Human lymphokine-activated killer cells: further isolation and characterization of the precursor and effector cell

In a series of experiments we have demonstrated the progressive enrichment (5- to 40-fold) in lymphokine-activated killer (LAK) precursor activity by adherence depletion, sheep red cell rosetting, and depletion of CD3- and DR-positive lymphocytes. The LAK precursor cell thus appears to fall within the 'null' cell population. CD16 and CD11 are cell surface antigens expressed on the surface of the LAK precursor as demonstrated in sorting experiments. A 6- to 100-fold enrichment compared to unseparated peripheral blood was noted when sorted cells positive for CD16 and CD11 were tested. The LAK effector has been identified as being primarily CD3- and CD2+. Similar sorting equipment demonstrated a 7- to 500-fold difference in lytic activity for fresh tumor when comparing CD2+/CD3- and CD2+/CD3+ cells. The CD16+/CD11+ lymphocyte can proliferate in response to interleukin-2 (IL-2) alone in the absence of accessory cells and can be expanded in IL-2 alone with maintenance of lytic activity.     

Molecular cloning and nucleotide sequence of cDNA encoding the entire precursor of rat liver medium chain acyl coenzyme A dehydrogenase

cDNA encoding the precursor of rat liver medium chain acyl-CoA dehydrogenase (EC 1.3.99.3) was cloned and sequenced. The longest cDNA insert isolated was 1866 bases in length. This cDNA encodes the entire protein of 421-amino acids including a 25-amino acid leader peptide and a 396-amino acid mature polypeptide. The identity of the medium chain acyl-CoA dehydrogenase clone was confirmed by matching the amino acid sequence predicted from the cDNA to the NH2-terminal and nine internal tryptic peptide sequences derived from pure rat liver medium chain acyl-CoA dehydrogenase. The calculated molecular masses of the precursor medium chain acyl-CoA dehydrogenase, the mature medium chain acyl-CoA dehydrogenase, and the leader peptide are 46,600, 43,700, and 2,900 daltons, respectively. The leader peptide contains five basic amino acids and only one acidic amino acid; thus, it is positively charged, overall. Cysteine residues are unevenly distributed in the mature portion of the protein; five of six are found within the NH2-terminal half of the polypeptide. Comparison of medium chain acyl-CoA dehydrogenase sequence to other flavoproteins and enzymes which act on coenzyme A ester substrates did not lead to unambiguous identification of a possible FAD-binding site nor a coenzyme A-binding domain. The sequencing of other homologous acyl-CoA dehydrogenases will be informative in this regard.     

Identification of cellular mechanisms operational in vivo during the regression of established pulmonary metastases by the systemic administration of high-dose recombinant interleukin 2

The systemic administration of high-dose recombinant IL 2 mediated significant reductions of established 3-day pulmonary micrometastases from both weakly immunogenic and nonimmunogenic sarcomas. However, when treatment with IL 2 was delayed for 10 days after the injection of tumor cells in an attempt to treat grossly visible pulmonary macrometastases, only those established from weakly immunogenic sarcomas remained susceptible. Established 10-day pulmonary nodules from the nonimmunogenic sarcomas became refractory to IL 2 therapy. We utilized selective depletion of lymphocyte subsets in vivo by the systemic administration of specific monoclonal antibodies to cells bearing either the L3T4 or Lyt-2 marker or a heteroantiserum to cells bearing the ASGM-1 glycosphingolipid to identify lymphocytes involved in IL 2-induced tumor regression. Cells with potent lymphokine-activated killer (LAK) activity against fresh tumor targets in vitro were identified in the lungs of IL 2-treated mice. By flow cytometry analysis, the majority of these effector cells were Thy-1+, L3T4-, Lyt-2-, ASGM-1+. Depletion in vivo of ASGM-1+ cells before the onset of IL 2 administration eliminated the successful therapy of 3-day pulmonary metastases from nonimmunogenic sarcomas, with concurrent elimination of LAK cell activity in the lungs. In mice with 3-day pulmonary metastases from weakly immunogenic sarcomas, both Lyt-2+ cells and ASGM-1+ cells were involved in IL 2-mediated tumor regression, but Lyt-2+ cells appeared to be the more potent mediator in the response. Lyt-2+ cells were also involved in the elimination of grossly visible 10-day macrometastases from these weakly immunogenic tumors. Depletion of L3T4+ cells had no effect on tumor regression. Thus, although LAK effectors derived from ASGM-1+ precursors can eliminate pulmonary micrometastases regardless of tumor immunogenicity, Lyt-2+ cells are predominant effectors in the elimination of both pulmonary micro- and macrometastases from weakly immunogenic sarcomas.     

Antibody-dependent cellular cytotoxicity mediated by murine lymphocytes activated in recombinant interleukin 2

The incubation of murine splenocytes in recombinant interleukin 2 (RIL 2) gives rise to lymphokine-activated killer (LAK) cells that can lyse fresh, NK-resistant tumor cells but not normal cells in 4-hr 51Cr-release assays. Lysis by this IL 2-activated cell population was enhanced up to 100-fold by prior reaction of target cells with specific antisera reactive with antigens on the target cells. This antibody-dependent cellular cytotoxicity (ADCC) also resulted in lysis of fresh normal target cells, which are not usually susceptible to LAK lysis. The ADCC was evident after 24 hr of incubation of splenocytes in RIL 2, but peak lytic activity was reached after 3 to 4 days of incubation. The concentrations of RIL 2 needed for the in vitro activation of the effectors in order to attain maximal ADCC was between 100 and 3000 U/ml and parallel the IL 2 concentrations required to generate LAK cells. ADCC mediated by IL 2-activated splenocytes was completely blocked by anti-FcR monoclonal antibodies. Although antisera directed against MHC antigens were used in most experiments, anti-B16 monoclonal antibodies have also shown the ability to induce ADCC mediated by RIL 2-activated syngeneic and allogeneic cells. Treatment of the precursor splenocyte populations with anti-asialo GM1 and complement eliminated the direct LAK activity and the antibody-dependent cytotoxicity, suggesting that both direct and indirect tumor cell lysis may be caused by the same effector cell. ADCC mediated by LAK cell populations represents another possible mechanism for the in vivo therapeutic effects of these cells.     

Viscosity and transient solvent accessibility of Trp-63 in the native conformation of lysozyme

We have measured the rates of isotope exchange at the nitrogen of the indole ring of Trp-63 of lysozyme and of L-tryptophan as a function of solution viscosity. We have used two cosolvents, glycerol and ethylene glycol, to modify the relative viscosity. We have derived the appropriate kinetic equations for the alternative possibilities that the exchange takes place either in solution or in the intact protein matrix. Because we chose to study the proton-catalyzed exchange reaction, the rate of it is not expected to be diffusion-limited. We confirmed this by measuring the exchange from tryptophan. These results and the known effects of glycerol and ethylene glycol on the solvation of indole allow us to predict that if the exchange reaction takes place in a protein matrix the effects of the two cosolvents when compared under isoviscous conditions should be identical. This is what we find for Trp-63 in lysozyme at 15, 20 and 26 degrees C. The slope of the linear plot of log k vs. log relative viscosity is 0.6. This strongly supports a model for conformational fluctuations where transient solvation takes place without major changes in protein folding. The most interesting feature of our findings is the fact that a slow reaction admittedly not diffusion-limited shows, when taking place in a protein matrix, a linear dependence on solution viscosity. We suggest that what we observe is the effect of damping of movement of the side chain expressed as a change in the friction along the reaction coordinate in the corresponding phase space. The presence of such effects stresses the validity and usefulness of Kramers model of rate processes for reactions taking place in a protein matrix. Such behavior is predicted by several of the recently proposed general mechanisms of enzyme catalysis.     

Purification and characterization of the restriction endonuclease RsrI, an isoschizomer of EcoRI

Rhodobacter sphaeroides strain 630 produces restriction enzyme RsrI which is an isoschizomer of EcoRI. We have purified this enzyme and initiated a comparison with the EcoRI endonuclease. The properties of RsrI are consistent with a reaction mechanism similar to that of EcoRI: the position of cleavage within the -GAATTC-site is identical, the MgCl2 optimum for the cleavage is identical, and the pH profile is similar. Methylation of the substrate sequence by the EcoRI methylase protects the site from cleavage by the RsrI endonuclease. RsrI cross-reacts strongly with anti-EcoRI serum indicating three-dimensional structural similarities. We have determined the sequence of 34 N terminal amino acids for RsrI and this sequence possesses significant similarity to the EcoRI N terminus.     

Cell-free translation of mRNA encoding an arterial smooth muscle cell proteoglycan core protein

The size and immunological reactivity of the primary gene products of a small non-aggregating dermatan sulfate proteoglycan from bovine and monkey arterial smooth muscle cells were examined after cell-free translation of mRNA. Antisera against the dermatan sulfate proteoglycans from bovine articular cartilage, DSPG II [Rosenberg et al. J. Biol. Chem. 260, 6304 (1985)] and human skin fibroblasts [Glossl et al. J. Biol. Chem. 259, 14144 (1984)] were used to show that the unmodified smooth muscle precursor core protein was immunologically related to both the cartilage and fibroblast core proteins. The size of the precursor core proteins within each species was identical regardless of the tissue source. Comparison of the precursor core proteins synthesized by primate and bovine cells revealed that the bovine core proteins were approximately 1500 Da larger than the primate core proteins as determined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. A similar size difference was observed when the mature core proteins of monkey smooth muscle cells and bovine articular chondrocytes were compared after removal of the glycosaminoglycan chains. These results indicate that arterial smooth muscle cells synthesize a dermatan sulfate proteoglycan whose core protein is similar to, if not the same as, the cartilage and fibroblast dermatan sulfate proteoglycan core proteins. These core proteins may be encoded by the same gene that has diverged in size during speciation.     

Transfer and co-amplification of a gene encoding a 96-kDa immune IFN-inducible human melanoma-associated antigen. Preferential expression by mouse melanoma host cells

An immune IFN-inducible human melanoma-associated glycoprotein Ag, 96-kDa MAA, having preferential distribution on metastases has been defined by mouse mAb CL203.4. To initiate molecular genetic analysis of 96-kDa MAA, the gene encoding the Ag was transfected into mouse B16 melanoma cell clone B78H1. Formation of B78H1-transfectant colonies expressing a surface Ag reactive with mAb CL203.4 in an immunorosetting assay was dependent on addition of chromosomal DNA from human melanoma cells [primary (1 degree) transfer] or from Ag-expressing transfectant cells (2 degrees, 3 degrees, 4 degrees transfer). The mAb CL203.4-reactive species expressed by the transfectant cells is a glycoprotein with a molecular mass 93-kDa, within the range of 93 to 96-kDa observed for the endogenous human Ag. In the presence of tunicamycin, an inhibitor of N-linked glycosylation, both mouse melanoma transfectants and human melanoma cells express a 50- to 51-kDa antigenic species. Human alu family repeat sequences (h-alu) are present in the genomes of 3 degrees transfectant cells. Continued presence of these h-alu after dilution of extraneous human DNA by three cycles of transfection suggests their association with the transferred 96-kDa MAA gene. Use of a selective co-amplification procedure led to transfectant cells' increased expression of 96-kDa MAA and to commensurate increases in their content of presumed 96-kDa MAA gene-associated h-alu. Preferential DNA-mediated transferability of the 96-kDa MAA+ phenotype into B78H1 cells as compared with LMTK- mouse fibroblasts suggests host cell specificity of 96-kDa MAA gene expression.