Correlation of apparent molecular weight and antigenicity of viral proteins: an SDS-page separation followed by acrylamide-agarose electrophoresis and immunoprecipitation

Characterization of prostate-tissue-directed monoclonal antibody, alpha-Pro 13

The alpha-Pro 13-secreting hybridoma was produced by immunizing mice with an equal mixture of PC-3, DU145, and LNCaP established prostatic carcinoma cell lines. The specificity of alpha-Pro 13 monoclonal antibody was evaluated by the criteria of differential binding to cultured cells; differential binding to extracts of malignant prostate, nonmalignant prostate, and malignant and nonmalignant tissues of various histiotypes in solid phase radioimmunoassay; and by immunoperoxidase staining of primary surgical tissues of varied histiotypes. The data generated by multiple assay investigation indicate that alpha-Pro 13 exhibits preferential binding to the ductal epithelium of prostate tissue; immunoperoxidase evaluation indicates a considerable heterogeneity of staining of ductal epithelial cells. The most prevalent cross-reactivity of alpha-Pro 13 monoclonal antibody with non-prostate tissue occurs with blood vessel endothelium of restricted tissues. Electrophoretic analysis of immunoprecipitates from radioiodinated prostatic tumor extracts indicates that the molecule recognized by alpha-Pro 13 is of 120,000 dalton apparent nonreduced molecular weight. Under reducing conditions, the antigen (p40) consists of a major component of 40,000 dalton apparent MW and a minor component of 17,000 dalton MW. p40 has an isoelectric point of 3.5-4.5. The antigen is intrinsically stable on the PC-3 cell surface; its release into spent culture medium is negligible. p40 is also stable upon complexation with alpha-Pro 13 antibody in that it is not shed from the cell surface as an immune complex nor is it endocytosed to any extent as an immune complex.

Monoclonal antibodies to different epitopes on a prostate tumor-associated antigen. Implications for immunotherapy

Mouse monoclonal antibodies alpha Pro3 and alpha Pro5 bind to different epitopes on an antigen (p54) of 54 kD reduced and 175 kD nonreduced MW. p54 antigen has been characterized previously with regard to tissue distribution using alpha Pro3 monoclonal antibody; the p54 antigen is present in substantially greater quantities in malignant prostatic tissue extracts than in benign prostatic and nonmalignant nonurogenital tissue extracts. In this report, we have established that alpha Pro5 and alpha Pro3 monoclonal antibodies exhibit same molecule-different epitope recognition. That both antibodies recognize the same molecular entity has been established by partial physiochemical characterization of the antigen recognized by the two antibodies and by sequential immunoprecipitation experiments. Different determinant recognition was established by lack of competitive surface binding between alpha Pro3 and alpha Pro5 to a prostatic carcinoma cell line. The p54 antigen can be labeled with glucosamine and immunoprecipitated from urea-solubilized membrane proteins; however, p54 cannot be detected by immunoprecipitation in a glycosylated form in spent culture medium removed from glucosamine-labeled cells. Experiments using indirect cellular immunoassays and directly radioiodinated monoclonal antibody have shown that both alpha Pro3 and alpha Pro5 form stable complexes with p54 antigen on the prostatic carcinoma cell surface. To the extent that modulation occurs upon interaction of p54 with alpha Pro3 and alpha Pro5; endocytosis of the immune complex appears to be the primary route of modulation. Furthermore, modulation by endocytosis is more intense when alpha Pro3 and alpha Pro5 are used in combination than when either monoclonal antibody is used alone. Although in vivo biologic behavior does not invariably correlate with in vitro behavior, careful in vitro analysis of monoclonal antibodies with respect to cell surface behavior, nevertheless, should precede in vivo evaluation. The data presented in this report indicate that preliminary in vitro analyses will expedite the effectiveness of in vivo immunotherapeutic trials; preliminary in vitro evaluations are absolutely essential if monoclonal-toxic agent (e.g., ricin A) conjugates, which must be internalized by the tumor cell to achieve cytotoxicity, are employed as immunotherapeutic agents.

A serologic approach to the definition of human prostatic carcinoma antigens

We have used an immunoaffinity system whereby immunoglobulin from patients with prostatic carcinoma was coupled to solid phase protein A; the immobilized IgG was subsequently exposed to radiolabeled antigen from autochthonous or allogeneic primary tumor extracts or to radiolabeled antigen from a nude mouse-supported prostatic carcinoma cell line. Material specifically bound by prostatic carcinoma patient immune IgG was quantitatively eluted from the immunoadsorbent and characterized with regard to molecular weight. Sequential adsorption analyses of patient sera with normal human tissue pools, normal prostatic tissue, prostatic carcinoma tissue, and tissue from other urogenital malignancies has allowed a definition of those antigenic specificities relevant in the immunobiology of prostatic carcinoma. The patient humoral response was observed to be directed primarily toward a complex array of antigens representing normal human tissue components; serorecognition of prostate tumor associated antigens was discernible from that of common tissue antigens only after rigorous adsorption analyses. Preliminary results indicate that the prostatic cancer patient humoral antibody response may be directed toward either altered histocompatibility complex antigens or toward antigens physically associated with histocompatibility complex antigens.