On 2023-12-16 09:35:20, user disqus_mtg7x7eXMb wrote:
In the previous comment (mtg7x7eXMb) posted on September 29th 2023 [1] to the earlier version of this manuscript (September 8th 2023, [2]), that can be found by clicking on the previous version of the Kim et al preprint https://www.biorxiv.org/con... , it was suggested that when increases in radiotracer uptake (SUV) in a given organ are accompanied by increases in radiotracer concentration in the plasma, it is necessary to adopt mathematical modeling techniques to extract the specific component from the non-specific component of the Time-Activity-Curves (TAC), in order to generate an estimate of the binding potential BP (the latter defined as the product of the ligand affinity (KA) and the molarity of the gp120 receptors in tissues (R0)). The modeling work by Mintun and colleagues in the early 80s shows that increases in probe uptake in the blood without changes in binding potential, leads to increases in SUV in the tissues but not to an increase in the ratio of the SUV in tissues over the SUV in the blood (relative-SUV). In other words, if an increase in SUV in a given organ takes place concomitant to an increase in SUV in the blood without changes in the ratio, the latter points to a fully non-specific component of the increase in SUV uptake in that particular tissue. The reason for my suggestion was because the images of the manuscript [2] clearly showed that increases in probe uptakes in several tissues were concomitant to an increase in blood pool activity uptake (which could be obtained through an ROI placed on the aortic outflow tract, which closely follows the uptake of the Heart, and that we will call, for simplicity in this document, as Heart SUV or blood-pool-activity BPA SUV), although the BPA SUV levels were not reported in the earlier version. <br />
On November 17th, the authors posted a new version of the Kim et al. pre-print [2], in which they have now disclosed in Supplemental Figure S3B and S3C the SUV of the Heart as well as the SUV of other organs normalized on the SUV of the Heart. Other criticisms in the previous September 29th comment [1] were also addressed by the authors who made several changes in their previous 2022 publication Samer et al. [3] (with respect to which, the current pre-print [2] is a follow up study) first on November 8th (by posting new supplementary files to modify videos, the fourth based on History Versions)) and later on November 22nd through an erratum corrige posted by the JCI-Insight. <br />
Through these corrections, the authors agreed that video 5\Figure 3F and video 8 of the previous versions (up to November 8th) of the Samer et al. [3]were incompatible, hence that there is no evidence of increase in probe uptake (post Galunisertib administration) in the Heart of any of the seven imaged animals; they also realized that the correct scale used to display the images of the 2022 publication was 0-1.0 SUVwb not 0-1.5 SUVwb like stated in the earlier versions (consistent with the content of the earlier September 29th comment [1]). See more under note z-1. <br />
The reason why the scale-correction does not show up in the erratum corrige published on November 22nd on the JCI-Insight website, is because the scale had been originally disclosed only in the legend of the supplemental material files, but not on the Figures or legends or text of the main paper, but changes in supplemental material are in general allowed without an erratum corrige, the latter being the only editorial tool that can keep track of the changes made in each version. This is a policy followed by some scientific journals, but its rationale is not clear to me as it seems to go against enhancing transparency in scientific publishing. <br />
Indeed, this change from 1.5 down to 1.0 seems relevant, because the new scale highlights a new concern about the images published in the 2022 [3] (which we now know that it displays images with scale 1.0) and the 2023 articles [2] (which displays images with scale 1.5, not 1.0). The baseline images (images acquired before the first Galunisertib administration) in the 2023 pre-print [2] reveal evidence of higher uptake in the heart compared to the images published in the 2022 paper [3]…the hearts appear more greenish in the 2023 pre-print Figure 2A\S1 Nov 17th version [2] and more blueish in the 2022 paper Figure 3 [3]. This difference is even more evident after we have now been informed that the SUV scale used to display images of the 2022 publication [3] is 1.0 and not 1.5. In other words, the two studies [2, 3], based on the newly corrected SUV scales, are showing clear evidence of differences in half-life of the radiotracer circulating in the plasma of the animals at 24 hr post radiotracer injection (higher Heart uptake (BPA) means longer half-life of the radiotracer). Could biophysical differences of the radiotracers used in- the 2022 and 2023 papers explain these seemingly different half-lives?
Moreover, the new Figures S3B and S3C of [2] show that, as opposite to the absolute SUV levels, the relative-SUV levels are not statistically significantly increased at the later cycles of the Galunisertib administration, which confirms the weakness of the SUV mathematical operator, alone, in highlighting areas of specific uptake (a notion that resonates with a popular paper in nuclear medicine literature: SUV, standard uptake or Silly Useless Value…? ). In absence of dynamic modeling of the TAC(t), the latter evidence points to a fully non-specific uptake of the probe in those organs for the reasons explained above, hence, additional validation techniques (discussed in the previous comment [1]) would need to be provided before claiming again, as we read in the conclusion of the new version of the pre-print, that this dataset ”demonstrates that the Galunisertib-driven increases in SUV were mostly specific, ..(and with the new data presented as) consistent with previous studies validating the specificity of the PET signal for areas of enhanced SIV replication in gut and lymph nodes(Santangelo et al Nature Methods 2015 [4], Santangelo et al Mucosa Immunol. 2018 [5] and Samer et al JCI-Insight 2022 [3])”, i.e. before concluding that the new data supports the three previous non-human primate studies that fueled the rationale of the current pre-print study, and whose reproducibilities were questioned in the September 29th comment [1].
In my opinion, the three earlier nonhuman primate studies [3-5] and the new corrections made by the authors after the September 29th comment [1] reveal a possible common denominator that I will try to articulate in the next lines.
The first two nhp studies (Santangelo et al. Nature Methods 2015[4] and Santangelo et al. Mucosa Immunol 2018[5]) showed increase in the anti-env probe uptake of the blood pool (heart, BPA) of SIV infected animals, but the SUV levels of organs normalized on SUV levels of the Heart were not presented in those studies either. Based on the mean levels described for instance in Figure 1G of [4], the average increase in SUV in LNs of SIV infected animals compared to uninfected control is lower than the average increase in SUV of the Heart, hence the ratios (SUV of LNs over SUV Heart= BPA, relative-SUV) will most likely be lower or unchanged in the infected animals compared to the uninfected animals in both publications, which again points to a fully non-specific nature of the increase in uptake seen in those organs of the infected hosts. <br />
With respect to the third 7d3 study [3], as discussed in the September 29th comment [1], the images of the seven animals published in that 2022 article before and after Galunisertib administration show that the increase in uptake post-Galunisertib can be, in principle, fully explained by non-specific uptake of the probe. Specifically, the increase in uptake in LNs could well be explained by unintentional subcutaneous administrations of the probe (as visible in the post-Galunisertib images, but not in the pre-Galunisertib images). The main reason for my conviction that those uptakes are not related to binding of the probe to the gp120 is that increases in probe uptakes post-Galunisertib are seen only in the clusters of lymph nodes close to those injection sites that show evidence of subcutaneous injection of the probe but they are not seen in other clusters of lymph nodes (and with the latter unintentional mistake made, coincidentally, only for images acquired post-Galunisertib administration). This evidence, alone, should be sufficient to present the extravasation due to an unintentional subcutaneous injection of the probe as a reasonable explanation for the observed increases in LNs probe uptake post-Galunisertib, as further articulated in that comment [1]. The latter, in conjunction with other evidence in antibody imaging literature cited and articulated in the previous comment [1], points also to a non-specific nature of the probe uptake in gut seen in some of the imaged animals post-Galunisertib administration. Another reason for my conviction, as also articulated in the previous comment, is that higher doses for longer period of administration in the 2023 study [2] did not produce in any of the 8 animals (after cycles 1) those high probe uptakes seen in the 2022 paper [3] (in which only one cycle was administered in most animals). <br />
To recap, none of the 7 animals of the Samer et al. 2022 paper [3] showed evidence of increase in the (absolute) SUV of the Heart, and there are reasons to believe that the increases in probe uptakes seen in LNs and the gut of the same paper are fully non-specific. This is similar to what the authors reported following the first cycle of the Galunisertib in the 2023 Kim et al. pre-print [2], in which , in fact, no statistically significant increases in absolute SUV levels were found in any tissue compartment, nor in the heart. So, the Samer et al.[3] images and the images of the first cycle in the Kim et al. pre-print [2] show whole-body biodistribution properties that are different from those seen in the images of the 2015 and 2018 monkey studies [4, 5] as well as in the later cycles of the 2023 pre-print study [2] in which animals showed increase in absolute SUV levels in tissues concomitant to increase in SUV levels of the Heart.<br />
In other words, if we agree that the increases in uptake in the LNs of the anti-env probe in Samer et al 2022 paper [3] would not be visible in those published images, had the needle of the i.v. injection been properly inserted into the vein, the common denominator of all these studies is that the SUV levels increase in the tissues only in animals in which the SUV levels of the heart also increase. <br />
A well posed question seems: what could cause changes in SUV levels of the heart?<br />
In general, as anticipated above, higher SUV levels in the heart, or blood pool activity, means longer half-life of the radiotracer. Factors that could lead to increase in half-life of radiolabeled antibody\F(ab’)2 fragments include changes in isoelectric point , changes in the molecular weight of the radiotracer, level of dissociation of the radioisotope in the preparation or in vivo. Radio-HPLC analysis of the radiolabeled compounds could help to exclude that changes in preparations of the radiotracers are behind changes in probe uptake of the Heart at 24 hr (for the [3] and [2]) or at 36 hr (for [4, 5]) post radiotracer injection.<br />
In the Samer et al [3] or in the new pre-print ,[2], based on what we read in the Methods sections, no pegylation was performed. But the latter was performed in the earlier two anti-env imaging studies [4, 5] . Pegylation can, in principle, change molecular size, isoelectric point, clearance, half-life of a modified probe….<br />
The letter “p” is not defined in the article [3] but based on this PhD thesis online https://www.proquest.com/do... or the website www.resourcenhpir.com of the program that distributes these probes, it indicates the primatized version of the murine 7d3. <br />
Not only the new probe is a F(ab’)2 fragment, but it is based on a primatized version of the 7d3 (not on the murine intact IgG1 version used in the earlier two studies [4, 5]) and, for the reasons discussed above, it appears that it was not pegylated. Given all these differences, it would help not only to provide evidence that its binding affinity is retained but also that the product is stable and most of the radioactivity in the product is explained by the radiolabeled protein, including in vivo. These data were not provided in any of the five monkey imaging studies so far in literature (by including in this count the 2023 pre-print), produced from the same imaging team, claiming the feasibility of imaging the virus in vivo using anti-env radiolabeled probes and nuclear medicine cameras [2-6] .
Moreover, the whole-body radiotracer retention could, in principle, highlight other differences in the preparations of the radiotracers. Indeed, the evidence that with SUV scale =1, most images of the 2022 papers reveal a liver that is green and some animals a kidney that is also green (hence with an SUV less than 1, because to be 1 or above 1 the organ must be red when displayed on a rainbow scale 0-1), suggests that there is quite low radiotracer retention in the body at only 24 hours post radiotracer injection. Why the radiolabeled fragment clears out of the body so fast?<br />
So, If the images have been correctly reconstructed with proper decay correction, it appears that the SUV levels in the whole-body are much lower than one would expect at baseline with a F(ab’)2 radiolabeled protein. This could happen for instance if the radionuclide dissociated early post radiotracer injection, and would be immediately excreted from the body without leaving traces of it. Only dynamic and serial imaging during the first 24 hours could highlight this phenomenon. If that is the case, i.e. if a high significant portion of the injected dose is excreted soon, QC data for each radiosynthesis would need to be carefully reviewed.
Note-z1.<br />
Note, while changes were made on November 8th in Figures and Supplemental material files of the Samer et al 2022 [3] paper, the main text is, for some reasons, still left unchanged, which would make the reading of the article very difficult (given the changes made in some of the Figures and video links), for instance there is still reference to video 9 or reference to changes in the heart, NALT and spinal chord of A14X004…. <br />
A new link has been however added to the JCI-Insight Samer et al [3] called Supplemental data-2 https://insight.jci.org/art... , highlighting the corrections that need to be made to the main text to make it compatible with the new changes made on the Figures as well as on the Supplemental Figures\Videos, although the reason for this unusual editorial format (changes to the main text reported in a supplemental material link rather than directly on the main text of the paper online) is unclear.<br />
The erratum corrige https://insight.jci.org/art... added by the Editor states : “ Figure 3F and Supplemental Video 5 were incorrectly scaled by the analytical software due to an input error”, and “In the online version, Supplemental Video 5 has been updated. The original Supplemental Video 8 showed the correct scaling of animal A14X004 and has been removed to avoid redundancy.”;<br />
In my opinion, however, it is not correct to state that the original Supplemental Video 8 (published on November 2022, up to November 8th 2023 version) showed the correct scaling of animal A14X004, because it was stated, up to the version preceding the November 8th 2023 version, that the scale was 1.5 not 1.0, consistent with the content of the September 29th comment [1]). So to enhance transparency a more appropriate explanation seems the following “The original Supplemental Video 8 of animal A14X004 was displayed with a lower scale than the one stated in the earlier version, like it was the case for the images of all other animals in the previous version of the paper, but Video 8 has been removed in the new version to avoid redundancy with Video 5\Figure 3F”.<br />
Even the latter explanation for the erratum corrige would not be sufficiently clear to the readers that have not read the previous versions. As explained above and in the earlier comment, [1], the video 5 and video 8 were dual representations of the same animal (A14X004) displayed with different SUV scales, because the objective was to highlight small differences in low levels uptakes between baseline and post-Galunisertib administration in organs, like the gut, that could not be well visualized by keeping all the organs in the same field of view with a low SUV scale. After the erratum corrige, one would still expect to be able to appreciate those differences (e.g. increase in gut uptake) with the earlier dual representation, which now is missing. Indeed, it is not possible to appreciate such differences in the gut of the new Video 5. In other words, the two representations did not seem “redundant”, because the original dual representation was an attempt made to convey a new information about the whole-body biodistribution of A14X004. <br />
Note, the corrigendum also states : “Data from baseline (BL) and post-galunisertib weeks 1 and 2 (W1/2) were compared using Wilcoxon matched pairs nonparametric test, and the differences were nonsignificant with α > 0.05. The authors regret the errors.”<br />
However, there seems to be no explanation in the Methods section on how the SUV data are treated for animals that were imaged at both week 1 and week 2, and what statistical analyses were run (Wilcoxon or a mixed-effect model with the Holm-Šídák multiple comparisons test?). Finally, the removal of the NALT SUV analysis in the new version is a bit surprising, because, although there is evidence of PET and CAT misalignment for this animal, the latter is visible only at week 2, so it is not clear why baseline and week 1 SUV analysis of the NALT were also removed from Figure 3H. <br />
Note, as stated elsewhere in this document, that while the text of the 2022 Samer et al. paper is still unmodified, the Figures and videos have been all updated. However, the PMC link version of the paper https://www.ncbi.nlm.nih.go... still shows the older video 5 (scaled 0-0.3) and the older video 8 (by mistake placed in the video 1 link, now the new video 5 of the new version post-erratum-corrigendum of the Samer et al. 2022 JCI Insight publication [3]) or the older Figure 3H.
Note, that Supplementary Figure S8 and video 8 of the new version ( JCI-Insight on November 22 2023 to the Samer et al 2022 [3]) still show rainbow scale 1.5, not 1.0 as stated in the new legends. Changing the scale from 1.5 down to 1.0 would further increase those red levels on the images for this “control” animal and highlight (although with n=1 only) potentially important differences in whole-body biodistribution of the isotype matched pIgG1 control (whose catalogue number or chemical nomenclature is missing in both papers [2, 3]) compared to the anti-env probe, not explained by its affinity to an irrelevant antigen.
Finally, we read in Samer et al 2022 [3]“Two additional rhesus macaques, A8L057 and 08M171, were infected with SIVmac239M2 …and used as controls for, respectively, Supplemental Figures 8 and 9 at, respectively, weeks 56 and 32 postinfection” ; 08M171 is also an ID in the 2023 pre-print [1]. This looks an editing mistake, the descriptions of the infection timeline for 08M171 in the two publications are indeed incompatible.
- mtg7x7eXMb, comment to Kim, ...Villinger, Martinelli BioRxiv September 8th 2023. 2023.
- Kim, J., TGF-β blockade drives a transitional effector phenotype in T cells reversing SIV latency and decreasing SIV reservoirs in vivo. 2023.
- Samer, S., et al., Blockade of TGF-beta signaling reactivates HIV-1/SIV reservoirs and immune responses in vivo. JCI Insight, 2022. 7(21).
- Santangelo, P.J., et al., Whole-body immunoPET reveals active SIV dynamics in viremic and antiretroviral therapy-treated macaques. Nat Methods, 2015. 12(5): p. 427-32.
- Santangelo, P.J., et al., Early treatment of SIV+ macaques with an alpha(4)beta(7) mAb alters virus distribution and preserves CD4(+) T cells in later stages of infection. Mucosal Immunol, 2018. 11(3): p. 932-946.
- Obregon-Perko, V., et al., Dynamics and origin of rebound viremia in SHIV-infected infant macaques following interruption of long-term ART. JCI Insight, 2021. 6(23).