About 300 carcinogens and non-carcinogens of a wide variety of chemical types have been tested for mu- There is considerable evidence that a large proportion of human cancer may be caused by exposure to toxic chemicals in the environment, very few of which have been tested for carcinogenicity or mutagenicity. A program of cancer prevention aimed at identifying and eliminating human exposure to hazardous chemicals requires the development of rapid, inexpensive, screening methods as complements to expensive, long-term animal tests, to pinpoint dangerous chemicals among the thousands to which humans are exposed. The Salmonella/microsome mutagenicity test (1-4) has been sufficiently developed and validated to be seriously considered for widespread use in this way. The considerable evidence (5), much of it obtained using this test (1)(2)(3)(4)(6)(7)(8)(9)(10)(11)(12)(13), that with few exceptions carcinogens are mutagens, supports the desirability of using this type of rapid and economical test system as a screening technique (1-3).Chemicals are tested for mutagenicity on petri plates with several specially constructed mutants of Salmonella typhimurium (2-4). Homogenates of rat (or human) liver, (S-9 Mix), are added directly to the petri plates, thus incorporating an important aspect of mammalian metabolism into the in vitro test (2). In this way, a wide variety of carcinogens requiring metabolic activation can be detected easily as mutagens (2, 4, 5). The system has been recently reviewed (6) and the test method described in detail (7).The present paper presents mutagenicity data on a large number of carcinogens and non-carcinogens of many different classes that have been examined in the system using a standard methodology (7) All non-mutagens, and most mutagens, have been tested, using the recently improved standard methodology (7), on the new R factor tester strains (4) as well as the earlier standard tester strains (3). Non-mutagens have been tested over a wide dose range both with and without the liver microsome activating system.In addition to our previously published studies and new work presented here, results have been contributed to this compilation by a number of laboratories using this test, including a large contribution from Japan. Some of the chemicals tested are also specified in a contract sponsored by the National Cancer Institute (V. Simmon and H. Rosenkranz, to be published). Some of the non-carcinogens we tested were specified in a contract sponsored by the Environmental Protection Agency to B. Commoner.We have not reported on any metal carcinogens, though three or four that have been tested are negative in the standard test. The test system is not suitable for metals entering the bacteria because of the large amount of Mg salts, citrate, and phosphate in the minimal medium. A number of carcinogenic metals have been shown to be mutagens in bacteria by means of a different methodology, e.g. ref.14.In addition to the compounds presented we have tested 46 common biochemicals that are non-ca...

Analogue peptides with enhanced binding affinity to major histocompatibility class (MHC) I molecules are currently being used in cancer patients to elicit stronger T cell responses. However, it remains unclear as to how alterations of anchor residues may affect T cell receptor (TCR) recognition. We correlate functional, thermodynamic, and structural parameters of TCR–peptide–MHC binding and demonstrate the effect of anchor residue modifications of the human histocompatibility leukocyte antigens (HLA)–A2 tumor epitope NY–ESO-1157–165–SLLMWITQC on TCR recognition. The crystal structure of the wild-type peptide complexed with a specific TCR shows that TCR binding centers on two prominent, sequential, peptide sidechains, methionine–tryptophan. Cysteine-to-valine substitution at peptide position 9, while optimizing peptide binding to the MHC, repositions the peptide main chain and generates subtly enhanced interactions between the analogue peptide and the TCR. Binding analyses confirm tighter binding of the analogue peptide to HLA–A2 and improved soluble TCR binding. Recognition of analogue peptide stimulates faster polarization of lytic granules to the immunological synapse, reduces dependence on CD8 binding, and induces greater numbers of cross-reactive cytotoxic T lymphocyte to SLLMWITQC. These results provide important insights into heightened immunogenicity of analogue peptides and highlight the importance of incorporating structural data into the process of rational optimization of superagonist peptides for clinical trials.

Recombinant vaccines encoding strings of virus- or tumor-derived peptides and/or proteins are currently being designed for use against both cancer and infectious diseases. These vaccines aim to induce cytotoxic immune responses against several Ags simultaneously. We developed a novel tetramer-based technique, based on chimeric HLA A2/H-2Kb H chains, to directly monitor the CTL response to such vaccines in HLA-A2 transgenic mice. We found that priming and boosting with the same polyepitope construct induced immune responses that were dominated by CTL of a single specificity. When a mixture of viruses encoding single proteins was used to boost the polyepitope primed response, CTL of multiple specificities were simultaneously expanded to highly effective levels in vivo. In addition, we show that a preexisting response to one of the epitopes encoded within a polyepitope construct significantly impaired the ability of the vaccine to expand CTL of other specificities. Our findings define a novel vaccination strategy optimized for the induction of an effective polyvalent cytotoxic response.