The effect of purification on the immunogenicity of tumor-specific transplantation antigens

Epitope- and antigen-specific cancer vaccines

Anti-idiotypic antibodies (Ab2) that functionally mimic epitopes associated with human cancer cells are the most specific cancer vaccines currently available. Ab2 can induce specific humoral anti-tumor immunity in cancer patients. However, the potential of Ab2 for inducing cellular immunity in cancer patients still requires demonstration. Clonotypic antibodies directed against the combining site for tumor Ag on human T-cell clones may provide highly effective reagents for inducing protective T-cell immunity against human cancer. A new generation of cancer vaccines, molecularly cloned tumor-associated antigens (Ag), has recently been developed. Recombinant Ag have been successfully expressed in vectors allowing large scale production of Ag for immunization of cancer patients. Recombinant tumor Ag was shown to induce specific and protective immunity in experimental animals. In contrast to Ab2, which may mimic a single cancer-associated epitope, recombinant Ag express multiple epitopes that are potentially immunogenic. Ag vaccines, therefore, may be more effective in arresting tumor growth than single epitope (Ab2) vaccines because tumor destruction by antibodies is dependent on antibody density on tumor cell surfaces. In light of the important roles that both B and T cells play in the control of tumor growth, the demonstration of induction of specific B and T cell-immunity by recombinant tumor Ag and Ab2 in experimental animals is encouraging. Ultimately, the immunomodulatory role of both types of vaccines has to be compared in cancer patients who are immunologically tolerant to many Ag/epitopes expressed by their growing tumors. The development of both Ab2 and recombinant Ag for single antigenic systems provides the first step towards this goal.

Tumor rejection antigens of chemically induced sarcomas of inbred mice

Chemically induced sarcomas of inbred mice are immunogenic in syngeneic hosts, and preimmunization with tumor cells leads to resistance to subsequent tumor transplants. The tumor rejection antigens (TRAs) that mediate this reaction are highly specific for each tumor; cross-protection between different syngeneic sarcomas is rare. Isolated membrane and cytosol fractions from two antigenically distinct BALB/c sarcomas, Meth A and CMS5, have TRA activity, and biochemical characterization of the active components from the cytosol and plasma membranes of these two tumors identified a glycoprotein of Mr 96,000. Immunization with unfractionated Meth A cytosol frequently leads to tumor enhancement, but the tumor-enhancing activity (TEA) is lost on fractionation and TRA activity becomes demonstrable. As Meth A and CMS5 lack expression of murine leukemia virus (MuLV) antigens or transcripts, MuLV-related antigens cannot be involved in the TEA or TRA activities of these tumors. In contrast to the lack of cross-reactivity between Meth A and CMS5 TRAs in transplantation tests, rabbit antiserum prepared against the Meth A Mr 96,000 antigen reacted with the CMS5 Mr 96,000 antigen. In view of the biochemical and antigenic similarities of Meth A and CMS5 TRAs, we propose that structurally related but distinct Mr 96,000 glycoproteins are expressed in chemically induced sarcomas and that these molecules are responsible for the individually specific immunogenicity of these tumors.

Noncytolytic extraction of cell surface antigens using butanol

Incubation of viable tumor cells in single-phase aqueous solutions of 1-butanol releases a subset of peripherally-associated membrane proteins. Among the extracted components are tumor-specific and tumor-associated antigens of several human and experimental neoplasms. The extraction technique is noncytolytic: extracted cells remain viable and proliferate both in vitro and in vivo. Examination of the denuded cells has elucidated several important differences in cell-surface phenotype that have proved useful in studying the biology of such diverse systems as cellular communications and the mechanisms of hematogenous metastasis. It is anticipated that noncytolytic butanol extraction will continue to prove a powerful approach for the isolation and characterization of a variety of cell-surface antigens.