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.

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