Severe Congenital Neutropenia Kostmanns Syndrome

1
Severe Congenital Neutropenia (Kostmanns
Syndrome)

• First described by Kostmann in 1956.
• Clinical manifestations
• Chronic severe neutropenia present at birth
• Accumulation of granulocytic precursors in the
  bone marrow
• Rare (1 in 100,000)
• Inherited in a sporadic, autosomal dominant, and
  autosomal recessive fashion
• A randomized trial has confirmed the efficacy of
  G-CSF to increase neutrophil counts and reduce
  the incidence and severity of infections.

2
Bone Marrow Examination
Normal
SCN

• Cardinal feature of SCN Isolated block in
  granulocytic differentiation

3
SCN and MDS/AML

• Cumulative risk of leukemia (all types) up to age
  40
• 1 in 639 (0.16) for men
• 1 in 794 (0.13) for women
• Cumulative risk of MDS/AML is 11.7 in SCN
• 9 for patients on G-CSF for lt6 years
• 23 for patients on G-CSF between 6 10 years
• 33 for patients on G-CSF gt10 years

ACS Cancer Facts Figures 2003
Rosenberg et al, Blood 2003102350a
4
Bone Marrow Failure is a Pre-Leukemic Condition

• High frequency of chromosome 7 abnormalities in
  AML arising in the setting of bone marrow
  failure (35-68) versus de novo AML (5)

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Cell Culture Studies in SCN

• Cell intrinsic defect in the granulocytic
  differentiation of progenitor cells
• Decreased responsiveness of progenitors to
  granulocyte colony-stimulating factor (G-CSF)
• Increased apoptosis of granulocytic cells upon
  growth factor deprivation

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Genetic Mutations Implicated in the Pathogenesis
of SCN
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G-CSFR Mutations in SCN

• G-CSF receptor
• Member of cytokine receptor superfamily
• Only known receptor for G-CSF
• G-CSF receptor mutations in SCN
• Acquired heterozygous mutations
• d715 (Q716X) mutation first described by Dong et.
• Result in loss of 3 of 4 cytoplasmic tyrosines.

C
C
C
C
C
C
C
C
Box 1
-Y
-Y
Box 2
-Y
-Y
-Y
G-CSFR
d715
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G-CSFR Mutations in SCN

• G-CSFR mutations are acquired!

• 30 of SCN patients have G-CSF receptor
  mutations
• These mutations are strongly associated with
  development of MDS and AML
• Collectively, 17/21 patients with MDS/AML have
  G-CSFR mutations.
• Mutations are rare in de novo AML
• 1 of 58 cases tested

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Questions

• How do cells expressing the mutant G-CSFR gain
  clonal dominance?
• Why are premature truncation mutations of the
  G-CSFR only seen in the setting of SCN?
• Do G-CSFR mutations contribute to leukemogenesis?
• Should the detection of mutant G-CSFR lead
  immediately to transplant for these patients?

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d715 G-CSFR Mice Summary

• Normal basal granulopoiesis
• No block in granulocytic differentiation
• Increased responsiveness to G-CSF
• Exaggerated blood neutrophil response to G-CSF
  treatment
• The number of myeloid progenitors and their in
  vitro proliferative response to G-CSF is
  increased
• Altered G-CSF signaling
• Delayed receptor internalization
• Accentuated activation of STAT5
• Impaired activation of SOC3, SHP2, SHIP and
  possibly lyn

11
(No Transcript)
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Competitive Repopulation Assay
1,000 cGy
Wild type host (Ly 5.1)
Donor
(d715 Ly 5.2)
Hematologic Recovery
and
(6 months)
(Wild-type Ly 5.1)
11 Ratio of Bone Marrow Cells
Bone Marrow Chimera
(5 x 106 cells)
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Flow Cytometry Assay
61.8
51.0
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d715 Chimeras 6 months after transplantation11
transplantation ratio
63.5
46.6
50.0
45.7
15
d715 Chimeras G-CSF (10ug/kg/d x 21 days)
BM 63.3 89.1
BM 75.8 98.6
T cell
Neutrophil
61.1 68.4
49.7 60.5
52.6 97.6
16
Analysis of Stem Cell Compartment
c-Kit
Sca-1
Untreated
G-CSF treated
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d715 Chimeras G-CSF (10ug/kg/d x 21 days)
53.3 97.8
61.1 68.4
49.7 60.5
52.6 97.6
18
d715 ChimerasSecondary Transplants2 months post
transplant
48.6
34.4
74.8
64.8
19
Wild Type Mice
Hoechst Staining
C-Kit
Sca-1
Lineage
20
D715 G-CSFR Mice
Hoechst Staining
C-Kit
Sca-1
Lineage
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Questions

• How do cells expressing the mutant G-CSFR gain
  clonal dominance?
• Why are premature truncation mutations of the
  G-CSFR only seen in the setting of SCN?
• Do G-CSFR mutations contribute to leukemogenesis?
• Should the detection of mutant G-CSFR lead
  immediately to transplant for these patients?

The G-CSFR mutations confer a growth and/or
survival advantage at the hematopoietic stem cell
level.
The G-CSFR mutations are dependent upon G-CSF.
In SCN systemic levels of G-CSF are high.
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Two-hit Model of Acute Leukemia
23
Chimeric Transcription Factor
RTK Signal
Leukemia
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d715 Tumor Watch
The d715 G-CSFR is not sufficient to induce AML
or MDS in mice even with chronic G-CSF stimulation
25
d715 Tumor Watch
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Questions

• How do cells expressing the mutant G-CSFR gain
  clonal dominance?
• Why are premature truncation mutations of the
  G-CSFR only seen in the setting of SCN?
• Do G-CSFR mutations contribute to leukemogenesis?
  
• Should the detection of mutant G-CSFR lead
  immediately to transplant for these patients?

The G-CSFR mutations confer a growth and/or
survival advantage at the hematopoietic stem cell
level.
The G-CSFR mutations are dependent upon G-CSF.
In SCN systemic levels of G-CSF are high.
?