While I agree that Fig 3 is an interesting observation and to the authors credit they have doubled the number of mice since the original report (making it less likely that a statistical fluke is involved) you will have to help me understand how the only interpretation of this is an immune effect, rather than a simple effect of angry macrophages or a method artifact from the theoretical metastatic model?
In Fig 5 the mice were treated with IL PBS or IL PV-10, and splenocytes isolated from the two treatment groups (page 3, second column, paragraph 3)......."To determine whether B16-specific T cells were induced after injection with PV-10, mice bearing B16 tumor were treated on day 7 with a single IL injection of 50 mL PBS or PV-10. One week later, spleens were collected and splenocytes were restimulated with B16 or MC-38 cells.”
These isolated splenocytes were then exposed to either MC-38 or B16 cells to determine if the splenocytes would recognize tumor cells in the test tube. The INF response to B16 vs MC-38 cells confirmed tumor specificity of the T cell response following PV-10 treatment (comparison of 5A and Fig 2 illustrates that IFN is a poor overall marker for PV-10 induced splenocyte immune activation)
The next step was to determine whether T cells would go on to kill the tumor cells they encountered in the test tube (pg 3, column 2, para 4 “Next, we measured the ability of T cells in splenocytes to lyse B16 cells. As shown in Figure 5B…” ). What the data in 5B shown us (splenocyte mediated killing of tumor cells in a test tube) is that over 50% of the PV-10 initiated in vitro killing is seen when animals were treated IL with PBS. This PBS killing rate is greater than base line killing rates (seen when splenocytes are exposed to the non-target tumor line MC-38). Conversely, the study in Fig 3 would have been enhanced if a separate group of animals had been studies in which the lungs of B16 skin lesion mice had been populated with MC-38 cells, to confirm the B16 specificity of the observed in-vivo response after IL-PV-10 treatment.
It is interesting that the apparent bystander effect for breast cancer (Fig 1a) is smaller than the effect in Fig 3b (but more in line with clinical data in MM), suggesting that the mouse lung data may be artificial.
I recognize what the authors are telling you Fig 3 means, but their mechanistic explanation is inconsistent based on the data provided, and the key studies that would clarify these questions are missing. IMO the present studies were designed with the end in mind, not as a true discovery process.
Again, these are likely reasons that the data is not published in a main stream immunology or oncology journal.
Hope that helps clarify the paper a bit |
