Technical influences on immunophenotyping by flow cytometry. The effect of time and temperature of storage on the viability of lymphocyte subsets

Effects of blood sample storage time, temperature, anti-coagulants and blood stabiliser on lymphocyte phenotyping

Medical diagnostic laboratories have come under further scrutiny to ensure quality standards of their service and external quality assurance (EQA) programs involving multiple laboratories have been used to gauge this quality based on a consensus. However, because of the geographical distances within a country or internationally, cell surface marker expressions may change due to time delays and transport temperatures. Attention was given to this issue some decades ago and hence requires a re-evaluation in consideration of updated methods, reagents and instruments for flow cytometry and phenotyping. We have undertaken an extensive study to examine the effects of various conditions on blood storage akin to that experienced by patient samples as well as EQA programs, examining expression of lymphocyte surface markers, CD3, CD4, CD8, CD2, CD19, CD20, CD16/56 and HLA-DR. Assessment of lithium-heparin anticoagulated whole blood showed an increase in percentage of CD3+ and CD8+ T cells and a decrease in CD16/56+ NK cells after storage at room temperature (RT) for 24 and/or 48 h. In comparison, storage at 4°C led to a decrease in percentage of CD4+ and increase in percentage of CD8+ cells. The low temperature also caused an increase in percentage of B cells (CD19+, CD20+). While storage at RT did not alter levels of HLA-DR+ CD3+ T cells, there was a significant increase in percentage of these cells after 48 h. Changes were also seen at both temperatures when EDTA was used as an anti-coagulant. Assessment of blood treated with a stabiliser, normally used in the EQA samples (Streck Cell Preservative), reduced the range of lymphocyte subsets affected, with only CD2+ and CD20+ cells being significantly different at both temperatures, We conclude that 24-48 h storage/transport can affect the percentage of CD3+, CD4+ T cells, CD8+ T cells, B cells, NK cells and HLADR+ T cells which can be minimised by using the blood stabiliser as per EQA programs and we emphasise the need to adopt this in the processing of patients' blood samples.

CD4 results with a bias larger than hundred cells per microliter can have a significant impact on the clinical decision during treatment initiation of HIV patients

BACKGROUND

CD4 counts are currently used to assess HIV patients for treatment eligibility and to monitor antiretroviral response to treatment. The emerging point-of-care devices could fill an important gap in resource-limited settings. However, the accuracy of CD4-counting instruments is diverse and data on how CD4 measurement errors have an impact on clinical decisions are lacking.

METHODS

Clinicians were queried on the use of CD4 results in their clinical setting. Subsequently, the effect of CD4 measurement errors on treatment initiation was put in a statistical model. Based on clinical CD4 databases from Belgium, Cambodia, and Senegal, the percentage of unchanged clinical decisions was calculated (treatment initiation should start within a 3-month delay [one visit]) for escalating CD4 measurement errors, taking into account the strict or preventive application of CD4 thresholds at 350 or 500 cells/µl used by clinicians.

RESULTS

To ensure that the treatment was initiated appropriately for at least 95% of patients, an error of 5 - 10 cells/µl was allowed. This is significantly smaller than the bias of ±50 cells/µl most clinicians considered acceptable. For limits of agreement (LOA, 1.96 x error) of 100 cells/µl, corresponding to most CD4 instrument evaluations, the misclassification rate of patients was found to be 3 - 28% at the threshold of 350 cells/µl (strict or flexible), and 13 - 20% at 500 cells/µl.

CONCLUSIONS

The maximum allowed CD4 bias on results from new CD4 technologies should not exceed 50 cells/µl (LOA 100 cells/µl) when applied for treatment initiation, to ensure at least 72% of correct clinical decisions. © 2016 International Clinical Cytometry Society.

CD3-positive B cells: a storage-dependent phenomenon

The majority of clinical studies requires extensive management of human specimen including e.g. overnight shipping of blood samples in order to convey the samples in a central laboratory or to simultaneously analyze large numbers of patients. Storage of blood samples for periods of time before in vitro/ex vivo testing is known to influence the antigen expression on the surface of lymphocytes. In this context, the present results show for the first time that the T cell antigen CD3 can be substantially detected on the surface of human B cells after ex vivo storage and that the degree of this phenomenon critically depends on temperature and duration after blood withdrawal. The appearance of CD3 on the B cell surface seems to be a result of contact-dependent antigen exchange between T and B lymphocytes and is not attributed to endogenous production by B cells. Since cellular subsets are often classified by phenotypic analyses, our results indicate that ex vivo cellular classification in peripheral blood might result in misleading interpretations. Therefore, in order to obtain results reflecting the in vivo situation, it is suggested to minimize times of ex vivo blood storage after isolation of PBMC. Moreover, to enable reproducibility of results between different research groups and multicenter studies, we would emphasize the necessity to specify and standardize the storage conditions, which might be the basis of particular findings.

Monitoring of chimerism following allogeneic haematopoietic stem cell transplantation (HSCT): technical recommendations for the use of short tandem repeat (STR) based techniques, on behalf of the United Kingdom National External Quality Assessment Service for Leucocyte Immunophenotyping Chimerism Working Group

Analysis of short tandem repeats (STR) is the predominant method for post-transplant monitoring of donor engraftment. It can enable early detection of disease relapse, level of engraftment and provide useful information on the graft-versus-host disease (GVHD)/graft-versus-tumour (GVT) effect, facilitating therapeutic intervention. Harmonization and standardization of techniques and result interpretation is essential to reduce the impact of laboratory variability on both clinical management and the results of multi-centre clinical trials. However, the United Kingdom National External Quality Assessment Service for Leucocyte Immunophenotyping (UK NEQAS LI) has highlighted significant issues inherent in STR testing that impact upon inter- and intra- laboratory variation. We present here consensus best practice guidelines and recommendations for STR chimerism testing, data interpretation and reporting that have been drawn up and agreed by a consortium of 11 UK and Eire clinical laboratories. This document uses data obtained from the UK NEQAS LI Post-Stem Cell Transplant (SCT) Chimerism Monitoring Programme.

Impact of blood processing variations on natural killer cell frequency, activation, chemokine receptor expression and function

Understanding the role of natural killer (NK) cells in human disease pathogenesis is crucial and necessitates study of patient samples directly ex vivo. Manipulation of whole blood by density gradient centrifugation or delays in sample processing due to shipping, however, may lead to artifactual changes in immune response measures. Here, we assessed the impact of density gradient centrifugation and delayed processing of both whole blood and peripheral blood mononuclear cells (PBMC) at multiple timepoints (2-24 h) on flow cytometric measures of NK cell frequency, activation status, chemokine receptor expression, and effector functions. We found that density gradient centrifugation activated the NK cells and modified the chemokine receptor expression. Delays in processing beyond 8h activated NK cells in PBMC but not in whole blood. Likewise, processing delays decreased chemokine receptor (CCR4 and CCR7) expression in both PBMC and whole blood. Finally, delays in processing PBMC were associated with a decreased ability of NK cells to degranulate (as measured by CD107a expression) or secrete cytokines (IFN-γ and TNF-α). In summary, our findings suggest that density gradient centrifugation and delayed processing of PBMC can alter measures of clinically relevant NK cell characteristics including effector functions; and therefore should be taken into account in designing clinical research studies.

The sample processing time interval as an influential factor in flow cytometry analysis of lymphocyte subsets

The objective of this paper is to propose a protocol to analyze blood samples in yellow fever 17DD vaccinated which developed serious adverse events. We investigated whether or not the time between sample collection and sample processing could interfere in lymphocyte subset percentage, for it is often impossible to analyze blood samples immediately after collection due to transport delay from collection places to the flow cytometry facility. CD4+CD38+ T, CD8+CD38+ T, CD3+ T, CD19+ B lymphocyte subsets were analyzed by flow cytometry in nine healthy volunteers immediately after blood collection and after intervals of 24 and 48 h. The whole blood lysis method and gradient sedimentation by Histopaque were applied to isolate peripheral blood mononuclear cells for flow cytometry analyses. With the lysis method, there was no significant change in lymphocyte subset percentage between the two time intervals (24 and 48 h). In contrast, when blood samples were processed by Histopaque gradient sedimentation, time intervals for sample processing influenced the percentage in T lymphocyte subsets but not in B cells. From the results obtained, we could conclude that the whole blood lysis method is more appropriate than gradient sedimentation by Histopaque for immunophenotyping of blood samples collected after serious adverse events, due to less variation in the lymphocyte subset levels with respect to the time factor.

Enumeration of lymphocyte subsets using flow cytometry: Effect of storage before and after staining in a developing country setting

Lymphocyte subset estimations by flow cytometry in population-based studies require transportation of samples from the field site to the laboratory. As samples arrive late in the day they have to wait overnight before being processed. The effect of two possible approaches, sample storage for 24 h before staining and immediate staining with analysis after 24 h and 48 h were evaluated. Two sets of experiments were performed with EDTA (ethylenediamine tetra-acetate) anticoagulated peripheral blood. In the first experiment, after collection, each sample was divided into two portions. One portion was stained at the time of blood collection and the other 24 h later after keeping it at room temperature (38-45°C). In the second experiment, blood samples were stained within 1-2 h. Each sample was analyzed immediately upon completion of staining process and subsequently after 24 h and 48 h of storage at 4°C. Results suggest that blood collected in EDTA can be processed using whole blood lysis method, after storage at room temperature (38-45°C) for 24 h with some but not significant alteration in T-cell subsets. Storage at 4°C after staining for 24 h results in a lesser and insignificant loss of cells or alteration of T-cell subsets and may be the method of choice.

Fixation and cryopreservation of whole blood and isolated mononuclear cells: Influence of different procedures on lymphocyte subset analysis by flow cytometry

BACKGROUND

Immunophenotyping of whole blood (WB) and isolated peripheral blood mononuclear cells (PBMCs) is a common tool used to evaluate immune system changes in clinical studies. The development of methods that would allow preservation of samples for flow cytometric analysis is important for the extension of this technology to field testing in settings where the equipment might be not readily accessible.

METHODS

Three-color flow cytometric analysis was used to determine percentages of T cells and their subsets (CD3(+), CD4(+), CD8(+)), B cells (CD19(+)), and natural killer cells (CD16(+)/56(+)) in WB and PBMCs using variations of a standard stain/fix WB staining procedure (Optilyse) that included staining following fixation and freezing of fixed samples before or after staining.

RESULTS

Comparable lymphocyte subset percentages in WB or PBMCs were observed regardless of Optliyse method used (all Ps >/= 0.8). However, differences in fluorescence intensity for several markers were observed across procedures. Compared with the standard stain/fix procedures, fix/stain decreased the mean fluorescence intensities for CD4, CD8, CD19 and CD16/56 in WB and PBMCs (P </= 0.03 for these markers P = 0.105 for CD8 in PBMCs). Further decreases in mean fluorescence intensity were seen with the fix/stain/freeze procedure. The stain/fix/freeze yielded intensities largely comparable to those seen with standard stain/fix procedure (P >/= 0.13), suggesting that, when the markers of interest are known at the time of field collection, implementation of this procedure might be desirable. Fix/freeze/stain resulted in diminution of intensity in general, but they tended to be more modest than those seen for fix/stain/freeze and therefore might be applicable to field studies in instances when the specific markers of interest cannot be defined upfront.

CONCLUSIONS

Freezing of fixed WB and PBMCs before or after cell surface staining is a reliable method for preserving specimens in field sites for later determination of lymphocyte subset percentages, which are commonly assessed in immunodeficient and cancer patients.

Lymphocyte subsets in peripheral blood of dogs--a flow cytometric study

Slight differences in the results of papers describing lymphocyte subsets distribution in the peripheral blood of healthy dogs may be explained by differences in monoclonal antibody clones and sources, breed and age of animals examined, methods of sample treatment, or methods of result analysis. In this paper, we described the effect of sample processing and of sample storage as well as the effect of age, breed, and gender of dogs on lymphocyte subset distribution. No significant differences were found between samples processed following a whole-blood lysis method and samples processed after density gradient separation. Furthermore, no significant differences were found between samples processed within 2h after collection and those stored at 4 degrees C for 12-16 h before processing. Age-related changes were evident in lymphocyte subset distribution in the peripheral blood of 38 Beagles divided according to their age into the six groups: (1) 5-6 days; (2) 2 months; (3) 6 months; (4) 1-2 years; (5) 3-5 years; and (6) >5 years. The percentage of B-lymphocytes (CD21-like positive cells) in the peripheral blood of newborn pups was 39.5+/-5.7 and decreased with advancing age. The percentage of CD8+ lymphocytes was 7.7+/-3.4 after birth and increased with advancing age. No age-related changes were observed in the percentages of CD4+ lymphocytes. The CD4+:CD8+ ratio decreased with advancing age. No significant age-related change was observed for lymphocytes bearing the gammadelta-TCR. Some breed differences were evident. Adult (1-5-year-old) Beagles, German Shepherds, Dalmatians, and Dachshunds were examined. The percentages of lymphocytes were higher in Beagles and Dachshunds than in Dalmatians and German Shepherds. The highest and the lowest absolute lymphocyte counts were found in Beagles and German Shepherds, respectively. As a consequence, German Shepherds showed the lowest absolute counts of the individual lymphocyte subpopulations and the widest neutrophil:lymphocyte ratio. Dalmatians showed the lowest percentage of CD3+ cells, the highest percentage of CD21+ cells, and the lowest CD4+:CD8+ ratio. German Shepherds showed the lowest percentage of CD21+ cells and the highest CD4+:CD8+ ratio. Females in Beagles and Dachshuns had nonsignificantly higher percentages of total lymphocytes, CD3+, CD4+, and nonsignificantly lower percentages of CD21+ lymphocytes. We concluded that there are age-, breed-, and perhaps also gender-related differences in lymphocyte subset distribution in the peripheral blood of dogs. Therefore, there is need to use appropriate control group in the experimental protocols. Among-breed differences could explain, at least partly, breed predisposition for some diseases.

Maturational changes in peripheral lymphocyte subsets pertinent to monitoring human immunodeficiency virus-infected Chinese pediatric patients

On the basis of results of testing of 212 peripheral blood samples from ethnic Chinese individuals in five age groups, ranging from birth to adulthood, by standardized flow cytometry techniques, we studied the maturational processes that are pertinent to monitoring the human immunodeficiency virus (HIV)-infected Chinese pediatric population. While the numbers of peripheral total white cells and percent lymphocytes declined from birth to adulthood, the percent CD3+ T lymphocytes was steady among all age groups studied. The numbers of CD3+ CD4+ (T-helper) cells decreased markedly after the first year of life, followed by a slower decline afterward and then a slight increase before adulthood. The trend for CD3+ CD8+(T-suppressor) cells, however, was an increase among individuals of all age ranges. The numbers of CD19+ CD3- (B cells) increased only during the first year of life and then declined steadily, while natural killer (NK) cells showed the opposite pattern. Comparison of the results with those of studies done with a Caucasian population showed that both peripheral T-helper and T-suppressor cell numbers were low after the first year of life in the Chinese pediatric population in comparison with those in a Caucasian pediatric population. Lower B-cell counts and higher NK-cell counts were seen after the first year of life in the Chinese population than in the Caucasian population. It is important that for each HIV-infected population normative ranges of the lymphocyte subset be established to monitor HIV-infected pediatric patients.

Stability of fresh and preserved fetal and adult lymphocyte cell surface markers

Delay between blood collection and immunophenotyping of peripheral blood (PB) and umbilical cord blood (UCB) lymphocytes occurs frequently. Holding media address this problem, but there are few reports of their limitations. We tested the ability of Cyto-Chex (CC) to preserve the ability of lymphocyte subpopulations to be immunophenotyped after time delays. Ten UCB and 10 PB specimens were kept up to 48 hr and then placed in CC for 1 week, with removal of aliquots for staining with CD3, CD4, CD8, CD19, and CD45 at intervals. There were no significant changes in the number of nonpreserved PB or UCB cells stained with any of the reagents after 48 hr. Aside from a small decrease in UCB B-cell numbers, there were no changes in UCB or PB lymphocyte numbers after placing them in CC for 1 week. However, PB and UCB CD19+ cells and CD8+ T cells lost capacity for bright staining after 1 week in CC. The results suggest that UCB and PB can be held for up to 48 hr before being placed in CC and then kept for up to 1 week in CC with no decrease in T-cell numbers and only a minor reduction of B-cell numbers, albeit with a marked reduction in staining intensity.

Preparation of cells from blood

Peripheral blood is a bountiful source of numerous cell types that are easily analyzed by flow cytometry for a variety of properties. The monodisperse nature of blood makes preparation of these cells relatively easy if the coagulation cascade is inhibited. For some studies the presence of serum can be a confounding factor, although this is often overcome by merely pelleting the cells from the serum and washing the remaining cells several times. Blood, particularly from humans and primates, should be considered highly infectious whether or not from a healthy donor. Therefore universal precautions should be followed at all times. Techniques and route of collection may have a profound influence on the condition and nature of the blood being obtained. Performing venipuncture with an extremely small gauge needle may disrupt cells and prevent satisfactory analysis. Venous blood and arterial blood may yield differing data. Even blood collection at different times of day may yield diurnal variations in some assays. The demands of each cell type and of each assay dictate specific preparation, fixation, storage, and staining protocols. However, the overall goal for preparation of cells from blood, for all of the assays, remains the same--collect and prepare the cells in such a manner that they accurately represent the in vivo state.

Cellular Immunity to β2-Glycoprotein-1 in Patients with the Antiphospholipid Syndrome

Patients with antiphospholipid syndrome (APS) suffer recurrent thromboses, thrombocytopenia, and/or fetal loss in association with Abs that can be detected in phospholipid-dependent assays. Despite the name, the Igs associated with APS are predominantly directed against epitopes on phospholipid-binding plasma proteins, such as β2-glycoprotein-1 (β2GP1) and prothrombin. The aim of this study was to examine the cellular immune response to β2GP1 in patients with APS. Using a serum-free stimulation assay, PBMCs from 8 of 18 patients with APS proliferated to purified β2GP1 or to the β2GP1 present in serum, whereas no stimulation was observed by PBMCs from healthy individuals, patients with other autoimmune diseases, or anticardiolipin Ab-positive patients without histories of thromboses or fetal loss. The immune response was Ag-specific, requiring class II molecules, CD4+ T cells, and APCs, and was associated with a selective expansion of CD4+ but not CD8+ T cells. The proliferating T cells produced IFN-γ but not IL-4, indicating a bias toward a type 1 immune response. Chronic low grade stimulation of autoreactive β2GP1-specific, IFN-γ-producing Th1 CD4+ T cells may contribute to the high risk of thromboses and pregnancy failure in patients with APS.

Lymphocyte subpopulation reference ranges for monitoring human immunodeficiency virus-infected Chinese adults

Two hundred eight healthy human immunodeficiency virus (HIV) type 1- and HIV type 2-seronegative Chinese adults (78 males and 130 females; mean age, 32 years; age range, 18 to 71 years) were analyzed for lymphocyte subsets by a standardized and quality-controlled flow cytometric immunophenotyping technique. While the leukocyte differential values were comparable to those found in studies of Caucasians, the means, medians, and 95% reference ranges of lymphocyte subsets were very different. The 95% reference ranges in absolute counts per microliter of whole blood (percentage of lymphocytes) for CD3+, CD3+ CD4+, CD3+ CD8+, CD3- CD19+ (B), and CD3- with CD16+ and/or CD56+ (NK) cells were 672 to 2,368 (54.8 to 83.0%), 292 to 1,366 (23.1 to 51.0%), 240 to 1,028 (17.9 to 47.5%), 82 to 560 (5.1 to 20.8%), and 130 to 938 (7.1 to 38.0%), respectively. CD3+ CD4+ cells showed significant sex difference (for males, mean of 702 [34.8%] and standard deviation of 258 [7.5%]; for females, mean of 728 [37.3%] and standard deviation of 254 [7.4%]) as well as an increase with age of 42 (1.6%) per decade. Investigations of the NK cell population did not show similar findings. Classification of HIV disease, treatment, and prophylactic regimens based on studies which relied heavily on estimations of lymphocyte subsets alone should be used with special caution for Chinese patients. Provided that adequate quality control measures are taken to ensure comparability of data, we recommend that these ranges be used on a day-to-day basis in laboratories that have not yet established their own reference ranges.

The effect of storage on immunophenotyping of sheep peripheral blood lymphocytes by flow cytometry

We have shown that when a whole blood method of cell staining is used for flow cytometric analysis of sheep lymphocytes (i.e. red cell lysis after addition of antibody), staining may be delayed for up to 48 h after blood collection without significant effect on expression of CD4, CD5, CD8 or B cell markers. If cells were stained immediately after blood collection, using the same whole blood method, and then fixed with paraformaldehyde, cell samples could be stored for 24 h without change in marker expression. However, by 7 days there was a significant decrease in the percentage of cells expressing CD8, T19 and B cell markers. Cryopreservation prior to staining was found to markedly affect the expression of all cell surface markers investigated. These results indicate that storage of sheep blood prior to flow cytometric analysis is feasible but may affect the results obtained. Thus is it important to standardise the handling of samples, especially when comparative studies are being undertaken.

Peripheral blood cell preparation influences the level of expression of leukocyte cell surface markers as assessed with quantitative multicolor flow cytometry

We have compared the influence of sample preparation upon the level of surface expression of T, B, and NK cell-related antigens as assessed by flow cytometry. Lysed whole blood (WBL), Ficoll-Paque separated peripheral blood lymphocyte (F-PBL), and frozen peripheral blood lymphocyte (Fr-PBL) were analyzed via single- and multicolor flow cytometry. The percentage of positive cells expressing the individual cell surface markers was not affected by the procedure for preparation of WBL, F-PBL, and Fr-PBL. In contrast, the fluorescence intensity level of individual cell surface markers varied depending on cell preparation. By using Quantum Simply Cellular (QSC) microbeads, the antibody binding capacity (ABC) of single-color stained cells was quantified and compared. The amount of monoclonal antibody (MAb) anti-CD3-FITC bound to Fr-PBL (mean ABC = 137,040) was significantly higher (P < 0.001) that the amounts bound to WBL (mean ABC = 112,410) and F-PBL (mean ABC = 107,738). In multicolor analysis, the fluorescence intensity of CD3-FITC and CD4-FITC was significantly higher on Fr-PBL than on WBL and F-PBL; CD8-PE and CD20-PerCP was significantly higher on WBL. Furthermore, the intensity of CD3 and CD4 was different on T-cell subsets. The intensity of CD3 staining in three-color analysis was lower than with single-color staining using the same fluorochrome. We conclude that particularly the method of cell preparation but also the selection of MAb combinations may influence the level of staining of certain lymphocyte antigens. This may be of relevance in the analysis of cellular activation and regulation of differentiation.