I don't think that the WTS will be in favour of this kind of "synthetic blood".
They will say that it is prohibited because the source that is used to make the product is human blood.
As far as stem cells go, Jehovah's Witnesses have been treated with stem cell transplantation for years already.
For example, in 2004, the American Society of Clinical oncology published a study that treated 26 Jehovah's Witnesses with autologous stem cell transplantation.
Autologous Stem-Cell Transplantation Can Be Performed Safely Without the Use of Blood
Purpose Autologous stem-cell transplantation has been shown to be a curative procedure for a variety of leukemias and lymphomas. Most transplants require RBC and platelet support. We report the ability to perform autologous transplantation without blood-product support.
Subjects and Methods In this study, we treated 26 patients with religious objection to blood products with autologous stem-cell support without the use of any blood products. Patients received a combination of granulocyte colony-stimulating factor (G-CSF), erythropoietin, and interleukin-11 or G-CSF alone to mobilize stem cells. Post-transplant patients received intravenous iron, erythropoietin, G-CSF, and epsilon aminocaproic acid.
Results There were two major bleeding complications (8%), with two treatment-related deaths (8%). There were three minor bleeding complications (12%). The median fall in hemoglobin level was 4.7 g/dL; the median hemoglobin level 30 days after transplantation was 9.2 g/dL. The median total number of days with platelet count less than 10 × 109/L was 4 days; the median days to platelet recovery greater than 20 × 109/L was 12 days.
Conclusion Autologous stem-cell transplantation can be performed safely without the use of any blood products.
And a 2015 study published in the same journal:
It appears that as long as the stem cell treatment does not use blood as a source, stem cell transplantation is not prohibited for Jehovah's Witnesses.
bafh: So technically, they are "manufactured" in that they came from a lab - but they are still blood cells. So my vote is they don't allow it even if it didn't come from a person or animal.
Hemopure, the synthetic blood (oxygen carrier/blood doping agent) made from bovine blood, is manufactured in a lab. Hemopure has WTS approval.
This one won't pass simply because the source is human blood. (and it might have something to do with the JWs who have interests in Hemopure).