The augmentation of lymphokine-activated killer activity following pulsing of human peripheral blood mononuclear cells with recombinant human interleukin-2

Summary The short-term exposure of peripheral blood mononuclear cells (PBMC) to recombinant human interleukin-2 (rhIL-2) at 37°C leads to the generation of lymphokine-activated killer (LAK) activity similar in magnitude to that obtained by the exposure of PBMC to rhIL-2 continuously for 3–5 days. In order to investigate whether the required signal for LAK induction occurred during the short exposure to rhIL-2 or at a later point in the induction phase, PBMC were exposed to rhIL-2 for 1 h at 4°C and then exposed to a low-pH wash to remove bound IL-2 from its receptor. PBMC treated in such a way showed increased LAK activity and proliferation compared to cells exposed to rhIL-2 alone. Expression of the p55 () subunit of the IL-2 receptor was also increased. In order to cause the augmentation, a lowering of the pH below 4.0 was necessary, and exposure of PBMC to low pH alone (in the absence of rhIL-2) failed to cause activation. Another relevant feature was a transient increase in the expression of the p75 subunit of the IL-2 receptor ( chain) immediately following the exposure to low pH and the release of interferon , tumour necrosis factor and IL-6; activation was blocked by the inclusion of neutralising antisera raised against rhIL-2 and interferon , thus demonstrating that the endogenous release of these cytokines is important for activation.     

Combined effect of epirubicin and lymphokine-activated killer cells on the resistant human breast cancer cells

Accumulating evidence suggests the concept that epirubicin and lymphokine-activated killer (LAK) cells cytotoxicity may be mediated by free radicals generation and P-glycoprotein-positive (Pg-p⁺) cancer cells are more sensitive for LAK cells than their drug-sensitive parental lines. We tested this hypothesis further by exposing drug-sensitive (WT) and epirubicin-resistant MCF-7 human breast tumor cells to epirubicin and LAK cells. Subsequently, we monitored cell proliferation as a measure of cytotoxicity. The cytotoxicity of epirubicin, LAK, and LAK + epirubicin (1/10 of IC₅₀) was evaluated in 400-fold epirubicin resistant MCF-7 EPI^R (P-glycoprotein overexpressing) and drug-sensitive MCF-7 WT cells. IC₅₀ values were measured using the MTT cytotoxicity test. The MCF-7 EPI^R cells exhibited an increased susceptibility to LAK cells than did the MCF-7 WT cells. P-gp⁺ MCF-7 EPI^R cells were lysed by human LAK cells to a greater extend than were their drug-sensitive counterparts. LAK + epirubicin combined treatment increased susceptibility of MCF-7 WT and MCF-7 EPI^R cells to LAK cells cytotoxicity. For both cell lines, cytotoxicity was dependent upon the concentration of the epirubicin and effector cell/target cell (E/T) ratio. The resistance of MCF-7 EPI^R cells to epirubicin appears to be associated with a developed tolerance to superoxide, most likely because of a tree-fold increase in superoxide dismutase (SOD) activity and 13-fold augmented selenium dependent glutathione peroxidase (GSH-Px) activity. Acting in concert, these two enzymes would decrease the formation of hydroxyl radical from reduced molecular oxygen intermediates. The addition of SOD decreased cytotoxicity of epirubicin and LAK cells. Taken together, these observations support the role of oxygen radicals in the cytotoxicity mechanism of epirubicin and suggest further that the development of resistance to this drug by the MCF-7 EPI^R tumor cells may have a component linked to oxygen free radicals. It is proposed that production of reactive oxygen species by the treatment of epirubicin and LAK cells can cause cytotoxicity of MCF-7 WT and MCF-7 EPI^R cells. SOD, catalase, GSH-Px, GST (glutathione S-transferase), and GSH (reduced glutathione) must be considered as part of the intracellular antioxidant defense mechanism of MCF-7 WT and MCF-7 EPI^R cells against reactive oxygen species.     

Supplementation with selenium augments the functions of natural killer and lymphokine-activated killer cells

This study examined the effects of dietary (2.0 ppm for 8 wk) and in vitro (1×10⁻⁷ M) supplementation with selenium (Se, as sodium selenite) on the activity of spleen natural killer (NK) cells and plastic-adherent lymphokine-activated killer (A-LAK) cells from C57B1/6J male mice. Dietary supplementation with Se resulted in a significant increase in the lytic activity of activated NK cells, and cells from these highly lytic effector cell populations expressed significantly higher numbers of intermediate affinity interleukin-2 receptors (II-2R)/cell. In the presence of high concentrations of II-2 and 1×10⁻⁷ M Se, resting populations of spleen NK cells developed into A-LAK cells that had a significantly enhanced ability to proliferate, as indicated by the significantly higher amounts of nuclear³H-thymidine incorporation, and a significantly augmented cytolytic activity against both NK-sensitive and NK-resistant target cells. Se appears to enhance the lytic activity of activated NK cells and to augment the proliferation, expansion, and lytic activity of A-LAK cells in the presence of high concentrations of Il-2 through its ability to enhance the expression of intermediate affinity Il-2R on these cells.     

Additive effects of antitumor drugs and lymphokine-activated killer cell cytotoxic activity in tumor cell killing determined by lactate-dehydrogenase-release assay

Summary The effect of pretreatment with antitumor drugs on lymphokine-activated killer (LAK) cell cytotoxic activity, determined by lactate-dehydrogenase(LDH)-release assay, was investigated. LAK cells were induced by incubating peripheral blood lymphocytes of healthy donors in medium containing interleukin-2 (IL-2) and monoclonal anti-CD3 antibody for 6–7 days. A human lung squamous carcinoma cell line, SQ-5, was used as an adherent target. After 24 h exposure of the target cells to cisplatin, doxorubicin, or mitomycin C, the drugs were washed off and LAK cells were added at an E/T ratio of 5. During further incubation for 48 h, LDH release from cisplatin- or doxorubicin-pretreated target cells was markedly higher than that from non-pretreated target cells. The combination of cisplatin and LAK cells has an additive cytotoxic effect and that of mitomycin C and LAK cells does not; there may also be an additive effect late in the toxicity mechanism between doxorubicin and LAK cells.     

Immune function of patients receiving recombinant human interleukin-6 (IL-6) in a phase I clinical study: Induction of C-reactive protein and IgE and inhibition of natural killer and lymphokine-activated killer cell activity

Interleukin-6 (IL-6) is a cytokine that acts on a variety of cell types, including myeloid progenitor cells and B and T lymphocytes. It has been found to activate cytotoxic T cells and natural killer (NK) cells and to induce T-cell-mediated antitumour effects in animal models. In a phase I clinical trial of recombinant human IL-6, 20 patients with advanced cancer were entered to receive daily subcutaneous injections of IL-6 over 7 days followed by a 2-week observation period and another 4 weeks of daily IL-6 injections. Doses varied between 0.5 g/kg and 20 g/ kg body weight and immune functions were monitored throughout. At all dose levels IL-6 administration led to a marked increase in serum levels of C-reactive protein and a moderate rise in complement factor C3. The proportions of CD4, CD8 or HLA-DR lymphocytes in peripheral blood did not alter with IL-6 treatment nor did the in vitro proliferation of peripheral blood mononuclear cells induced by either phytohaemagglutinin, pokeweed mitogen or fixedStaphylococcus aureus. By contrast, NK cell activity, lymphokine-activated killer (LAK) cell activity and proliferation induced by in vitro culture with interleukin-2 (IL-2) were suppressed at doses exceeding 2.5 g/kg. Serum IgE levels were consistently elevated over the IL-6 dose range but IgM, IgG and IgA levels were unaffected. In summary there is a dose-dependent induction of acutephase proteins by in vivo IL-6 treatment. At higher IL-6 doses there is a suppressive effect on NK and LAK activity measured in vitro. IL-6 may thus be useful in combination cytokine therapies that seek to suppress LAK and favour cytotoxic T lymphocyte responses. The rise in IgE levels in response to IL-6 was unexpected and suggests a more pivotal role than previously known for the control of IgE production; this could include IgE-related diseases.Supported by a Mildred Scheel Research-Fellowship from the Deutsche Krebshilfe     

Effectivein vivo induction of lymphokine-activated killer (LAK) cells by pretreatment with a streptococcal preparation,OK-432

Effects of a streptococcal preparation, OK-432, on precursors of lymphokine-activated killer (LAK) cells were observedin vivo. Total number of splenocytes and the ratio of asGM ₁ ⁺ cells increased gradually after i.v. administration of OK-432, reaching their peaks at 3 to 4 days. It was found that as GM ₁ ⁺ cells were nonadherent and large in size. There were little differences in the ratios of Thy-1⁺, Lyt-2⁺, and L3T4⁺ cells before and after OK-432 treatment. Mice were injected i.p. with recombinant interleukin 2 (rIL-2) at a dose of 5 × 10⁴ U per mouse 4 days after OK-432 administration and LAK activity in their splenocytes was examined using natural killer (NK) resistant EL-4 target cells. Splenocytes in mice treated with both OK-432 and rIL-2 showed higher LAK activity than those in mice treated with rIL-2 alone.In vivo treatment with anti asGM, antibody prior to rIL-2 injection abolished completely such augmentation of LAK activity in OK-432 treated mice. These results demonstrated that asGM ₁ ⁺ LAK precursor cells induced by OK-432 were effectively differentiated into LAK cells by rIL-2.     

Spermine is not essential for growth of Saccharomyces cerevisiae: identification of the SPE4 gene (spermine synthase) and characterization of a spe4 deletion mutant

Spermine, ubiquitously present in most organisms, is the final product of the biosynthetic pathway for polyamines and is synthesized from spermidine. In order to investigate the physiological roles of spermine, we identified the SPE4 gene, which codes for spermine synthase, on the right arm of chromosome XII of Saccharomyces cerevisiae and prepared a deletion mutant in this gene. This mutant has neither spermine nor spermine synthase activity. Using the spe4 deletion mutant, we show that S. cerevisiae does not require spermine for growth, even though spermine is normally present in the wild-type organism. This is in striking contrast to the absolute requirement of S. cerevisiae for spermidine for growth, which we had previously reported using a mutant lacking the SPE3 gene (spermidine synthase) [Hamasaki-Katagiri, N., Tabor, C.W., Tabor, H., 1997. Spermidine biosynthesis in Saccharomyces cerevisiae: Polyamine requirement of a null mutant of the SPE3 gene (spermidine synthase). Gene 187, 35–43].     

Mouse spermine oxidase: a model of the catalytic cycle and its inhibition by N,N1-bis(2,3-butadienyl)-1,4-butanediamine

Spermine oxidase (SMO) is a recently described flavoenzyme belonging to the class of polyamine oxidases (PAOs) and participating in the polyamine metabolism in animal cells. In this paper we describe the expression, purification, and characterization of the catalytic properties of a recombinant mouse SMO (mSMO). The purified enzyme has absorbance peaks at 457nm (epsilon=11mM(-1)cm(-1)) and 378nm, shows a molecular mass of approximately 63kDa, and has K(m) and k(cat) values of 170microM and 4.8s(-1), using spermine as substrate; it is unable to oxidize other free or acetylated polyamines. The mechanism-based PAO inhibitor N,N(1)-bis(2,3-butadienyl)-1,4-butanediamine (MDL72,527) acts as a competitive inhibitor of mSMO, with an apparent dissociation constant K(i)=63microM. If incubated for longer times, MDL72,527 yields irreversible inhibition of the enzyme with a half-life of 15min at 100microM MDL72,527. The mMSO catalytic mechanism, investigated by stopped flow, is consistent with a simple four-step kinetic scheme.     

Use of human leukocyte antigen-mismatched allogeneic lymphokine-activated killer cells and interleukin-2 in the adoptive immunotherapy of patients with malignancies

Clinical effects and side effects were studied in the adoptive immunotherapy of patients bearing malignant diseases using human leukocyte antigen (HLA)-mismatched allogeneic lymphokine-activated killer (LAK) cells. Allogeneic LAK cells were induced from peripheral blood lymphocytes (PBL) of normal donors by means of initial stimulation with pokeweed mitogen (PWM). Six of 15 patients applied in the adoptive immunotherapy showed clinical effects such as partial or complete regression of pulmonary metastasis, pleural effusion and primary tumor. All pulmonary metastatic lesions were eliminated in one case by this adoptive immunotherapy combined with chemotherapy. Generally toxic effects were chillness, fever and general fatigue which were reversible, and no allergic side effects occurred even though allogeneic LAK cells were injected frequently except one patient who showed preshock like symptom accompanied with leukocytopenia and continuous hypotension immediately after infusion but was finally rescued. In the patients who received more than 10¹¹ of allogeneic LAK cells, anti-HLA class I antibodies appeared without any evidence of autoantibody. However, immunological side effects were never experienced after injection of allogeneic LAK cells even when the anti-HLA class I antibodies appeared in the patients. Taken together, allogeneic LAK cells could be considered as alternative therapy for patients with malignancies who could not supply sufficient materials of autologous LAK cells.Abbreviations PWM pokeweed mitogen - LAK lymphokine-activated killer - IL-2 interleukin 2 - PEL peripheral blood lymphocytes - TIL tumor-infiltrating lymphocytes - GVHD graft-versus-host disease - HLA human leukocyte antigen     

Heregulin induces increase in sensitivity of an erbB-2-overexpressing breast cancer cell type to lysis by lymphokine-activated killer cells

 The erbB-2 oncoprotein is overexpressed in 30% of tumors from breast and ovarian cancer patients and it is related to poor overall and disease-free survival. In vitro studies on erbB-2-overexpressing cells have found a strong correlation between this oncogene overexpression and relative resistance to lymphokine-activated killer (LAK) cell lysis. gp30/heregulin/NDF (neu differentiation factor), indirect activators of erbB-2, are able to induce a more differentiated phenotype on erbB-2-overexpressing, erbB-3- and/or erbB-4-positive breast cancer cells. We tested the ability of these highly homologous growth factors to stimulate LAK cell lysis of breast cancer cells. Our experiments demonstrated a marked increase in LAK cell cytotoxicity towards an erbB-2-overexpressing, erbB-3-positive cell line by treatment of these cells with heregulin for 72 h. In contrast we did not observe any enhancement of lysis of MCF-7, a cell line that does not overexpress erbB-2 and is positive for the erbB-3 and erbB-4 receptors, after treatment with heregulin. The increased lysis was associated with up-regulation of intercellular adhesion molecule 1 (ICAM-1), down-regulation of erbB-2 and increased binding between breast cancer cells and LAK cells. Pre incubation of target (SKBR3) cells with blocking anti-ICAM-1 antibody completely abrogated the enhanced cytotoxicity. A similar effect was observed by pretreatment of the effector (LAK) cells with antibodies directed against LFA-1, the receptor for ICAM-1. These results suggest the possible utilization of gp30/heregulin in the treatment of breast cancer patients by its ability to stimulate patient immune responses. Received: 6 March 1995 / Accepted: 7 June 1996     

Polyaminooligonucleotide: NMR structure of duplex DNA containing a nucleoside with spermine residue,N-[4,9,13-triazatridecan-1-yl]-2′-deoxycytidine

Background

The nature of the polyamine–DNA interactions at a molecular level is not clearly understood.

Methods

In order to shed light on the binding preferences of polyamine with nucleic acids, the NMR solution structure of the DNA duplex containing covalently bound spermine was determined.

Results

The structure of 4-N-[4,9,13-triazatridecan-1-yl]-2′-deoxycytidine (dCSp) modified duplex was compared to the structure of the reference duplex. Both duplexes are regular right-handed helices with all attributes of the B-DNA form. The spermine chain which is located in a major groove and points toward the 3′ end of the modified strand does not perturb the DNA structure.

Conclusion

In our study the charged polyamine alkyl chain was found to interact with the DNA surface. In the majority of converged structures we identified the presumed hydrogen bonding interactions between O6 and N7 atoms of G4 and the first internal –NH2⁺− amino group. Additional interaction was found between the second internal –NH2⁺− amino group and the oxygen atom of the phosphate of C3 residue.

General significance

The knowledge of the location and nature of a structure-specific binding site for spermine in DNA should be valuable in understanding gene expression and in the design of new therapeutic drugs.     

Synthesis of novel 4-Boc-piperidone chalcones and evaluation of their cytotoxic activity against highly-metastatic cancer cells

In this study, six curcuminoids containing a tert-butoxycarbonyl (Boc) piperidone core were successfully synthesized, five of them are novel compounds reported here for the first time. These compounds were prepared through an aldolic condensation by adding tetrahydropyranyl-protected benzaldehydes or substituted benzaldehyde to a reaction mixture containing 4-Boc-piperidone and lithium hydroxide in an alcoholic solvent. A 44–94% yield was obtained supporting the developed methodology as a good strategy for the synthesis of 4-Boc-piperidone chalcones. Cytotoxic activity against LoVo and COLO 205 human colorectal cell lines was observed at GI₅₀ values that range from 0.84 to 34.7 μg/mL, while in PC3 and 22RV1 human prostate cancer cell lines, GI₅₀ values ranging from 17.1 to 22.9 μg/mL were obtained. Results from biochemical assays suggest that the cytotoxicity of the 4-Boc-piperidone chalcones can be linked to their ability to induce apoptosis, decrease the activity of NFκB and cellular proliferation. Our findings strongly support the potential of Boc-piperidone chalcones as novel cytotoxic agents against highly-metastatic cancer cells.     

Human lymphokine-activated killer (LAK) cells: III. Effect ofl-phenylalanine methyl ester on LAK cell activation from human peripheral blood mononuclear cells: Possible protease involvement of monocytes,natural killer cells and LAK cells

Summary We have shown that depletion of monocytes from human peripheral blood mononuclear cells (PBMC) byl-phenylalanine methyl ester (PheOMe) enhanced lymphokine-activated killer cell (LAK) generation by recombinant interleukin-2 (rIL-2) at high cell density. In this study, we have investigated the mechanism of action of PheOMe on LAK activation by using trypsin, chymotrypsin, tosylphenylalaninechloromethanol (TPCK, a chymotrypsin inhibitor), tosyl-l-lysinechloromethane (TLCK, a trypsin inhibitor), phenylalaninol (PheOH), and benzamidine. PBMC were treated with 1–5 mM PheOMe for 40 min at room temperature in combination with the various agents, washed and assessed for their effects on natural killer (NK) activity against K562 cells and monocyte depletion. The treated cells were then cultured with or without rIL-2 for 3 days. LAK cytotoxicity was assayed against⁵¹Cr-labeled K562 and Raji tumor target cells. TPCK at 10 µg/ml partially inhibited depletion of monocytes by PheOMe. TLCK did not prevent depletion of monocytes nor inhibition of NK activity induced by PheOMe. TPCK and TLCK inhibited NK activity by themselves. TPCK but not TLCK inhibited rIL-2 induction of LAK cells. On the other hand, PheOH and benzamidine (analogs of PheOMe) lacked any effect on monocyte depletion but abrogated the inhibitory effect of PheOMe on NK activity. They had no effect on rIL-2 activation of LAK activity enhanced by PheOMe. Trypsin potentiated the inhibitory effect of PheOMe on NK activity and monocyte depletion. Trypsin partially inhibited IL-2 activation of LAK activity enhanced by PheOMe. Chymotrypsin had little effect on NK activity but prevented the inhibitory effect of PheOMe on NK activity. It had little effect on monocyte depletion induced by PheOMe. PheOMe was hydrolysed by monocytes and chymotrypsin to Phe and methanol as determined by HPLC. TPCK inhibited hydrolysis of PheOMe by monocytes. Our data suggest that the effects of PheOMe on monocytes, NK cells and LAK activation involve protease activities of monocytes.     

Interaction of PD-L1 on tumor cells with PD-1 on tumor-specific T cells as a mechanism of immune evasion: implications for tumor immunotherapy

Programmed death receptor ligand 1 (PD-L1, also called B7-H1) is a recently described B7 family member. In contrast to B7-1 and B7-2, PD-L1 does not interact with either CD28 or CTLA-4. To date, one specific receptor has been identified that can be ligated by PD-L1. This receptor, programmed death receptor 1 (PD-1), has been shown to negatively regulate T-cell receptor (TCR) signaling. Upon ligating its receptor, PD-L1 has been reported to decrease TCR-mediated proliferation and cytokine production. PD-1 gene–deficient mice developed autoimmune diseases, which early led to the hypothesis of PD-L1 regulating peripheral tolerance. In contrast to normal tissues, which show minimal surface expression of PD-L1 protein, PD-L1 expression was found to be abundant on many murine and human cancers and could be further up-regulated upon IFN- stimulation. Thus, PD-L1 might play an important role in tumor immune evasion. This review discusses the currently available data concerning negative T-cell regulation via PD-1, the blockade of PD-L1/PD-1 interactions, and the implications for adoptive T-cell therapies.     

Vaccinia virus inhibits the maturation of human dendritic cells: a novel mechanism of immune evasion

Vaccinia virus employs multiple mechanisms to evade the immune system, yet is highly immunogenic. We studied the interaction between vaccinia and human dendritic cells (DCs), potent APCs. DCs develop from precursor cells in two stages: an immature stage in which Ag uptake and processing occur, and a mature stage in which there is up-regulation of costimulatory and HLA molecules and efficient T cell activation. Vaccinia virus undergoes an abortive replication in both stages of DCs and induces apoptotic cell death. Furthermore, maturation of immature DCs and consequently T cell activation are inhibited. Obstruction of DC maturation may constitute a novel mechanism by which vaccinia attempts to evade the immune response.     

Recombinant interleukin-2 and lymphokine-activated killer cells in renal cancer patients: I. phenotypic and functional analysis of the peripheral blood mononuclear cells

Summary The efficacy of recombinant interleukin-2 (rIL-2) or rIL-2 plus lymphokine-activated killer (LAK) cells in cancer therapy has been demonstrated by several groups both in experimental models in animals and clinical trials in humans, but their effects in vivo have yet to be clarified.Starting February 1988, we have treated 12 patients affected by advanced renal cancer with rIL-2 + LAK cells according to an open, non-randomized, phase II trial. Immediately before each rIL-2 infusion and during the last day of infusion, immunological tests were performed on the patients' peripheral blood mononuclear cells. During rIL-2 infusion we have observed a slight increase of the spontaneous cell proliferation and of natural killer (NK) and LAK activity; phenotypic analysis showed a significant decrease in the CD4⁺ T-lymphocyte subset, both in percentage and in absolute number. Conversely, before each cycle CD4⁺ cells increased when compared to basal values. No significant variations were observed in the CD8⁺ T-lymphocyte subset. Furthermore, a significant increase of the NK cells (CD3^– CD56⁺ CD16⁺) was evident during rIL-2 infusion.     

Graft-versus-host disease following interleukin-2/lymphokine-activated killer (LAK) cell immunotherapy in a patient with acute myelogenous leukaemia in second complete remission: autologous LAK cells following allogeneic bone marrow transplantation are donor-derived

A 48-year-old man was treated by allogeneic bone marrow transplantation (BMT) in first remission of M4 acute myelogenous leukaemia (AML). He experienced no graft-versus-host disease (GVHD) and 7 months later he relapsed. Following further chemotherapy, he entered a second complete remission; however, he refused a further allogeneic or autologous BMT but agreed to immunotherapy with interleukin-2 and autologous lymphokine-activated killer (LAK) cells. He tolerated this treatment well but went on to develop grade II skin GVHD. Polymerase chain reaction studies of DNA microsatellites of the autologous LAK cells showed that they were of donor origin. The patient remained well for 9 months until, immediately following the introduction of prednisolone for his persistent GVHD, he relapsed. He declined further active treatment and died 5 months later. The case shows that IL-2/LAK cells can be safely given to patients who have experienced no GVHD following allo-BMT and are likely to be effective through an ongoing graft-versus-leukaemia effect.     

Growth of MCF-7 human breast carcinoma in severe combined immunodeficient mice: Growth suppression by recombinant interleukin-2 treatment and role of lymphokine-activated killer cells

Summary The severe combined immunodeficient (SCID) mouse, lacking functional T and B lymphocytes, has been considered by many groups to be a prime candidate for the reconstitution of a human immune system in a laboratory animal. In addition, this immuno-deficient animal would appear to have excellent potential as a host for transplanted human cancers, thus providing an exceptional opportunity for the study of interactions between the human immune system and human cancer in a laboratory animal. However, because this animal model is very recent, few studies have been reported documenting the capability of these mice to accept human cancers, and whether or not the residual immune cells in these mice (e.g. natural killer, NK, cells; macrophages) possess antitumor activities toward human cancers. Thus, the purpose of this study was (a) to determine whether or not a human breast carcinoma cell line (MCF-7) can be successfully transplanted to SCID mice, (b) to determine whether or not chronic treatment of SCID mice with a potent lymphokine (recombinant interleukin-2, rIL-2) could alter MCF-7 carcinoma growth, and (c) to assess whether or not rIL-2-activated NK cells (LAK cells) are important modulators of growth of MCF-7 cells in SCID mice. To fulfill these objectives, female SCID mice were implanted s.c. with MCF-7 cells (5 × 10⁶ cells/mouse) at 6 weeks of age. Six weeks later, some of the mice were injected i.p. twice weekly with rIL-2 (1 × 10⁴ U mouse^–1 injection^–1). Results clearly show that MCF-7 cells can grow progressively in SCID mice; 100% of the SCID mice implanted with MCF-7 cells developed palpable measurable tumors within 5–6 weeks after tumor cell inoculation. In addition, MCF-7 tumor growth was significantly (P <0.01) suppressed by rIL-2 treatment. rIL-2 treatment was non-toxic and no effect of treatment on body weight gains was observed. For non-tumor-bearing SCID mice, splenocytes treated in vitro with rIL-2 (lymphokine-activated killer, LAK, cells) or splenocytes derived from rIL-2-treated SCID mice (LAK cells) had significant (P <0.01) cytolytic activity toward MCF-7 carcinoma cells in vitro. In contrast, splenocytes (LAK cells) derived from tumor(MCF-7)-bearing rIL-2-treated SCID mice lacked cytolytic activities toward MCF-7 cells in vitro. No significant concentration of LAK cells in MCF-7 human breast carcinomas was observed nor did rIL-2 treatment significantly alter growth of MCF-7 cells in vitro. Thus, while rIL-2 treatment significantly suppressed growth of MCF-7 breast carcinomas in SCID mice, the mechanism of this growth suppression, albeit clearly not involving T and B lymphocytes, does not appear to be mediated via a direct cytolytic activity of LAK cells toward the carcinoma cells. However, rIL-2-activated SCID mouse splenocytes (LAK cells) do possess the capability of significant cytolytic activity toward MCF-7 human breast carcinoma cells. Thus, treatment of SCID mice with a potent lymphokine (rIL-2) induces a significant antitumor host response, a response that does not involve T and B lymphocytes and appears not to involve NK/LAK cells. This host response must be considered in future studies designed to investigate the interactions of reconstituted human immune systems and human cancers within this highly promising immuno deficient experimental animal model.