The document discusses severe combined immunodeficiency (SCID) caused by adenosine deaminase (ADA) deficiency. It notes that ADA deficiency accounts for 20% of SCID cases and is the most severe form, affecting both cell-mediated and humoral immunity. Without treatment, ADA-deficient individuals die from infections within the first year of life. The most successful treatments are bone marrow transplantation or enzyme replacement therapy with polyethylene glycol-modified bovine ADA.

1. ‫است‬ ‫آتشین‬ ‫بحر‬ ‫صد‬ ‫ه‬‫ر‬ ‫این‬ ‫در‬ ‫شبنمی‬ ‫هر‬
‫د‬‫ر‬‫ندا‬ ‫بیان‬ ‫و‬ ‫شرح‬ ‫معما‬ ‫این‬ ‫که‬ ‫دا‬‫ر‬‫د‬

2. ‫فرخی‬ ‫ف‬‫ر‬‫عا‬‫فرد‬
‫بهار‬92
Aref farrokhi
aarreeff@ymail.com

3.  1. primary
 innate diseases
 genes coding for immune system components
 2. secondary
 secondary immune disorders based on
primary cause

4. presence of underlying disease
 malignancy (malignancy)
 infection (e.g. HIV)
 malnutrition
 immunosuppresive drugs

5.  Antibody
 agammaglobulinaemia
 hypogammaglobulineamia
 deficit of specific antibodies
 deficit of isotype switch
 Cellular, combined
 severe combined (SCID)
 cytokine signalization
 T-cell receptor signalization
 recombination of T-cell receptor
genes
 purine metabolism
 expression of HLA molelules
 combined
 intercelluar signalization
 intracellular signalization
 cellular motility
 chemokine signalization
 transcription factors
 IFN gamma/IL-12 pathway
 Phagocyte
 number of phagocytes
 adhesion
 function (intracellur killiing)
 Complement
 particular components
 regulatory factors
 Malfunction of regulation
 cytotoxicity
 negative feedback
 apoptosis
 Syndromes with compromised
DNA repair

6. 70%
1%
20%
9%
humoral
cellular and
combined
phagocytic
complement

7.  SCID is a group of inherited disorders that
drastically compromises innate and
adaptive immune responses.
 disruption in the development of T cells.
 lack of B cell function.
 Without treatment, opportunistic
infections eventually cause death.
 Although there are 10 different types
that we know of, the two most common
are X-linked Severe Combined
Immunodeficiency (XSCID) and Adenosine
deaminase deficiency (ADA) SCID.
 SCID is estimated to occur in 100,000 to
500,000 births per year (Fischer, 2000). Retrieved from:
http://bio116.pbworks.com/f/1245522611/1245522611/chr2
1-22-X-Ysm.gif

8.  ADA mutations give rise to ADA SCID.
 A defective ADA protein will not be able to effectively detoxify metabolic products (e.g.
ATP, S-adenosyl homocysteine) of the purine salvage pathway. Thus, lymphocytes undergo
apoptosis (Kalman et al., 2004). This has an earlier onset than the other forms.
 IL-2RG mutations are associated with XSCID. A defective IL-2RG prevents activation of B
cells by Helper T cells (TH1). These mutations disrupt the gamma chain protein, which is a
common subunit for receptors for IL2, 4, 7, 9, and 15 (Cavazzana-Calvo, 2000).
 These help differentiation of T cells, B cells and NK cells.
Type of gene Abnormal
genes in SCID
patients
Cytokine-receptor
genes
IL-2RG, JAK3,
IL-7Rα
Antigen-receptor
genes
RAG1, RAG2,
Artemis,
CD3δ, CD3ε
Other genes ADA, CD45
Buckley, 2004

10. SCID-Severe Combined Immunodeficiency Syndrome
AMP
Adenosine
Inosine
H20
Pi
H20
NH3
Hypoxanthine
Nucleotidase
Adenosine deaminase*
ADA catalyzes the irreversible
deamination of adenosine to form
inosine, and of deoxyadenosine to
deoxyinosine.

11. N
N N
N
Ribose-P
NH2
N
N N
N
Ribose-P
OH
H2O NH3
AMP deaminase
N
N N
N
Ribose
NH2
Nucleotidase
H2O
Pi
HN
N N
N
Ribose
O
Adenosine deaminase
H2O NH3
Nucleotidase
H2O
Pi
Purine nucleoside
phosphorylase
HN
N N
N
H
O
may be reused
through
salvage pathway
Pi
Ribose-1-P
hypoxanthine
Degradation
of AMP

12.  Diagnosis is usually made at 6 months of age (Kalman et al., 2004).
 Before this time, newborns are relatively protected by the mother’s antibodies
in the colostrum.
 Frequent infections in babies include oral candidiasis (thrush) and persistent
diarrhea. Growth impairment and/or interstitial pneumonitis can also occur
(Fischer, 2000).
 They do not respond to usual therapy.
 SCID patients have recurrent viral, fungal, and bacterial infections that usually
occur in the respiratory tract and gut (Fischer, 2000).
 SCID patients often do not respond to the antibiotics used to treat bacterial
infections.
Oral candidiasisPneumonia
Diffuse rash in an
infant with ADA
deficiency.

13.  clinical symptoms
 early in life
 chronic diarrhea, failure to thrive
 graft versus host disease (on skin)
 complications after vaccination with live
vaccines
 unusual infections, severe course
 family history

15.  Adenosine deaminase (ADA) is an essential enzyme of
purine metabolism and is highly conserved throughout
phylogeny.
 investigations indicated that ADA deficiency accounts for
approximately 20% of cases of human SCID and that it is
the most severe of the immunodeficiency diseases,
affecting both cell-mediated and humoral immunity
(Buckley et al., 1997; Hershfield and Mitchell, 2001).
 Soon after their discovery that defects in ADA were
associated with immunodeficiency, Giblett and colleagues
examined other immunodeficient individuals for
deficiencies in purine catabolic enzymes and found that
defects in purine nucleoside phosphorylase also result in
immunodeficiency disease.

17.  molecular weight of 41 kDa .
 adenosine aminohydrolase, EC 3.5.4.4
 monomeric, zinc-dependent enzyme.
 encoded by 12 exons.
 ADA gene is 32 kb.
 The gene is on chromosome 20q13.11.
 mostly an intracellular enzyme.
 found throughout body.
 part of the purine catabolism pathway.
 most active in lymphocytes.
 functions in eliminating adenosine and deoxyadenosine.
 (Garrett and Grisham 2010; Genetic Science Learning Center 2008;
Genetics Home Reference 2009; Hershfield 1998)

18.  Associated with the loss of ADA activity ,The thymus is absent or small and
dysplastic in ADA-deficient individuals (Borzy et al., 1979).
 They have severely reduced numbers of peripheral T, B, and natural killer
(NK) cells(Buckley et al., 1997).
 ADA-deficient SCID is the only immunodeficiency in which all three cell
types are severely reduced in number.
 Autosomal recessive disease .
 In the absence of ADA lymphocytes are destroyed.

19.  Deoxyadenosine and deoxyguanosine are toxic to human lymphoid cells
in culture and have been implicated in the pathogenesis of the
immunodeficiency states associated with adenosine deaminase and
purine nucleoside phosphorylase deficiency, respectively.
 deoxyadenosine is not destroyed, is converted to dAMP and then into
dATP.
 There marked increase in cellular concentrations of dATP due to the lack
of conversion of excess deoxyadenosine to deoxyinosine and
hypoxanthine .
 dATP is a potent feedback inhibitor of deoxynucleotide biosynthesis and
DNA replication

20. Lymphopenia
Defect in T-cell activation
e.g. in vitro PHA
low serumimmunoglobulins
beware – antibody transferred
from mother
Elevated IgE
Peripheral eosinophilia
Elevated plasma adenosine
Elevated plasma and urine 2-
deoxyadenosine levels
Elevated dATP levels in erythrocytes.

21.  Total lymphocyte counts are taken.
 For more reliable results, flow cytometry is used to enumerate T, B,
and NK cells. Lymphocyte function is also tested by analyzing in vitro
responses of lymphocytes to common antigens (Kalman et al., 2004).
 ADA enzyme activity can be measured as well (Kalman et al., 2004).
 Diagnosis can be confirmed by DNA-sequence analysis, or protein
analysis (Kalman et al., 2004). This is important for carriers of XSCID.
(Kalman et
al., 2004)

22.  Prenatal: DNA-sequence analysis, ADA enzyme levels in umbilical-cord
blood (Kalman et al., 2004).
 Prenatal diagnosis has been accomplished by assay of the enzyme in
cultured amniocytes and chorionic villus Samples.
 ADA is markedly reduced or undetectable in affected patients
(homozygotes), and approximately one-half normal levels are found in
individuals heterozygous for ADA deficiency.

23. A considerable number of mutations have been
identified, most of them single amino acid changes.
A 329V, a relatively common mutation, has been
found in a number of unrelated patients so has
R211H.

24.  Purine nucleoside phosphorylase (PNP) deficiency has been associated with T-
lymphocyte dysfunction in some patients .
 The mechanism(s) whereby these enzyme deficiency states affect lymphocyte
development and/or function has not been fully elucidated.
 Whereas ADA deficiency results in combined bone marrow-derived (B)- and
thymus derived (T)-lymphocyte deficiency , PNP-deficient patients exhibit T-
cell dysfunction with normal B lymphocyte function.

25.  While there are a number of proposed mechanisms to
explain the association of lymphotoxicity with ADA
deficiency The cause of the T-cell deficiency associated
with the absenice of PNP activity has received less
attention.
 It was postulated that an accumulation of the PNP
substrate, inosine, inhibited ADA activity causing
finentional ADA deficiency.

26. Purine nucleoside phosphorylase (PNP, EC 2.4.2.1) deficiency causes a
clinical syndrome of SCID indistinguishable from that of ADA defciency.
It was also discovered by Giblett and colleagues .
PNP catalyzes the reversible cleavage of inosine and guanosine to their
respective bases hypoxanthine and guanine.
Deoxyinosine and deoxyguanosine are also substrates.

27. PNP deficiency is unique among immunodeficiency diseases,
because it presents with hypouricemia and urinary excretion
of uric acid is reduced.
Deficiency of enzymatic activity can be demonstrated in
erythrocyte lysates or cultured lymphroblasts.
Prenatal diagnosis may be made by assay of cultured
amniocytes or chorionic villus cells.
Heterozygotes may have intermediate levels of activity.

29.  Immunodeficiency is the most thoroughly studied
feature of human ADA deficiency; however, other
abnormalities have been reported :
1. Liver abnormalities
2. Neurological abnormalities
3. Pulmonary insufficiencies of unknown etiology
4. Renal abnormalities

30.  Ectoenzymes are membrane proteins that have their enzymatically active
site outside the plasma membrane, in the extracellular environment.
 Many ectoenzymes are type II integral membrane proteins with a short
amino terminus in the cytosol or are glycosylphosphatidylinositol-linked
molecules. Many ectoenzymes (such as CD26, CD38, CD73, autotaxin
and vascular adhesion protein 1) are also found as soluble forms in
biological fluids

31.  Early evidence from work in brain synaptosomes suggested
that the enzyme could be an ectoenzyme.
 In lymphoid cells, ectoenzymatic activity of ADA1 was also
found.
 The obvious role of this enzyme located on the cell surface
of lymphocytes and monocytes was to deaminate
adenosine, making it less available for uptaking and
metabolism, and also for adenosine-receptor activation.

32.  Cell surface ADA1-binding proteins have been identified.
 Interestingly, the interaction of ADA1 with these anchoring proteins leads
to costimulation of T-cell activation.
 Recent studies performed with professional antigen-presenting cells and
T lymphocytes have shown that ADA1 can bridge the two cell types
together by a cross-linking established between different anchoring
molecules in each cell.
 Some aspects of ADA action are similar to that of growth factors.
 In fact, ADA1 is a member of the adenosine deaminase growth factor
(ADGF) family.
 Some molecular mechanisms that occur in ADA-related SCID and the role
ADA1 may play in acquired immunodeficiency are also reviewed here.

33.  T cell depletion in ADA SCID may be at least partially due to
blocks in TCR-driven thymocyte maturation by adenosine, as well
as to direct apoptotic effects of intracellular adenosine, 2′-
deoxyadenosine.
 and dATP propose that there may be at least two alternative or
simultaneously operating mechanisms of T cell depletion:
 (a) intracellular lymphotoxicity of intracellularly accumulated
adenosine, 2′-deoxyadenosine, and dATP.
 (b) inhibition of TCR signaling and, hence, the inhibition/block of
TCR-driven processes ofT cell selection.

34. A smaller population of ADA-deficient patients
presents later in life with a less severe form of
immunodeficiency that coincides with less
severe loss of ADA enzymatic activity and
associated metabolic disturbances (Santisteban
et al., 1993).
Without intervention, ADA-deficient
individuals die from overwhelming
infections within the first year of life.

35.  The most successful treatment for ADA deficiency is
histocompatible bone marrow transplantation from an HLA-
matched sibling.
 Because this treatment option is seldom available, alternative
treatments have been identified, including T cell–depleted
haploidentical bone marrow transplantation from a parent.
 However, these approaches have met with limited success.

36. A successful biochemical approach for the treatment
of ADA deficiency involves the use of enzyme
replacement therapy wherein a polyethylene glycol–
modified form of bovine ADA (PEG–ADA) is provided to
patients by twice weekly intramuscular injection
(Hershfield et al., 1993).

39.  Polyethylene glycol appears to protect the bovine ADA
from proteolytic and immunologic attack, hence
increasing the circulating half-life of this exogenous
enzyme.
 ADA replacement therapy is effective in reducing the
metabolic impact of ADA deficiency and has prolonged the
life of individuals who have in some cases been treated for
more than 8 years (Hershfield, 1995).

40.  Relatively few complications have been reported
with respect to allergic reactions or
immunogenicity to PEG–ADA.
 it appears to be the best option for the prolonged
treatment of ADA-deficient patients who lack
HLA-identical marrow donor.

41. gene therapy
 the hope is that efficient transfer of a recombinant ADA
gene into hematopoietic cells will result in the outgrowth
of a genetically repaired immune system.
 For these and other reasons, ADA gene therapy studies
were the first to use ex vivo approaches to stably
introduce new genetic information into patients.