Detection of Tumor-associated Antigens in the Sera of Lung Cancer Patients by Three Monoclonal Antibodies

One hundred sixty-one sera from lung cancer patients, including 46 samples from patients who had not yet received treatment were screened for tumor-associated antigens with 3 monoclonal antibodies, CSLEX1, CSLEA1, and CLEX5, by a new cell binding inhibition assay. We had previously determined that the antigens recognized by CSLEX1 and CSLEA1 are sialosylated Lewisx and sialosylated Lewisa, respectively. Either of these two antibodies alone reacted with about 65% of the 46 untreated patients' sera. Eighty-seven % of the 46 showed positive results with at least one of the two antibodies. The CLEX5 monoclonal antibody is presented here as recognizing a potential tumor-associated antigen. CLEX5 reacted with 54% of the 46 sera from nontreated lung cancer patients. When the results for all three antibodies were combined, the percentage of positive sera was 89% (of 46). Some interesting patterns in the serum levels of the antigens detected by these antibodies were observed. Levels of sialosylated Lewisx were significantly higher in sera from nontreated advanced stage (III and IV) patients ( P < 0.0003). In addition, levels of the antigens detected by CSLEX1 and CSLEA1 were dependent on whether or not the patient had been receiving treatment. These observations suggest potential applications of monoclonal antibodies to diagnosis and monitoring of therapies.