Background on Zap70 SCID

1. Background on Zap70 SCID Slides from Arthur Weiss GEMS Journal Club August 2012

2. 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

3. 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

4. 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)

5. 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

6. Causes of severe T cell deficiency Liston, Enders, Siggs NRI, 2008

7. Unusual Phenotype of ZAP-70 Deficient SCID: Absence of Peripheral CD8 T Cells Chan, et al., Science, 1994

8. ZAP-70 Deficient CD4 T Cells Fail to Signal in Response to TCR Stimulation Chan, et al., Science, 1994 Patient Normal TCR Stimulation Western Blot anti-phosphotyrosine

9. ZAP-70 Mutations Accounting for SCID

10. What is the Function of ZAP-70?

11. TCR Signaling is Initiated by Coordinated Actions of Two Cytoplasmic Tyrosine Kinases: Lck and ZAP-70 Wang, et al, CSHL, 2009

12. How Does the Absence of ZAP-70 Affect T cell Development ?

13. A Brief Introduction to T Cell Development T Cell Developmental Checkpoints CD4 SP DP CD8 SP CD4 DN CD8 Pre-TCR Positive & selection Negative Selection

14. Complete T cell Developmental Arrest in ZAP-70 Deficient Mice Normal ZAP-70 KO Thymocytes CD4 Lymph node cells CD4 CD8

15. Decreased Function of ZAP-70 Can Lead to Autoimmunity

16. 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

17. Hypomorphic Mutant Allele of ZAP-70 with Decreased Catalytic Activity Associated with ANA Positive Autoimmunity in Mice Siggs, et al., Immunity, 2007

18. Signal strength Thymocyte selection is dependent on signaling through the TCR Signal strength = Affinity X TCR signaling intensity

19. Signal strength 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 = Affinity X TCR Signaling Intensity

20. Asymmetric effects on immunogenic and tolerogenic TCR signaling may account for autoimmunity with partial immunodeficiency Liston, Enders, Siggs NRI, 2008