The number of circulating CD34+ cells varies by individual, and by age.
I volunteered for an unstimulated collection when we were validating the process of stem cell collection at my work. I was at the upper limit of normal, but I technically had enough in CD34+ cells in my circulation to do a transplant even without stimulation, and I was in my early 30s at the time.
A single CD34+ cell can probably make a lot of RBCs. (Ok, to be pedantic, I'm not 100 percent sure they are really CD34+ cells, I was taught that CD34+ is a marker for myeloblasts, and the cell population you would probably want are the CD34- hematogones as they are self-replenishing. The article didn't seem to say either way).
Some can and do, but there are some challenges for it being a general solution:
- Some people don't know they need rare blood (because they didn't have the antibody at first, then found they had it later).
- Some people may donate blood to have it available for a need, then a need comes up (either themselves or someone else). At that point, the blood gets used up - what happens when the need is greater than the number of stored units?
- Some people may not be able to donate. We had a patient with something north of 9 antibodies who, due to sickle cell disease wasn't able to donate - (banking blood for long term storage requires freezing, which doesn't work with blood from patients with sickle cell disease).
> so they either need to take on the financial burden of flying to wherever their blood is needed or refusing to take on the financial burden and knowingly allowing someone to die.
Is that a real case or hypothetical? If real, I would like to explore further as it does seem rather inappropriate.
In my experience, the blood can be drawn locally and then sent to the recipient. That's also true for bone marrow & peripheral blood stem cell donations.
I would love to see more donor centers allow hemochromatosis patients to donate.
I think there is not actually regulatory ban. Last I looked into this, it was because of the conflict of interest - the FDA requires blood from donors with hemochromatosis be labeled as such.
And even that requirement can be worked around. See, for example, https://clinicalcenter.nih.gov/blooddonor/donationtypes/hemo.... Background, most centers charge for therapeutic phlebotomy but obviously not for volunteer blood donation. The exception is permissable if the center agrees to allow the patient's blood to be drawn for free, whether or not they would qualify as a blood donor.
The issue with "getting value" from donating is that people sometimes lie in order to be able to get that value. The downstream issues can be very painful -
I have personally taken care of patients who got HIV or hepatitis from blood transfusion. I am pretty sure any of them would emphatically agree it is important to ensure the blood supply is as safe as possible.
So it can be done, but it has to be done carefully.
There are more than 35 red blood cell groups (see https://www.science.org.au/curious/people-medicine/blood-typ... for a nice writeup). For each of those blood groups, there is more than one possible configuration of some protein or carbohydrate (something like more than one possible genetic sequence leading to more than one kind of molecule on the surface of the RBCs).
For the other blood groups, I think every case the groups were identified because a patient somewhere made an antibody, causing either a transfusion reaction (if not tested ahead of time) or, more likely, a positive (incompatible) reaction on in compatibility testing.
Each of those blood groups will have two or more versions. For example, there is the Kell blood group, which has two primary versions: you can express big K, little k, or both as Kell is a codominant system. Most people are homozygous little k (kk). When you are homozygous little k, you can make antibodies to big K (which is expressed on people who are Kk or KK). So, if you are homozygous little k, you are at risk of making antibodies on exposure to big K. Of course, not everyone is either big K or little k, that would be too simple. There are, I think, more than 20 variants of K out there...
More or less, each of those blood groups can cause antibody formation if you lack an antigen on the surface of those antibodies. In practice, the likelihood of an antigen causing antibody formation varies by antigen (the term there is "antigenic"). Also, the immunologic status of the recipient matters - obviously, someone who is immunosuppressed from an organ transplant may be less likely to form antibodies (that's the point of of the immunosuppression). Conversely, some people are more likely than most to form antibodies.
Also, it appears that the immune system is more likely to form antibodies in other blood groups if a person already has antibodies. In practice, there is a recommendation from NHLBI to match for C, E, and K in patients who are going to be transfused often to try to avoid forming new antibodies.
People 'naturally' form antibodies to A and to B antigens that they lack (I am group O and have both anti-A and anti-B antibodies). This is because they are exposed to those antigens in everyday life (the A and B antigen is found on some gut bacteria). And Rh-D is very immunogenic and clinically significant.
When we test blood prior to transfusion, we attempt to identify what antibodies the patient may have. If they have no unexpected antibodies, just honoring blood and Rh-D type is usually enough. If they have unexpected antibodies, we go through a complicated process to identify blood that lacks those antibodies to try to avoid a transfusion reaction.
(Now to modify that testing point, we know some antibodies are not clinically significant - that is, they do not cause significant transfusion reactions. So, we can, if we have to, give blood that is incompatible for clinically insignificant antibodies. We still try to provide blood negative for those antigens because we wouldn't find out this patient is the first to have a clinically significant version of the antibody. Also, the blood tests as incompatible with clinically insignificant antibodies, and we would prefer to give blood that tests as compatible).
Sorry this is rambling a bit - I have to take my daughter to school. Happy to expand/clarify/etc. when I can get back to it.
Source: I am a practicing physician board certified in "Blood Banking/Transfusion Medicine". My statements in this are still likely inaccurate, but hopefully in a useful way. I am not your lawyer, and I am not your physician.
Nice write up! I'm happy with the answer, but I'd not mind if you decide to expand it. Anyway, I think it would be more useful if you reply to other questions in this thread, but you already have been doing that. I'll upvote your comment, but this is one of the ocasiones when I'd like a x2 upvote.
Edit: If you don't mind a question: What do you [1] do with the people with big K that want to be blood donors? Ask them not to donate[2]? Do you tell them? Label the blood as big K and be more careful?
[1] "You" as the impersonal "you". I could have written "the system" or something more accurate.
[2] I guess they can donate. Otherwise they will be extremely unhappy.
[1,2]: Most people don't have antibodies, so big K+ blood is fine for most people (we worry about avoiding transfusing big-K positive blood into big-K negative people who will be transfused many times, such as somebody with sickle cell disease, it's not really a major issue for most people getting a rare transfusion).
So, K+ people are definitely allowed to donate. Also, there are people who have antibodies to little-k, and so they would actually need big-K homozygous blood.
When we need blood that is big-K negative, such as for a chronically transfused patient or one with antibodies to big-K, we try find units from people whose units were previously identified to be big-K negative. If they don't have any, the donor center can screen blood for them. We then verify compatibility with a crossmatch (reacting plasma from the patient with RBCs from the unit to make sure there is no reaction).
Remember there are lots of other blood types - big-K is one we have to match sometimes. Little-k is another. There are at least 70 altogether, so we can't really even try to match all of them. Even matching C, E, and K is straining the ability of the system to provide special antigen-negative blood.
It will be interesting to see what the long-term applications of lab-grown blood will be. I do worry about rare blood not being as available.
Right idea, but I think maybe you may have used the wrong word.
The donation is to get antibodies.
Antigens are are the stimulus that causes the body to form antibodies.
We give the Rh- mom antibodies so they bind to antigens on the blood from baby; the idea being that "hiding" the antigens from mom's immune system will prevent her from making her own antibodies.
I volunteered for an unstimulated collection when we were validating the process of stem cell collection at my work. I was at the upper limit of normal, but I technically had enough in CD34+ cells in my circulation to do a transplant even without stimulation, and I was in my early 30s at the time.
A single CD34+ cell can probably make a lot of RBCs. (Ok, to be pedantic, I'm not 100 percent sure they are really CD34+ cells, I was taught that CD34+ is a marker for myeloblasts, and the cell population you would probably want are the CD34- hematogones as they are self-replenishing. The article didn't seem to say either way).