Biologic Association Annual Summit: 2020 Report

Comparative single-cell transcriptional and proteomic atlas of clinical-grade injectable mesenchymal source tissues

Bone marrow aspirate concentrate (BMAC) and adipose-derived stromal vascular fraction (ADSVF) are the most marketed stem cell therapies to treat a variety of conditions in the general population and elite athletes. Both tissues have been used interchangeably clinically even though their detailed composition, heterogeneity, and mechanisms of action have neither been rigorously inventoried nor compared. This lack of information has prevented investigations into ideal dosages and has facilitated anecdata and misinformation. Here, we analyzed single-cell transcriptomes, proteomes, and flow cytometry profiles from paired clinical-grade BMAC and ADSVF. This comparative transcriptional atlas challenges the prevalent notion that there is one therapeutic cell type present in both tissues. We also provide data of surface markers that may enable isolation and investigation of cell (sub)populations. Furthermore, the proteome atlas highlights intertissue and interpatient heterogeneity of injected proteins with potentially regenerative or immunomodulatory capacities. An interactive webtool is available online.

Review of Dohan Eherenfest et al. (2009) on "Classification of platelet concentrates: From pure platelet-rich plasma (P-PRP) to leucocyte- and platelet-rich fibrin (L-PRF)"

This classic discusses the original publication of Dohan Eherenfest et al. on "Classification of platelet concentrates: from pure platelet-rich plasma (P-PRP) to leucocyte- and platelet-rich fibrin (L-PRF)", in which the authors propose four categories of platelet concentrates depending on their leucocyte and fibrin content (P-PRP, leucocyte- and platelet-rich plasma (L-PRP), pure platelet-rich fibrin (P-PRF), and L-PRF) to group a "jungle" of products in which the term platelet-rich plasma (PRP) was used indistinctly. They were able to identify common factors such as: (1) the use of anticoagulants and immediate centrifugation of the blood after its collection; (2) most preparation techniques allowed platelet concentrate preparation within an hour; (3) the centrifugation aimed to separate the blood in layers that would allow the extraction of specific fractions; and (4) the product was activated with thrombin or calcium chloride. The reviewed manuscript has been listed among the most cited PRP articles in regenerative medicine, with more than 800 citations, driving current scientific research and clinical practise by categorising L-PRP and P-PRP (now, leucocyte-poor PRP). The classification has also opened the door to understanding intrinsic biological mechanisms between platelets, leukocytes, fibrin, and growth factors, which will later be considered for studying the proliferation and differentiation of cells in different tissues affected by PRP. Since the initial classification of platelet concentrates, several other classification systems have been proposed and published in the current literature such as platelet, activation, white blood cell (PAW), Mishra, platelet, leucocyte, red blood cells, and activation (PLRA), dose of platelet, efficiency, purity, and activation (DEPA), method, activation, red blood cells, spin, platelets, image guidance, leukocytes, and light activation (MARSPILL), etc. These classifications have identified important aspects of PRP that affect the biological composition and, ultimately, the indications and outcomes. To date, there is still a lack of standardisation in sample preparation, cohort heterogeneity, and incomplete reporting of sample preparation utilised, leading to a lack of clarity and challenging researchers and clinicians.

Experts Achieve Consensus on a Majority of Statements Regarding Platelet-Rich Plasma Treatments for Treatment of Musculoskeletal Pathology

PURPOSE

To establish consensus statements on platelet-rich plasma (PRP) for the treatment of musculoskeletal pathologies.

METHODS

A consensus process on the treatment of PRP using a modified Delphi technique was conducted. Thirty-five orthopaedic surgeons and sports medicine physicians participated in these consensus statements on PRP. The participants were composed of representatives of the Biologic Association, representing 9 international orthopaedic and musculoskeletal professional societies invited due to their active interest in the study of orthobiologics. Consensus was defined as achieving 80% to 89% agreement, strong consensus was defined as 90% to 99% agreement, and unanimous consensus was indicated by 100% agreement with a proposed statement.

RESULTS

There was consensus on 62% of statements about PRP.

CONCLUSIONS

(1) PRP should be classified based on platelet count, leukocyte count, red blood count, activation method, and pure-plasma versus fibrin matrix; (2) PRP characteristics for reporting in research studies are platelet count, leukocyte count, neutrophil count, red blood cell count, total volume, the volume of injection, delivery method, and the number of injections; (3) the prognostic factors for those undergoing PRP injections are age, body mass index, severity/grade of pathology, chronicity of pathology, prior injections and response, primary diagnosis (primary vs postsurgery vs post-trauma vs psoriatic), comorbidities, and smoking; (4) regarding age and body mass index, there is no minimum or maximum, but clinical judgment should be used at extremes of either; (5) the ideal dose of PRP is undetermined; and (6) the minimal volume required is unclear and may depend on the pathology.

LEVEL OF EVIDENCE

Level V, expert opinion.

Substantial Variability in Platelet-Rich Plasma Composition Is Based on Patient Age and Baseline Platelet Count

Purpose

To evaluate the effect of age, sex, body mass index (BMI), and baseline blood count on the final composition of platelet rich-plasma (PRP) and to evaluate the variability of PRP applied in the same patient at 2 different times.

Methods

Potential subjects treated with PRP between January 2019 and December 2021 were identified in an institutional registry. Patient demographics and baseline blood count were prospectively recorded in a consecutive series of patients treated with PRP for a musculoskeletal condition in our Institution. The influence of sex, BMI, age, and baseline blood count on final platelet concentrations in PRP was evaluated. Finally, intrapersonal variability was evaluated.

Results

A total of 403 PRP injections from 357 patients were analyzed from an institutional prospective registry of PRP between January 2019 and December 2021. A directly proportional variation in PRP platelet count of 3.8× was observed for each unit increase in baseline blood platelet count. For every decade increase, we observed an approximate decrease of 32,666 platelets. When the first dose of PRP platelet counts was compared with the second dose of PRP platelet counts between the same patients, significant differences were found. A mean of 890,018 platelets in the first PRP and a mean of 1,244,467 in the second PRP with a mean difference of 354,448 was found (P = .008). We did not find differences in the final concentration of platelets regarding sex, BMI, or PRP protocol.

Conclusions

Overall the final composition of PRP (platelet count) was significantly influenced by patient's age and baseline platelet count. In contrast, BMI, sex and the rest of the components of the baseline blood count did not have a significant influence on final PRP. Furthermore, in patients who received 2 doses of PRP, the final concentration of platelets varied significantly between the 2 preparations.

Level of Evidence

Level IV, prognostic case series.

A Simple Double-Spin Closed Method for Preparing Platelet-Rich Plasma

Objective: To describe and analyze a new protocol for the extraction of platelet-rich plasma (PRP) for use in clinical practice and compare this technique with methods that have been previously described in the medical literature.

Methods: Sixteen blood samples from healthy volunteers were collected. PRP was prepared using our new double-spin technique, consisting of successive centrifugation of blood samples with two different spins, without opening the container. Descriptive analysis of cell counts in baseline and PRP samples was undertaken. Comparison between cell and platelet count in baseline and PRP samples, as well as the statistical analysis, were done.

Results: The mean platelet concentration ratio was 3.47 (SD: 0.85; 95% CI: 3.01-3.92; range: 2.48-5.71). The baseline whole blood platelet count correlated positively to the PRP platelet count (rP = 0.56; 95% CI: 0.09-0.88; P = 0.023). The PRP was enriched for lymphocytes and monocytes but presented significantly lower counts of neutrophils and eosinophils in comparison to baseline.

Conclusion: Results show a safe and easily reproducible method to obtain PRP for use in clinical daily practice.