The use of non-human primates for production of antisera to human tumor-associated antigens

A3--a novel colon and pancreatic cancer reactive antibody from a primate phage library selected using intact tumour cells

The identification of novel tumour-associated antigens (TAAs) is pivotal for progression in the fields of tumour immunotherapy and diagnosis. In the present study, we have developed, based on flow cytometric evaluation and use of a mini-library composed of specific antibody clones linked to different antibiotic resistance markers, methods for positive and subtractive selection of phage antibodies employing intact cells as the antigen source. An scFv phage library (2.7 x 10(7)) was constructed from a primate (Macaca fascicularis) immunised with pooled human colon carcinomas. This library was selected for 3 rounds by binding to Colo 205 colon adenocarcinoma cells and proteolytic elution followed by phage amplification. Several antibodies reactive with colon carcinomas and with restricted reactivity to a few epithelial normal tissues were identified by immunohistochemistry. One clone, A3 scFv, recognised an epitope that was homogeneously expressed in 11/11 of colon and 4/4 pancreatic carcinomas studied and in normal tissue restricted to subtypes of epithelia in the gastrointestinal tract. The A3 scFv had an apparent overall affinity approximately 100-fold higher than an A3 Fab, suggesting binding of scFv homodimers. The cell surface density of the A3 epitope, calculated on the basis of Fab binding, was exceptionally high, approaching 3 million per cell. We also demonstrate efficient T-cell-mediated killing of colon cancer cells coated with A3 scFv fused to the low MHC class II binding superantigen mutant SEA(D227A). The identified A3 molecule thus represents a TAA with properties that suggest its use for immunotherapy of colon and pancreatic cancer.

In vivo tumor localization using tumor-specific monkey xenoantibody, alloantibody, and murine monoclonal xenoantibody

Specific in vivo localization of antibodies reactive with human melanoma cell membrane tumor associated antigens (TAA) has been attempted using congenitally athymic nude mice bearing subcutaneous human melanoma tumor xenografts as the experimental model. IgG fractions were prepared from each of several immune and control sera. Antimelanoma antibody sources included human alloantibody obtained from melanoma patients immunized against allogeneic melanoma cells, a monkey antiserum raised by immunization against a single human melanoma cell line, and a murine monoclonal antimelanoma antibody-secreting hybridoma cell line. Localization of these radiolabeled antibodies and of control IgG preparations to tumor tissue was determined by whole body scintigraphy and by differential tissue counting. Compared with the different control IgG preparations, each of the antimelanoma IgG preparations exhibited significant specific accumulation within the melanoma tissue. However, variation existed in the ability of each antimelanoma IgG to tumor preparation to localize despite attempts to control model parameters such as tumor source, in vivo passage number and mass. This variation appears to reflect basic biologic differences between tumors in different animals and possibly differences in the antigen-binding capacities of each IgG preparation following radioiodination. This technique for tumor localization is very promising and has obvious potential for clinical application.

Characterization of melanoma cell membrane tumor-associated antigens using xenoserum, alloserum, and autoserum: I. immunofluorescence

Xenoantiserum, alloantiserum, and autoantiserum prepared against human melanoma cells from cell lines maintained in tissue culture were evaluated by indirect immunofluorescence (ind IF) for their content of antibodies reactive with melanoma cell membrane tumor-associated antigens (TAA). Following absorptions which removed all detectable anti-human species, anti-RBC, and anti-HLA antigen activity, the antisera were tested against a panel of human cell lines. Three apparently distinct melanoma-associated cell membrane antigens were detected. The first of these was present on all human cells maintained in tissue culture including cells of both malignant and nonmalignant origin. The second antigen was expressed on all cells of malignant origin and also by fetal fibroblasts. The third antigen was detectable only on melanoma cells and was expressed by a majority of the melanomas tested. No evidence was obtained to suggest the presence of melanoma TAA unique to a single melanoma cell line. Marked differences were observed in the antigenic profile detected by the three antisera.

The use of non-human primates for production of antisera to human tumor-associated antigens

High-titered antisera against human melanoma- and leukemia-associated antigens have been produced in non-human primates. The data from this and from other studies suggest that this model may prove a valuable source of highly specific antisera against a variety of human tumor-associated antigens or alloantigens. Our methods for production and characterization of these antisera are reported.