Sam Zaremba

Agonist peptide from a cytotoxic t-lymphocyte epitope of human carcinoembryonic antigen stimulates production of tc1-type cytokines and increases tyrosine phosphorylation more efficiently than cognate peptide†

The identification of an agonist peptide (YLSGADLNL, designated CAP1‐6D) to an immunodominant cytotoxic T‐lymphocyte (CTL) epitope (designated CAP1) of human carcinoembryonic antigen (CEA) has previously been reported. The agonist peptide harbors a single amino acid substitution at a non‐MHC anchor residue and is proposed to exert its effects at the level of the T‐cell receptor (TCR). The type and magnitude of cytokines produced by CAP1‐reactive CTL upon stimulation with the agonist peptide, CAP1‐6D, were compared to those obtained upon stimulation with the cognate CAP1 peptide. In addition, early events in the TCR signaling pathway were examined for differences in tyrosine phosphorylation. Upon stimulation with the agonist peptide CAP1‐6D, several different CEA‐specific CTL lines exhibited a marked shift in the peptide dose response, which resulted in as much as a 1,000‐fold increase in the levels of GM‐CSF and γ‐IFN produced as compared with the use of the CAP1 peptide. However, levels of IL‐4 and IL‐10, which are associated with anti‐inflammatory effects, were very low or non‐existent. The cytokine profile of CAP1‐ and CAP1‐6D‐specific CTL is consistent with a Tc1‐type CTL. Consistent with these findings, CEA‐specific CTL showed increased tyrosine phosphorylation of TCR signaling proteins ZAP‐70 and TCR ζ chains in response to both peptides. However, when CAP1‐6D was compared with the wild‐type peptide, the increase in ZAP‐70 phosphorylation was greater than the increase in ζ phosphorylation. CTL generated with the CAP1‐6D agonist were shown capable of lysis of human carcinoma cells expressing native CEA. The ability to upregulate the production of GM‐CSF, γ‐IFN, TNFα and IL‐2 with the agonist peptide, as compared with CAP1, may help in initiating or sustaining anti‐tumor immune responses and thus potentially prove to be useful in the treatment of CEA‐positive tumors. Int. J. Cancer 85:829–838, 2000.

Cancer vaccine development.

A new era involving the evaluation of recombinant cancer vaccines has begun with the concurrent emergence of insights and technologies in the fields of molecular biology and immunology. These advances include: The identification and cloning of an array of genes associated with the neoplastic process, such as oncogenes, suppressor genes, genes encoding oncofoetal antigens and tissue-lineage determinants. The development of a variety of viral and bacterial vectors to deliver and present gene products. The identification of numerous T-cell costimulatory molecules and an understanding of their mode of action. The cloning and analysis of the modes of action of an array of cytokines and other immunomodulatory molecules. More sophisticated knowledge of the mode(s) of antigen presentation and T-cell activation. One current challenge in cancer therapy is the delineation of strategies toward the rational design and implementation of recombinant vaccines that will be of therapeutic benefit to cancer patients and/or members of groups at high risk for specific neoplasias. Numerous concepts are emerging in this regard. The study of immunologic intervention using laboratory animal models demonstrates that no one approach will prevail for all cancer types or, perhaps, for the various stages of the neoplastic process of a given tumour type. The immunological role(s) of CD8+, CD4+, natural killer and other cell types, as well as the roles of antibodies, must all be taken into consideration. This article reviews some of the strategies currently undergoing evaluation toward the development of recombinant vaccines for several carcinoma types.

BIOLOGIC PROPERTIES OF A CH2 DOMAIN DELETED RECOMBINANT IMMUNOGLOBULIN

Monoclonal antibody (MAb) B72.3 reacts with TAG-72, a high-molecular-weight mucin expressed on several types of human carcinoma, and is currently being used in clinical trials for the diagnosis and therapy of human carcinoma. An expression construct containing cDNA encoding an immunoglobulin (Ig) heavy chain, with the variable region of murine MAb B72.3 and a human Ig constant region with a deletion of the CH2 domain, was generated. Immunoglobulin from the transfectoma with the highest expression of the TAG-72 immunoreactive antibody was designated MAb chimeric (c) B72.3 delta CH2. The pharmacokinetics of serum clearance of iodine-labeled MAbs cB72.3 delta CH2 and the intact cB72.3 were compared in athymic mice. By 24 hr, less than 1% of the cB72.3 delta CH2 was left in the plasma, while 36% of the cB72.3 still remained. The T1/2 alpha values of the cB72.3 delta CH2 and cB72.3 MAbs were 1.7 and 2.4 hr, respectively. The T1/2 beta values were 7.8 hr for the domain-deleted cMAb and 48.9 hr for cB72.3. Biodistribution studies in athymic mice bearing LS-174T xenografts showed a reduction in the percentage of injected dose per gram in tumor with 131I-cB72.3 delta CH2; however, the 131I-cB72.3 delta CH2 both localized to tumors faster and cleared from the blood faster than the 125I-cB72.3 MAb. Only trace amounts of the 131I-cB72.3 delta CH2 were detected in normal tissues, including kidney. The faster clearance rate, more rapid tumor targeting and lack of metabolic uptake in normal tissues demonstrated with the iodine-labeled CH2 domain-deleted cMAb may be an advantage for certain clinical protocols.