A pair of congenic mice for imaging of transplants by positron emission tomography using anti-transferrin receptor nanobodies
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eLife Assessment
In this innovative study, Carpenet C et al explore the use of nanobody-based PET imaging to track proliferative cells after in vivo transplantation in mice, in a fully immunocompetent setting. The development of a unique set of PET tracers and mouse strains to track genetically-unmodified transplanted cells in vivo is an important novel asset that could potentially facilitate cell tracking. The evidence provided is compelling as the new method proposed might facilitate overcoming certain limitations of alternative approaches, such as full sized immunoglobulins and small molecules, while the specific claims would gain further support by additional experimentation and methodological details.
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Abstract
Two anti-transferrin receptor (TfR) nanobodies, V H H123 specific for mouse TfR and V H H188 specific for human TfR (huTfR) were used to track transplants non-invasively by PET/CT in mouse models, without the need for genetic modification of the transferred cells. We provide a comparison of the specificity and kinetics of the PET signals acquired when using nanobodies radiolabeled with 89 Zr, 64 Cu and 18 F. We used a knock-in mouse that expresses a TfR with a human ectodomain (huTfR +/+ ) as a source of transplants into C57BL/6 recipients and show that V H H188 detects such transplants by PET/CT. Conversely, C57BL/6 transplants into huTfR +/+ recipients can be imaged with V H H123. In C57B/6 mice impregnated by huTfR +/+ males we saw an intense V H H188 signal in the placenta showing that TfR-specific V H Hs accumulate at the placental barrier but do not enter the fetal tissue. The model presented here can be used to track many transplanted cell types by PET/CT, provided cells express TfR, as is typically the case for proliferating cells such as tumor lines.
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Author response:
Reviewer #1 (Public review):
Summary:
The topic of nanobody-based PET imaging is important and holds great potential for real-world applications since nanobodies have many advantages over full sized immunoglobulins and small molecules.
Strengths:
The submitted manuscript contains quite a bit of interesting data from a collaborative team of well-respected researchers. The authors are to be congratulated for presenting results that may not have turned out the way they had hoped, and doing so in a transparent fashion.
Weaknesses:
However, the manuscript could be considered to be a collection of exploratory findings rather than a complete and mature scientific exposition. Most of the sample sizes were 3 per group, which is fine for exploratory work, but insufficient to draw strong statistically robust conclusions for …
Author response:
Reviewer #1 (Public review):
Summary:
The topic of nanobody-based PET imaging is important and holds great potential for real-world applications since nanobodies have many advantages over full sized immunoglobulins and small molecules.
Strengths:
The submitted manuscript contains quite a bit of interesting data from a collaborative team of well-respected researchers. The authors are to be congratulated for presenting results that may not have turned out the way they had hoped, and doing so in a transparent fashion.
Weaknesses:
However, the manuscript could be considered to be a collection of exploratory findings rather than a complete and mature scientific exposition. Most of the sample sizes were 3 per group, which is fine for exploratory work, but insufficient to draw strong statistically robust conclusions for definitive results.
We thank reviewer #1 for the review of our work. We appreciate reviewer’s #1 comment on our intent to publish our results in the most transparent fashion, which is the case. We would point out that due to the technical challenges and cost of generating all the different nanobody-radiometal tracer conjugates, we included 3 repeats per group, which is the minimum required to perform statistical comparisons. We plan to add additional controls to the manuscript that were not initially included to limit the length of the manuscript. These additional controls will lend more weight to our conclusions.
Reviewer #2 (Public review):
Summary:
This is a strong and well-described study showing for the first time the use and publicly available resources to use a specific PET tracer to track proliferating transplanted cells in vivo, in a full murine immunecompetent environment.
In this study the authors described a previously developed set of VHH-based PET tracers to track transplants (cancer cells, embryo's) in a murine immune-competent environment.
Strengths:
Unique set of PET tracer and mouse strain to track transplanted cells in vivo without genetic modification of the transplanted cells. This is a unique asset, and a first-in-kind.
Weaknesses:
- Some methodological aspects and controls are missing
- No clinical relevance?
We thank reviewer #2 for their review of our work. We support reviewer’s 2 view on the strength of being able to track transplanted cells in vivo without the need of any sort of manipulation of the transferred cells. We plan to add additional controls to the manuscript that were not initially included to limit the length of the manuscript. These additional controls will lend more weight to our conclusions. We emphasize that although no clear clinical applications immediately derive from our studies, this work still offers better-suited tools for pre-clinical studies that require the ability to track transplanted cells in in vivo . We will resubmit a revised version shortly.
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eLife Assessment
In this innovative study, Carpenet C et al explore the use of nanobody-based PET imaging to track proliferative cells after in vivo transplantation in mice, in a fully immunocompetent setting. The development of a unique set of PET tracers and mouse strains to track genetically-unmodified transplanted cells in vivo is an important novel asset that could potentially facilitate cell tracking. The evidence provided is compelling as the new method proposed might facilitate overcoming certain limitations of alternative approaches, such as full sized immunoglobulins and small molecules, while the specific claims would gain further support by additional experimentation and methodological details.
-
Reviewer #1 (Public review):
Summary:
The topic of nanobody-based PET imaging is important and holds great potential for real-world applications since nanobodies have many advantages over full sized immunoglobulins and small molecules.
Strengths:
The submitted manuscript contains quite a bit of interesting data from a collaborative team of well-respected researchers. The authors are to be congratulated for presenting results that may not have turned out the way they had hoped, and doing so in a transparent fashion.
Weaknesses:
However, the manuscript could be considered to be a collection of exploratory findings rather than a complete and mature scientific exposition. Most of the sample sizes were 3 per group, which is fine for exploratory work, but insufficient to draw strong statistically robust conclusions for definitive results.
-
Reviewer #2 (Public review):
Summary:
This is a strong and well-described study showing for the first time the use and publicly available resources to use a specific PET tracer to track proliferating transplanted cells in vivo, in a full murine immunecompetent environment.
In this study the authors described a previously developed set of VHH-based PET tracers to track transplants (cancer cells, embryo's) in a murine immune-competent environment.
Strengths:
Unique set of PET tracer and mouse strain to track transplanted cells in vivo without genetic modification of the transplanted cells. This is a unique asset, and a first-in-kind.
Weaknesses:
-some methodological aspects and controls are missing
-no clinical relevance?
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