Injectable Hydrogels for Improving Cardiac Cell Therapy—In Vivo Evidence and Translational Challenges
Round 1
Reviewer 1 Report
This review on hydrogel in cardiac cell therapy is very interesting and well written and will bring a knowledge of the current state of the art of the topic.
For a non-specialist the TESI technique could be a little more explicit.
I don't understand well the paragraph on CIHF and NIDCM regarding calcium and AMI. It should be clarified.
In the pre-clinical part one article is missing and should be added: Mathieu, E.. (2012). Intramyocardial Delivery of Mesenchymal Stem Cell-Seeded Hydrogel Preserves Cardiac Function and Attenuates Ventricular Remodeling after Myocardial Infarction. PLoS ONE, 7(12), e51991. https://0-doi-org.brum.beds.ac.uk/10.1371/journal.pone.0051991
There is confusion between assisted cell therapy, where we want to keep the nature of cells for paracrine products, and tissue engineering, where we want to differentiate cells so that they participate directly in tissue regeneration. To separate and argue
In the micro-encapsulation chapter (7.2) I disagree with the need for electrostatically sprayed. This is not the only way to make microcapsules. Aren't there emulsion and micro-fuildic?
For the next paragraph on single cell coating, why do we have to freeze any time ?
After these minor revisions, it will be a good paper.
Author Response
We are pleased with the assessment of the manuscript and thank the reviewers for the good comments. Below, we have addressed the different comments, and they are also inserted in the revised manuscript.
Comment
For a non-specialist the TESI technique could be a little more explicit.
Answer
The following text has been included in the section:
“TESI is performed using a catheter to enter the left ventricle through the venous system. The conductivity of the ventricle can be mapped using the NOGA mapping system, creating a map of the non-conductive infarct area. Clinicians look at the X-ray for TESI injection and are able to map injection site in the NOGA program. As such, it is possible to deliver cells to the peri-infarct area through minimally invasive methods.”
Comment
I don't understand well the paragraph on CIHF and NIDCM regarding calcium and AMI. It should be clarified.
Answer
This was a reference to an injectable hydrogel being applied in AMI, which was mentioned in the previous section. An additional sentence has been added to explain the point in more detail and refer to the previous section:
“As mentioned above, hydrogels have been developed for in-situ cross-linking due to higher calcium levels in AMI. However, for both CIHF and NIDCM, the amount of myocardial apoptosis and therefore release of calcium is lower compared to AMI.”
Comment
In the pre-clinical part one article is missing and should be added: Mathieu, E.. (2012). Intramyocardial Delivery of Mesenchymal Stem Cell-Seeded Hydrogel Preserves Cardiac Function and Attenuates Ventricular Remodeling after Myocardial Infarction. PLoS ONE, 7(12), e51991. https://0-doi-org.brum.beds.ac.uk/10.1371/journal.pone.0051991
Answer
We agree that Mathieu et al. is an important reference. It has been included in the introduction. However, since the articles included in the pre-clinical part are meant as the most recent research (from 2016 to now), we will not include it in this section.
Comment
There is confusion between assisted cell therapy, where we want to keep the nature of cells for paracrine products, and tissue engineering, where we want to differentiate cells so that they participate directly in tissue regeneration. To separate and argue
Answer
We agree that tissue engineering should be mentioned, as clarification for the readers. We have not previously mentioned tissue engineering, since this also includes non-injectable approaches. At the beginning of Chapter 4, we divided the investigated cell types into paracrine mechanisms and contracting cell types. We have now integrated the distinction between assisted cell therapy and tissue engineering in this section as well:
“The approaches to cell therapy for cardiac regeneration can generally be divided into two categories. 1: To boost endogenous repair mechanisms. Most adult stem cell therapies including mesenchymal stromal cells (MSCs) and derived paracrine mediators fall into this category. This may also simply be called cell therapy and assisted cell therapy if hydrogels or other carriers are used. 2: To provide new contracting cells. Pluripotent stem cell-derived cardiomyocytes, myoblasts, and cardiopoietic cells can be included into this category. The application of such an ex vivo generated construct is also called tissue engineering. Cardiac tissue engineering approaches include ex vivo generated scaffolds or cell sheets combined with contracting or differentiating cell types, but also includes the application of injectable hydrogels with these cells. Some cell types fall into both categories, and therefore the treatment is both cell therapy and tissue engineering.”
Comment
In the micro-encapsulation chapter (7.2) I disagree with the need for electrostatically sprayed. This is not the only way to make microcapsules. Aren't there emulsion and micro-fuildic?
Answer
The reviewer is correct, that there are alternative methods for micro-encapsulating cells. Such methods have not been applied in any of the most recent in vivo studies, and therefore we did not previously include this. We agree that this mention will make for a good addition to the section. The following has been added:
“Another use of hydrogels for cell delivery is microencapsulation of a number of cells [12]. This method can be more demanding than bulk delivery, since the cell suspension and hydrogel is often electrostatically sprayed together to form microcapsules. Another method of encapsulation is emulsion, where the cell suspension is simply mixing cell suspension with hydrogel and oil. This is an inexpensive method, but with a low degree of control over capsule size which makes it unsuitable for clinical production without extensive optimization. An increasingly popular method of overcoming the need for electrostatic spraying is to encapsulate the cells by microfluidics. This provides precise control of microcapsule size and number of cells, even down to single-cell encapsulation. The use of microfluidics is more feasible to implement as part of GMP production, as well as provide a great degree of control over the final cell-hydrogel product. The specific microfluidic system depends on the hydrogel and cross-linker used, and will need to be optimized for the cell type of interest, since factors such as nozzle size affect cell viability and function. None of the recent studies included in Table 2 used microfluidics for encapsulation.”
Comment
For the next paragraph on single cell coating, why do we have to freeze any time?
Answer
This was meant as the most feasible way of applying coating to the treatment, if the treatment is allogeneic. It could also be applied immediately prior to treatment, and this has been added with the sentence:
“For cryopreserved allogeneic treatment, this either require the coating to be freezable, or pre-treatment mixing with the freshly thawed cell product in a sterile environment.”
Reviewer 2 Report
In the manuscript entitled “Injectable hydrogels for improving cardiac cell therapy – In vivo evidence and translational challenges”, Hoeeg and coworkers reviewed latest injectable hydrogel researches for delivery of cardiac cell therapy. This review contains recent literatures, and potential roadblocks for clinical translation and recommendations for future research, and is well presented. I have only few minor editing suggestions as described below:
- Page 8-11, Table 2: please define the abbreviation “VPM”.
- Page 14, line 443: Although electrospray may be one of the most commonly used techniques for encapsulating cells, there are other techniques such as microfluidics and emulsification. Therefore this sentence should be modified accordingly.
- In general, “crosslink” and “cross-link” have been used throughout the manuscript. It should be unified.
Author Response
We are pleased with the assessment from the reviewer, and have addressed the comments below and in the manuscript.
Comment
Page 8-11, Table 2: please define the abbreviation “VPM”.
Answer
This has been added in the table legend.
Comment
Page 14, line 443: Although electrospray may be one of the most commonly used techniques for encapsulating cells, there are other techniques such as microfluidics and emulsification. Therefore this sentence should be modified accordingly.
Answer
We agree with the reviewer, and have included the following text in the section:
“Another use of hydrogels for cell delivery is microencapsulation of a number of cells [12]. This method can be more demanding than bulk delivery, since the cell suspension and hydrogel is often electrostatically sprayed together to form microcapsules. Another method of encapsulation is emulsion, where the cell suspension is simply mixing cell suspension with hydrogel and oil. This is an inexpensive method, but with a low degree of control over capsule size which makes it unsuitable for clinical production without extensive optimization. An increasingly popular method of overcoming the need for electrostatic spraying is to encapsulate the cells by microfluidics. This provides precise control of microcapsule size and number of cells, even down to single-cell encapsulation. The use of microfluidics is more feasible to implement as part of GMP production, as well as provide a great degree of control over the final cell-hydrogel product. The specific microfluidic system depends on the hydrogel and cross-linker used, and will need to be optimized for the cell type of interest, since factors such as nozzle size affect cell viability and function. None of the recent studies included in Table 2 used microfluidics for encapsulation.”
Comment
In general, “crosslink” and “cross-link” have been used throughout the manuscript. It should be unified.
Answer
This has been unified.
