens.
Supported in part by grants from the Medical Research Council of Canada (MA-5637) and from the National Cancer Institute (USPHS Research Grant CA 05108).