Comparison of radioisotope methods and a non-radioisotope method to measure platelet survival in the baboon

Human platelets labeled at two discrete biotin densities are functional in vitro and are detected in vivo in the murine circulation: A promising approach to monitor platelet survival in vivo in clinical research

BACKGROUND

The production of platelet concentrates (PCs) is evolving, and their survival capacity needs in vivo evaluation. This requires that the transfused platelets (PLTs) be distinguished from those of the recipient. Labeling at various biotin (Bio) densities allows one to concurrently trace multiple PLT populations, as reported for red blood cells.

STUDY DESIGN AND METHODS

A method is described to label human PLTs at two densities of Bio for future clinical trials. Injectable-grade PLTs were prepared in a sterile environment, using injectable-grade buffers and good manufacturing practices (GMP)-grade Sulfo-NHS-Biotin. Sulfo-NHS-Biotin concentrations were chosen to maintain PLT integrity and avoid potential alloimmunization while enabling the detection of circulating BioPLTs. The impact of biotinylation on human PLT recirculation was evaluated in vivo in a severe immunodeficient mouse model using ex vivo flow cytometry.

RESULTS

BioPLTs labeled with 1.2 or 10 μg/ml Sulfo-NHS-Biotin displayed normal ultrastructure and retained aggregation and secretion capacity and normal expression of the main surface glycoproteins. The procedure avoided detrimental PLT activation or apoptosis signals. Transfused human BioPLT populations could be distinguished from one another and from unlabeled circulating mouse PLTs, and their survival was comparable to that of unlabeled human PLTs in the mouse model.

CONCLUSIONS

Provided low Sulfo-NHS-Biotin concentrations (<10 μg/ml) are used, injectable-grade BioPLTs comply with safety regulations, conserve PLT integrity, and permit accurate in vivo detection. This alternative to radioisotopes, which allows one to follow different PLT populations in the same recipient, should be valuable when assessing new PC preparations and monitoring PLT survival in clinical research.

Platelet recovery and survival measured in patients by quantitative polymerase chain reaction of mitochondrial DNA

BACKGROUND

Mitochondrial (mt) DNA markers have been identified as potential targets for the quantification of endogenous and allogeneic platelets (PLTs) in the blood of individuals who received transfusions. Our goal was to develop a routine polymerase chain reaction (PCR) assay for ex vivo monitoring of PLT survival in patients after transfusion.

STUDY DESIGN AND METHODS

Targets were selected for real-time (RT)-PCR of mt DNA based on the frequency distribution of nucleotide polymorphisms and assay sensitivity in vitro. The assays were then evaluated with ex vivo samples to measure PLT survival and recovery of therapeutic doses of apheresis PLTs in hematooncologic patients with thrombocytopenia.

RESULTS

Nucleotides in two positions (73/310 hypervariable region [HVR] 2) and three positions (295 HVR 2, 16069/16311 HVR 1) had allele frequencies of approximately 0.5 and 0.85, respectively, in a population of 960 Caucasian PLT donors. They provided targets for sensitive assays detecting at least 1 × 10(3) PLTs per whole blood sample with adequate reproducibility (interassay coefficient of variation <4.0%). Transfusions of single-donor PLT concentrates in patients with thrombocytopenia (n = 30) were monitored with these markers. The mean 24-hour corrected count increment was 8.3 and the mean calculated survival time was 3.3 days. Results for a second marker were available for 13 transfusions. The survival time values derived from both markers for the same transfusion were almost identical (linear regression: r(2)  = 0.957, slope = 0.87).

CONCLUSION

This RT-PCR method detects mt DNA polymorphisms in Caucasians for a highly sensitive and reproducible quantification of endogenous and allogeneic PLT numbers in blood samples from transfused patients with thrombocytopenia.

In vivo tracking of transfused platelets for recovery and survival studies: an appraisal of labeling methods

The measurement of recovery and survival of platelets is an important decisive factor when 'new' platelet products have been developed. Recovery and survival measurements are mostly performed with radioactive-labeled platelets in healthy volunteers. This approach is required by the FDA for acceptance of platelet products that differ substantially in production or storage conditions from standard methods. However, due to regulatory obstacles, such radiolabeling studies are only carried out in designated institutes. Many countries do not require radioactive labeling studies in volunteers prior to accepting new products, and rather rely on surrogate tests. Also, the European guide to the preparation of blood components does not require this step. This paper reviews alternative, non-radioactive methods, which includes biotinylation of platelets, and discrimination of transfused platelets based on HLA discrepancy. The benefits and disadvantages of these methods will be discussed.

A sensitive quantitative single-platform flow cytometry protocol to measure human platelets in mouse peripheral blood

BACKGROUND

The NOD/SCID mouse is a widely used model for human cord blood (CB) transplantation. Engraftment is generally estimated with semiquantitative methods, measuring the percentage of human cells among mouse cells. To compare protocols aiming to improve hematopoietic recovery, quantitative methods to enumerate human cells would be preferred. This study describes a single-platform protocol to count human platelets (hPLTs) after transfusion and CB transplantation in the peripheral blood (PB) of the mouse.

METHODS

With an anti-human CD41 antibody against hPLTs and counting beads, the sensitivity to detect hPLTs in mouse blood by flow cytometry was validated. PLT recovery after hPLT transfusions and PLT kinetics after transplantation with CB CD34+ cells was followed in time in NOD/SCID mice.

RESULTS

hPLTs could be reliably detected to a level as low as 1 PLT per microL with this single-platform protocol, what appeared to be at least 10 times more sensitive than detection with the dual-platform protocol. To verify the applicability for mouse studies, hPLTs were measured serially in transfusion and transplantation studies in NOD/SCID mice. The results showed that earlier detection of PLT recovery was feasible with the single-platform protocol.

CONCLUSION

A single-platform flow cytometry method can repeatedly measure low numbers of circulating hPLTs in the PB of the same mouse. This method may be helpful in search of new protocols aiming at accelerating PLT recovery after CB transplantation, but also in a number of clinical settings, such as monitoring PLT reconstitution after hematopoietic stem cell transplantation.

The survival and function of baboon red blood cells, platelets, and plasma proteins: a review of the experience from 1972 to 2002 at the Naval Blood Research Laboratory, Boston, Massachusetts

The studies reported in this monograph were performed between 1972 and 2002 when it was possible to study healthy male and female baboons. A colony of baboons was maintained for 30 years without any adverse events observed in these baboons in the numerous studies that were performed. These protocols were reviewed and approved by the institutional animal care and use committees (IACUC) at the sites where the studies were performed and by the veterinarian services of the U.S. Navy's Bureau of Medicine and Surgery, the Office of Naval Research, and the Department of Defense. The physiology of red blood cells (RBCs), platelets (PLTs), and plasma proteins in the baboon was investigated together with the viability and function of preserved RBCs, PLTs, and plasma proteins. These studies in the baboon could not have been performed in normal volunteers and patients. The data obtained have provided critical information to explain the clinical observations reported in normal volunteers and patients after transfusion of fresh and preserved blood products. These studies were supported by the U.S. Navy's Bureau of Medicine and Surgery and the Office of Naval Research. In addition, the support of the late Congressman J. Joseph Moakley from Massachusetts is acknowledged because without his support many of these studies could not have been performed. The authors acknowledge the contributions of the numerous research collaborators identified in the 52 peer-reviewed publications that cite other funding agencies that supported the research that is reported, the editorial assistance of Ms Cynthia Ann Valeri, and the assistance of Ms Deborah Tattersall who prepared the figures and tables reported in this publication.