Selection of anti-SCLC antibodies for diagnosis of bone marrow metastasis.

The binding profile of 17 monoclonal antibodies (MAbs) to small lung cancer cell lines and normal bone marrow and peripheral blood cells was studied by immunocytochemistry and flow cytometry. At antibody concentrations that stained PJD tumour cells, only four MAbs (MOC1, MOC31, NrLu10, 81A6) were devoid of cross-reactivity with normal cells, whereas significant binding to subtypes of bone marrow and blood cells was seen for 13 antibodies. For the eight most promising MAbs the binding to ten SCLC cell lines was moderate to strong in 47 MAb/cell line combinations, and low or insignificantly in 33 combinations. Three cell lines lacked antigen for all MAbs studied. Flow cytometry was significantly less sensitive than immunocytochemistry in assessing MAb binding to both normal and tumour cells. The antigen expression was for several MAbs higher in exponentially growing tumour cells than in cells in stationary growth phase. Seven of the MAbs, which originally showed low to moderate cross-reactivity with normal cells, were titrated down to the lowest concentrations at which they stained H-146 tumour cells with high levels of antigen expression. At these concentrations five (MLuC1, Oat-1, SM-1, NCC-Lu-243, LAM2) of the seven Mabs showed acceptably low binding to bone marrow cells. At optimal concentrations altogether four to nine of the 17 antibodies studied may be used to detect tumour cell involvement in bone marrow of SCLC patients.