adenosine deaminase (ada) immunodeficiency
TRANSCRIPT
بسم الله الرحمن
الرحیم
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IMMUNODEFICIENCIES
1. primary innate diseases genes coding for immune system components
2. secondary secondary immune disorders based on
primary cause
SECONDARY IMMUNODEFICIENCY
presence of underlying disease
malignancy (malignancy) infection (e.g. HIV) malnutrition immunosuppresive drugs
CLASSIFICATION OF PRIMARY IMMUNODEFICIENCIES
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
PREVALENCE OF PRIMARY IMMUNODEFICIENCIES (PID)
70%
1%
20%
9%
humoral
cellular andcombined
phagocytic
complement
INTRODUCTION 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/chr21-22-X-Ysm.gif
CAUSES OF SCID 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
X-SCID
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.
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 nucleosidephosphorylase
HN
N N
N
H
O
may be reusedthroughsalvage pathway
Pi
Ribose-1-P
hypoxanthine
Degradationof AMP
SYMPTOMS 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.
SEVERE COMBINED IMMUNODEFICIECY (SCID)
clinical symptomsearly in lifechronic diarrhea, failure to thrive graft versus host disease (on skin)
complications after vaccination with live vaccines
unusual infections, severe course family history
ADENOSINE DEAMINASE (ADA) IMMUNODEFICIENCY
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.
BIOCHEMICAL FEATURES OF ADENOSINE DEAMINASE (ADA) ENZYME
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)
ADA-DEFICIENT SCID 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.
MOLECULAR MECHANISM
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
LABORATORY FINDINGS
Lymphopenia
Defect in T-cell activatione.g. in vitro PHA
low serumimmunoglobulinsbeware – antibody transferred from mother
Elevated IgE
Peripheral eosinophilia
Elevated plasma adenosine
Elevated plasma and urine 2-deoxyadenosine levels
Elevated dATP levels in erythrocytes.
DIAGNOSIS
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)
DIAGNOSIS 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.
ADA MUTATIONS
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.
(PNP)DEFICIENCY
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.
(PNP)DEFICIENCY
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.
PNP DEFICIENCY
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.
PNP DEFICIENCY
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.
EFFORTS TO UNDERSTAND THE METABOLIC BASIS OF THE IMMUNODEFICIENCY ASSOCIATED WITH ADA DEFICIENCY HAVE LED TO ADVANCES IN THE TREATMENT OF CERTAIN LEUKEMIAS.
OTHER ABNORMALITIES WITH ADA DEFICIENCY
Immunodeficiency is the most thoroughly studied feature of human ADA deficiency; however, other abnormalities have been reported:
1. Liver abnormalities2. Neurological abnormalities3. Pulmonary insufficiencies of unknown etiology4. Renal abnormalities
ADA AS AN ECTOENZYME
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
ADA AS AN ECTOENZYME
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.
QUITE UNEXPECTEDLY, ADA1 WAS SHOWN TO ACT EXTRAENZYMATICALLY.
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.
CONCLUSION 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.
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.
TREATMENT
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.
TREATMENT
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).
RECONSTITUTION OF CD4+ T CELLS WITH TIME AFTERINITIATION OF PEG-ADA THERAPY.
ENZYME REPLACEMENT THERAPY
ENZYME REPLACEMENT THERAPY
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).
ENZYME REPLACEMENT THERAPY
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.
TREATMENT
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.
STEM CELL GENE THERAPY FOR ADA DEFICIENCY
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