For patients with immunodeficieny problems:

 

Why can't we harvest bone marrow stem cells, culture them and mass produce them so they divide infinitely (weren't stem cells suppose to be able to?). Then introduce various extra-cellular factors that allows them to differentiate into T-Cells, B-Cells, neutrophils, basophils, etc. and then re-introduce them into those patients with immunodeficiency problems? The MHC would still work effectively if the bone marrow stem cells were obtained from the same patient.

I can see that this wouldn't really work in leukemia, since it is already the proliferation of WBC's, however, wouldn't this approach work in a insulin-like manner by daily injections of those with a low WBC count?

Bone marrow stem cells aren't nearly as good as embryonic and cord blood.

But rakuenso brings up a good point. Even if we get stem cells from a fetus, couldn't we mass produce them to such a degree that we no longer need fetuses, bone maro, or cord blood? It's still an ethically questionable to get them from a fetus, but the problem is immensely mitigated by requiring (ideally) only one fetus.

Bone marrow stem cells aren't nearly as good as embryonic and cord blood.

 

But it doesn't matter because embryonic stem cells would have to differentiate into Bone marrow cells anyways

The original question depends on what th reason for the immunodeficiency is. Deliberate immunodeficiency for transplant victims would need to be maintained as the transpolanted part will still have a different histocompatibility from the rest of the body.

Patients with acquired immume deficiency won't be helped as the virus will attack immune cells from whatever source. Trying to eradicate the virus by a complete blood and bone marrow exchange has been tried but HIV is very good at hiding and this technique would not add anything.

In the case of congenital conditions such as SCID, either harvested bone marrow stem cells will have the same condition or the condition affects the deployment of activation and will affect the new cells as much as the old.

If the patient has lost his bone marrow, say through radiation, then a bone marrow transplant will be more effective as it will be quicker to have an effect.

 

In other words, this would be a solution, if a difficult painstaking and expensive one, to a problem that does not exist in isolation.

 

You have found a cure for which there is no known disease!