No abstract

Monoclonal antibodies (MAbs) reactive with the ganglioside fucosyl GM1 (Fuc-GM1), an antigen associated with small-cell carcinoma of the lung (SCLC), were tested for their ability to mediate tumor-cell killing in vitro in conjunction with humoral and cellular effectors and to inhibit tumor engraftment in nude mice in vivo. MAbs F12 and F15, both IgG3k, induced human complement-mediated cytolysis of 3 Fuc-GM1-expressing tumor cell lines: one rat hepatoma cell line, H4-II-E, and 2 human SCLC cell lines, NC1 H69 and NC1 H128. F12 and F15 also induced ADCC of these cell lines in the presence of either murine or human effector cells. Addition of sub-cytolytic amounts of fresh human serum as complement source resulted in enhanced ADCC induced by MAb F12 (IgG3). Also a Fuc-GM1-reactive MAb of IgM isotype, F9, was able to induce such complement-aided ADCC (CADCC). F12 and F15 both proved to effectively inhibit engraftment of H4-II-E tumors in nude mice. A single dose of a modest amount (40 micrograms) of MAb conferred 65 to 100% protection against development of tumors. Our results demonstrate that Fuc-GM1 can act as a target antigen on tumor cells for specific immunotherapy in vitro and in a mouse model in vivo. Complement and murine and human mononuclear effector cells were effective mediators of tumor cytolysis in vitro in the presence of murine Fuc-GM1-reactive MAbs. Our results also suggest that humoral and cellular effectors may co-operate in specific tumoricidal reactions and that these may be induced by antibodies of both IgG and IgM isotypes.

Lindholm, L. Immunohistochemical detection of two small cell lung carcinoma-associated antigens defined by MAbs F12 and 123C3 in bronchoscopy biopsy tissues. APMIS 99: 797-802, 1991.We have studied MAbs* for their ability to detect SCLC and differentiate this tumor type from the other lung tumor histotypes in cryostat sections of biopsy specimens taken at bronchopscopy from patients with suspected primary lung tumor disease. MAb F12, specific for the ganglioside fucosyl-GM1, reacted with 58% of the cases with SCLC (n= 19) and with less than 3% of those with non-SCLC (n=38). MAb 123C3, specifically reactive with NCAM, reacted with 78% of the SCLC cases (n=23). With this MAb no positive staining was seen in the non-SCLC cases (n=41). None of the two MAbs reacted with tissue sections without tumor. In combined analysis with MAbs F12 and 123C3, all SCLC cases (n= 15) were positive with either and 47% with both of the MAbs. Our results show that both MAbs F12 and 123C3 are highly specific for SCLC in bronchoscopic biopsy tissue specimens, whereas the sensitivity for this histotype tends to be higher with MAb 123C3 than with F12 (P=0.14). When used in combination, all SCLC cases could be identified. These MAbs may therefore be valuable as complements to current histopathologic characterization and differentiation of lung cancer.

Fucosyl-GM1 (Fuc-GM1) [Fucalpha1 --> 2Galbeta1 --> 3GalNAcbeta1 --> 4(NeuAcalpha2-3)Galbeta1 --> 4Glcbeta1 --> O-Cer] is a small-cell-lung-cancer (SCLC)-associated ganglioside initially defined by the murine monoclonal antibody F12. On the basis of its known distribution, Fuc-GM1 is a potential target for active immunotherapy in SCLC patients. Fuc-GM1 has been extracted and purified from bovine thyroid. The immunogenicity of Fuc-GM1 was tested in mice either alone, mixed with carrier protein keyhole limpet hemocyanin (KLH) or covalently linked with KLH, plus immunological adjuvant QS-21. The Fuc-GM1-KLH conjugate plus QS-21 adjuvant was found to be optimal. It induced consistent IgM and IgG enzyme-linked immunosorbent assay (ELISA) titers against Fuc-GM1. These antibodies were strongly reactive with the strongly Fuc-GM1-positive rat hepatoma cell line H4-II-E, and they were moderately reactive with the moderately positive human SCLC cell line H146 by flow cytometry and complement-mediated lysis. Both ELISA and fluorescence-activated cell sorting (FACS) reactions were inhibited with Fuc-GM1or H4-II-E but not with the structurally related ganglioside GM1 or Fuc-GM1-negative colon cancer cell line LS-C. On the basis of these results, a vaccine comprising Fuc-GM1-KLH plus QS-21 is being prepared for testing in patients with SCLC.

With the aid of specific monoclonal antibodies, tumor tissues from 68 patients with lung cancer were examined for their expression of two small cell lung carcinoma (SCLC) antigens, Fuc-GMl (fucosyl GM1; IV²FucII³NeuAc GgOse₄) and neural-cell adhesion molecule (NCAM), and two broader tumor antigens, carcinoembryonic antigen (CEA) and carbohydrate cancer-associated antigen CA 50. Expression of Fuc-GMl was seen in 75% and NCAM in 78% of the SCLC specimens, but also in 12 and 20% of non-SCLC. Either or both of these antigens were expressed in more than 90% of SCLC and in 25% of non-SCLC. CEA was found in more than 80% of SCLC and non-SCLC. Expression of CA 50 was seen in 65–68% of non-SCLC and SCLC, showing preference for SCLC and lung adenocarcinoma. In SCLC, cellular expression of Fuc-GM1 was generally seen together with NCAM and CA 50, but rarely with CEA. There was considerable inter- and intratumor heterogeneity in the expression of all four antigens. The results suggest that CEA is the antigen of choice for the detection of lung cancer regardless of histotype. In combined analysis of CEA, CA 50, Fuc-GM1 and NCAM, two patterns of antigen expression were recognized that appear to discriminate between SCLC and non-SCLC tumors, respectively. A considerable fraction of SCLC and non-SCLC tumors, however, exhibited similar patterns of antigen expression. The biological and clinical significance of these observations remains to be investigated.