Identification of fetal DNA and fetal cell markers in maternal plasma or serum
The present invention relates to the identification of fetal specific nucleic acids and fetal cell markers in maternal plasma or serum. In particular, the present invention relates to methods which rely on the analysis of polymorphic alleles of a population to determine an allele which is possessed by the fetus but absent from the mother. Fetal specific alleles identified using the methods of the invention can be used to quantify fetal DNA from maternal plasma or serum. In addition, antigens encoded by alleles identified using the methods of the invention can be targeted in methods of isolating or detecting fetal cells.
1. A method of isolating fetal cells from a sample, the method comprising:
(a) identifying an allele, encoding a polymorphic antigen, which allele is present in the DNA of the fetal cells but absent from maternal DNA, comprising
i) obtaining a sample from the pregnant female comprising fetal and maternal nucleic acids, and
ii) screening nucleic acids from the sample for at least one allele not present in the maternal cells,
wherein the father is not typed for any alleles, wherein the allele is from a class I HLA locus, is HLA-A
(b) binding to the fetal cell an affinity reagent which recognises the polymorphic antigen, and
(c) selecting cells bound by the affinity reagent.
2. The method of claim 1 , wherein the sample is obtained during the first trimester of pregnancy.
3. The method of claim 1 , wherein if the pregnant female has not been typed for an allele before the method is performed the method further comprises typing alleles of at least one locus from maternal cells.
4. The method of claim 3 , wherein the typing is performed by obtaining a genomic DNA sample from the pregnant female and exposing the DNA to amplification and/or sequencing procedures.
5. The method of claim 3 , wherein the typing is performed by using antibodies which bind the protein products of specific alleles.
6. The method of claim 3 , wherein typing alleles of at least one locus from maternal cells is performed on nucleated blood cells, saliva or hair follicles.
7. The method of claim 1 , wherein the sample is derived from plasma, serum or urine.
8. The method of claim 1 , wherein the sample is subjected to affinity chromatography to enrich nucleic acids from the sample.
9. The method of claim 1 , wherein numerous potential alleles at a particular locus are investigated in the sample simultaneously by a multiplex amplification procedure.
10. The method of claim 1 , wherein nucleic acid in the sample is DNA or RNA.
11. The method of claim 1 , wherein the pregnant female is a mammal.
12. The method of claim 11 , wherein the mammal is a human.
13. The method of claim 1 , wherein the affinity reagent which recognises the antigen is an antibody.
14. The method of claim 13 , wherein the antibody is detectably labelled.
15. A method of isolating fetal cells from a sample, the method comprising
(a) identifying an allele, encoding a polymorphic antigen, which allele is present in the DNA of a fetal cell but absent from maternal DNA comprising;
i) obtaining a sample from a pregnant female comprising fetal and maternal nucleic acids,
ii) typing at least one locus from the sample obtained in step i),
iii) comparing the alleles identified in step ii) with alleles of the same locus possessed by the pregnant female, and
iv) selecting an allele typed in step iii) which is not possessed by the pregnant female, wherein the father is not typed for any alleles, and wherein the allele is from a class I HLA locus is HLA-A,
(b) binding to the fetal cell an affinity reagent which recognises the polymorphic antigen, and
(c) selecting cells bound by the affinity reagent.