A synthetic dDAF (CD55) gene based on optimal codon usage for transgenic animals

The human DAF (CD55) gene was chosen as a representative molecule in a xenotransplantation study. The gene was synthesized in order to adapt its codons to those which are more frequent in mammals, especially pigs, and the expression levels were then examined in Chinese hamster ovarian (CHO) cells, swine endothelial cell (SEC) and transgenic mice. A significant increase in protein production with no detectable mRNA elevation was observed in the transfectants of synthetic DAF (sDAF), compared with the wild-type DAF (wtDAF) and delta-SCR1 wild-type DAF (Delta1wtDAF). Consistent with the in vitro data, the expression of DAF in mice that carry sDAF was higher than Delta1wtDAF in many organs, especially the pancreas. The sDAF showed a high level of expression in SEC and transgenic mice, suggesting that it will be useful in the development of transgenic pigs with high levels of expression.     

CD58 and CD59 molecules exhibit potentializing effects in T cell adhesion and activation.

We have generated stable Chinese hamster ovary (CHO) cell transfectants expressing either CD58 or CD59 or both molecules to compare their respective parts played in T cell adhesion and activation. Using a rosetting assay, we have shown the following: 1) The CD59 molecule was directly responsible for adhesive interaction between human T cells and CD59+ CHO transfectants. CD59-mediated adhesion induced 12 +/- 2% (mean +/- SEM, n = 25) of rosettes. 2) The CD58 molecule expressed on CD58+ CHO transfectants induced 29 +/- 6% (mean +/- SEM, n = 8) of rosettes. 3) Double transfected CD58+CD59+ CHO cells formed up to 80% of rosettes, largely exceeding the sum of rosettes formed by single transfectants, thus disclosing at least an additive and possibly a synergic action of both molecules in mediating adhesion to T cells. Culturing purified human T cells in the presence of fixed CHO transfectants and submitogenic doses of PHA + rIL-1 alpha showed that: 1) CD59+ CHO transfectants induced sevenfold T cell proliferation enhancement, demonstrating the direct involvement of the CD59 molecule in T cell activation; 2) CD58+ CHO transfectants induced 20-fold T cell proliferation increase; and 3) the enhancement induced by CD58+CD59+ CHO cells was more than 40-fold. These results suggest that CD58 and CD59 molecules present on the surface of accessory cells might exert synergic function in T cell adhesive interactions and in the stimulation of T cell activation.     

Function of human factor H and I on xenosurface

The cell membrane-bound forms of mini-factor H with 1-4 short consensus repeats (fH-PI) and factor I (fI-PI) were constructed. Swine endothelial cell (SEC) lines and Chinese hamster ovary (CHO) cell expressing fH-PI or fI-PI were established and confirmed by flow cytometry. The cell lysate of the SEC line expressing fH-PI showed strong cofactor activity for the cleavage of C3b, and fI-PI demonstrated the protease activity for C4b and C3b not only in the fluid phase but also on the cell membrane. In addition, fH-PI blocked human complement-mediated cell lysis by approximately 30-40%. An SEC line with a low expression of fI-PI showed a weak inhibition of cell lysis in human serum, whereas a CHO cell transfectant with a high expression of fI-PI showed over a 60% inhibition of cell lysis. The results suggest that fH-PI and fI-PI have potential for use in clinical xenotransplantation.     

Involvement of HVEM receptor in activation of nuclear factor kappaB by herpes simplex virus 1 glycoprotein D

The UV-inactivated herpes simplex virus 1 (HSV-1) and glycoprotein D (gD) of HSV-1 have been shown to activate nuclear factor kappaB (NF-kappaB) in U937 cells, but mechanisms involved in this activation have not been elucidated. Here we report that: (i) UV-inactivated HSV-1 induced an increased NF-kappaB activation in cells expressing human HVEM (for herpesvirus entry mediator) at surface level, naturally or following stable transfection, but not in cells in which this receptor was not detected by flow cytometry analysis, (ii) treatment with soluble gD induced a dose-dependent NF-kappaB activation in THP-1 cells naturally expressing HVEM, and a monoclonal antibody that prevents binding of gD to HVEM significantly reduced NF-kappaB activation by soluble gD in the same cells, (iii) coculture with transfectants expressing wild-type gD on their surface induced an approximately twofold increase in NF-kappaB activation in cells naturally expressing HVEM, while coculture with transfectants expressing a mutated form of gD, lacking its capability to bind HVEM, did not induce a similar effect and (iv) treatment with soluble gD induced a dose-dependent NF-kappaB activation in CHO transfectants expressing HVEM, but not in control CHO transfectants lacking any functional gD receptor. Overall, these results establish that HVEM is involved in NF-kappaB activation by HSV-1 gD.     

Reduction of the major xenoantigen on glycosphingolipids of swine endothelial cells by various glycosyltransferases

The effect of the various glycosyltransferases on glycosphingolipids was examined, using transfected swine endothelial cell (SEC) lines. The reactivity of parental SEC to normal human serum (NHS) and Griffonia simplicifolia IB(4) (GSIB4) lectin, which binds to the Gal alpha1-3 Gal beta 1-4 GlcNAc-R (alpha-galactosyl epitope), was reduced by approximately 20% by the treatment with D-PDMP (D-threo-1-phenyl-2-decan- oylamino-3-morpholino-1-propanol), suggesting that glycosphingolipids contained by SEC have a considerable amount of the alpha-galactosyl epitope. The overexpression of two different types of glycosyltransferase, N-acetylglucosaminyl transferase III (GnT-III), as well as alpha2, 6-sialyltransferase (ST6Gal I), alpha2,3-sialyltransferase (ST3Gal III), and alpha1,2-fucosyltransferase (alpha1,2FT), suppresses the total antigenicity of SEC significantly. However, the reduction in reactivities toward NHS and GSIB4 lectin in the case of GnT-III transfectants was milder than those in other transfectants. Western blot analysis indicated that the glycoproteins in all transfectants had diminished reactivity to NHS and GSIB4 lectin to approximately the same extent. Therefore, the neutral glycosphingolipids of these transfectants were separated by thin layer chromatography, followed by immunostaining with NHS and GSIB4 lectin. The levels of the alpha-galactosyl epitope in glycosphingolipids were not decreased in the GnT-III transfectants but were in the ST6Gal I, ST3Gal III, and alpha1,2FT transfectants. These data indicate that ST6Gal I, ST3Gal III, and alpha1,2FT reduced the alpha-galactosyl epitope in both glycoproteins and glycosphingolipids, while GnT-III reduced them only in glycoproteins.     

Features of a newly cloned pig C1 esterase inhibitor

The pig cDNA encoding C1 esterase inhibitor (C1-INH) was isolated and the homology of the sequence was compared with that from other animals. The structure of pig C1-INH contains a two disulfide bridge pattern identical to the human C1-INH. In the amino acid sequence of the first Cys-91 to the C-terminal end, the pigC1-INH has a 76.2% homology with the human protein, and the sequence of the reactive site is close to the human. A surface-bound form of pig and human C1-INH, pC1-INH-PI and hC1-INH, respectively, were next constructed. Stable Chinese hamster ovarian tumor (CHO) cell lines and pig endothelial cell (PEC) lines expressing these C1-INH-PI were prepared by transfection. The basic function and the species specificity of pCI-INH were then investigated using these transfectants. pC1-INH and hC1-INH have almost the same suppressive effect on pig, human, dog and rabbit sera in complement-dependent cell lysis, indicating little species specificity.     

Gene mapping and somatic cell hybrid analysis of the role of human lymphocyte function-associated antigen-3 (LFA-3) in CTL-target cell interactions

LFA-3 is expressed on a wide variety of human cell lines, including those which have been used as recipients for gene transfer of human class I gene products, whereas a murine counterpart is either absent or significantly different such that the anti-LFA-3 monoclonal antibody (MAb) does not bind. By using a somatic cell genetic approach, we demonstrate that LFA-3 is not a major histocompatibility complex-encoded molecule, and that its gene locus maps to human chromosome 1. When LFA-3 and HLA-A2 are coexpressed on the mouse cell surface, anti-LFA-3 MAb interfered with specific recognition and lysis of these target cells by human CTL capable of lysing HLA-A2-expressing mouse transfectants. A significant contribution of the LFA-3 molecule to CTL reactivity was not observed, however, because the presence of LFA-3 did not restore recognition by CTL clones previously found incapable of lysing HLA-A2-expressing mouse transfectants, nor was it required by those human CTL that could lyse mouse cell transfectants. Thus, we have used genetic techniques to demonstrate that LFA-3 may serve a role in CTL-target cell interactions at the target cell level, but is not a molecule absolutely required for human allospecific CTL recognition of HLA antigens expressed on mouse cells. We suggest that LFA-3 may not participate directly in CTL function under normal circumstances, but delivers a more general inhibitory signal only when provoked by bound MAb.     

Efficient selection for high-expression transfectants with a novel eukaryotic vector.

We have developed a new expression vector which allows efficient selection for transfectants that express foreign genes at high levels. The vector is composed of a ubiquitously strong promoter based on the beta-actin promoter, a 69% subregion of the bovine papilloma virus genome, and a mutant neomycin phosphotransferase II-encoding gene driven by a weak promoter, which confers only marginal resistance to G418. Thus, high concentrations of G418 (approx. 800 micrograms/ml) effectively select for transfectants containing a high vector copy number (greater than 300). We tested this system by producing human interleukin-2 (IL-2) in L cells and Chinese hamster ovary (CHO) cells, and the results showed that high concentrations of G418 efficiently yielded L cell and CHO cell transfectants stably producing IL-2 at levels comparable with those previously attained using gene amplification. The vector sequences were found to have integrated into the host chromosome, and were stably maintained in the transfectants for several months.     

Enhanced transport of anticancer agents and leukotriene C4 by the human canalicular multispecific organic anion transporter (cMOAT/MRP2).

We established stable human canalicular multispecific organic anion transporter (cMOAT/MRP2) cDNA transfectants, CHO/cMOAT from non-polarized Chinese hamster ovary (CHO)-K1 and LLC/cMOAT from polarized pig kidney epithelial LLC-PK1. Human cMOAT was mainly localized in the plasma membrane of CHO/cMOAT and in the apical membrane of LLC/cMOAT. The ATP-dependent uptake of leukotriene C4 (LTC4) into CHO/cMOAT membrane vesicles was enhanced compared with empty vector transfectants. Km values in CHO/cMOAT membrane vesicles were 0.24 microM for LTC4 and 175 microM for ATP. Drug sensitivity to vincristine and cisplatin in human cMOAT cDNA transfectants decreased, but not to etoposide. Cellular accumulation of vincristine and cisplatin in human cMOAT cDNA transfectants decreased, but not of etoposide. The uptake of LTC4 into CHO/cMOAT membrane vesicles was inhibited by exogenous administration of vincristine or cisplatin, but not that of etoposide. Moreover, this inhibition was more enhanced in the presence of glutathione. These consequences indicate that drug resistance to vincristine or cisplatin appears to be modulated by human cMOAT through transport of the agents, possibly in direct or indirect association with glutathione.     

Herpes simplex inhibits the capacity of lymphoblastoid B cell lines to stimulate CD4+ T cells

HSV establish a lifelong persistent infection in their host even among immunocompetent persons. The viruses use a variety of immune evasion strategies, presumably to assist persistent replication in the human host. We have observed that infection of human B lymphoblastoid cells (B-LCL) by HSV resulted in a strong inhibition of their ability to induce CD4(+) T cell clone proliferation and cytokine secretion. This inhibitory effect occurs in a variety of both HSV- and HIV-specific clones from three different patients. The inhibition is observed when the Ag is provided either as a soluble protein or as a synthetic peptide and is not associated with detectable down-modulation of the MHC class II molecules or costimulatory molecules. Expression of the HSV-1 unique sequence 1 gene (US1) is necessary and sufficient to induce this inhibition of APC function. US1 gene expression also made B-LCL less susceptible to CD4(+) T cell-mediated lysis. These data indicate a novel immune evasion strategy by HSV-1 in which Ag-processing cells that become infected by HSV-1 are inhibited in their ability to induce subsequent CD4(+) T cell activation.     

Human cytomegalovirus UL18 alleviated human NK-mediated swine endothelial cell lysis

Human cytomegalovirus UL18, a MHC class I homologue, is known to serve as a natural killer cell (NK) decoy and to ligate NK inhibitory receptors to prevent lysis of an infected target cell. To explore whether the cell surface expression of UL18 represents a potential immune suppressive approach to evade NK-mediated cytotoxicity in the prevention of xenograft rejection, we examined the effect of the UL18 expression in vitro upon human NK-mediated cytotoxicity against swine endothelial cells (SECs). UL18 expression on SECs by a retroviral vector (PLNCX2) significantly suppressed NK-mediated SEC lysis by approximately 25-100%. The protective effect of UL18 could be mediated through ILT-2 inhibitory receptor on NKs. Additionally, the interaction between UL18 and NKs resulted in the significant reduction of IFN-gamma production. This study demonstrates that UL18 can serve as an effective tool for the evasion of NK-mediated cytotoxicity and for the inhibition of IFN-gamma production during xenograft rejection.     

A "chimeric" C57l-derived Ly49 inhibitory receptor resembling the Ly49D activation receptor.

Ly49D is a natural killer (NK) cell activation receptor that is responsible for differential mouse inbred strain-determined lysis of Chinese hamster ovary (CHO) cells. Whereas C57BL/6 NK cells kill CHO, BALB/c-derived NK cells cannot kill because they lack expression of Ly49D. Furthermore, the expression of Ly49D, as detected by monoclonal antibody 4E4, correlates well with CHO lysis by NK cells from different inbred strains. However, one discordant mouse strain was identified; C57L NK cells express the mAb 4E4 epitope but fail to lyse CHO cells. Herein we describe a Ly49 molecule isolated from C57L mice that is recognized by mAb 4E4 (anti-Ly49D). Interestingly, this molecule shares extensive similarity to Ly49D(B6) in its extracellular domain, but its cytoplasmic and transmembrane domains are identical to the inhibitory receptor Ly49A(B6), including a cytoplasmic ITIM. This molecule bears substantial overall homology to the previously cloned Ly49O molecule from 129 mice the serologic reactivity and function of which were undefined. Cytotoxicity experiments revealed that 4E4(+) LAK cells from C57L mice failed to lyse CHO cells and inhibited NK cell function in redirected inhibition assays. MHC class I tetramer staining revealed that the Ly49O(C57L)-bound H-2D(d) and lysis by 4E4(+) C57L LAK cells is inhibited by target H-2D(d). The structural basis for ligand binding was also examined in the context of the recent crystallization of a Ly49A-H-2D(d) complex. Therefore, this apparently "chimeric" Ly49 molecule serologically resembles an NK cell activation receptor but functions as an inhibitory receptor.     

Trophoblast cell line resistance to NK lysis mainly involves an HLA class I-independent mechanism

The lack of classical HLA molecules on trophoblast prevents allorecognition by maternal T lymphocytes, but poses the problem of susceptibility to NK lysis. Expression of the nonclassical class I molecule, HLA-G, on cytotrophoblast may provide the protective effect. However, the class I-negative syncytiotrophoblast escapes NK lysis by maternal PBL. In addition, while HLA-G-expressing transfectants of LCL.721.221 cells are protected from lymphokine-activated killer lysis, extravillous cytotrophoblast cells and HLA-G-expressing choriocarcinoma cells (CC) are not. The aim of this work was therefore to clarify the role of HLA class I expression on trophoblast cell resistance to NK lysis and on their susceptibility to lymphokine-activated killer lysis. Our results showed that both JAR (HLA class I-negative) and JEG-3 (HLA-G- and HLA-Cw4-positive) cells were resistant to NK lysis by PBL and were equally lysed by IL-2-stimulated PBL isolated from a given donor. In agreement, down-regulating HLA class I expression on JEG-3 cells by acid treatment, masking these molecules or the putative HLA-G (or HLA-E) receptor CD94/NKG2 and the CD158a/p58.1 NKR with mAbs, and inducing self class I molecule expression on JAR cells did not affect NK or LAK lysis of CC. These results demonstrate that the resistance of CC to NK lysis mainly involves an HLA class I-independent mechanism(s). In addition, we show that the expression of a classical class I target molecule (HLA-B7) on JAR cells is insufficient to induce lysis by allospecific polyclonal CTL.     

A yeast DNA repair gene partially complements defective excision repair in mammalian cells.

The RAD10 gene of Saccharomyces cerevisiae is required for nucleotide excision repair of DNA. Expression of RAD10 mRNA and Rad10 protein was demonstrated in Chinese hamster ovary (CHO) cells containing amplified copies of the gene, and RAD10 mRNA was also detected in stable transfectants without gene amplification. Following transfection with the RAD10 gene, three independently isolated excision repair-defective CHO cell lines from the same genetic complementation group (complementation group 2) showed partial complementation of sensitivity to killing by UV radiation and to the DNA cross-linking agent mitomycin C. These results were not observed when RAD10 was introduced into excision repair-defective CHO cell lines from other genetic complementation groups, nor when the yeast RAD3 gene was expressed in cells from genetic complementation group 2. Enhanced UV resistance in cells carrying the RAD10 gene was accompanied by partial reactivation of the plasmid-borne chloramphenicol acetyltransferase (cat) gene following its inactivation by UV radiation. The phenotype of CHO cells from genetic complementation group 2 is also specifically complemented by the human ERCC1 gene, and the ERCC1 and RAD10 genes have similar amino acid sequences. The present experiments therefore indicate that the structural homology between the yeast Rad10 and human Ercc1 polypeptides is reflected at a functional level, and suggest that nucleotide excision repair proteins are conserved in eukaryotes.     

Detection of antibodies to herpes simplex virus type 2 with a mammalian cell line expressing glycoprotein gG-2

The gene (US4) coding for herpes simplex virus type 2 (HSV-2) glycoprotein G (gG-2) was cloned and constitutively expressed in Chinese hamster ovary (CHO) cells. The expression vector containing the dihydrofolate reductase (dhfr) gene, and the HSV-2 US4 gene under the control of the Simian virus 40 early promoter (SV40 EP), was transfected into dhfr-deficient CHO cells. The transfected cells were selected and amplified using methotrexate (MTX). To demonstrate that the gG-2 produced in these transformed cells had antigenic determinants in common with the native glycoprotein, CHO cells expressing gG-2 were used in an immunofluorescent assay (IFA) for the detection of HSV-2 type-specific antibodies in human serum samples. Seven of eight serum samples from adults with prior episodes of culture proven HSV-2 infections were found to be positive by the IFA method whereas none of seven serum samples from young children with culture documented HSV-1 infections were positive by IFA. Thus the recombinant CHO : gG-2 cells have diagnostic utility in an HSV-2 specific serologic assay.     

Herpes simplex virus type 1 strain HSV1716 grown in baby hamster kidney cells has altered tropism for nonpermissive Chinese hamster ovary cells compared to HSV1716 grown in vero cells

Chinese hamster ovary (CHO) cells are traditionally regarded as nonpermissive cells for herpes simplex virus type 1 (HSV-1) infection as they lack the specific entry receptors, and modified CHO cells have been instrumental in the identification of HSV-1 receptors in numerous studies. In this report we demonstrate that the HSV-1 strain 17+ variant HSV1716 is able to infect unmodified CHO cells but only if the virus is propagated in baby hamster kidney (BHK) cells. Infection of CHO cells by BHK-propagated HSV1716 results in expression of immediate-early, early, and late viral genes, and infectious progeny virions are produced. In normally cultured CHO cells, up to a maximum of 50% of cells were permissive for BHK-propagated HSV1716 infection, with 24 h of serum starvation increasing this to 100% of CHO cells, suggesting that the mechanism used by BHK-propagated virus to infect CHO cells was cell cycle dependent. The altered tropism of HSV1716 was also evident in another nonpermissive mouse melanoma cell line and is an exclusive property resulting from propagation of the virus using BHK cells, as viruses propagated on Vero, C8161 (a human melanoma cell line), or indeed, CHO cells were completely unable to infect either CHO or mouse melanoma cells.     

Species specificity in the interaction of CD8 with the alpha 3 domain of MHC class I molecules.

The alpha 1 and alpha 2 domains of the class I MHC molecule constitute the putative binding site for processed peptides and the TCR, although the alpha 3 domain has been implicated as a binding site for the CD8 molecule. Species specificity in the binding of CD8 to the alpha 3 domain has been suggested as an explanation for the low xenogeneic T cell response to class I molecules, but results on this point have been conflicting and controversial. We have addressed this issue using CTL lines from HLA-A2.1 transgenic mice that specifically recognize and lyse A2.1-expressing cells infected with influenza A/PR/8 or pulsed with influenza matrix peptide M1(57-68). Species specificity was examined using transfectants that expressed hybrid molecules containing the alpha 1 and alpha 2 domains from HLA-A2.1 and the alpha 3 domain from a murine class I molecule. Lower levels of M1(57-68) peptide were required to sensitize L cell transfectants expressing a chimera that contained an H-2Dd alpha 3 domain than targets expressing the intact A2.1 molecule. However, at high doses of peptide, lysis of these two targets was similar. However, no reproducible difference in sensitization was observed using EL4 or Jurkat transfectants expressing A2.1 or A2.1 chimeric molecules that contained an H-2Kb alpha 3 domain. In all cases, however, lysis of peptide-pulsed A2.1 expressing targets was more sensitive to inhibition with anti-CD8 mAb than lysis of cells expressing these chimeric molecules. Thus, under suboptimal conditions such as low Ag density or in the presence of anti-CD8 mAb, these CTL preferentially recognize class I molecules with a murine alpha 3 domain. This suggests that there is some species specificity in the interaction of CD8 with the alpha 3 domain of the class I molecule. However, CTL recognition was inhibited by point mutations in the alpha 3 domain of HLA-A2.1 that have been shown to inhibit binding of human CD8 and recognition by human CTL, suggesting that murine CD8 interacts to some degree with human alpha 3 domains, and that similar alpha 3 domain residues may be important for murine and human CD8 binding. The relevance of these results to an understanding of low xenogeneic responses is discussed.     

Role of carbohydrate structures in CEA-mediated intercellular adhesion

Human carcinoembryonic antigen (CEA) is a member of a family of cell surface glycoproteins representing a subset of the immunoglobulin superfamily and is a major tumor marker. CEA has been demonstrated to function in vitro, at least, as a homotypic intercellular adhesion molecule. CEA can also inhibit the differentiation of several different cell types and contribute to tumorigenesis, an activity that requires CEA-CEA interactions. Post-translational modifications that could modulate CEA-CEA binding are therefore of interest. CEA is heavily glycosylated with 28 consensus sites for the addition of asparagine-linked carbohydrate structures, leading to a molecule with a bottle brush-like structure. In order to modulate the glycosylation of CEA, we transfected the functional cDNA of CEA into Chinese hamster ovary (CHO) mutant cells, Lec1, Lec2, and Lec8, which are deficient in enzymes responsible for various steps in the glycosylation processing pathway. Aggregation assays of cells in suspension were performed with stable CEA transfectants of these cell lines and showed that all of the aberrant CEA glycoforms could still mediate adhesion. In addition, the specificity of adhesion of these glycoforms was unchanged, as shown by homotypic and heterotypic adhesion assays between the transfectants. Lec1 and Lec2 transfectants did, however, show an increased speed and final extent of aggregation, which is consistent with models in which sugar structures interfere with binding through protein domains. Lec8 transfectants, on the other hand, with more truncated sugar structures than Lec2, showed less aggregation than wild type (WT) transfectants. We therefore conclude that carbohydrates do not determine the adhesion property of CEA or its specificity, in spite of the unusually high degree of glycosylation; they do, however, modulate the strength of adhesion.     

Increased sensitivity of a Chinese hamster ovary cell line to alkylating agents after overexpression of the human metallothionein II-A gene.

The elevation of intracellular levels of metallothionein has been associated with the development of resistance to the cytotoxic effects of some alkylating agents. In order to study the mechanisms underlying metallothionein associated drug resistance we transfected the alkylating agent sensitive CHO cell line MMC-1 (Robson et al., 1985) with an episomally replicating plasmid coding for the human metallothionein II-A gene. Two transfectants were isolated which carried about 10 copies of the plasmid. The basal expression of metallothionein was increased from undetectable levels in the recipient cell line MMC-1 to between 22 and 26 micrograms metallothionein per 10(7) cells in the transfectants. Treatment with cadmium salts increased metallothionein levels a further 1.7-fold. Cytotoxicity assays revealed that MTII-A transfection increased the sensitivity of the parental MMC-1 cells to N-methyl-N'-nitro-N-nitrosoguanidine and N-nitroso-N-methylurea. These results suggest that metallothionein does not act as a simple scavenger of alkylating agents, but interacts with unknown factor(s) in host cells.     

Human oncogene-transfected tumor cells display differential susceptibility to lysis by lymphokine-activated killer cells (LAK) and natural killer cells

NIH 3T3 tertiary transfectants containing the N-ras or c-Ha-ras oncogenes derived from human tumors were tested for susceptibility to lymphokine-activated killer (LAK) cell and natural killer (NK) cell lysis. N-ras tertiary transfectants contained a human acute lymphocytic leukemia-derived N-ras oncogene. C-Ha-ras transfectants contained either the position 61-activated form of the oncogene (45.342, 45.322, and 45.3B2) or the position 12-activated form (144-162). In 4 hr 51Cr release assays, seven of seven in vivo grown human oncogene transfected NIH 3T3 fibroblasts were lysed by murine LAK effectors, whereas six of seven were lysed by human LAK effectors. There was no difference in susceptibility to lysis between cells transfected with the N-ras oncogene, the position 61 activated c-Ha-ras oncogene, or the position 12 activated c-Ha-ras oncogene. Cultured NIH 3T3 fibroblasts, as well as in vitro and in vivo grown NIH 3T3 tertiary transfectants were resistant to lysis by murine NK effectors and were relatively resistant (4/6 were not lysed) to lysis by human NK effectors. We conclude that human oncogene-transfected tumors are susceptible to lysis by both murine and human LAK cells while being relatively resistant to lysis by murine and human NK cells. Different oncogenes or the same oncogene activated by different point mutations do not specifically determine susceptibility to lysis by LAK or NK. Also the presence of an activated oncogene does not appear to be sufficient for inducing susceptibility to these cytotoxic lymphocyte populations.