Olivier Leger

A recombinant humanized anti-insulin-like growth factor receptor type I antibody (h7C10) enhances the antitumor activity of vinorelbine and anti-epidermal growth factor receptor therapy against human cancer xenografts.

Interaction of insulin‐like growth factor receptor I (IGF‐IR) with its ligands has been reported to induce cell proliferation, transformation and blockade of cell apoptotic functions. IGF‐IR is overexpressed on numerous tumor cell types and its blockade could be of importance for anti‐cancer therapy. We have generated a humanized anti‐IGF‐IR antibody h7C10 that blocks in vitro IGF‐I and IGF‐II‐induced cell proliferation of MCF‐7 breast cancer cells. Analysis of the IGF‐I transduction cascade demonstrated that the humanized anti‐IGF‐IR antibody and its murine parental form block IGF‐I‐induced tyrosine phosphorylation, both its β‐chain and IRS‐1 tyrosine phosphorylation. This presumably leads to cell cycle arrest and, consequently, growth inhibition. Treatment of nude mice bearing either human breast cancer cells (MCF‐7) or non small lung cancer cells (A549) with h7C10, or its murine parental form 7C10, inhibited significantly tumor growth. An almost complete inhibition of A549 tumor growth was observed when mice were treated with the anti‐IGF‐IR antibody combined with either a chemotherapeutic agent, Vinorelbine or an anti‐epidermal growth factor receptor (EGFR) antibody, 225. Combined therapy prolonged significantly the life span of mice in an orthotopic in vivo model of A549; the combination of the anti‐IGF‐IR antibody with an anti‐EGFR antibody was superior to the Vinorelbine combination. The present results indicate that the humanized anti‐IGF‐IR antibody h7C10 has a great potential for cancer therapy when combined with either a chemotherapeutic agent or an antibody that targets other growth factor receptors, such as the epidermal growth factor receptor.

Primary structure of the variable regions encoding antibody to NG2, a tumour-specific antigen on the rat chondrosarcoma HSN. Correlation of idiotypic specificities with amino acid sequences

Eight syngeneic rat monoclonal antibodies that recognize structurally overlapping epitopes on the chondroitin proteoglycan NG2, a tumour-specific antigen on the chemically induced rat chondrosarcoma HSN, have been analysed for the sequence of their immunoglobulin heavy (H) and light (L) chain variable (V) regions. This analysis defined five groups of antibodies which are very similar for both the H and L chains and revealed that a wide range of different V regions are capable of binding to the same antigenic determinant. However, three mAbs, 11/160, ALN/12/17 and ALN/9/94, which recognize a sequential epitope, were found to use almost identical heavy (V-D-J) and light (V-J) chains in regions demonstrating an exclusivity in specific protein-protein interaction for this particular epitope. Two other mAbs, ALN/11/53 and AL/3/12, used similar V and J segments but totally different D regions. With the exception of the pair ALN/11/53 and AL/3/12, this grouping of antibodies matches that derived from the idiotypic specificity study we have reported previously. The reactivity pattern of Ab1 11/160, ALN/12/17 and ALN/9/94 with six anti-idiotopic mAbs raised against 11/160 demonstrated that the idiotope recognized by Ab2 HIM/3/41 was defined by a single amino acid, Asn, at position 52 within the CDR2 loop of the VH region; whereas the D region of Ab1 ALN/11/53 was implicated as the structural correlate of idiotypy. The substitution of AsnH52 influenced the Id recognition but Ag binding was not affected suggesting that Ab2 HIM/3/41 did not mimic the NG2 Ag.

Isolation and characterization of a monoclonal rheumatoid factor specific for the hinge region of rat IgG2b

The isolation and characterization of an isotype-specific autoantibody-secreting hybridoma NET/2/3 from rats bearing the syngeneic tumour HSN is described. This rheumatoid factor of the IgM class recognizes an epitope within the hinge region of rat immunoglobulins of the IgG2b subclass which is destroyed by reduction of disulphide bonds. The specificity of NET/2/3, although not allotype-restricted, is highly isotype-restricted, as it does not bind to rat Ig other than IgG2b, nor does it react with the majority of mouse IgG, although some reactivity occurs with mouse IgG3. One remarkable feature of NET 2/3 is that it binds more strongly to F(ab)2 and Fab fragments of rat IgG2b, obtained by digestion with pepsin, than to the whole molecule. This anti-isotype response is not peculiar to the HSN tumour model as NET/2/3-like antibodies have been found in the sera of rats immunized with various protein and cellular antigens. The possible biological role of this anti-isotype antibody is discussed.