Hi @vanesasam and welcome to Mayo Connect.
Having a Allogenic bone marrow transplant does give you a completely new immune system. It takes cells from a donor, not your own cells. The goal of this is to allow the person who receives the transplant to now make healthy blood products. So they would no longer have sickle cell anemia.

However, people who have stem cell transplants can become infertile.
I found some information on Cancer.com which discusses this side effect of transplant. This is an excerpt from that article.

“Stem cell transplants and fertility
Most people who have stem cell transplants become infertile (unable to have children). This is not caused by the cells that are transplanted, but rather by the high doses of chemo and/or radiation therapy used. These treatments affect both normal and abnormal cells, and often damage reproductive organs.

If having children is important to you, or if you think it might be important in the future, talk to your doctor about ways to protect your fertility before treatment. Your doctor may be able to tell you if a particular treatment will be likely to cause infertility.”

From experience your blood type will most likely change to that of your donor, because, after all it is their marrow in your bones. It happened to me but I’m past childbearing age. I’ve mentored younger female patients in their late teens who’ve had eggs harvested and frozen for the future.

However, if you’re female and have sickle cell anemia. Those eggs would still be carrying the damaged DNA and most likely those eggs would not be useable. The same thing if you’re a male…the frozen sperm would still contain the defective DNA. If you’re male and your fertility wasn’t compromised by the pre-conditioning prior to transplant, then you might still able to father a child because you could produce new sperm when you recover. You’d have to have the sperm examined for its health.

Those would be good questions for the transplant team to see if this is a possibility for you if you went ahead with the transplant.
There can be trade offs for getting that amazing second chance at life. Are you scheduled for transplant?