Levamisole meets sulfhydryl requirements of CTLL-2 cells and mediates enhanced proliferative response to mitogen stimulation without increasing interleukin-2 production.

We examined the effect of levamisole (LMS) on the proliferative response and interleukin-2 (IL-2) concentration in OKT3-, phytohemagglutinin-, and concanavalin-A-stimulated lymphocyte cultures. Although proliferative response was enhanced in lymphocyte cultures stimulated in the presence of LMS, similar levels of IL-2 were observed in stimulated and unstimulated cultures. The mechanism of the enhancement effect of LMS on proliferative response was further characterized by studying its effects on the growth of IL-2-dependent CTLL-2 cells in culture. Since this cell line has been shown to require 2-mercaptoethanol (2-ME) for normal growth in recombinant IL-2, the effect of LMS on several parameters of its growth was compared with that of 2-ME. Unlike 2-ME, LMS did not enhance 35S-cystine uptake. Both compounds increased thiol concentration in the cell culture, but (oxidized) 2-ME induced a greater increase. Generally, the effects of LMS on CTLL-2 growth were quite similar to those of structurally unrelated compounds known to have antioxidant properties, and the demonstrated thiol requirement of this cell line for growth in recombinant IL-2 was met by substituting LMS for 2-ME. When the effect of LMS on IL-2 receptor (IL-2R) expression in CTLL-2 cells was examined by a receptor-ligand binding assay involving low levels (10-80 pM) of 125IL-2, a modest increase in the level of IL-2R expression was observed. The biologically active high-affinity IL-2R complex is believed to be preferentially bound at the low levels of 125IL-2 used here, suggesting a functional relevance for this effect of LMS. These observations should be useful in minimizing the cost and duration of in vitro expansion of lymphocytes for use in adoptive immunotherapy and should be applicable in improving the response of immunologically impaired patients to immunotherapy.

Detection of a tumor-associated nucleoprotein antigen in mink lung cells transformed by two different viral oncogenes.

Salt-precipitated chromatin was prepared from cultured MvlLu line mink lung cells and from these cells transformed by either of the oncogenes v-mos (MIMS-102 line) or v-fes (F3C7 line). Xenoantisera were raised to chromatin from each of the three cell types and cross-tested in microcomplement fixation assays to determine immunospecificity. Chromatin from cells transformed by either v-mos or v-fes revealed antigenic profiles statistically indistinguishable (P less than 0.2 to 0.5) from one another with their respective cross-tested antisera, but did not react significantly with antisera to chromatin from the untransformed parental cell line. Likewise, little cross-reaction was observed with chromatin from the untransformed cells and antisera raised to chromatin from either of the oncogenically transformed lines (P less than 0.001), although each chromatin demonstrated high reactivity with its homologous antiserum preparation. These immunological data are consistent with the observed normal or transformed characteristics for each cell type, including morphology, anchorage-independent growth, and growth in the absence of serum.

Effects of divalent metal cations on composition and neoplasia-specific antigenicity of chromatins.

The antigenicity and composition of chromatins differ markedly in chromatin preparations obtained by different procedures. Rat Novikoff hepatoma chromatin (NC) obtained by the "salt precipitation" and the micrococcal nuclease digestion procedures using significant levels of EDTA and NaCl each shows a common complement fixation (CF) capacity, exceeding chromatin preparations obtained from normal rat liver when tested with rabbit antisera raised to dehistonized NC. In contrast, "structured" NC preparations, which have been postulated to retain a native physical conformation, show minimal CF capacity when tested with the same antiserum but show high CF following elution of histones. While further progressive elution of non-histone proteins (NHPs) did not alter the CF capacity per unit DNA, the completely separated DNA and NHP fractions each showed minimal CF. The data suggest that the antigens detected in the CF assay predominantly represent an artifactual but specific complex of DNA and NHP arising from a denaturation of the native chromatin following elution of metal ions or histones. A qualitatively similar profile of NHPs in salt-precipitated NCs shows a range of total protein/DNA ratios, suggesting that the NHPs found in chromatin preparations may not be intrinsic to the native chromatin structure.