Effects of thermal exposure on immunophenotyping combined with in situ PCR, measured by flow cytometry.

BACKGROUND: The combination of in situ PCR and cell phenotyping by antibody labeling (ISPCR/Flow) allows for the identification of cell subsets carrying a particular genetic sequence. ISPCR utilizes thermal cycling for genetic amplification, which can reduce the effectiveness of surface antibody labeling. This study explored and characterized the effects of thermal exposure on antibody labeling using CD4 and CD45. METHODS: Single temperature incubations and thermal cycling exposures were performed on leukocytes labeled with either direct antibody conjugates or with biotinylated antibodies and PE-streptavidin. RESULTS: Fluorescence emission decreased above 70 degrees ( )C when cells were stained with directly conjugated antibodies or a biotinylated antibody and PE-streptavidin prior to high heat exposure. If counter stained with PE-streptavidin after heat, fluorochrome fluorescence was detectable. We tested a second CD4 clone, that provided poor results under similar labeling conditions, suggesting the combination of fixation and heat may have an epitope specific effect for the same cellular antigen. CONCLUSIONS: Immunophenotyping can be combined with ISPCR, but each antibody must be tested to determine its efficacy. The denaturation of protein above 70 degrees C appears to be the main reason for loss of fluorescence. The best procedure is to first stain cells with a biotinylated antibody to an epitope that survives fixation and thermocycling. The cells are then subjected to the desired PCR procedure. Finally they are stained with a fluorochrome conjugated streptavidin.

Amplification and detection of a Y-chromosome DNA sequence by fluorescence in situ polymerase chain reaction and flow cytometry using cells in suspension.

A procedure for amplifying and detecting nucleic acid sequences in situ using cells in suspension and flow cytometry has been developed. The process involves the use of the polymerase chain reaction (PCR) and a fluorescent in situ hybridization (FISH) protocol developed in our laboratory to detect the amplified PCR product. For these studies, a Y-chromosome specific repeat DNA sequence was amplified. Daudi cells, a B-cell lymphoma culture line established from a male, was used as a positive control and HL-60, a promyelocytic leukemia culture line established from a female, was used as a negative control. During the in situ PCR process cellular autofluorescence (noise) increases causing markedly reduced detection sensitivity of the probe (signal) bound to the amplified product within the positive cells. An autofluorescence reduction circuit was applied which was integrated into as standard bench top flow cytometer to reduce this noise, thereby producing a 10-fold increase in detection sensitivity of the signal. Without the application of the autofluorescence reduction circuit, the positive control histogram distribution was virtually indistinguishable from the negative control sample distributions. After autofluorescence reduction, the data showed that the Y-chromosome DNA was only amplified in the Daudi cells subjected to the complete in situ PCR protocol. This increased sensitivity also provided direct detection of the Y-chromosome repeat sequence, albeit exhibiting less signal compared to the amplified target after the in situ PCR.

Quantitative RT-PCR for measuring gene expression.

Classical Northern blot analysis for measuring mRNA requires too many cells to be practical for cell sorting. Yet, measurement of gene expression in small subsets within a heterogeneous population of cells is often desired. The PCR in combination with prior reverse transcription (RT-PCR) of the mRNA of interest provides a means for measuring gene expression using as few as one cell. When RT-PCR is performed, the reliability of the data can be highly subjective due to the efficiency of both RT and PCR steps. This subjectivity can be eliminated by a technique for quantitating specific RNA molecules using an internal RNA competitive reference standard (RNA-CRS), which is identical to the sequence of interest except for a deletion of 80 bases. Here we illustrate a strategy for quantitative PCR using a RNA-CRS, synthesized solely using nonplasmid-based PCR techniques. The competitive reaction consists of a constant quantity of wild-type mRNA (from 100-1000 cells) added individually to tubes containing a serially decreasing amount of RNA-CRS. The RT-PCR is performed on these samples, then the resulting product is analyzed by gel electrophoresis and densitometry. The procedure for preparing the RNA-CRS and subsequent RT-PCR steps are described in detail.

Fluorescent in situ hybridization en suspension (FISHES) using digoxigenin-labeled probes and flow cytometry.

Fluorescent in situ hybridization has become a major technique for visualizing genetic material in fixed cells. Currently, many systems utilize the hybridization of labeled molecular probes to cells that are attached to slides. We have developed a technique that allows for in situ hybridization to be performed using cells in suspension. By using digoxigenin-labeled DNA probes and a fluoresceinated antibody directed against the digoxigenin, we can measure the resulting signal on a flow cytometer and the cells can be attached to microscope slides for visual analysis.

Influenza immunization: clinical studies with ether-split subunit vaccines.

Clinical studies of ether-split influenza antigen vaccines have been in progress for almost a decade. One series of such studies, completed before the Hong Kong virus appeared, compared identically constituted conventional and antigen vaccines for serological effectiveness in 1700 vaccinees from the staff of a metropolitan hospital. A series of 6 annual trials included both "old" subjects (vaccinated the previous year) and "new" subjects (no vaccination the previous year). The serological response to the type A2 component of the antigen vaccines was 3-4 times better than that to intact virus in both the old and new populations. The response to either vaccine by new subjects significantly exceeded the response by the old subjects. The type B component of both vaccines induced an equivalent response in both populations. Monovalent Hong Kong vaccines, both conventional and antigen, given just prior to the Hong Kong epidemic induced an anamnestic response in a geriatric group. No influenza-like disease was seen in this high-risk group during the epidemic.

Inactivation of adenovirus and simian virus 40 tumorigenicity in hamsters by vaccine processing methods.

The effectiveness of the adenovirus vaccine inactivation process in destroying the tumorigenic potential for hamsters of adenoviruses, simian virus 40 (SV-40), and adenovirus-SV-40 hybrids was studied. Baby hamsters injected with untreated virus and with samples subjected to the complete inactivation process and to portions of the process were observed for tumor development for periods in excess of 300 days. Over 20,000 hamsters were injected. From 1 to 7 hr of exposure to formaldehyde at a concentration of 0.031 m at 37 C was sufficient to destroy the tumorigenicity observed in the nontreated preparations. Since the inactivation process included 48 hr of exposure at 37 C to 0.031 m formaldehyde plus treatment with ultraviolet (UV) and with beta-propiolactone (BPL), it was concluded that the process has a large margin of safety. Adenovirus isolates free from tumorigenic potential are difficult, if not impossible, to obtain. Therefore, a proven inactivation process appears to provide the best assurance for obtaining adenovirus vaccines free from such potential. Data presented suggest that the tumorigenic property of the viruses studied might be independent of the infectivity of the preparation. The tumorigenic property was found to be highly susceptible to formaldehyde, but less sensitive to BPL or UV treatment. In contrast, treatment with UV or BPL decreased viral infectivity more readily than tumorigenicity. The three-stage inactivation process (formaldehyde, UV, and BPL) inactivated both tumorigenicity and infectivity.