What are the side effects of a blood and bone marrow transplant?

Hopefully none...: The most feared side effect from what you posted is rejection! hopefully with the proper medical regimen this will not occur; then one has to consider the potential side effects of the anti-rejection meds...It gets complicated. Best of luck!

There are many: It depends on the type of transplant. If you get your own cells (autologous) there is no risk of rejection and no need for rejection medicines but there can be nausea, diarrhea, mouth sores and others. If you get donor cells (allogeneic) you often need immune suppressing meds and there are many more side effects including graft-versus-host disease where the immune system attacks your body.