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Background on Zap70 SCID
Slides from Arthur Weiss
GEMS Journal Club
August 2012
Case Presentation
A 1 year old Hispanic female was referred to UCSF for the
possibility of a bone marrow transplantation.
She had a history of:
recurrent pneumonias
chronic gastroenteritis
failure to thrive
oral/cutaneous candidiasis
history of disseminated varicella
Her parents were first cousins.
One of her three sibs (brother) died at age 9 months.
Physical Exam was unremarkable
Laboratory Evaluation
• B cell number: Normal
• Immunoglobulin levels: Decreased IgM, IgG and IgA
• Abnormal lymphocyte phenotype:
CD3 76%; CD4 74%; CD8 0-2%
• T cells are polyclonal
• In vitro proliferation studies:
B cells proliferate normally to mitogens
CD4 T cells:
Fail to respond to PHA or anti-CD3 mAb
Positive proliferative response to IL-2
Positive proliferative response to PMA plus ionomycin
Severe Combined Immunodeficiency Syndrome
SCID
•
Primary Defect
- Absent T cell function
- Variable T cell counts (absent to elevated)
• Associated Defects
- Decreased B cell responses (intrinsic or extrinsic)
- Variable B cell counts (often normal)
Multiple Molecular Causes of SCID
• X-linked Common  chain (IL-2, IL-4, IL-7, IL-9,
and IL-15 receptors) - 50%
• Jak 3 tyrosine kinase
• IL-7 receptor alpha chain
• Adenosine Deaminase (ADA)
• Purine Nucleoside Phosphorylase (PNP)
• Recombinase Activating Genes (Rag 1 and Rag 2)
• CD3  and 
• CD45 tyrosine phosphatase
• Bare lymphocyte syndrome (absent MHC molecules)
• ZAP-70 tyrosine kinase
Causes of severe T cell deficiency
QuickTime™ and a
decompressor
are needed to see this picture.
Liston, Enders, Siggs
NRI, 2008
Unusual Phenotype of ZAP-70 Deficient SCID:
Absence of Peripheral CD8 T Cells
Chan, et al., Science, 1994
ZAP-70 Deficient CD4 T Cells Fail to Signal
in Response to TCR Stimulation
Chan, et al., Science, 1994
Patient
TCR Stimulation
Western Blot
antiphosphotyrosine
Normal
ZAP-70 Mutations Accounting for SCID
What is the Function of ZAP-70?
TCR Signaling is Initiated by Coordinated
Actions of Two Cytoplasmic Tyrosine Kinases:
Lck and ZAP-70
Wang, et al, CSHL, 2009
How Does the Absence of ZAP-70 Affect
T cell Development ?
A Brief Introduction to T Cell
Development
T Cell Developmental Checkpoints
pre-TCR
CD4CD8TCR -
CD4CD8pTCR +
TCR
CD4
SP
CD4+
CD8TCR high
DP
CD4+
CD8+
TCR low
CD4CD8+
TCR high
Pre-TCR
selection
r ag
CD3 
TCR
p r e- T 
lck/ f y n
ZA P-7 0 / Sy k
Positive &
Negative
TCR
Selection
MHC class I
MHC class II
2 microglobulin
CD8
SP
CD4
DN
CD8
CD8 block only
CD4 block only
CD8 block only
CD4
ZAP 70 KO
ZAP 70 KOin
ZAP 70 KO
Complete
T cellWTDevelopmental
Arrest
A
SLAP and ZAP-70
c-Cbl both
partially
rescue
x SLAP the
KO ZAP-70
x c-Cbl K
Deficient Mice
7.8
0.8
2.5
4.7
Thymocytes
WT
ZAP 70 KO
ZAP 70 KO
ZAP 70 KO
A
Normal
1.2
ZAP-70 KO
7.8
x SLAP KO
0.2
0.8
x c-Cbl K
0.7
2.5
4.7
CD4
CD8
Thymocytes
CD4
LN T cells
B
WT
1.2
0.2
ZAP 70 KO
0.7
ZAP 70 KO
x SLAP KO
ZAP 70 KO
x c-Cbl K
CD8
CD4
LN T cells
BCD4
32.4
1.1
WT
ZAP 70 KO
18.4
32.4
CD4
2.7
Lymph
node cells
ZAP
70 KO
ZAP 70 KO
x SLAP KO
x c-Cbl K
0.4
1.1
CD8
2.8
0.1
2.7
2.8
CD8
Decreased Function of ZAP-70 Can
Lead to Autoimmunity
Spontaneous Development of Erosive Arthritis in SKG mice
Sakaguchi, et al, Nature, 2003
• Incidental finding in Balb/c mouse colony
• 100% penetrant, males and females affected
• Onset at 2 months (joint swelling and hyperemia)
or following activation of the innate immune response
• Interphalangeal joints -> symmetrical involvement including
wrist and ankle joints. Spares large joints and spine (except
base of tail) Destruction of joint space.
• RF+, mediated by CD4 T cells
Hypomorphic Mutant Allele of ZAP-70 with Decreased
Catalytic Activity Associated with ANA Positive
Autoimmunity in Mice
Siggs, et al., Immunity, 2007
Thymocyte selection is dependent on signaling
through the TCR
Signal strength
Signal strength = Affinity X TCR signaling intensity
Thymocyte selection is dependent on signaling
through the TCR
Decreasing
TCR Signaling
by ZAP-70
mutation
alters the
TCR repertoire
of thymocytes
surviving both
positive and
negative
selection
Signal strength
Signal strength = Affinity X TCR Signaling Intensity
Asymmetric effects on immunogenic and
tolerogenic TCR signaling may account for
autoimmunity with partial immunodeficiency
QuickTime™ and a
decompressor
are needed to see this picture.
Liston, Enders, Siggs
NRI, 2008