The influence of fixation of biological samples on cell count and marker expression stability in flow cytometric analyses

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.

Autoimmune versus Non-autoimmune Cutaneous Features in Monogenic Patients with Inborn Errors of Immunity

Cutaneous manifestations are one of the most common presentations among patients with inborn errors of immunity (IEI). These skin manifestations are often among the first presenting features in the majority of patients preceding the IEI diagnosis. We studied 521 available monogenic patients with IEI listed in the Iranian IEI registry up to November 2022. We extracted each patient's demographic information, detailed clinical history of cutaneous manifestations, and immunologic evaluations. The patients were then categorized and compared based on their phenotypical classifications provided by the International Union of Immunological Societies. Most patients were categorized into syndromic combined immunodeficiency (25.1%), non-syndromic combined immunodeficiency (24.4%), predominantly antibody deficiency (20.7%), and diseases of immune dysregulation (20.5%). In total, 227 patients developed skin manifestations at a median (IQR) age of 2.0 (0.5-5.2) years; a total of 66 (40.7%) of these patients initially presented with these manifestations. Patients with cutaneous involvement were generally older at the time of diagnosis [5.0 (1.6-8.0) vs. 3.0 (1.0-7.0) years; p = 0.022]. Consanguinity was more common among patients who developed skin disorders (81.4% vs. 65.2%, p < 0.001). The overall skin infection rate and the type of dominant pathogens were significantly different among the IEI patients in different phenotypical classifications (p < 0.001). Atopic presentation, including urticaria, was highly prevalent among patients with congenital defects of phagocytes (p = 0.020). The frequency of eczema was also significantly higher among cases with both syndromic and non-syndromic combined immunodeficiency (p = 0.009). In contrast, autoimmune cutaneous manifestations, including alopecia and psoriasis, were most common in patients with immune dysregulation (p = 0.001) and defects in intrinsic or innate immunity (p = 0.031), respectively. The presence of autoimmune cutaneous complications significantly improved the survival rate of IEI patients (p = 0.21). In conclusion, cutaneous manifestations were observed in nearly 44% of Iranian patients with monogenic IEI. A considerable number of patients with cutaneous involvements developed these disorders as their first manifestation of the disease, which was particularly noticeable in patients with non-syndromic combined immunodeficiency and phagocytic defects. The neglected skin disorders in IEI patients might delay diagnosis, which is generally established within a 3-year interval from the development of skin-related problems. Cutaneous disorders, especially autoimmune features, might indicate a mild prognosis in IEI patients.

Stabilization of leukocytes from cerebrospinal fluid for central immunophenotypic evaluation in multicenter clinical trials

Analysis of cerebrospinal fluid (CSF) represents a valuable window into the pathogenesis of neuroinflammatory diseases, such as multiple sclerosis (MS). However, analysis of the cellular fraction of CSF is often neglected because CSF cells die rapidly ex vivo. Immunophenotyping of CSF cells in multicenter clinical trials requires sample preservation and shipping to a centralized lab. Yet, there is no consensus on the best method to preserve intact CSF cells and no detailed evaluation of subset-specific cell loss. We used flow cytometry to compare major leukocyte populations in fresh CSF (processed within 2 h) to cells fixed for 48 h with TransFix-EDTA® or cryopreserved and thawed after 96 h. We observed a statistically significant loss of total mononuclear cells, total T cells, CD3+ CD8- T cells, and CD3+ CD8+ T cells after cryopreservation compared to fresh or fixed (p < 0.001), with no significant difference between fresh and fixed. Thus, our results demonstrate that TransFix-EDTA® was superior to cryopreservation for preserving intact CSF T cells. Surprisingly, neither cryopreservation nor fixation had a significant effect on recovery of low frequency cell subsets in CSF, including B cells, NK cells, NKT-like cells, CD14+ monocytes, or CD123+ DCs, versus fresh CSF. To determine the effect of prolonged fixation on cell recovery, we analyzed major CSF cell subsets by flow cytometry after 24, 48, or 72 h of fixation with TransFix-EDTA®. We observed a consistent and progressive loss in the absolute counts of all subsets over time, although this effect was not statistically significant. We conclude that for immunophenotyping of major CSF cell subsets by flow cytometry, fixation with TransFix-EDTA®, shipment to a central lab, and analysis within 48 h is a feasible method to ensure stability of both absolute cell number and relative frequency. This method is a valuable alternative to fresh CSF analysis and can be implemented in multicenter clinical trials.

Technological features of blast identification in the cerebrospinal fluid: A systematic review of flow cytometry and laboratory haematology methods

BACKGROUND

Involvement of the central nervous system (CNS) by acute leukemias (ALs) has important implications for risk stratification and disease outcome. The clinical laboratory plays an essential role in assessment of cerebrospinal fluid (CSF) specimens from patients with ALs at initial diagnosis, at the end of treatment, and when CNS involvement is clinically suspected. The two challenges for the laboratory are 1) to accurately provide a cell count of the CSF and 2) to successfully distinguish blasts from other cell types. These tasks are classically performed using manual techniques, which suffer from suboptimal turnaround time, imprecision, and inconsistent inter-operator performance. Technological innovations in flow cytometry and hematology analyzer technology have provided useful complements and/or alternatives to conventional manual techniques.

AIMS

We performed a PRISMA-compliant systematic review to address the medical literature regarding the development and current state of the art of CSF blast identification using flow cytometry and laboratory hematology technologies.

MATERIALS AND METHODS

We searched the peer reviewed medical literature using MEDLINE (PubMed interface), Web of Science, and Embase using the keywords "CSF or cerebrospinal" AND "blasts(s)".

RESULTS

108 articles were suitable for inclusion in our systematic review. These articles covered 1) clinical rationale for CSF blast identification; 2) morphology-based CSF blast identification; 3) the role of flow cytometry; 4) use of hematology analyzers for CSF blast identification; and 5) quality issues. 9 /L, which is much lower than the original machine count and platelet transfusion was warranted.

DISCUSSION

1) Clinical laboratory testing plays a central role in risk stratification and clinical management of patients with acute leukemias, most clearly in pediatric ALs; 2) studies focused on other patient populations, including adults and patients with AML are less prevalent in the literature; 3) improvements in instrumentation may provide better performance for the classification of CSF specimens.

CONCLUSION

Current challenges include: 1) more precisely characterizing the natural history of AL involvement of the CNS, 2) improvements in automated cell count technology of low cellularity specimens, 3) defining the role of flow MRD testing of CSF specimens and 4) improved recognition of specimen quality by clinicians and laboratory personnel.

Impact of Pre-Analytical and Analytical Variables Associated with Sample Preparation on Flow Cytometric Stainings Obtained with EuroFlow Panels

Simple Summary

Objective interpretation of flow cytometry may be hampered by a lack of standardized sample preparation procedures. The EuroFlow consortium conducted a series of experiments to determine the potential impact of different pre-analytical and analytical factors on the variability of results in terms of relative cell populations distribution and marker expression levels. The experiments were performed on healthy donors and patients with different hematological malignancies (e.g., acute leukemia, lymphoma, multiple myeloma, and myelodysplastic syndrome) to mimic real-world clinical settings. Overall, the results showed that sample storage conditions, anticoagulant use, and sample processing protocol might need to be tailored for sample and cell type(s), as well as to the specific markers evaluated. However, defining of well-balanced boundaries for storage time to 24 h, staining-acquisition delay to 3 h, and choosing a washing buffer of pH within the range of 7.2 to 7.8 would be a valid recommendation for most applications and circumstances described herein.

Abstract

Objective interpretation of FC results may still be hampered by limited technical standardization. The EuroFlow consortium conducted a series of experiments to determine the impact of different variables on the relative distribution and the median fluorescence intensity (MFI) of markers stained on different cell populations, from both healthy donors and patients’ samples with distinct hematological malignancies. The use of different anticoagulants; the time interval between sample collection, preparation, and acquisition; pH of washing buffers; and the use of cell surface membrane-only (SM) vs. cell surface plus intracytoplasmic (SM+CY) staining protocols, were evaluated. Our results showed that only monocytes were represented at higher percentages in EDTA- vs. heparin-anticoagulated samples. Application of SM or SM+CY protocols resulted in slight differences in the percentage of neutrophils and debris determined only with particular antibody combinations. In turn, storage of samples for 24 h at RT was associated with greater percentage of debris and cell doublets when the plasma cell disorder panel was used. Furthermore, 24 h storage of stained cells at RT was selectively detrimental for MFI levels of CD19 and CD45 on mature B- and T-cells (but not on leukemic blasts, clonal B- and plasma cells, neutrophils, and NK cells). The obtained results showed that the variables evaluated might need to be tailored for sample and cell type(s) as well as to the specific markers compared; however, defining of well-balanced boundaries for storage time, staining-to-acquisition delay, and pH of washing buffer would be a valid recommendation for most applications and circumstances described herein.