We’re not talking about xenotransplantation of living tissues though. I appreciate that. I did have the idea that the stringency of the washes in decellularization wouldn't be enough to get rid of viruses. Looked into it and it turns out that might not be true. Washing might be enough: https://www.ncbi.nlm.nih.gov/pubmed/12115437

Not sure how compatible this is w/ the protocol used in the OP.