Rapid progression to AIDS in HIV individuals with a structural variant of chemokine receptor CX3CR1

1
Rapid progression to AIDS in HIV individuals
with a structural variant of chemokine receptor
CX3CR1

• Sophie Faure, Laurence Meyer, Dominique
  Costagliola, Celine Vaneensberghe, Emmanuelle
  Genin, Brigitte Autran, French ALT, and IMMUNOCO
  study group, David H. McDermott, Philip M.
  Murphy, Patrice Debre, Ioannis Theodorou,
  Christophe Combadiere
• By Kendra Sipres

2
Human Immunodeficiency Virus (HIV)

• HIV enters cells in vitro by CD4 T-Lymphocytes
  and a coreceptor
• The structure of a CD4 cell makes it an easy
  target for HIV so it attacks the cell
• HIV uses the cells as a breeding ground for new
  virus particles
• Eventually CD4 cells are killed off and chances
  of getting a severe disease or opportunistic
  illness is increased greatly

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HIV Coreceptors

• A coreceptor is required for HIV to enter cells
• Coreceptors such as CXCR4 enables certain strains
  of HIV to fuse with and enter immune cells called
  T cells
• CCR5 are necessary for the entry of HIV into
  immune cells called macrophages
• CCR5 is a binding site for chemokines that play a
  role in suppressing HIV infection
• chemokines suppress HIV replication by binding to
  the same receptors needed by certain strains of
  HIV to enter immune cells

4
CX3CR1

• CX3CR1 is another coreceptor of HIV
• This coreceptor is observed in caucasions
• It is a leukocyte chemotactic/adhesion receptor
  for the chemokine fractalkine

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CX3CR1-1249 M280

• This is a variant haplotype affecting two amino
  acids
• Isoleucine-249 methionine-280 are affected
• HIV infected patients who are homozygous for this
  haplotype progress to AIDS more rapidly
• Those with other haplotypes progress slower to
  AIDS

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CX3CR1-1249 M280

• CX3CR1 analysis indicated that fractalkine
  binding is reduced among those homozygous for
  this certain haplotype
• CX3CR1-1249 M280 is a recessive genetic risk
  factor in HIV and AIDS

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Variability in HIV contraction and progression

• Factors responsible for variability are not fully
  known
• Mutations in HIV coreceptors were shown to affect
  transmission progression
• Strongest form of resistance for HIV and AIDS
  progression is CCR5 32

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CCR5 32

• It is a mutant allele that encodes an inactive
  form of the chemokine receptor CCR5
• Heterozygosity of this allele leads to slower
  disease progression
• Homozygosity of this allele has high resistance
  to initial infection of HIV

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CCR5

• Another CCr5 variant has been found

10

• The known variants account for only a small
  percentage of people who appear to have HIV
  resistance
• Identification of other resistance factors is an
  important key

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Rationale

• Investigate CX3CR1 chemotactic activity and
  investigate its possible resistance powers
• Search for genetic variants and its effects on
  regulating HIV

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Method

• 78 random French Caucasian blood donors were
  screened for the CX3CR1 coding sequence mutations
• 5 single nucleotide polymorphisms (SNPs) were
  identified
• All were in the transmembrane domains of the
  receptor

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Results

• 4 SNPs were found to be nonsynonymous

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Method

• Distribution of V2491 and T280M was studied in
  565 individuals from 3 HIV cohorts
• Patients with intermediate progression (IMMUNOCO
  cohort)
• Patients with asymptomatic long-term progression
  (ALT cohort)
• Patients with a known date of serocnversion
  (SEROCO cohort)

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Results

• Of the 9 possible genotypes, 6 were observed
• Frequencies were observed from 50 for the
  homozygous wild type to 2 for the doubly mutated
  homozygote

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Results

• 3 were never detected
• G/G at codon 249 followed by C/T at codon 280
• G /G at codon 249 followed by T/T at codon 280
• G/A at codon 249 followed by T/T at codon 280
• The absence suggests SnPs are tightly linked
  the C/T substitiution at the position 280 occored
  only when theres an A at codon 249

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• A likelihood ratio test was done for linkage
  equilibrium
• The test confirmed that the SNPs were in
  complete linkage disequilibrium
• So only 3 haplotypes of CX3CR1 were found in the
  Caucasian population
• V249 T280 haplotype
• I249 T280 haplotype
• I249 M280 haplotype
• Respective frequencies were 71.4, 12.3 16.2

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TABLE 1
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Disease progression

• Case analysis showed more people with the I249
  M280 haplotype in the IMMUNOCO cohort compart
  with ALT cohort had higher rate of disease
  progression
• The CCR5 32 allele was more frequent in the ALT
  cohort
• Results suggest the CX3CR1 1249 M280 haplotype
  adversely affects HIV progression

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Table 2
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Disease progression

• A Kaplan-Meier survival analysis of those from
  the SEROCO cohort showed faster progression to
  AIDS for CX3CR1-M280 homozygotes than CX3CR1-T280
  homozygotes (fig. 1-A)
• Disease progression was similar for heterozygotes
  and wild-type homozygotes
• This suggests that the effect of the CX3CR1-1249
  M280 haplotype is recessive
• (in contrast, CCR5-32 AND CCR2-64I alleles have
  dominant effects)

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Figure 1-A 1-B
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Figure 1-B

• Those who were partially protected by the CCR5-32
  allele were excluded from the analysis
• When this was done, the acceleration to AIDS or
  CD4 decline was more pronounced
• This is exhibited in figure 1-B

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Analysis of CX3CR1 SNP distribution

• The CX3CR1 gene is on the chromosome 3p21
• This is in the vicinity of the CCR5 and CCR2
  genes
• The SNP was analyzed to verify that the effect is
  ue to CX3CR1
• The CX3CR1 SNP was analyzed in relation to the
  CCR5-32 and CCR2-641 alleles

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Results

• Neither CX3CR1 SNPexhibited any linkage
  disequilibrium with CCR2-641 or CCR5-32
• No linkage disequilibrium was found between
  CX3CR1 V249I and T289M
• Therefore, the CX3CR1-I249 M280 haplotype is
  independent of any previously defined
  disease-modifying mutations in CCR5 CCR2

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Comparison of fractalkine binding primary
peripheral blood mononuclear cells (PBMCs)

• 2 CX3CR1 SNPs defining the haplotype are in the
  coding sequence
• These could affect the receptor function
• To test this fractalkine binding and PBMCs were
  compared from HIV infected patients
• Patients were homozygous for CX3CR1-V249 T280 VS.
  CX3CR1-1249 M280

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Results

• Tests showed reduced binding affinity of
  125I-labeled fractalkine to cells from
  CX3CR1-1249 M280 homozygotes vs. wild-type cells
• This shows 2 SNPs affect the integrity of the
  receptor
• Total of binding sites pre cell was reduced in
  CX3CR1-I249 M280 homozygotes vs. wild-type

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Characterization of fractalkine binding parameters

• This was done in order to determine the specific
  effect on the function of each SNP constituting
  the CX3CR1-I249 M280 haplotype
• They were characterized for PBMCs from 2 pateints
• Patients were homozygous for haplotype
  CX3CR1-I249 T280

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Results

• Receptor expression did not differ enough from
  the other haplotypes
• Fractalkine binding affinity differed fro
  comparision with CX3CR1-V249 T280 CX3Cr1-I249
  M280
• This data shows that T280M may directly affect
  ligand recognition
• Further research is needed

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Conclusion

• The results of this experiment show that CX3CR1
  is polymorphic in Caucasian population
• Variant haplotype CX3CR1I249 M280 is associated
  with accelerated HIV disease
• Reduced receptor expression fractalkine binding
  could compromise normal immune responses
• This could lead to accelerated progression of HIV
  AIDS
• Further research is needed