The ISOBM TD-6 Workshop is the first international workshop on monoclonal antibodies against the Sialyl Lewis^a (SLe^a) antigen. Eight research groups participated in a blind study to characterize the epitope binding, relative affinity and performance in immunoradiometric assays, of a panel of 20 monoclonal antibodies. The antibodies were tested against a diverse panel of neoglycoconjugates, purified antigens and human serum pools from gastrointestinal malignancies. Epitope specificities were determined for the majority of antibodies in the panel. Cross-reactivity with related saccharide structures was noted in several antibodies. Overall, the results of the TD-6 Workshop show further development of SLe^a immunoassays may yield yet more specific assays for the detection and management of gastrointestinal and other malignancies.

Six hybridoma clones were obtained secreting monoclonal antibodies (Mab) against differentiating antigens of human hemopoietic cells. ICO-1 Mab detect Ia-like (Dr) antigens. Mab react with B-lymphocytes and monocytes without detecting antigens on granulocytes and T-cells. Antigen expression was enhanced following cell activation in a blast cell transformation test and mixed lymphocyte culture (MLC). ICO-1 Mab blocked MLC. The molecular weights of the antigen were 29 and 34 kilodaltons. Comparative studies of ICO-1 Mab with other Mab against Ia-like antigens revealed their identical reactivity. ICO-11 Mab detect the antigen on 4% of blood lymphocytes, 75% thymocytes, monoblasts, and CFU-GM. These Mab block NK-cell activity of blood mononuclear cells. ICO-GM-1 Mab detect the antigen on myelomonocytic cells and their precursors, but not CFU-GM. These Mab block binding of the C3Bi complement component to CR3 receptor and NK-cell activity. ICO-G2 Mab detect the antigen expressed at final stages of granulocyte differentiation. ICO-10 Mab detect the antigen on early thymocytes and ICO-02 on undifferentiated blast cells. Mab were shown to be applicable for human leukemia and lymphoma immune diagnosis.

Solid tumour cells were shown to express VLA-beta and Thy-1 antigens. For identification of these molecules two monoclonal antibodies, K-20 and ICO-10, characterised in detail previously, were used. Four groups of solid tumours have been identified according to their immunophenotype: VLA-beta+ and Thy-1-; VLA-beta+ and Thy-1+; VLA-beta- and Thy-1+; VLA-beta- and Thy-1-. To a certain extent these groups have been shown to reflect tumour histogenesis: tumours of epithelial origin never expressed an ICO-10+, K20-phenotype while soft tissue sarcomas and neuroblastoma cells never expressed the beta-chain of VLA molecular complexes.

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