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G Weil-Hillman

Publications and source records attributed to G Weil-Hillman.

17 recordsLinked to original sources
PubMed1991

Activation of human T cells obtained pre- and post-interleukin-2 (IL-2) therapy by anti-CD3 monoclonal antibody plus IL-2: implications for combined in vivo treatment.

The role of activated T cells in the mediation of antitumor responses has been documented in several experimental models. In some of these, interleukin-2 (IL-2) has been used as a means to induce and expand the antitumor effects of the T cells. IL-2 has been tested in clinical trials for cancer treatment. Surprisingly, T cells appear to be inactivated by IL-2 in these clinical trials. T cells obtained from peripheral blood after IL-2 therapy showed decreased responses to mitogens and alloantigens, did not proliferate in vitro in response to IL-2, and did not mediate non-major histocompatibility complex-restricted cytotoxicity or targeted lysis in the presence of bispecific monoclonal antibodies. In this study, we present evidence that these post-IL-2 therapy T cells are not irreversibly inactivated; they can be activated in vitro by anti-CD3 monoclonal antibody together with IL-2 to upregulate the p55 component of the IL-2 receptor and proliferate. Nevertheless, following activation by anti-CD3 and IL-2, the level of targeted T-cell cytotoxicity mediated by the post-IL-2 therapy T cells was significantly lower than that by pre-IL-2 therapy T cells. Although in vivo treatment with IL-2 alone induces natural killer (NK) cells to mediate lymphokine-activated killer activity, these data suggest that the T-cell lytic function is inhibited by this treatment and only partially reversible by subsequent T-cell receptor activation using anti-CD3 mAb. Exposure of T cells to anti-CD3 mAb prior to in vivo IL-2 treatment generates T-cell lytic activity in vitro. These results, together with preclinical murine studies, suggest that a combined in vivo protocol of anti-CD3 mAb and IL-2, starting first with the anti-CD3 mAb, may cause activation of the T cells in addition to the activation of NK cells and thus warrant clinical testing.

Antibodies, Monoclonal↗
PubMed1991

Increase in concanavalin A cap formation on lymphoma cells following interaction with inactive influenza viruses.

Binding of the lectin Con A to its ligand on the cell surface of normal circulating lymphocytes induces capping in 28-32% of these cells. This Con A cap formation is markedly decreased in malignant cells from the human hematopoietic system. Among others, the human lymphoma Daudi cell line exhibit a cap formation with Con A in only 5-10% of the cells. In this study, we found that inactivated influenza viruses induced changes in the cell surface membrane of Daudi cells resulting in an increased percentage of Con A cap forming cells (30-40%). This phenomenon occurred independently of viral replication and was initiated by adsorption of inactivated viral particles or isolated hemagglutinin and neuraminidase viral glycoproteins. This phenomenon may be due to the binding of Con A molecules to viral receptors and to cell receptors leading to crosslinking of Con A receptors that will induce their mobility and the formation of a cap. Alternatively, experiments performed with cytochalasin B and colchicine suggest that the viral interaction with the cell membrane may have induced changes in the cytoskeleton at the level of microtubules. These changes induced increased lateral movement of the Con A receptors resulting into formation of a cap.

Adsorption↗
PubMed1990

Increased expression of the interleukin 2 (IL-2) receptor beta chain (p70) on CD56+ natural killer cells after in vivo IL-2 therapy: p70 expression does not alone predict the level of intermediate affinity IL-2 binding.

The expression of the 70-kD beta subunit of the interleukin 2 receptor (IL-2R) has been examined on peripheral blood lymphocytes (PBL) obtained from patients receiving systemic infusions of IL-2. Using monoclonal antibodies directed against p70, flow cytometric analyses revealed a greater than threefold increase in expression of the IL-2R beta chain on CD56+ natural killer (NK) cells from post-IL-2 therapy PBL relative to pre-therapy cells. The level of p70 expression on the post-therapy cells was three- to fourfold greater (based on fluorescence intensity) than the level of p70 expression on YT cells, an NK-like cell line that expresses approximately 12,000 intermediate affinity IL-2 binding sites/cell. Despite the high level of p70 expression, in 125I-IL-2 binding assays only 790-1,290 intermediate affinity IL-2 binding sites/cell were detected on post-therapy cells from six patients. These data represent the first report of increased p70 expression after in vivo IL-2 administration and suggest a requirement for at least one additional subunit for the formation of functional intermediate affinity IL-2Rs. Furthermore, the presence on the surface of post-therapy NK cells of excess p70 that does not bind IL-2 with intermediate affinity implies that the formation of intermediate affinity IL-2Rs is not solely determined by the level of p70 expression, and that the response of NK cells to IL-2 might be regulated by altering the expression of p70 or some other IL-2R subunit.

Antibodies, Monoclonal↗
PubMed1990

Natural killer cells activated by interleukin 2 treatment in vivo respond to interleukin 2 primarily through the p75 receptor and maintain the p55 (TAC) negative phenotype.

Interleukin 2 (IL-2) induced activation of unstimulated resting natural killer (NK) cells or resting T-cells initially occurs following binding of IL-2 through the p75 receptor that is expressed primarily by these cells. However, this IL-2/p75 interaction induces TAC chain synthesis and formation of high affinity IL-2 receptor required for the proliferation of resting peripheral blood lymphocytes. In this study, we present data indicating that NK cells activated by in vivo IL-2 treatment, in contrast to resting NK cells, respond and proliferate to further IL-2 in vitro using primarily the p75 receptor with only a minor component of cells responding through the high affinity receptor. These in vivo activated NK cells minimally expressed the TAC chain and maintained this TAC negative phenotype while proliferating in response to IL-2. The primary involvement of the p75 receptor in the proliferative response of these cells to IL-2 was demonstrated by the need for concentrations of IL-2 higher than 44 pM to obtain a significant response and by the dramatic inhibition of this response by anti-p75 monoclonal antibody. Anti-TAC monoclonal antibody inhibited only the poor proliferation obtained at low doses of IL-2 suggesting a minor role for TAC and high affinity IL-2 receptors. This was in contrast to the partial inhibition of proliferation by anti-p75 or anti-TAC observed in unstimulated pretherapy peripheral blood lymphocytes suggesting that these cells respond to IL-2 through both high affinity receptors and intermediate affinity p75 receptors. The T-cells isolated from in vivo activated peripheral blood lymphocytes, despite expressing TAC, were not responsive to IL-2, suggesting that these cells express predominantly nonfunctional low affinity TAC receptors. NK cells activated by IL-2 in vivo represent a unique model system of IL-2 dependent cells that respond and proliferate to IL-2 essentially through the p75 IL-2 receptor.

Antibodies, Monoclonal↗
PubMed1990

Addition of interleukin-2 in vitro augments detection of lymphokine-activated killer activity generated in vivo.

The in vivo administration of repetitive weekly cycles of interleukin-2 (IL-2) to patients with cancer enhances the ability of freshly obtained peripheral blood lymphocytes (PBL) to lyse both the natural-killer(NK)-susceptible K562 and the NK-resistant Daudi targets. Lysis of both targets is significantly augmented by inclusion of IL-2 in the medium during the cytotoxicity assay. This boost is much greater for cells obtained following the in vivo IL-2 therapy than for cells obtained prior to the initiation of therapy or for cells from healthy control donors. In addition to direct lytic activity, the PBL obtained following in vivo IL-2 show a rapid increase in lymphokine-activated killer (LAK) activity with more prolonged in vitro IL-2 exposure, indicating that LAK effectors primed in vivo respond with "secondary-like" kinetics to subsequent IL-2 in vitro. Lymphocytes from healthy control individuals, cultured in IL-2 under conditions attempting to simulate the in vivo IL-2 exposure, function similarly to PBL obtained from patients following IL-2, in that low-level LAK activity was significantly boosted by inclusion of IL-2 during the cytotoxic assay and the cells also responded with secondary-like kinetics to subsequent IL-2 in vitro. The augmentation of the LAK effect was also dependent on the dose of IL-2 added during the 4-h 51Cr-release cytotoxicity assay, with higher doses of IL-2 having a more pronounced effect. While continuous infusion of IL-2 induces a greater cytotoxic potential per milliliter of blood obtained from patients, the peak serum IL-2 levels attained are greater with bolus IL-2 infusions. These pharmacokinetic results, together with the IL-2 dose dependence of LAK activity generated in vivo shown in this report, suggest that a combination of treatment with bolus IL-2 infusions superimposed on continuous IL-2 infusion may transiently expose IL-2 dependent LAK cells, activated in vivo, to higher concentrations of IL-2, facilitating their in vivo cytotoxic potential.

Cells, Cultured↗
PubMed1990

Limiting dilution analysis of lymphokine-activated killer cell precursor frequencies in peripheral blood lymphocytes of cancer patients receiving interleukin-2 therapy.

Eleven patients receiving weekly cycles of therapy with recombinant interleukin-2 (IL-2) were evaluated with a sensitive limiting dilution analysis to determine lymphokine-activated killer (LAK) cell precursor frequencies in peripheral blood lymphocytes. An increase in LAK precursor frequency above baseline was suggested by day 6 of this protocol and was clearly significant by day 20, indicating an expansion of the circulating precursor pool results from in vivo IL-2 administration. Correlations were not significant between LAK precursor frequency during IL-2 therapy and the total number of circulating lymphocytes, the percentage of CD56+ lymphocytes, IL-2 proliferative responses, or LAK activity of peripheral blood lymphocytes, indicating that the precursor frequency identification based on functional testing of individual cells is not accurately reflected by these analyses of heterogeneous bulk populations. Selective cell depletion analyses revealed that the majority of LAK precursors after in vivo IL-2 therapy were cells with the natural killer phenotype. Analysis of LAK precursors may help define the in vivo IL-2 administration, alone or in combination with other hematopoietic or immunodifferentiative cytokines, necessary to further augment in vivo effector cell numbers and activity for patients with cancer.

Cell Division↗
PubMed1989

Repetitive weekly cycles of interleukin 2: effect of outpatient treatment with a lower dose of interleukin 2 on non-major histocompatibility complex-restricted killer activity.

Fifteen patients with advanced malignancy who had failed conventional therapy were entered into a protocol consisting of 1 inpatient mo of repetitive weekly cycles of interleukin 2 (IL-2) at 3 x 10(6) units/m2/day by constant infusion for the first 4 days of each week. This was followed by IL-2 administered on an outpatient basis at the same schedule but at a dose of 1 x 10(6) units/m2/day for the next 1 to 6 mo. Nine patients had renal carcinoma, four had melanoma, and two had lymphoma. Thirteen patients completed the induction month, and ten patients completed greater than or equal to 1 mo of outpatient therapy. Only one patient had therapy discontinued because of toxicity due to IL-2. No major toxicities occurred during outpatient therapy. After 1 mo of IL-2 at 3 x 10(6) units/m2/day, profound changes similar to those previously documented were seen in peripheral blood lymphocyte (PBL) counts (4.7-fold increase), lymphokine-activated killer activity (16-fold increase), and the percentage of PBL with natural killer-associated markers including a 3.6-fold increase in the percentage of PBL expressing the Leu 19 (NKH-1) marker, a 3.7-fold increase in Leu 11 (FcIgGR), and a 3.0-fold increase in Leu 17 (OKT10). These indicators of IL-2 effect all remained elevated relative to the baseline at the end of 1 and 2 mo of outpatient therapy at the lower dose. However, lymphokine-activated killer activity and Leu 17 percentage were significantly reduced relative to the effect of the higher induction dose. PBL taken from patients while receiving maintenance therapy showed strong and rapid responses to IL-2 in vitro, confirming the in vivo effects of prolonged IL-2 treatment. Nevertheless, there were no complete or partial antitumor responses seen. This study demonstrates that an immunologically active dose of IL-2 can be given long term as outpatient therapy with tolerable toxicity and results in highly IL-2-responsive "primed" lymphokine-activated killer cells.

Adult↗
PubMed1989

Lymphokine-activated killer activity induced by in vivo interleukin 2 therapy: predominant role for lymphocytes with increased expression of CD2 and leu19 antigens but negative expression of CD16 antigens.

The phenotype and function of lymphocytes from cancer patients treated with repetitive weekly cycles of continuous i.v. infusions of recombinant interleukin 2 (IL-2) were examined. Peripheral blood lymphocytes (PBL) obtained after IL-2 therapy showed an increased percentage of cells bearing the CD16 and leu19 markers which are associated with natural killer cells. These PBL mediated significantly increased levels of IL-2-dependent lymphokine-activated killer (LAK) activity against the Daudi cell line. Depletion of CD16+ cells from PBL obtained after in vivo IL-2 caused only slight inhibition of their LAK activity or their proliferative response to IL-2 in vitro. This indicates that CD16+ cells are involved but play only a minor role in these responses. In contrast, depletion of leu19+ cells, from PBL activated in vivo with IL-2, virtually abrogated their LAK activity and their proliferative response to IL-2. Two-color flow cytometry studies showed that a leu19+/CD16- population was expanded by in vivo IL-2 therapy and was responsible for the majority of LAK activity by in vivo-activated PBL. Moreover, this CD16- population showed an increased density of leu19 and CD2 (E rosette receptor) antigens when compared to the resting PBL obtained prior to IL-2 treatment. These data show that the predominant population mediating in vitro LAK activity, induced by in vivo IL-2 therapy, consists of activated natural killer cells with a high density of leu19 and CD2 antigens but negative for the CD16 antigen.

Antigens, Differentiation↗
PubMed1989

The cellular immunotherapy of cancer: current and potential uses of interleukin-2.

The potential for immune-mediated destruction of neoplasms was suggested nearly one century ago. Despite this, no "magic bullet" has yet been identified. Nevertheless, the physiology of cell-mediated immune reactions has been well characterized in molecular, cellular, and clinical studies of allograft and microbial immunity. Extensive studies performed in laboratory animal models have documented the in vitro and in vivo destruction of various neoplastic tissues by immune cells. This destruction can be directed against autologous, syngeneic, or allogeneic tumors in several systems with varying degrees of "tumor specificity". Two approaches exist towards utilizing these immune reaction in vivo. The first involves providing the tumor bearer with immunostimulatory agents, either specific or nonspecific, designed to activate and amplify the destructive potential of the individual's endogenous immune cells able to recognize and destroy autologous tumor. The second approach provides immune cells with antitumor capacity to a tumor-bearing individual, these cells having been activated exogenously. A number of successful regimens involving these two approaches, and combinations of them, have been delineated in animal tumor models. These experimental studies lay a strong foundation for initiating clinical trials of these concepts for patients with cancer. This review summarizes the diverse experimental studies in animals leading to clinical trials, presents recent data from ongoing clinical trials directly testing the potential for cellular immunotherapy, and then presents some of the major challenges facing further development and application of this potential therapeutic approach.

Animals↗
PubMed1989

Antigen-specific recognition of autologous leukemia cells and allogeneic class-I MHC antigens by IL-2-activated cytotoxic T cells from a patient with acute T-cell leukemia.

Culturing of leukemic blood lymphocytes from a patient with acute T-cell lymphoblastic leukemia (T-ALL) with interleukin-2 (IL-2) yielded T-cell line AK-1 with a remarkable cytotoxic specificity. This line mediated strong lysis of tumor target lines expressing major histocompatibility complex (MHC) class I antigens, such as Raji, CEM, and Molt-4 cells, but no killing of K562 and Daudi cells, which are deficient in MHC class I. In contrast, lymphokine-activated killer (LAK) cells from normal donors destroyed all these tumor targets, without MHC restriction. Line AK-1, originating from residual normal T cells present in the leukemic blood, lysed autologous leukemic blasts and peripheral blood lymphocytes (PBL) from many but not all allogeneic individuals but failed to kill autologous remission lymphocytes. Destruction of the autologous leukemic targets by AK-1 could be inhibited by unlabeled competitor target cells that were lysed by AK-1, but not by target cells that were not lysed. This suggests that AK-1 specifically recognized an alien determinant on the autologous ALL cells, crossreactive with allogeneic MHC class I antigens. This reactivity with some degree of tumor specificity may be a leukemic equivalent to responses reported for populations of tumor infiltrating lymphocytes (TIL) seen in some solid tumors.

Adult↗
PubMed1988

In vivo induction of the lymphokine-activated killer phenomenon: interleukin 2-dependent human non-major histocompatibility complex-restricted cytotoxicity generated in vivo during administration of human recombinant interleukin 2.

The availability of purified human recombinant interleukin 2 (IL-2) has enabled clinical trials to test its in vivo effects. We report here the immunological effects of 7 consecutive days of IL-2 treatment given to 25 patients with cancer in a clinical Phase I study. Peripheral blood lymphocytes obtained from patients following therapy with IL-2 had enhanced proliferative responses to IL-2 and enhanced direct cytotoxic activity on K562 target cells. This lytic activity was further augmented by the addition of IL-2 during the 51Cr release assay. Fresh peripheral blood lymphocytes from some patients who had just completed treatment at the higher IL-2 dose levels were able to kill both the natural killer-resistant Daudi cell line and fresh tumor cells while pretreatment samples and peripheral blood lymphocytes from healthy controls were not. This lytic activity was best detected when IL-2 was present in the in vitro effector assay. These results demonstrate that the administration of IL-2 to patients with cancer induces a population of effector cells able to directly destroy natural killer-resistant target cells, when assayed in the presence of IL-2.

Cells, Cultured↗
PubMed1988

Transient decrease in IL-2-responsive lymphocytes 24 hours after initiation of continuous IL-2 infusion in cancer patients.

Cancer patients were treated with recombinant interleukin-2 (IL-2) in a Phase I clinical trial. Patients were given four repetitive weekly cycles of four days of continuous i.v. IL-2 infusions followed by 3 days of observation. A transient 80% decrease in the number of circulating peripheral blood lymphocytes (PBLs) was noted 24 h after initiation of the IL-2 infusion. The in vitro IL-2 induced proliferative response, and natural killer (NK) activity of the PBLs recovered at this time was only 10-20% of that by the same number of PBLs obtained prior to IL-2 therapy. This effect was transient and rebound increases in circulating lymphocytes expressing high NK and lymphokine-activated killer functions were demonstrated at the end of a 4 day IL-2 infusion. To study further whether the drop in lymphocyte activity observed at initiation of IL-2 therapy was due to activation of a suppressor mechanism, patient PBLs isolated 24 h into the IL-2 infusion were mixed with their pre-IL-2 therapy PBLs at different ratios and assayed in NK and proliferation assays. These mixing experiments did not prove suppression to be the mechanism for the decreased response; rather, the PBLs obtained 24 h into IL-2 therapy merely diluted out the in vitro response of PBLs obtained prior to therapy. Although there was a considerable drop in circulating PBLs 24 h after initiation of each of three subsequent weekly IL-2 treatment cycles, these remaining lymphocytes in the peripheral blood were functional in both NK and IL-2 proliferative assays. These PBLs obtained 24 h into each of the subsequent three cycles showed a progressive increase in their in vitro NK and IL-2-induced proliferative activity, reaching levels two to three times higher than that of pretherapy PBLs by the fourth cycle. Thus, IL-2 caused a transient disappearance of lymphocytes from the circulation at the initiation of each cycle, but lymphocyte function was impaired only in the first IL-2 cycle. These data suggest that resting IL-2 responsive cells initially leave the circulation upon exposure to IL-2, but that such cells become activated and some remain detectable in the circulation when subsequent weekly cycles of IL-2 are given.

Blood Cell Count↗
PubMed1987

Combined immunochemotherapy of human solid tumors in nude mice.

In vivo immunochemotherapy of human solid tumors was studied in a nude mouse model. Large tumors (3 to 6 cm3) were induced by s.c. injection of the acute lymphoblastic leukemia T-cell line CEM. Transient tumor inhibition could be achieved by intratumoral injection of an intact-ricin immunotoxin that specifically recognizes a determinant CD5 (T,p67) expressed on the cell surface. Injection of the in vitro active cyclophosphamide congener mafosfamid had little effect on the progression of tumor growth. A combination regimen of immunotoxin and mafosfamid induced the most dramatic antitumor effect; a 72 to 100% reduction in tumor volume was observed within 3 to 4 days posttreatment. However, tumors relapsed within 5 to 13 days. Persistent, tumor regression was observed only when protocols using successive injections of combined immunotoxin/mafosfamid were used. All seven mice undergoing this treatment had a precipitous decrease in tumor size, and 86% survived greater than 30 days posttreatment. No residual tumor was detectable on Day 30 in five of seven mice. Regression was partly attributed to the selective activity of immunotoxin, since successive injections of an irrelevant control immunotoxin coupled to ricin in combination with mafosfamid did not reduce tumor size. Thus, we have demonstrated that a combination of anticancer chemotherapy and immunotoxin therapy yielded a greater antitumor effect than either therapy alone.

Animals↗
PubMed1985

Arrest of Daudi cell growth by inactive influenza virus in-vitro.

We investigated the destructive capability of three influenza A strains, Victoria, PR8, and their recombinant X47, against the human lymphoma cell line Daudi. Both Victoria and X47 strains share the same envelope glycoproteins (H3N2), while PR8, the second parental strain of X47, differs in its envelope glycoproteins (HON1). The H3N2 strains and particularly the X47 recombinant were cytotoxic to Daudi cells while the HON1 strain was not. To reduce the virulence of the oncolytic viruses, we inactivated them either with heat (56 degrees C/45 min) or with formalin. Both treatments significantly reduced the infectivity of the viruses. The X47 virus treated with formalin retained its hemagglutinin (HA) and neuraminidase (NA) activities but lost its cytotoxic potential. On the other hand, the heat-treated X47 virus retained its HA activity, lost its NA activity, but preserved its cytotoxic potential. Thus, the heat-inactivated X47 virus (X56) was the most effective non-virulent oncolytic agent we tested. The X56 virus arrested Daudi cell multiplication in-vitro by inhibiting cellular DNA synthesis. The mechanism by which X56 inhibited Daudi cell DNA synthesis was not related to interferon induction in Daudi cells, and did not necessarily involve the activation of the Epstein-Barr virus (EBV) genome present in Daudi cells. Although the mechanism remains unclear, the oncolytic potential of the X56 virus on Daudi cells was demonstrated.

Burkitt Lymphoma↗
PubMed1985

Visualization of the fate of inactive influenza viruses in Daudi cells by electron microscopy.

The replication of active and inactivated influenza viruses in Daudi lymphoma cells was studied by immunofluorescence and electron microscopy. In a previous study, we demonstrated that active and heat-inactivated X47 (H3N2) virus arrested Daudi cell growth by inhibiting cellular DNA synthesis while formalin-treated X47 virus did not. Transmission electron microscopic studies revealed that both the active and the heat-inactivated X47 virus penetrated into the cells. Only the active X47 (XA) virus replicated completely in Daudi cells and produced new viral particles by budding. The formalin-treated X47 virus did not damage or change the cells, and although the viral particles remained adsorbed to the cells, there was little penetration. The heat inactivated X47 virus (which was the most effective, non-virulent, oncolytic agent we studied) was visualized as large aggregates of particles adsorbed to the cell surface by electron microscopy. The cells themselves formed clumps. The viral aggregation and cell clumping likely resulted from the loss of viral neuraminidase activity due to heat treatment. The penetration of heat-inactivated viral particles was massive and involved numerous particles. Production of new viral particles was not demonstrated in this study even though nucleocapsids from the original virus were found in the cytoplasm. Thus, it appears that the massive penetration of the viral particles into cells damages the plasma membrane and may be responsible for the oncolytic potential of the heat-inactivated virus on Daudi cells.

Burkitt Lymphoma↗
PubMed1985

Cytotoxic effect of anti-Mr 67,000 protein immunotoxins on human tumors in a nude mouse model.

We have studied the potential use of immunotoxins (ITs) for therapeutic treatment of human tumors in an experimental model of human neoplasia. We tested intact ricin IT for its antitumor activity against established tumors. CEM, a human T-cell leukemia line expressing an Mr 67,000 cell surface antigen, and Daudi, a human B-cell lymphoma line which does not express the antigen, were found to be consistently tumorigenic in nude mice. ITs were synthesized using T101, a high-affinity monoclonal antibody reacting with the Mr 67,000 protein determinant and intact ricin. We have shown for the first time that established CEM solid tumors in nude mice will regress following intratumoral injection of T101-ricin IT, while Daudi tumors will not. Selective activity of T101-ricin is dependent on systemic i.v. administration of lactose and local intratumoral injection of the T101-ricin IT with lactose. Intact ricin ITs require the presence of lactose to block native ricin binding and render them antigen specific when linked to monoclonal antibody. Killing of target was cell specific since (a) nonspecific (irrelevant) ITs did not cause the regression of CEM tumors, and (b) injection of large amounts of free T101 antibody prior to T101-ricin IT blocked antitumor activity. Selectivity was not absolute, since regression occurred in one of six animals given irrelevant IT, and blocking was observed in two of four mice. Intratumoral IT treatment with 1 or 2 micrograms of T101-ricin IT plus lactose was not harmful to mice in contrast to intratumoral ricin treatment, which killed all treated tumor-bearing mice at a dose of 0.3 micrograms. Without i.v. injection of lactose, intratumoral injection of T101-ricin IT was also effective in eliminating established tumors. However, this treatment did not result in the selective elimination of tumor, since Daudi tumors also regressed following T101-ricin IT treatment. IT, made with ricin A chain only (T101-A chain IT), was also tested against established CEM tumors. We found that high dosages of T101-A chain IT did not destroy CEM tumors when injected intratumorally, even in the presence of activating agents such as NH4Cl or the carboxylic ionophore X-537 A. In contrast, in vitro experiments demonstrated that T101-A chain IT plus activating agents had potent and selective cytotoxic effect against CEM cells. We conclude that ITs are specifically toxic to established tumors. Although selectivity is not absolute, ITs exhibit potential as a new class of antitumor reagents.

Animals↗