Specialized Blood component; How special are they?

I. LEUKOREDUCED RBCs:
Leukocytes are unwanted components in PRBC(packed red blood cells) and Platelet units. However some patients need Leukocytes transfusion in the form of Granulocytes transfusion , this topic will not be discussed here in this blogpost.

Donor leukocytes are not wanted because they causes:
(1). FNHTR (Febrile non- Hemolytic Transfusion Reaction)
(2). TAGVHD (Transfusion Associated Graft versus Host disease)
(3). HLA Alloimmunization
(4). CMV infections

On an average 1 unit of PRBC contains 2×10⁹ leukocytes.
However the standards differ from country to country. So it is worth noting that, In US, the desired Leukocytes per 1 unit of PRBC should be less than 5×10⁶, whereas in Europe, the desired Leukocytes in 1 unit of PRBC should be less than 1×10⁶.
In order that the PRBC unit will have reduced HLA Alloimmunization and reduced CMV infections, leukocytes count in such PRBC Leukoreduced units must be less than 1×10⁶.
Nowadays all blood banks around the world get to use Leukoreduced Filters which are very much beneficial to the patient.

II. WASHED RBCs AND FROZEN/DEGLYCEROLIZED RBCs:
Washing of PRBC is done by Normal Saline which is washed in the Blood Centre.

The question is why do we need to wash PRBC? The reasons are given below:
(i). Some individuals lack IgA( immunoglobulin A) in their body.These individuals are known as IgA deficient individuals. Such individuals develops anti-IgA antibodies in their serum . Such individuals if they need blood transfusion, RBCs has to be washed so that IgA in the blood unit along with plasma proteins will be removed .This done primarily to prevent allergic reaction.

(ii)For storage of:
(1). Autologous blood and
(2). Storage of Rare blood group units

In both of the above conditions PRBC units are stored by freezing them. Freezing of RBCs allows long term storage .Such units are glycerolized prior to storage.
When it is time to use , RBCs are deglycerolized before using by washing these PRBC units.

III. CMV NEGATIVE CELLULAR BLOOD COMPONENTS:
CMV(Cytomegalovirus) is carried in latent form or infectious form in neutrophils and monocytes. That is why leukoreduction is important to prevent CMV transmission. So transmission of CMV infected blood units causes transmission of CMV. CMV infection is reduced by using leukoreduction filters or by providing CMV negative blood to the patients.
Leukoreduced blood components, or CMV negative blood components are indicated for recipients who are CMV negative or patients who are at risk for severe sequelae of CMV infections.
It is given mostly in CMV negative pregnant women for benefit of the fetus.
It is also given in recipient of CMV negative Bone marrow, or HPSC transplant, also given in premature infant weight, which is less than 1200 grams.

IV. IRRADIATED CELLULAR BLOOD COMPONENTS:
Irradiation of cellular blood components is done only if the following three conditions are there:
Transmission or transplantation of immunocompetent T cells.
The patient is immunocompromised.
Histocompatibility differences between graft and recipient, (major or minor HLA or histocompatibility antigen).
After bone marrow or HPSC transplant, GVHD may occur and this affects the skin, the gut and the liver.

What is TAGVHD(Transfusion Associated Graft Versus Host Disease)?:
When cellular blood components are transfused, and if the component has viable T lymphocytes, this causes TAGVHD, it has got a very high mortality rate.
How do we prevent TAGVHD?
Gamma radiation, 2500 to 5000 centigray of the cellular blood components. Higher dose is more effective, but this higher dose may damage the RBCs.
Irradiation decreases, or it may eliminate the mitogenic or the blastogenic capacity of the transfused T cells, which will render it immuno incompetent .

People who are at risk of getting TAGVHD are:

(1). congenital immunodeficiency, like in case of severe combined immunodeficiency, Di George syndrome, Wiscott Aldrich syndrome.
(2). Hodgkin lymphoma.
(3). Bone marrow transplant, either allergenic or autologous,
(4). Intra uterine transfusion of fetus

(5). Exchange Transfusion

(6). Transfusion of blood from first degree relatives
(7). Transfusion of HLA matched Platelets

Why do TAGVHD occur if the donor is a first degree relative?

TAGVHD can occur if the donor is a first degree relative, and then recipient is either immunocompromised or even immunocompetent sometimes. What is the reason behind ? The related donor is most of the time homozygous for one of the recipient’s HLA haplotype, so the recipient is incapable of rejecting the donors T lymphocytes. Because of that, this this leads to the donor T lymphocytes getting engrafted. And this engrafted donor T lymphocytes act against the HLA antigens encoded by the recipient’s other haplotype leading to the Donor lymphocytes rejecting the recipient.

How can TAGVHD be prevented?
TAGVHD is prevented by Irradiation and not by leukoreduction .