Summary A recently developed enzyme assay, utilizing ['251]-iododeoxyuridine as substrate, and capable of detecting normal levels of serum deoxythymidine kinase (s-dTk), was used in an investigation of sera from 155 untreated patients with non-Hodgkin's lymphoma (NHL). The patients were classified at the discovery of disease, both according to spread (stages I-IV according to the Ann Arbor classification) and to tumour histology (the Kiel classification). The results showed a significant correlation between s-dTk level and the extent of disease, as well as to the malignancy; i.e. the more advanced the disease or the more aggressive the tumour, the higher the s-dTk values. Greater than 100-fold increases in s-dTk levels were found in some patients compared to those reported for healthy individuals. A high pretreatment level of s-dTk for patients in stages III-IV correlated with a poor prognosis for the patient in terms of survival. This was consistent even when only patients in stages III-IV with "high-grade" malignant lymphomas were included in the analysis. Longitudinal studies of s-dTk levels in 19 NHL patients showed that s-dTk increases with progression of the disease, decreases during successful therapy, and finally increases during relapse. It is concluded that s-dTk could be used both as a prognostic marker and to monitor the effect of therapy in NHL patients.
An improved method for the detection of deoxythymidine kinase (TK) in human sera is reported. The method which utilizes 125I-iododeoxyuridine (IdUrd) as a substrate was used to measure TK in sera from patients with different diseases. Sera collected during the acute stage of infectious mononucleosis were found to contain elevated levels of TK, in most cases 10-40 times the normal value. The serum TK activity disappeared gradually and reached a normal level within 4 weeks. Sera from patients with other viral infections contained in most cases normal serum TK levels except in connection with measles, rubella, varicella, herpes simplex virus and cytomegalovirus infections. Additional studies revealed that sera from patients with different types of advanced lymphomas, acute leukemias, chronic granulocytic leukemia and lung cancer of the small-cell type with metastases, contained high TK levels which fluctuated in parallel with alterations in activity of the disease. The TK activity in sera from patients with both mononucleosis and tumor disease was characterized by electrophoresis and by its ability to utilize cytidine triphosphate as the phosphate donor. The results showed that the serum TK has the same properties as the human cytosolar TKI, except in connection with varicella.
Human immunodeficiency virus (HIV) RNA testing is the gold standard for monitoring antiretroviral therapy in HIV-infected patients. However, equipment and reagent costs preclude widespread use of the assay in resource-limited settings. The Perkin-Elmer Ultrasensitive p24 assay and the Cavidi Exavir Load assay both offer potentially simpler, less costly technologies for monitoring viral load. These assays were compared to the Roche Amplicor HIV-1 Monitor Test, v1.5, using panels of clinical samples (subtype B) from HIV-positive subjects and HIV-spiked samples (subtypes A, C, D, CRF_01AE, CRF_02AG, and F). The Ultrasensitive p24 assay detected 100% of the spiked samples with virus loads of >250,000copies/ml and 61% of the clinical samples with virus loads of 219 to 288,850 copies/ml. Detection rates were improved substantially if an external lysis buffer was added to the procedure. The Cavidi assay detected 54 to 100% of spiked samples with virus loads >10,000 copies/ml and 68% of the clinical samples. These detection rates were also greatly improved with a newly implemented version of this kit. Coefficients of variation demonstrate good reproducibility for each of these kits. The results from the Cavidi v1.0, Cavidi v2.0, and Perkin-Elmer, and the Perkin-Elmer Plus external buffers all correlated well with the results from the Roche Monitor Test (r ؍ 0.83 to 0.96, r ؍ 0.84 to 0.99, r ؍ 0.58 to 0.67, and r ؍ 0.59 to 0.95, respectively). Thus, the use of these two assays for monitoring patients, together with less-frequent confirmation testing, offers a feasible alternative to frequent HIV RNA testing in resource-limited settings.The human immunodeficiency virus (HIV) pandemic has affected countries worldwide, but the impact on resource-limited countries has been especially devastating. Pressure to lower the cost of antiretroviral therapies (ART) has been critical in fighting this battle. The current challenge is to identify simplified assays for monitoring patients on ART that are less expensive and less technically demanding with respect to facilities and instrumentation (6, 12). In the past, the compromise for using simplified methods has often been reduced sensitivity or poor correlation with the gold standards used in industrialized settings (4, 10). We compare here two commercially available kits that measure HIV-specific proteins, p24 and reverse transcriptase (RT), respectively, and utilize simpler technologies to perform the tests. The first method is the Ultrasensitive HIV p24 enzyme-linked immunosorbent assay (ELISA; HIV-1 p24 ELISA plus the ELAST ELISA Amplification System; Perkin-Elmer Life Sciences, Inc.), and the second is the RT assay (Exavir Load Assay; Cavidi Tech AB, Sweden). Both kits offer less expensive alternatives for detecting HIV.For the Ultrasensitive p24 assay, a standard ELISA format is used for the capture and detection of HIV p24 coupled with a specific signal amplification to increase the assay sensitivity. Heat denaturation of the plasma prior to binding in the ELISA step he...
We describe a procedure (ExaVir Load) to carry out human immunodeficiency virus-1 (HIV-1) viral load testing using reverse transcriptase (RT) recovered from HIV-1 virions in plasma. Samples from individuals infected with HIV-1 were treated with a sulphydryl-reactive agent to inactivate endogenous polymerases. Virions were then immobilised on a gel and washed in individual mini columns to remove RT-inhibiting antibodies, antiviral drugs, and other RT inhibitors. Immobilised virions were lysed finally, and the viral RT eluted. The amount of RT recovered was quantified by a sensitive RT activity assay using either colorimetry or fluorimetry to detect DNA produced by RT. The "RT load" values of 390 samples from 302 HIV-1 patients living in Sweden were compared to results obtained with an HIV-1 RNA viral load assay. The correlation between the two tests was r = 0.90, P < 0.0001. Four of 202 samples from healthy blood donors gave low positive values in the RT test. All samples in a panel with 10 HIV-1 subtypes were positive by the RT load. The RT load test provides a technically less demanding and cost-effective alternative to methods based on nucleic acid amplification. Being insensitive to genetic drift occurring in HIV, the assay should be of particular use in resource-limited settings, where different subtypes and recombinant HIV strains occur.
A more sensitive version of ExaVir Load, a test that utilizes reverse transcriptase (RT) activity from virions in plasma to determine HIV-1 viral load, is described. The virions were immobilized on a gel that was washed, followed by lysis of the virions, elution of purified RT, and finally RT activity determination. The changes made to the original test were: (1) improved washing of the immobilized virions by addition of a non-lytic detergent to the wash buffer, (2) improved virion lysis procedure, including changes in salt, detergent and pH, (3) the use of larger sample volumes in the RT assay, and (4) prolonged RT reaction time. The alterations gave a tenfold increased sensitivity compared to the original version. The correlation between RT load by the current test and RNA PCR was the same as previously (r=0.90). Using colorimetric product detection, the average detection limit in a panel of 262 patient plasma from Stockholm was 0.5 fg RT/ml, corresponding to approximately 170 RNA copies/ml. None of 54 HIV-1 RNA negative samples exhibited RT. The amount of RT load positive samples were 19% for samples containing 50-400 RNA, 71% for samples with 400-1,500, and 100% among samples with >8,000 copies/ml (according to Roche Amplicor). The sensitivity could be increased further using fluorimetric detection. In conclusion, the modifications of the test described result in an important increase in sensitivity. It can now be regarded as a competitive alternative method for HIV viral load determinations.
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