Production and characterisation of novel human monoclonal antibodies against malignant melanoma
Malignant melanoma is an immunogenic tumour capable of inducing a humoral immune response, as shown by tumour-reactive serum antibody in patients. Lack of effective chemotherapy in association with the immunogenic nature of the malignancy, has stimulated interest in the immunological management of the malignancy by antibody. Many mouse monoclonal antibodies against melanoma antigens have been developed, and some have been shown to induce tumour regression. However, a limitation on the use of mouse monoclonal antibodies in patients is the induction of an immune response against the immunising xenogeneic protein. The employment of human monoclonal antibodies, may be expected to reduce the patient's immune response against the allogeneic protein. Although more difficult to produce than mouse monoclonal antibodies, several human monoclonal antibodies have been established which induce tumour regression. Here I describe the establishment of mouse/human heterohybridomas producing human monoclonal antibody, from tumour-draining lymph nodes. A series of novel assay systems, initially developed and characterised using melanoma reactive mouse monoclonal antibodies, were sequentially employed for the selection of human antibody exhibiting high tumour specificity. Several clones producing melanoma reactive human antibody were established. Clone MDT. 1 was selected for further characterisation, because of its highly selective reactivity against viable melanoma and other neuroectodermal cell lines, but lack of reactivity against other common malignant and non-malignant cell lines. Such restricted cell reactivity is characteristic of reactivity with class 2 tumour associated antigens. MDT. 1 was shown, in ELISA, to exhibit reactivity to ganglioside antigens GD3, GD2, GD1b, GM3 and GM2. These antigens are commonly associatedw ith the malignant transformation of melanocytes and other neuroectodermal cells. Enzymatic modification of GM3, with neuraminidase, identified the reactive minimal essential epitope as Neua2- 3Galß1-4GIc-. Reactivity with rat monoclonal antibody 9G4 and molecular analysis showed MDT. 1 is encoded by the highly conserved VH4 gene, VH4-21. Like other VH4-21 encoded autoantibodies MDT. 1 exhibits reactivity with the cold agglutinin T. Analysis of the structures of `i' and sialogangliosides has identified similar structural epitopes, which may confer MDT. 1 reactivity. VH4-21 encoded autoantibody 216 exhibits similar reactivity with tumour associated ganglioside antigens as MDT. 1. Sialo-ganglioside/`i' reactive VH4-21 encoded antibodies, could therefore represent an important aspect of autoantibodies in the overall host immune response to tumour.