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R W Kozak

Publications and source records attributed to R W Kozak.

At least 19 recordsLinked to original sources
PubMed1999

Alpha-emitting bismuth cyclohexylbenzyl DTPA constructs of recombinant humanized anti-CD33 antibodies: pharmacokinetics, bioactivity, toxicity and chemistry.

UNLABELLED: The alpha-particle-emitting radionuclides have several physical characteristics that make them attractive candidates for radioimmunotherapy: (a) high linear energy transfer; (b) short path lengths (50-80 microm); and (c) limited ability of cells to repair damage to DNA. This article describes the pharmacokinetic, bioactivity, toxicity and chemical characteristics of alpha-particle-emitting, 213Bi and 212Bi radiometal conjugated HuM195 (anti-CD33) constructs. Conjugation of HuM195 to SCN-CHX-A-DTPA resulted in the attachment of up to 10 chelating ligand molecules per antibody. RESULTS: Radiolabeling efficiency of the CHX-A-DTPA-HuM195 construct with 213Bi was 78%+/-10% (n = 46) after 10 min at specific activities of up to 1110 MBq/mg. The immunoreactivity of the 213Bi-labeled CHX-A-DTPA-HuM195 construct was 84%+/-10% (n = 28) and was independent of the specific activity. The bismuth-labeled CHX-A-DTPA-HuM195 construct was rapidly internalized into the cell in a time-dependent manner ranging from 50% at 1 h to 65% at 24 h. 205Bi/206Bi-labeled constructs were stable for at least 2 d in vitro in the presence of human serum at 37 degrees C. After injection into mice, there was no uptake or loss of bismuth to mouse tissues, which do not express CD33, or to the kidney, which has avidity for free bismuth. Mice injected intraperitoneally with doses of (213Bi)CHX-A-DTPA-HuM1 95 ranging from 18.5 to 740 MBq/kg showed no toxicity, but at 2590 MBq/kg, two of the three mice died within 2 wk and a third mouse showed significant reductions in white blood cell counts. Mice injected intravenously with doses of (213Bi)CHX-A-DTPA-HuM195 up to 370 MBq/kg exhibited little toxicity, but 666 MBq/kg was above the MTD for mice. Leukemia cell killing in vitro with bismuth-labeled HuM1 95 showed dose- and specific activity-dependent killing of CD33+ HL60 cells; approximately 50% killing was observed when two bismuth atoms (50 fM radiolabeled antibody) were initially bound onto the target cell surface. CONCLUSION: Alpha-emitting antibodies are among the most potent cytotoxic agents known, yet are specific and appear safe in vivo. The physical and biochemical characteristics of the 213Bi isotope and its generation, as well as the biochemistry of the 213Bi-labeled CHX-A-DTPA-HuM195 construct, make it possible to use the constructs safely and feasibly in humans at therapeutic levels.

Alpha Particles↗
PubMed1996

Evaluation of dithiol chelating agents as potential adjuvants for anti-IL-2 receptor lead or bismuth alpha radioimmunotherapy.

The dithiol chelating agents 2,3-dimercapto-1-propanesulfonic acid (DMPS) and meso-2,3-dimercaptosuccinic acid (DMSA) were evaluated for use as potential adjuvants to reduce or prevent radiotoxicity in anti-interleukin-2 receptor (IL-2R) Lead-212 or Bismuth-212 alpha-radioimmunotherapy. DMPS was less toxic than DMSA to tumor cell lines in culture. No adverse effects on the ability of an anti-IL-2R monoclonal antibody (MAb) to bind to its specific antigen were detected using DMPS or DMSA at concentrations up to 600 ug/mL in 10% or 100% mouse serum. After a 5-day oral administration of chelating agent, neither acute nor chronic toxicities on blood hematology, blood chemistry or organ weights were observed for treated mice. DMPS and DMSA were effective in accelerating whole body clearance of the gamma-emitting tracer Bismuth-206. Both chelates significantly reduced femur uptake of tracer when compared to nontreated control mice. However, only DMPS prevented early (2 h postinjection) renal accumulation. These studies support the use of DMPS as a potential adjuvant chelation therapy in Lead-212 or Bismuth-212 radioimmunotherapy protocols.

Adjuvants, Immunologic↗
PubMed1996

Transmissible spongiform encephalopathies (TSE): minimizing the risk of transmission by biological/biopharmaceutical products: an industry perspective.

Several guidelines and recommendations have been published on assessing the potential risk of a biological product being contaminated with an agent causing a Transmissible Spongiform Encephalopathy (TSE). Basic principles which can be used during the manufacturing of biological products to minimize the risk of transmission of TSE agents include the following: (i) obtaining animals, tissues or animal-derived raw materials from countries in which the relevant TSE agent is reported to be absent; (ii) screening animal-derived material for appropriate animal husbandry, feeding practices, health certification, tissue procurement and processing practices, and human-derived material for appropriate medical history information and, if relevant, plasma donor exclusion criteria; (iii) selection of tissue source of raw material with reference to potential risk for harbouring or amplifying TSE agents; (IV) human tropism of TSE agent of concern; (v) quantity of raw material used to manufacture a dose of product; (vi) number of daily doses required for indication; (vii) route of administration; (viii) indication and age of patient; and (ix) clearance capabilities by the product purification scheme. A risk evaluation will be represented for Trasylol (Aprotinin) which is manufactured from bovine lung tissue. Trasylol is a protease inhibitor used in the control of blood loss during open heart surgery. Bovine Spongiform Encephalopathy (BSE) is a concern when a product is derived from a bovine source. Even though only bovine lung tissue from BSE-free countries is used to manufacture Trasylol, it was decided, based on the primary tissue source selection, to evaluate the potential of the purification process to clear a TSE agent. Duplicate "spiking experiments" were performed using a mouse-adapted strain of scrapie as the model for BSE. Four steps in the purification process were evaluated. Titration of "spiked" loading material and output samples was performed at dilutions of 10(-4) to 10(-7) and undiluted to 10(-7), respectively. The sum of the purification steps evaluated provided a clearance factor in excess of 18 log10 for a TSE agent. An overall safety factor of 30 is obtained using the notification document issued by the Federal Health Office (Germany), dated February 16, 1994, on "Safety Requirements for Medical Products Derived from Body Constituents of Cattle, Sheep, or Goats to Avoid Risk of Transmission of BSE or Scrapie". Based on a six-parameter risk assessment, this document considered a product of low-risk for transmitting TSE agents if obtaining or exceeding a score of 20. Principles for minimizing the risk of transmission of TSE agents in products derived from primary tissues are contrasted to strategies for biotechnology products.

Animals↗
PubMed1994

Radioimmunotherapy of nude mice bearing a human interleukin 2 receptor alpha-expressing lymphoma utilizing the alpha-emitting radionuclide-conjugated monoclonal antibody 212Bi-anti-Tac.

The efficacy, specificity, and toxicity of bismuth (212Bi) alpha particle-mediated radioimmunotherapy was evaluated in nude mice bearing a murine lymphoma transfected with the human CD25 [human Tac; interleukin 2 receptor alpha (IL-2R alpha)] gene. The therapeutic agent used was the tumor-specific humanized monoclonal antibody anti-Tac conjugated to 212Bi. The human IL-2R alpha-expressing cell line was produced by transfecting the gene encoding human Tac into the murine plasmacytoma cell line SP2/0. The resulting cell line, SP2/Tac, expressed approximately 18,000 human IL-2R alpha molecules/cell. Following s.c. or i.p. injection of 2 x 10(6) SP2/Tac cells into nude mice, rapidly growing tumors developed in all animals after a mean of 10 and 13 days, respectively. The bifunctional chelate cyclohexyldiethylenetriaminepentaacetic acid was used to couple 212Bi to the humanized anti-Tac monoclonal antibody. This immunoconjugate was shown to be stable in vivo. Specifically, in pharmacokinetic studies in nude mice, the blood clearance patterns of i.v. administered 205/206Bi-anti-Tac and coinjected 125I-anti-Tac were comparable. The toxicity and therapeutic efficacy of 212Bi-anti-Tac were evaluated in nude mouse ascites or solid tumor models wherein SP2/Tac cells were administered either i.p. or s.c., respectively. The i.p. administration of 212Bi-anti-Tac, 3 days following i.p. tumor inoculation, led to a dose-dependent, significant prolongation of tumor-free survival. Doses of 150 or 200 microCi prevented tumor occurrence in 75% (95% confidence interval, 41-93%) of the animals. In the second model, i.v. treatment with 212Bi-anti-Tac 3 days following s.c. tumor inoculation also resulted in a prolongation of the period before tumor development. However, prevention of tumor occurrence decreased to 30% (95% confidence interval, 11-60%). In both the i.p. and s.c. tumor trials, 212Bi-anti-Tac was significantly more effective for i.p. (P2 = 0.0128 50/100 microCi 212Bi-anti-Tac versus 50/100 microCi Mik beta; P2 = 0.0142 150/200 microCi anti-Tac versus 150/200 microCi Mik beta) and for s.c. tumors (P2 = 0.0018 100 microCi anti-Tac versus 100 microCi Mik beta; P2 = 0.0042 200 microCi anti-Tac versus 200 microCi Mik beta 1) than the control antibody Mik beta 1 coupled to 212Bi at comparable dose levels. In contrast to the efficacy observed in the adjuvant setting, therapy of large, established s.c. SP-2/Tac-expressing tumors with i.v. administered 212Bi-anti-Tac (at doses up to 200 microCi/animal) failed to induce tumor regression.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Low versus high density of immobilized anti-CD3 influences IL-4 regulation of T-cell immune responses.

Varying the concentration of anti-CD3 immobilized on Sepharose beads allowed us to study both the inhibitory and the stimulatory effects of IL-4 on purified T cells and contrast IL-4 versus IL-2-driven T-cell proliferative responses. In the presence of low density immobilized anti-CD3, IL-4 was unable to stimulate purified T cells and was inhibitory to IL-2-driven T-cell responses. The inhibitory effects of IL-4 were enhanced by preincubation of T cells with IL-4 prior to stimulation. In contrast, the inhibitory effects of IL-4 could be avoided by delaying the addition of IL-4 until Days 3-5 of culture or they could be reversed by the addition of IL-1. In the presence of high-density anti-CD3, IL-4 elicited an IL-2-independent proliferative response by purified T cells or sorted CD8+ cells. Comparison of IL-4-driven versus IL-2-driven T-cell responses demonstrated that IL-2 was able to upregulate mRNA for IL-4 receptors and interferon-gamma, while IL-4 had minimal effects on upregulating mRNA for either the p55 or the p75 IL-2 receptor subunits or interferon-gamma. The timing of the presence of IL-4, the state of T-cell activation, and the nature and strength of the stimulatory signal influenced the regulatory effect of IL-4 on the immune response.

CD3 Complex↗
PubMed1992

Recombinant toxins containing the variable domains of the anti-Tac monoclonal antibody to the interleukin-2 receptor kill malignant cells from patients with chronic lymphocytic leukemia.

We have previously shown that the variable domains of the monoclonal antibody anti-Tac [anti-Tac(Fv)] can be fused to derivatives of Pseudomonas exotoxin (PE) or diphtheria toxin (DT) to produce recombinant immunotoxins that kill interleukin-2 (IL-2) receptor-bearing cells. We now report that two of these single-chain recombinant immunotoxins, anti-Tac(Fv)-PE40KDEL and DT388-anti-Tac(Fv), are cytotoxic toward peripheral blood mononuclear cells (PBMCs) from patients with chronic lymphocytic leukemia (CLL). In anti-Tac(Fv)-PE40KDEL, anti-Tac(Fv) is genetically fused to the amino terminus of PE40KDEL, a recombinant form of PE which contains amino acids 253-608 of PE and the -KDEL mutation at the carboxyl terminus. In DT388-anti-Tac(Fv), anti-Tac(Fv) is fused to the carboxyl terminus of the first 388 amino acids of DT. PBMCs from 14 patients were incubated with the recombinant toxins for 60 hours, and [3H]-leucine incorporation was measured. Anti-Tac(Fv)-PE40KDEL was cytotoxic to 7 of the 14 patient samples, with half-maximal inhibition of protein synthesis (IC50) achieved at 1.2 to 9 ng/mL (1.8 to 13 x 10(-11) mol/L). DT388-anti-Tac(Fv) was cytotoxic to 11 of the 14 samples, with IC50s ranging from less than 1 to 250 ng/mL. DT388-IL-2, in which the first 388 amino acids of DT are attached to IL-2, was marginally cytotoxic toward only 4 of 13 CLL samples tested with IC50s ranging from 100 to 550 ng/mL. Trypan blue staining of cells from several patients indicated that inhibition of protein synthesis correlated with cell death. Binding assays using [3H]-anti-Tac indicated that the CLL cells from nine of the patients contained between 400 and 2,500 sites per cell. Cells from another patient, which were resistant to both anti-Tac(Fv)-PE40KDEL and DT388-anti-Tac(Fv), had less than 100 sites per cell. We conclude that anti-Tac(Fv)-PE40KDEL and DT388-anti-Tac(Fv) can kill CLL cells which have low numbers of IL-2 receptors, and should be investigated further for therapy of this disease.

ADP Ribose Transferases↗
PubMed1992

Expression and function of insulin-like growth factor receptors on anti-CD3-activated human T lymphocytes.

The pattern of expression of receptors for insulin-like growth factors (IGF-I and IGF-II) and insulin was studied on monocyte-depleted human peripheral blood T cells activated via anti-CD3. Binding assays demonstrated the sequential appearance of receptors for IGF-I, IGF-II, and insulin on activated T cells. IGF-IR appeared early, their expression reaching maximum levels at or before the peak of cellular proliferation. IGF-IIR expression generally followed that of the IGF-IR and was more transient, with increases and decreases in expression paralleling the rise and decline of cellular proliferation. Insulin receptor expression remained low throughout the activation time course. The identity of the IGFR on anti-CD3-activated T cells was confirmed in affinity cross-linking experiments. These data demonstrated a 135,000 Mr peptide that specifically binds radiolabeled IGF-I and corresponds to the alpha subunit of the type I IGF-IR, and a 260,000 Mr peptide that specifically binds radiolabeled IGF-II and corresponds to the type II IGFR. We have additionally found that IGF-I and IGF-II (in nanomolar concentrations) produce as much as a threefold enhancement of T cell proliferation early in the activation process, correlating with the early appearance of IGF-IR. The effect of both IGF appeared to be mediated through the type I receptor, since an antibody (alpha IR3), which blocks binding to the alpha subunit of this receptor, inhibited enhancement by up to 83%. Furthermore, we have found expression of IGF-IR on T cells after activation to be associated with both CD4+ and CD8+ T cell subpopulations. These observations provide a foundation for investigating the contribution of IGF in regulating T cell proliferation, differentiation, and effector function.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1992

Regulatory considerations when developing biological products. Report of the Center for Biologics Evaluation and Research.

The Center for Biologics Evaluation and Research, whose regulatory authority includes monoclonal antibodies, cytokines, vaccines, toxins and somatic cellular therapies, communicates to sponsors issues for consideration in the development of biological products through the publication of "Points to Consider" and "Guideline" documents. This paper summarizes the available "Points to Consider" and "Guideline" documents and outlines recommendations from these documents for characterizing the cells used to produce biological products.

Animals↗
PubMed1992

In vitro and in vivo suppression of interleukin-2-activated killer cell activity by chimeric proteins between interleukin-2 and Pseudomonas exotoxin.

The biological effects of IL-2 are mediated through high (complex of alpha and beta chain) or intermediate (beta chain) affinity IL-2 receptors. Previously, chimeric proteins composed of IL-2 and Pseudomonas exotoxin (IL-2-PE) were shown to be specifically cytotoxic to cells bearing IL-2 receptors. It has also been shown that IL-2-PE chimeric proteins can abrogate T cell-mediated immune response in vitro. In the current study, we have investigated the effects of IL-2-PE on LAK activity both in vivo and in vitro. We administered either IL-2-PE40 (comprised of IL-2 and 40-kDa portion of PE) or IL-2-PE66 (comprised of IL-2 and 66-kDa molecule of PE) to normal C57BL/6 mice for 3 or 8 days and LAK activity was assessed in various organs of mice. We found that IL-2-PE40 generated LAK activity in various compartments of mice and the level of activity was slightly lower than that observed with an equivalent amount of recombinant (r) IL-2 alone. However, IL-2-PE66 failed to generate LAK activity which would have been induced due to an equivalent concentration of rIL-2. IL-2-PE66 also did not induce LAK activity from the splenocytes during in vitro culture while IL-2-PE40 generated good LAK activity. An equivalent amount of IL-2 also generated potent LAK activity. The suppression of LAK activity by IL-2-PE66 was also evident in cells preactivated with IL-2; however, this inhibition was partial. The suppressive activity of IL-2-PE66 was shown to be mediated through IL-2 receptor interactions as excess amounts of rIL-2 were able to abrogate its effect. Both IL-2 toxins were equivalently cytotoxic to IL-2 receptor-bearing HUT 102 cells and both were able to compete from high and intermediate affinity IL-2 receptors. Taken together, our data indicate that IL-2-PE66 is highly cytotoxic to LAK cells while IL-2-PE40 is less cytotoxic. Thus, data from our study and from other published reports indicate that IL-2-PE66 is more potent immunosuppressive agent than IL-2-PE40.

ADP Ribose Transferases↗
PubMed1992

Introduction to the issues: recently developed methods for characterizing cell lines.

Cell line characterization is an integral part of establishing quality control over the manufacturing process of a biological product. Characterizing the general and unique features of the continuous cell line and the absence or presence of contaminants establishes a fundamental knowledge about the raw material from which the biological product is being derived. Such information can be used for cell line selection, design of the purification scheme and extent of ensuing validation studies. Developing the selected cell line into a cell bank system allows for a constant source of starting material and decreases the likelihood of contamination. Characterization of the cell bank system may include a) identification of the cell line species of origin, b) identification of unique reference markers, and c) pre-testing for cross-contamination and adventitious agents. This paper introduces issues surrounding present and upcoming methods used for authenticity and characterization testing of cell banks.

Animals↗
PubMed1990

IL-2-PE40 prevents the development of tumors in mice injected with IL-2 receptor expressing EL4 transfectant tumor cells.

A number of different immunotherapeutic reagents are currently being developed to target IL-2R for the treatment of leukemia, graft rejection, and certain autoimmune diseases. Previously, we have shown that IL-2-PE40, a chimeric protein composed of human IL-2 linked to the N-terminus of a truncated form of Pseudomonas exotoxin (PE), could effectively kill a variety of cell lines in vitro expressing either low, intermediate, or high affinity IL-2R. Here, we demonstrate that IL-2-PE40 can successfully retard or prevent the growth of a lethal ascites tumor or a solid tumor composed of EL4J murine thymoma cells transfected with the p55 murine IL-2R. The transfected line, EL4J-3.4, expresses 1,000 to 3,000 high affinity IL-2R. Survival extension in the ascites model was achieved by initiating treatment either after 4 to 6 h or within 5 days post-tumor injection in both athymic nude and C57BL/6 mice. Similarly, the growth of an aggressive s.c. solid tumor could also be inhibited. Extension of survival was not achieved either by using the truncated toxin alone not attached to IL-2 or by using an IL-2-PE40Asp553 mutant lacking a functional toxin. Survival extension was not caused by IL-2 activated NK or other host effector mechanisms as IL-2-PE40 was unable to prevent the receptor-negative EL4J parental line from forming a lethal ascites or a solid tumor. Thus, IL-2-PE40 is a potent, specific cytolytic reagent that may prove useful in the arsenal of anti-IL-2R immunotherapeutics.

ADP Ribose Transferases↗
PubMed1990

Selective elimination in vitro of alloresponsive T cells to human transplantation antigens by toxin or radionuclide conjugated anti-IL-2 receptor (Tac) monoclonal antibody.

The human allogeneic mixed lymphocyte reaction is the in vitro correlate of graft rejection. Cytotoxic effector cells generated during an allogeneic mixed lymphocyte reaction were previously shown to express the human p55 IL-2 receptor subunit, whereas resting cells do not express this receptor peptide. In this study, we asked whether Pseudomonas exotoxin or bismuth-212 (an alpha-particle emitting radionuclide) coupled to the anti-IL-2 receptor mAb, anti-Tac, were able to selectively eliminate alloresponsive cells generated during an allogeneic mixed lymphocyte reaction. After assembly, anti-Tac immunoconjugates retained their binding integrity, specificity, and selectivity. Deletion of alloresponsive cells was shown by the removal of alloproliferating cells as assessed by quantitating cell recovery and by measurement of thymidine incorporation into newly synthesized DNA. Both toxin and radionuclide immunoconjugates eliminated established cytotoxic effector cells generated in an allogeneic mixed lymphocyte reaction, while leaving intact the PHA-inducible mitogenic response of the nonactivated cells. The addition of excess anti-Tac blocked all of the effects of these cytotoxic reagents. The therapeutic reagents in vitro were most effective when added just prior to the peak of the alloproliferative response, when receptor expression would be close to maximum. Thus, anti-Tac conjugated either with toxin or radionuclide is effective in vitro in specifically eliminating cytotoxic effector cells.

ADP Ribose Transferases↗
PubMed1989

Nature of the bifunctional chelating agent used for radioimmunotherapy with yttrium-90 monoclonal antibodies: critical factors in determining in vivo survival and organ toxicity.

One factor that is critical to the potential effectiveness of radioimmunotherapy is the design of radiometal-chelated antibodies that will be stable in vivo. Stability in vivo depends on the condition that both the chelate linkage and radiolabeling procedures not alter antibody specificity and biodistribution. In addition, synthesis and selection of the chelating agent is critical for each radiometal in order to prevent inappropriate release of the radiometal in vivo. In the present study, we compare the in vivo stability of seven radioimmunoconjugates that use different polyaminocarboxylate chelating agents to complex yttrium-88 to the mouse anti-human interleukin-2 receptor monoclonal antibody, anti-Tac. Chelate linkage and radiolabeling procedures did not alter the immunospecificity of anti-Tac. In order to assess whether yttrium was inappropriately released from the chelate-coupled antibody in vivo, iodine-131-labeled and yttrium-88 chelate-coupled antibodies were simultaneously administered to the same animals to correlate the decline in yttrium and radioiodinated antibody activity. The four stable yttrium-88 chelate-coupled antibodies studied displayed similar iodine-131 and yttrium-88 activity, indicating minimal elution of yttrium-88 from the complex. In contrast, the unstable yttrium-88 chelate-coupled antibodies had serum yttrium-88 activities that declined much more rapidly than their iodine-131 activities, suggesting loss of the radiolabel yttrium-88 from the chelate. Furthermore, high rates of yttrium-88 elution correlated with deposition in bone. Four chelating agents emerged as promising immunotherapeutic reagents: isothiocyanate benzyl DTPA and its derivatives 1B3M, MX, and 1M3B. All four isothiocyanate agents showed prolonged yttrium-88 vascular survival which was essentially identical to that of their iodine-131 activity with only minimum accumulation (1.4-1.8%/g) of the yttrium-88 injected dose into bone. Thus, these four chelating agents were very stable in vivo and suitable for yttrium-monoclonal antibody radioimmunotherapy.

Animals↗
PubMed1989

Cell receptor assays.

There are four general assay methods used to quantify a drug/biologic in a preparation, including: (1) in vivo bioassays; (2) in vitro bioassays; (3) immunoassays; and (4) receptor assays. The cell receptor assay is used to evaluate the first step in the molecular action of the drug biologic, its interaction with a specific cellular receptor. Subsequently, the drug biologic must initiate other events, such as internalisation, signal transduction, and/or alterations of one or more cellular constituents in order to elicit its biological effect. Major factors to consider in cell receptor assay development include: (1) establishment of a reference standard preparation; (2) labelling; purifying and characterisation of the biologic drug; (3) cell receptor source; (4) methodology, e.g. separation of bound and free, and other factors affecting accuracy and reproducibility; (5) ligand specificity; and (6) correlation with bioactivity. It should be emphasised that cell receptor binding cannot be assumed to correlate with biological activity because of the requirement that subsequent steps must take place prior to achieving the final response. Chemically altered drugs biologics may bind to a specific cell receptor without eliciting a biological activity. Thus, utilisation of a cell receptor assay requires careful evaluation at both the chemical and biological levels prior to its acceptance as a measure of potency.

Animals↗
PubMed1988

Interleukin 2 (IL2) PE40 is cytotoxic to cells displaying either the p55 or p70 subunit of the IL2 receptor.

IL2-PE40 is a chimeric protein composed of human interleukin 2 (IL2) genetically fused to the amino terminus of a modified form of pseudomonas exotoxin (PE). Internalization of IL2 via the individual p55 and p70 subunits of the IL2 receptor was studied using IL2-PE40 on several mouse and human cell lines expressing either the p55, the p70, or both IL2 receptor subunits. Internalization was assessed by measuring inhibition of protein synthesis caused by the toxin moiety of IL2-PE40. The results demonstrate that IL2 internalization is mediated by either the p55 receptor subunit or by the p70 subunit but is much more efficient when high affinity receptors composed of both subunits are present. IL2-PE40 is a powerful reagent for studying IL2 receptor interactions and for analyzing pathways of the immune response and its regulation.

ADP Ribose Transferases↗
PubMed1987

Type I and II insulin-like growth factor receptors on human phytohemagglutinin-activated T lymphocytes.

Human T cells activated with mitogens, antigens, or antibodies to the T-cell receptor complex acquire a cascade of new receptors, including the receptors for interleukin-2, transferrin, and insulin. We investigated whether receptors for insulin-like growth factors (IGF) also were expressed on activated T cells. Based on competitive binding studies, immunoprecipitation of labeled cell surface receptors and blocking of radiolabeled peptide binding by a specific monoclonal antibody (alpha IR-3) to the type I IGF receptor, as well as affinity crosslinking of radiolabeled peptides to their receptors, we concluded that both type I and type II IGF receptors are expressed on activated T cells. A specific binding site for IGF-II also was observed on the type I IGF receptor which was not inhibited by alpha IR-3. Receptors for IGF were more numerous on activated T cells than on resting T cells, and their peak expression appeared by the peak of DNA synthesis. Thus, human activated T cells were shown to express both type I and II IGF receptors which could potentially play a role in the regulation of T-cell proliferation, differentiation, and function.

Cells, Cultured↗
PubMed1987

Contribution of a p75 interleukin 2 binding peptide to a high-affinity interleukin 2 receptor complex.

There are at least two forms of cellular receptors for interleukin 2 (IL-2); one with a very high affinity and the other with a lower affinity. We identified a non-Tac IL-2 binding peptide with a relative molecular weight of 75,000 (p75). Cell lines bearing either the p55 Tac or the p75 peptide alone manifested low-affinity IL-2 binding, whereas a cell line bearing both peptides manifested both high- and low-affinity receptors. After the internalization of labeled IL-2 through high-affinity receptors, the p75 peptide could not be detected by cross-linking studies. Furthermore, fusion of cell membranes from low-affinity IL-2 binding cell lines bearing the Tac peptide alone with membranes from a cell line bearing the p75 peptide alone generated hybrid membranes bearing high-affinity receptors. These results suggest a multichain model for the high-affinity IL-2 receptor in which high-affinity receptors would be expressed when both Tac and p75 IL-2 binding peptides are present and associated in a receptor complex.

Cell Line↗