Tc Generator Research Articles

The impact of acemannan on the generation and function of cytotoxic T-lymphocytes.

Acemannan, an antiviral agent with immune enhancement capabilities, was studied for its impact on cytotoxic T-lymphocyte (Tc) function generated in response to alloantigen. To investigate whether acemannan directly stimulated the generation of Tc from primary mixed lymphocyte cultures (MLC), the drug was added at the initiation of the MLC. There was a dose-related, statistical increase in killer T-cell generation produced by acemannan in the clinically relevant dose range. The lowest test dose of the drug (2.6 x 10(-9) M) increased chromium release nearly two-fold; the 2.6 x 10(-8) M dose gave a maximal 3.5 fold increase in cytotoxic T-cells. To study whether acemannan enhanced the capacity of Tc once generated to alloantigen to destroy targets bearing the sensitizing antigens, MLR were established in the absence of any drug. Acemannan at the two highest doses increased the functional capacity of Tc to destroy target cells to which they had been sensitized in the MLR. To control for the possibility that acemannan was directly cytotoxic to target cells, targets were incubated alone with drug and without sensitized killer T-cells. No dose of acemannan was found to be cytotoxic to these cells. In conclusion, acemannan did enhance the generation of cytotoxic T-cells when added at the initiation of the MLR. When acemannan was added at the completion of allostimulation, an increase of almost 50% killing by Tc was also observed. These effects can not be explained by direct drug related toxicity and suggest a functional correlate to the previously described immune enhancing properties of the agent. As this drug is being tested for the treatment of HIV infections, these data provide at least one immunologic mechanism by which acemannan may be clinically salutory.

Separation of Fission 99Mo on Charcoal Columns Impregnated with Tin(IV) Chloride for Use in Preparation of 99mTc Generators

Separation of Fission ⁹⁹Mo on Charcoal Columns Impregnated with Tin(IV) Chloride for Use in Preparation of ^99mTc Generators

Development of a New 99mTc Generator Using Neutron Irradiated Titanium Molybdate as Cotumn Matrix

Development of a New ^99mTc Generator Using Neutron Irradiated Titanium Molybdate as Cotumn Matrix

The Elution characteristics of alpha-emitting impurities from Molybdenum-99/Technetium-99 m chromatographic generators

Technetium-99 m generators produced from fission-based 99Mo may be contaminated with α-emitting impurities formed during irradiation of the uranium target material; these α contaminants may be partly extracted during the elution cycles of the generators. Because of the radiotoxic hazards associated with α impurities the British and U.S. Pharmacopoeias (1.2) prescribe strict limits for the allowable levels if gross α contaminants in 99 m Tc eluates derived from this source. As most commercially available 99Mo/ 99 m Tc generators consist of a small chromatographic column containing a solid stationary phase, (3–5) the elution behaviour of α contaminants from the stationary phase material is important in establishing a comprehensive quality assurance regime for routinely monitoring these impurities in the eluates. This note describes the desorption behaviour of radioactive neptunium, uranium and plutonium from alumina and serium-coated alumina stationary phase materials using an isotonic saline eluant.

99mTc Generator — Prevention of Radiolytically Induced Reduction of Elution Yield

For 99mTc generator activities ranging from 74–92.5 GBq, an adsorbent consisting of a mixture of alumina and silica gel was modified by copper addition. The quantity of copper adsorbed on alumina was in the range of 10–15 mg Cu/g alumina. It was found that saline solution does not influence the performance of the columns. A high elution yield of 99mTc and good quality of the eluate was obtained both for the “wet” and “dry” column.

Construction and Examination of Collimators Identyfying Position of Radiation Sources Designed to Estimate the Agricultural Machine Functionality with a Sower as an Example

A measure of functionality of agricultural sower is the layout of grains sown in the soil and labelled by radioisotope a method. To determine the precise position of the grains which are sown is a figure of merite. To resolve the problem, a detection system with focusing multihole collimator was used. A probe with collimator travelled on a self-propelled carriage. The detector pulses were ratio transmited to the field isotope lab. To label the grains of cereals, cucumber and beet the isotope 99mTc obtained from Mo–Tc generator was applied.

Improved elution efficiency of 99 mTc generators following purification of the eluting saline

The 99Mo/ 99 m Tc generator system is susceptible to many outside influences. This note describes the deleterious effect of dissolved organic compounds in the eluant on the elution efficiency and demonstrated the use of a charcoal trap to overcome this effect.

Large scale production of fission 99Mo by using fuel elements of a research reactor as starting material

A procedure is described for the production of fission 99Mo. Starting from short period irradiated fuel elements of a research reactor the following steps are included: dissolution of the aluminium cladded fuel element in 6 N HNO 3, separation of 99Mo from uranium and the bulk of other fission products by adsorption/desorption on alumina, and purification of the molybdenum fraction by means of high temperature volatitization. The procedure is particularly suitable for those who do not dispose of highly enriched uranium from high flux reactors. The total yield proved to be about 1200 Ci 99Mo from one fuel element containing 36 g 235U after irradiation at 5·10 13 neutrons/cm 2s for 200 h. The final product is well suited for manufacturing high-quality 99 m Tc generators.

Calculation of 99Tc in generator-produced 99 mTc

A knowledge of the levels of 99Tc present with 99 m Tc eluted from 99Mo 99 m Tc generators is important because of the effect that the long-lived nuclide may have on radio-pharmaceutical labelling. This paper outlines the calculation of 99Tc/ 99 m Tc atom ratios in generator eluates for any elution-usage sequence.

A review of 99mTc generator technology

The 99 m Tc generator has found widespread use because it is ideally suited for scintigraphy. The preparation of 99 m Tc generators using alumina and other ion exchange systems is described. Other methods of separating 99Mo and 99 m Tc, such as solvent extraction and sublimation, are also discussed. Some of the problems associated with the alumina column type 99 m Tc generator are listed with possible causes and solutions to their problems. The current biomedical applications of the 99 m Tc radioisotope are the basis of a $100 million nuclear medicine business. The importance of the 99 m Tc generator makes it imperative that we understand and solve the problems associated with its manufacture.

Technologie du générateur de 99mTc, elumatic III du commissariat à l'energie atomique, France

Technology of the 99 m Tc generator, elumatic III made by commissariat à l'energie atomique, France The article describes the choices leading to the development of an “integrated” 99Mo- 99 m Tc generator meeting the following requirements: (a) total activity eluted in a volume of 5 ml; (b) adequate radioprotection both for the user and the manufacturer; (c) injectable eluate.

T-cell recognition of influenza-infected cells

different type-A influenza viruses. Although we have done a lot of work with spleen-cell populations in intranasally infected mice, I should like to document several points by data obtained with a cloned and recloned cytotoxic T-cell line (L4) which we have maintained in the presence of T- cell growth factors for over a year. This BALB/c clone is H-2<restricted and is crossreactive for all type A influenza viruses, but does not kill cells infected with type B influenza virusL Lin and I could demonstrate that transfer of L4 Tc reduces the replication of both homologous or heterologous type A influenza virus in the lung of intranasally infected mice. L4 cells will also protect against a lethal influenza infection of lightly irradiated mice 2. L4 Tc carry the Lyt-2 marker, and although they can actively kill influenza virus-infected cells, they can also induce a delayed skin reaction in footpad challenged with the homologous or heterologous A-influenza virus 2. This crossreactivity for all type A viruses is not limited to Tc but can also be demon- strated for I-region-restricted T-helper cells amplifying both the generation of Tc and antibody production by B cells (experiments with D. B. Thomas, to be published). T cells therefore have a very different recognition pattern for influenza than do the B cells where the variable regions of the HA molecule are immunodominant. This crossreaction of T cells has important practical as well as theoretical implications. The.crossprotection experiments indicate that Tc are an important arm of the immune response in influenza. This means that the present vaccination methods will have to be re-evaluated since vaccines in use induce very poor and short-lived memory for crossreactive Tc 3. The actual recognition pattern by T cells of virus and self determinants on influenza-infected cells is still a question mark. With R. G. Webster, we found that some mono- clonal antibodies to HA inhibit cytotoxicity in cor-~junction with certain anti-H-2 antibodies, probably through steric hindrance. We are still searching for antibodies directed to the actual recognition site but the data would suggest that a homologous area of the HA may be recognized in close association with H-24. On the other hand we have to keep an open mind, since data are accumulating in a number of laboratories which suggest that antigen plus 'self' alters the conformation of 'self' and looks like %11o'. We also have evidence that our clone L4 Tc which is restricted to the D end of H-2 d, crossreacts with the 1) end of H-2 k and kills H-2kuninfected as well as infected cells (Askonas and Lin, to be published). This H-2 k crossreaction is the property of our particular L4 clone and is difficult to find in bulk spleen-cell cultures of BALB/c mice after influenza infection. Clearly, the cytotoxic T-cell receptor still remains elusive, and we have to learn a lot more about the T-cell repertoire to understand T-cell specificity and recognition of virus infected cells.

Formula omitted] generators — II. Physicochemical factors in the radiolytic reduction of pertechnetate

The effect of pulsed and continuous irradiation on aqueous solutions of pertechnetate was studied using radical scavengers, aerobic and anaerobic conditions, and changes in concentration and pH. It was determined that TcO 4 − in homogeneous aqueous solutions is reduced to a lower oxidation state by external γ-irradiation and that this reduction is strongly dependent on pH. At neutral pH, TcO 4 − is reduced by e aq −, and the bimolecular rate constant of the reaction is 1.9 × 10 10M −1s −1. Reduction by H radicals could not be demonstrated. At pH 2.0, reduction by H radicals is efficient, even more so than that by e aq − at neutral pH. Systems composed of various 99 Mo− 99m Tc generator components were irradiated under aerobic and anaerobic conditions to investigate the influence of these components on reduction. It was found that presence of water in the generator system is essential for the reduction of TcO 4 − and that alumina and/or molybdenum enhance the process.

The Effect of Specific Antibody on the Generation of Cytotoxic T Lymphocytes and the Recovery of Mice from Influenza Virus Infection

A study has been made of the effect of humoral antibody on the generation of specific cytotoxic T cells (Tc) in the spleen or lungs after intravenous injection or intranasal inoculation of infectious influenza virus. Antibody injected before or at the same time as virus inhibited completely the generation of Tc in the spleen. If injected 1 h after virus, the inhibition was reduced by 50%, and little inhibition occurred if antibody was injected 6 h after virus. This suggested that antibody failed to influence Tc generation once infection of stimulating cells had occurred. Antibody injected intravenously 24 h after intranasal inoculation of virus into normal mice did not affect the level of cytotoxic activity present in the lungs, and trace amounts only (less than 1 log10 EID50) could be recovered from the lungs at 6 days. As there is a high titre (greater than 6 log10 EID50) of infectious virus in the lungs of mice 24 h after infection, this represents a very efficient control mechanism. The same protocol carried out with athymic mice gave only a partial clearance (c. 3 log10 EID50) of virus in the lungs. It was suggested that a major role of humoral antibody was to limit infection by the virus, and in this respect it complemented the action of Tc.

Specific depletion of alloreactive cytotoxic lymphocyte precursors

THE major barrier to replacement therapy in various clinical immunodeficiency states is the likelihood that the transferred immunocompetent T lymphocytes would react against alloantigens of the recipient and produce graft-versus-host (GVH) disease1. The logical resolution of this problem would be to delete or inactivate those clones of T cells which are specifically coded to react against the histocompatibility antigens of the recipient tissues. The remaining cell population could then fully reconstitute the recipient without danger of GVH reactions. Specific clonal deletion of this kind has been obtained in experimental animal situations by pre-circulation through a third-party host2,3 or by induction of specific anti-idiotype immunity4. These studies show the validity of this approach but are technically complicated and have limited application. A simpler method of obtaining this result has been sought based on the following strategy. To reconstitute a strain A mouse by transfer of lymphocytes from an allogeneic strain B, the strain B lymphocytes are first incubated on a monolayer of cells of strain A. Those clones which recognise the strain A alloantigens should adhere to the monolayer; the non-adherent populations of cells should now be unable to react against alloantigens of strain A but should still respond to alloantigens of other haplotypes. Although this kind of technique has been widely effective in removing fully activated cytotoxic lymphocytes (Tc)5–9, its use to deplete alloreactive Tc precursors has given variable results8,10–16. Significant depletion of precursors has been reported primarily when the non-adherent cells have been assayed in vivo13–16, but this has been claimed to be due to change in the responder cells, not depletion, as the same population assayed by in vitro generation of Tc shows no evidence of depletion16. We present here a simple depletion method developed from our finding that when splenic lymphocytes are incubated for a few hours before being formed into a monolayer, they can effectively absorb alloreactive Tc precursors even when assayed by the sensitive in vitro assays.

Long-lived 99Tc in generator-produced 99 mTc, its determination and significance

Taking into account the whole “history” of the 99Mo− 99 m Tc generator the amount of long-lived 99Tc contained in generator produced 99 m Tc is calculated. Some differences between the results obtained and those published in the literature were found. The calculation presented is especially useful for predicting the amount of 99Tc in the product of the extraction generator. The absorbed dose due to long-lived 99Tc was estimated for the case of two 99 m Tc radiopharmaceuticals—pertechnetate and EHDP.

Fission product 99 mTc generator

A 99 m Tc generator system has been developed with much improved characteristics. The generator system takes advantage of the low, but usable, loading capacity (2 mg-Mo/g alumina at pH of 5–6) of the acid form of alumina and the high specific activity (∼10 5 Ci/g Mo) of 99Mo produced by the fission of 235U. No pre- or post-loading treatment of the alumina is needed when the pH of the loading 99Mo solution is between 5 and 6. Greater than 95% 99 m Tc yields were obtained when using 4 ml of a saline eluant with 99Mo loadings of 1 mCi to 20 Ci; high radiation levels do not reduce the 99 m Tc yield. The major advantages of a 99 m Tc generator made from fission product 99Mo as compared to one made by 98Mo(n, γ) 99Mo are ease of production, consistently higher 99 m Tc yields, lower 99Mo breakthrough, higher activity generator and higher 99 m Tc concentration.

Considerations in the radiolabeling of albumin

Labeled albumins for blood-pool, albumin-metabolism, and gastrointestinal-blood-loss studies have been readily available for years, and their clinical use is well established. Labeled albumin for cisternography was once widely used; now it is restricted due to pyrogen contamination at levels too low to be detected by the official U.S.P. pyrogen test but still high enough to cause a significant incidence of aseptic meningitis when injected intrathecally. The more sensitive Limulus test for pyrogens may be used to overcome this problem. Labeled albumin for nuclear angiogrophy and gated cardiac blood-pool studies is presently limited to 99m Tc-albumin. Lack of a commercially available radiopharmaceutical for this purpose has been a limiting factor in the clinical application of these studies. Kits can be used to prepare 99m Tc-albumin from 99m Tc generator eluates, but they have not yet been perfected to the point where radiochemical contaminants are not a problem. Unbound pertechnetate and insoluble technetium cause unnecessary degradation of resolution and prolongation of the studies. This problem can be solved by daily quality-control testing of kit preparations or by the development of commercial sources of prelabeled and pretested 99m Tc-human serum albumin.

Technetium 99m compounds for visualization of body organs

Technetium 99m is readily available from a⁹⁹Mo-^99mTc generator and possesses nearly ideal physical properties for organ visualization when used with either a scanner or scintillation camera. Brain phantom studies indicate that comparable resolution of pseudotumors containing^99mTc may be obtained with either unit. Studies of more than 100 patients suspected of having brain lesions indicated that^99mTc in the pertechnetate form is satisfactory for cranial scintiphotography. Albumin is tagged radioactively with^99mTc in our laboratories and used for placental localization. A colloid of this material is obtained by controlling heating. Small particles (200_μ) are used for visualization of liver and spleen. Macroaggregates (50_μto 100_μ) obtained by continued heating are used for lung scintiphotograms. Animal and human studies with preparations of albumin labeled with radioactive technetium (^99mTc) have yielded good results with no adverse side effects noted.

Technetium 99m Compounds for Visualization of Body Organs

Technetium 99m is readily available from a 99 Mo- 99m Tc generator and possesses nearly ideal physical properties for organ visualization when used with either a scanner or scintillation camera. Brain phantom studies indicate that comparable resolution of pseudotumors containing 99m Tc may be obtained with either unit. Studies of more than 100 patients suspected of having brain lesions indicated that 99m Tc in the pertechnetate form is satisfactory for cranial scintiphotography. Albumin is tagged radioactively with 99m Tc in our laboratories and used for placental localization. A colloid of this material is obtained by controlling heating. Small particles (200 μ ) are used for visualization of liver and spleen. Macroaggregates (50 μ to 100 μ ) obtained by continued heating are used for lung scintiphotograms. Animal and human studies with preparations of albumin labeled with radioactive technetium ( 99m Tc) have yielded good results with no adverse side effects noted.