Fatal alloimmune thrombocytopenia due to anti-HLA alloimmunization in a twin pregnancy: A very infrequent complication of assisted reproduction

The first reported case of neonatal alloimmune thrombocytopenia due to low-frequency human platelet antigen-6b antibodies in the United Kingdom

BACKGROUND

Neonatal alloimmune thrombocytopenia (NAIT) is a potentially serious clinical condition caused by maternal alloantibodies directed to human platelet antigens (HPA), inherited from the father and expressed on fetal/neonatal platelets. We report a case of an otherwise well, full term child, with a profound thrombocytopenia (33 x 109/L). There was no bleeding or obvious explanation for the low platelet count. Samples were sent for the investigation of NAIT.

METHOD

Serological investigations were performed on maternal serum taken at day (D)+4 and D+78. The platelet immunofluorescence test (PIFT) and monoclonal antibody immobilization of platelet antigens (MAIPA) assays were performed with a panel of HPA typed donor platelets and against paternal platelets in a crossmatch. HPA 1-6, -9 and -15 and HLA genotyping was performed by in-house PCR-sequence based typing (SBT) and next generation sequencing (NGS).

RESULTS

HPA antibody screening of D+4 maternal serum indicated that platelet-specific antibodies were absent. HPA genotyping of the father and child revealed the presence of the low frequency HPA antigen (LFHPA), HPA-6b, which was absent in the mother. Maternal samples were crossmatched against paternal platelets and were positive by PIFT and glycoprotein (GP) IIb/IIIa and HLA class I in the MAIPA assay. The infant required no platelet transfusion support as the thrombocytopenia resolved spontaneously.

DISCUSSION

We conclude that the positive crossmatch reaction was due to anti-HPA-6b alloantibodies. This case further emphasizes the importance of platelet crossmatching and HPA genotyping of LFHPA in cases where there is a high clinical suspicion of NAIT but initial screening is negative.

Neonatal alloimmune thrombocytopenia due to anti-HPA 5a in a HPA-5a homozygous neonate

The most frequently involved antigen in severe fetal and neonatal alloimmune thrombocytopenia (FNAIT) is the human platelet antigen 1a. Cases of FNAIT caused by HPA-5a antigen are extremely rare, and usually not severe. We report a case of FNAIT caused by anti-HPA antibodies directed to the HPA-5a antigen. The thrombocytopenia was moderate with a minimal platelet count of 36 × 10⁹/L by day 3, and spontaneously resolved by day 10. The pregnancy had been obtained by in vitro fertilization using embryo donation, creating a complete genetic disparity between the HPA 5b5b mother and the HPA 5a5a homozygous neonate. The use of ART with gamete donation can increase the risk and the severity of alloimmune thrombocytopenia and must be considered in new and subsequent pregnancies.

A combined effect of anti-HPA-1a and anti-HLA Class I in pregnancy?

BACKGROUND

Maternal anti-human leukocyte antigen (HLA) Class I is commonly detected alongside anti-human platelet antigen (HPA)-1a in fetal and neonatal alloimmune thrombocytopenia (FNAIT). Little is known regarding whether the presence of anti-HLA Class I may exert an additive effect on the risk and severity of FNAIT.

METHODS AND MATERIALS

We reanalyzed samples originally collected as part of a large Norwegian screening study on FNAIT during 1995-2004. This study identified and managed 170 pregnancies where the mother was HPA-1a negative and had detectable anti-HPA-1a during pregnancy. Maternal samples from 166 of these pregnancies were rescreened for anti-HLA Class I, revealing 111 (67%) that were antibody positive. Various regression models were used to assess if and how maternal anti-HLA Class I influenced the neonatal platelet count.

RESULTS AND CONCLUSIONS

Unadjusted neonatal platelet counts and the frequency of neonatal thrombocytopenia was not significantly affected by the presence of anti-HLA Class I alongside anti-HPA-1a, but results from regression analyses revealed a possible increased risk when the mother was nulliparous. These results warrant further investigation.

Implication of antibodies against human leukocyte antigen in simultaneous presentation of fetal and neonatal alloimmune thrombocytopenia and neutropenia

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) and neonatal alloimmune neutropenia (NAN) are two rare complications of newborns caused by antibodies against paternal inherited antigens. Human platelet (HPA) and neutrophil antigens (HNA) are the common targets. Human leukocyte antigen (HLA) class I proteins are also expressed on platelets and neutrophils and anti-HLA antibodies have occasionally been implicated in these complications. We report a premature twin infant who presented with severe thrombocytopenia and neutropenia clinically compatible with FNAIT and NAN, from a mother with no identifiable HPA or HNA antibodies, but with very high levels of complement-fixing antibodies against paternal inherited HLA. These antibodies were also detected in the infant. HLA antibodies are commonly present in multiparous women who deliver healthy infants. They can, however, be cytotoxic and cause clinical complications after blood products transfusion (TRALI and becoming refractory to platelets transfusion) and after organ transplantation (allogeneic organ rejection).