A clinical case study: the potential impact of maternal anti-Co4 antibody on Pregnancy Conceived by in vitro fertilization (IVF) Free

The Colton blood group system (CO, ISBT 015), is a blood group system characterized by antigens present on aquaporin-1 (AQP1), a multi-pass water channel glycoprotein expressed on RBCs and kidney tubules and encoded by AQP1 gene on chromosome 7. The system includes four recognized antigens: three high-prevalence antigens, Co^a(Co1), Co3, and Co4 and one low-prevalence antigen, Co^b (Co2). Antibodies against Colton antigens (Co^a, Co^b and Co3), are reported to cause Hemolytic Transfusion Reactions (HTR) and mild to severe Hemolytic Disease of the Fetus and the Newborn (HDFN). However, anti-Colton 4 antibody is extremely rare and to our knowledge, only 3 cases were reported previously. Since there is limited published data regarding the clinical significance of anti-Co4 antibodies, the severity and association of HTR and HDFN with anti-Co 4 antibody is virtually unknown.

We present a case of a 37 year old female (G2P0100) of Iranian descent with anti-Co 4 antibody who successfully delivered a baby at 37 weeks and 3 days gestation by emergent C-section. Her pregnancy was conceived by in vitro fertilization (2^nd IVF). She is a carrier of Pendred syndrome. Her 1st IVF pregnancy was terminated at 26 weeks due to fetal cardiac anomalies followed by transfusion with multiple units of Packed Red Blood Cells and Fresh Frozen Plasma. Her antibody screen was negative at that time. Later on, she developed panagglutinins after multiple units of blood transfusion but before initiation of current 2^nd IVF pregnancy.

In her current 2^nd trimester pregnancy, panagglutinins were identified and reported as “other” at Inova Fairfax Hospital Blood Bank. The American Red Cross (ARC) initially characterized the panagglutinins as anti-Co3 with an initial titer of 4 that increased up to 32 as monitored throughout pregnancy. Patient's RBCs tested against anti-Co^a, anti-Co^b and anti-Co(a+b+) antibodies and test results were all negative. Patient's serum reacted with Co(a-b+) & Co(a+b-) RBCs. However, her serum was non-reactive when tested with Co(a-b-, null phenotype) RBCs antigens. Maternal and paternal RBCs were typed as “A Rh positive” and both were genotyped with an initial predicted Co(a+ b−) phenotypes. Subsequent sequencing of the AQP1 gene from the maternal sample revealed homozygosity for the rare c.140A>G (p.Gln47Arg) variant, designated in ISBT system as CO*01.-04. This genotype variant corresponds to the serologic phenotype Co(a−b−3+4−). However, no variant genotype/phenotype were detected in paternal sequencing sample. Crossmatch assay showed incompatibility when patient's serum was tested against RBCs from husband, brothers, cousins and random donors (100% donors tested were incompatible). Monocyte Monolayer Assay (MMA) was highly reactive and reported as 52.5% (normal 3% or less). Due to history of aspirin intake during pregnancy, ThromboElastoGraphy (TEG 6S) with platelet mapping assay was performed to see aspirin related platelets functional defects. No platelet inhibition was present (MA value 62.7 mm and no inhibition). American rare donor registry search results (national and international) could not find any compatible PRBC unit except one frozen unit (autologous unit) which could not be used. No PRBC transfusion was required before and after delivery. New born baby is “A positive”. The DAT done on the cord blood was negative. No genomic study was done for the baby. Anti-Co4 antibody, serial titer, MMA,TEG assays as well as doppler study were done to understand the clinical significance of this rare antibody.

In light of the molecular findings, particularly the AQP1 variant associated with the Co4 antigen, the antibody specificity is more accurately attributed to anti-Co4 rather than anti-Co3. At the time of this writing, this IVF pregnancy ended with successful delivery of healthy normal baby without needing for PRBC transfusion to mom or intra-uterine transfusion. Both mother and baby are in good condition with normal hemoglobin and normal bilirubin. Since anti-Co4 antibody is exceedingly rare and no published clinical data on the outcome and adverse reactions is available, the present clinical follow up for HTR and HDFN was of utmost importance.

This case is important and ubique in the sense that the pervious three reported anti-Co4 antibodies were not associated with IVF pregnancy, or HDFN as compared to our current case where both mother and baby of IVF pregnancy were at significant risk for HTR and HDFN.