Characterization and use of neuraminidase-modified L1210 plasma membranes for protection against tumor growth.

Purified plasma membranes were prepared from L1210 ascites tumor cells and analyzed for their protein and carbohydrate composition. Conditions were developed for treating the isolated plasma membranes with Vibrio cholerae neuraminidase (VCN) so that 88% of the N-acetylneuraminic acid was removed without changing membrane proteins or other membrane carbohydrate constituents. The VCN-induced modifications were characterized by labeling VCN-treated and untreated L1210 cells by the galactose oxidase:sodium [3H]borohydride procedure. This showed that N-acetylneuraminic acid is the predominant saccharide at the nonreducing terminus of plasma membrane glycoproteins and that galactose and/or N-acetylgalactosamine residues are penultimate to these. VCN modification exposed the penultimate residues and was not limited to any single plasma membrane glycoprotein. DBA/2J mice were given i.p. injections of VCN-treated or untreated membranes and were challenged 3 weeks later with 10(4) viable L1210 cells. Mice pretreated with VCN-treated membranes resisted the tumor challenge; those receiving untreated membranes or no treatment succumbed to the tumor. Our results demonstrate that appropriately modified plasma membranes can be used to induce resistance to tumor growth. They also suggest that tumor cell membrane carbohydrate structures have an important role in this phenomenon.

Immunotherapy of L1210 leukemia using neuraminidase-modified plasma membranes combined with chemotherapy.

Purified L1210 plasma membranes treated with Vibrio cholerae neuraminidase (VCN) were used for active immunotherapy of L1210 tumors in DBA/2J mice. Immunotherapy with VCN-treated membranes was effective only when combined with 1-(2-chloroethyl)-3-(4-methylcyclohexyl)-1-nitrosourea (MeCCNU). Successful therapy was a function of the dose of MeCCNU, the dose of VCN-treated membranes, and the time after MeCCNU treatment when VCN-treated membranes were administered. Optimum conditions for treating animals with tumors initiated with 10(4) cells were MeCCNU (20/kg) given 3 days after tumor inoculation and 0.25 mg VCN-treated membranes given 1 day after chemotherapy. Control membranes, not treated with VCN, that were administered 1 day after MeCCNU were ineffective; when given 4 days after chemotherapy, the caused accelerated mortality, suggesting immunological enhancement of tumor growth. Our results indicate that VCN-treated plasma membranes can be used for active immunotherapy of established tumors and underscore the importance of carefully designing immunotherapy protocols to achieve optimum desirable effects.

The role of polarization of Xe by di- and monovalent cations in 129Xe NMR studies in zeolite A.

We consider the role of polarization in the adsorption of Xe in zeolites of type A by direct comparative analysis of the adsorption isotherms, distributions of occupancies, and 129Xe NMR chemical shifts of Xe(n) in cages containing CaxNa12-2x ions per alpha cage (x = 0, 1, 2, 3, 5). We find that the qualitative trends in the adsorption isotherms, and in the progressions of Xe(n) chemical shifts (for n = 0-8 in cages with x = 0, 1 Ca2+ ions and for n = 0-5 in cages with x = 2, 3 Ca2+ ions) upon increasing the level of Ca2+ ion for Na+ ion substitution could only be accounted for by including polarization of the Xe atom by the zeolite framework and its ions. This system, which permits observation of individual Xe(n) peaks and of directly comparable adsorption isotherms in several cage types, provides a good model system for the interpretation of the more general case in which only the overall average 129Xe NMR chemical shift is observed in open network zeolites, arising from free exchange of Xe among cavities of variable occupancy and variable cation distribution.

129Xe magic-angle spinning spectra of xenon in zeolite NaA. Direct observation of mixed clusters of co-adsorbed species.

We present the first demonstration that the individual 129Xe resonances corresponding to Xen (n = 1-8) clusters inside the alpha-cages of zeolite NaA can be narrowed under magic-angle spinning (MAS). Under these high-resolution conditions we also observe upon addition of Kr the individual peaks corresponding to mixed clusters, XenKrm, inside the alpha-cages, which will allow the first direct determination of the distribution of co-adsorbates in a microporous solid. Under MAS the chemical shifts of the Xen clusters are shown to be highly sensitive to "disorder" in the zeolite and provides new, quantitative information about the presence of alpha-cages of several types.