It is possible to prevent most viruses by recoding the human genome (requires embryo engineering or pre-embryo engineering) to use alternate codons that existing natty viruses don't use. This wouldn't prevent synthetic viruses from being developed that use the alternate codons, of course. See (1) https://diyhpl.us/wiki/transcripts/hgp-write/2016-05-10/ultr... and (2) https://diyhpl.us/wiki/transcripts/hgp-write/2017-05-09/ultr... and (3) https://x.com/RokoMijic/status/1720875112541364535 for some background.

As for "curing cancer", I suspect that Anthropic or OpenAI will use their high status/reputation to launder the existing solutions (germline, p53, enhanced DNA damage repair pathways, higher tumor-suppressor-to-oncogene copy number, more robust tumor-suppressor networks, more self-anti-cancer apoptosis, CD47 suppression, etc) that society has refused to accept. They might have enough reputation to get people to look at these ideas. It won't cure people with stage 5 turbo-cancer a.k.a the walking dead, but hopefully we won't be moving the goal posts _that_ much on them.