Flow cytometric "rare event analysis": a standardized approach to the analysis of donor cell chimerism

Absolute circulating pericyte progenitor cell counts in mice by flow cytometry: comparison of 2 single-platform technologies

BACKGROUND

Accumulating evidence indicates that circulating pericyte progenitor cells (CPPCs) may be angiogenic biomarkers in cancer and diabetes. Their validity as biomarkers depends on the accuracy of techniques used for enumeration. In this report, absolute CPPC counts were performed by 2 single-platform technologies. The reliability of the 2 methods, including retest reliability and intraobserver and interobserver variability, was assessed according to the intraclass correlation coefficient (ICC). The linear correlation and agreement among both methods were assessed, and the stability of CPPC numbers in blood samples was analyzed.

METHODS

The blood samples were obtained from ICR mice. The samples were processed through a no-lyse, 1-wash procedure, and Syto16+CD45-CD31-CD140b+ CPPCs were analyzed by exclusion of dead cells and by fluorescence-minus-one control. CPPCs were enumerated by 2 methods: bead-based 123count eBeads count (eBioscience) and direct volume-based Accuri C6 Flow Cytometer count (BD). The cells were measured immediately and after storage of blood samples for 24 and 48 hours.

RESULTS

There were excellent retest correlations and intraobserver and interobserver agreement in both methods. The 2 methods showed a high linear correlation (R2 = 0.923) and with a high level of agreement (0.986). It was demonstrated that CPPCs are unstable in blood samples.

CONCLUSIONS

In this study, 2 reproducible protocols for CPPC quantification were established. These protocols should facilitate future studies to further define the role of CPPCs as cellular biomarkers.

Lost in translation? Microchimersim detection in experimental and clinical transplantation

The importance of further elucidating the properties surrounding microchimerism in various experi- mental models and clinical transplantation are limited by current techniques and the sensitivity of available platforms. Development of reliable methods and use routine use of microchimerism detection in clinical practice could guide clinical decision making regarding rejection, stable function, and tolerance.

A flow cytometric protocol for enumeration of endothelial progenitor cells and monocyte subsets in human blood

BACKGROUND

Accumulating evidence intensively advises circulating endothelial progenitor cells (EPCs) and monocyte subsets as surrogate cellular biomarkers in cardiovascular and cancer disease. However, a general standard on their quantification is still elusive, thus precluding a routine monitoring and comparative interpretation of clinical studies.

OBJECTIVE

We intend to develop an advanced and express flow cytometric protocol for proper ex vivo quantification of monocyte subsets and EPCs in human blood.

METHODS

We employ now lyse/no-wash procedure and bead-based determination of absolute cell counts. We use three-color antibody panels at appropriate compensation. Analysis of rare events and low antigen expression in the EPC experiment is strengthening by sequential gating with exclusion of dead cells, as well as by matching high-intensity fluorochromes to low-density markers and by implementing the fluorescence-minus-one control.

RESULTS

Analysis of peripheral blood of ten healthy donors revealed median (IQR) value of 1.88 (1.35-2.85) viable CD45(dim)CD34)VEGFR2+ EPCs per microliter. Analysis of monocytes revealed 329.5 (264.5-374.8), 16.0 (8.0-22.2) and 26.5 (19.8-36.3) cells per microliter for classical CD14++(high))CD16⁻, intermediate CD14++CD16+(mid) and non-classical CD14+(low))CD16++ monocytes.

CONCLUSION

Our current protocol provides quantitative information under a simple gating logic while using commonly accepted fluorochromes. This assay is therefore highly adapted for routine use.

Sequence-specific analysis of microchimerism by real-time quantitative polymerase chain reaction in same-sex nonhuman primates after islet and bone marrow transplantation

BACKGROUND

Accurate and sensitive detection of microchimerism in nonhuman primates (NHPs) after hematopoietic cell transplantation is essential for monitoring cell engraftment, for evaluating the success of transplant protocols, and for expanding the utility of NHP in transplantation studies. Because limited sequences are available for NHP major histocompatibility complex polymorphic loci, methods that can accurately determine low levels of donor cells in recipients with same-sex bone marrow transplantation are essential.

METHODS

Thirty-seven pairs of primers, 16 from monkey and 21 from human, were screened with cynomolgus DNA samples. Real-time quantitative polymerase chain reaction was developed for accurately determining low levels of donor-specific DNA in the peripheral blood of islet/bone marrow transplant recipients of same sex cynomolgus monkeys.

RESULTS

A total of six sets of primer and Taqman(R) probe combinations were included in this study, which are the most informative primer and probe sets ever reported for cynomolgus monkeys. Three pairs of primers were chosen from exon 2 of the Macaca DRB1 gene and another three pairs were chosen from human HLA DRB1 and DRB3 loci. Three of the six primer-probe sets were also found to work well for baboon (Papio hamadryas) and rhesus monkeys (Macaca mulatta). Sensitivity of the assay ranged from 0.03% to 0.1%, depending on the primer-probe set and donor-recipient pair. The methods are reproducible with relatively low standard error and coefficient of variation.

CONCLUSIONS

This method is an informative, practical and sensitive method for the determination of donor-specific cells in the peripheral blood of NHP recipients of bone marrow transplant.

Chimerism and outcomes after allogeneic hematopoietic cell transplantation following nonmyeloablative conditioning

Allogeneic hematopoietic cell transplantation (HCT) following nonmyeloablative conditioning has been extensively evaluated in patients with hematologic malignancies who are ineligible for conventional HCT because of age or medical comorbidities. Nonmyeloablative regimens have led to an initial state of mixed hematopoietic chimerism defined as coexistence of donor- and host-derived hematopoiesis. While nonmyeloablative regimens have been associated with reduced regimen-related toxicities in comparison with conventional myeloablative conditioning, graft rejection, graft-versus-host disease (GVHD), and disease progression have remained significant challenges. In this article, after briefly introducing current techniques for chimerism assessment, we describe factors affecting donor chimerism levels after nonmyeloablative conditioning, and then review data suggesting that chimerism assessment early after HCT might help identify patients at risk for graft rejection, GVHD and relapse/progression. Finally, we discuss how these observations have opened the way to further research protocols evaluating manipulation of postgrafting immunosuppression, and/or infusion of donor immune cells.

Tolerance to composite tissue allografts across a major histocompatibility barrier in miniature swine1

BACKGROUND

Tolerance to composite tissue allografts might allow the widespread clinical use of reconstructive allotransplantation if protocols to achieve this could be rendered sufficiently nontoxic. The authors investigated whether tolerance could be generated in miniature swine to composite tissue allografts across a major histocompatibility (MHC) barrier. A clinically relevant tolerance protocol involving hematopoietic cell transplantation without the need for irradiation or myelosuppressive drugs was tested.

METHODS

Seven recipient animals were transiently T-cell depleted and a short course of cyclosporine was initiated. Twenty-four hours later, a donor hematopoietic cell transplant consisting of cytokine-mobilized peripheral blood mononuclear cells or bone marrow cells and a heterotopic limb transplant were performed. In vitro anti-donor responsiveness was assessed by mixed-lymphocyte reaction and cell-mediated lympholysis assays. Acceptance of the limb allografts was determined by gross and histologic appearance. Chimerism in the peripheral blood and lymphohematopoietic organs was assessed by flow cytometry.

RESULTS

All seven experimental animals accepted the musculoskeletal elements but rejected the skin of the allografts. All but one of the animals displayed donor-specific unresponsiveness in vitro. The animals that received cytokine mobilized-peripheral blood mononuclear cells showed chimerism but had clinical evidence of graft-versus-host disease (GVHD). None of the animals that received bone marrow cells showed stable chimerism and none developed GVHD.

CONCLUSIONS

This protocol can achieve tolerance to the musculoskeletal elements of composite tissue allografts across an MHC barrier in miniature swine. Stable chimerism does not appear to be necessary for tolerance and may not be desirable because of the risk of GVHD.

Four-color flow cytometric analysis of peripheral blood donor cell chimerism

Passenger leukocytes have been demonstrated to play significant roles in initiating and also regulating immune reactions after organ transplantation. Reliable techniques to detect donor leukocytes in recipients after organ transplantation are essential to analyze the role, function, and behavior of these leukocytes. In this report we describe a simple, reliable method to detect donor cells with low frequencies using peripheral blood samples. Detection of small numbers of major histocompatibility complex (MHC) mismatched cells was first studied using four-color flow cytometry in artificially created cell mixtures. By selecting the CD45(+) population and simultaneous staining with several leukocyte lineage markers (CD3, CD4, CD8, CD56, and CD19), MHC-mismatched leukocytes were consistently detected in cell suspensions prepared from directly stained whole blood samples with a threshold sensitivity as low as 0.1%-0.2%. When the fresh peripheral blood mononuclear cells were separated by conventional Ficoll gradient purification, similar, but slightly lower levels of donor cells were detected. Blood samples obtained 1-5 months after liver, kidney, and intestine transplants revealed that the kind of organ allograft influenced levels and lineage pattern of the circulating donor cells. This procedure provided a simple and reliable method in determining early chimerism in transplant recipients. However, the detection of MHC-mismatched leukocytes of all lineages was much lower when frozen peripheral blood mononuclear cells were used.