Bacterial DNA is implicated in the inflammatory response to delivery of DNA/DOTAP to mouse lungs

Phase 1 clinical trials of liposome-mediated gene therapy for cystic fibrosis have been completed and in all cases the expression level achieved has been low and transient. Clearly, improvements in the efficiency of gene transfer are required. It is now being recognised that delivery of high doses of DNA/liposomes to the mouse airway epithelium can achieve reproducible evidence of transgene, but is often associated with an unacceptable level of inflammation/ toxicity. It has recently been shown that instillation of bacterial DNA causes inflammation in the lower respiratory tract of rodents. The increased number and unmethylated status of CpG motifs, particularly when present in a particular base context, was identified as an important factor in this response. It was suggested that the immune system recognises this molecular pattern as 'foreign' thus activating appropriate immune responses. We have found that methylation of DNA decreases the level of several inflammatory cytokines in lavage fluid and surprisingly has a differential effect on expression of the plasmids pCMV CFTR-int6ab and pCMV CAT which only differ in the actual transcription cassette. The severe lung pathology observed did not show a corresponding decrease with methylation suggesting that these cytokines are not the only contributors to the toxicity/inflammation observed. Gene Therapy (2000) 7, 384-392.

Enhancing the efficiency of introducing precise mutations into the mouse genome by hit and run gene targeting

The creation of precise clinical mutations by targeting is important in elucidating disease pathogenesis using mouse models. 'Hit and run' gene targeting is an elegant method to achieve this goal. This uses first a positive selection to introduce the targeting vector carrying the required mutation and then a negative selection to identify clones which have removed vector and wild-type sequences by intrachromosomal recombination. However, this approach has only been successfully used in a handful of cases. We used this procedure to introduce precise clinical mutations into the exon 10 region of the cystic fibrosis transmembrane conductance regulator (Cftr) gene. Using a CMV promoter driven hygromycin/thymidine kinase (hyg/tk) fusion gene as both our dominant and negative selectable marker, we targeted the Cftr locus very efficiently but only identified false runs after the negative selection step. This defect in thymidine kinase induced toxicity to gancyclovir correlated with methylation of the transgene. Consequently we devised a stringent screening procedure to select only true 'run' clones. Unfortunately these 'run' clones had lost the mutation so we altered the vector design to bias the run step to retain the mutation and used a different tk selection cassette with a HSVtk promoter sequence. This new vector design allowed both efficient 'hit and run' for two cystic fibrosis (CF) mutations with no false positives and successful germline transmission of the novel G480C missense mutation.

Specific sterols required for the internalization step of endocytosis in yeast

Sterols are major components of the plasma membrane, but their functions in this membrane are not well understood. We isolated a mutant defective in the internalization step of endocytosis in a gene (ERG2) encoding a C-8 sterol isomerase that acts in the late part of the ergosterol biosynthetic pathway. In the absence of Erg2p, yeast cells accumulate sterols structurally different from ergosterol, which is the major sterol in wild-type yeast. To investigate the structural requirements of ergosterol for endocytosis in more detail, several erg mutants (erg2Delta, erg6Delta, and erg2Deltaerg6Delta) were made. Analysis of fluid phase and receptor-mediated endocytosis indicates that changes in the sterol composition lead to a defect in the internalization step. Vesicle formation and fusion along the secretory pathway were not strongly affected in the ergDelta mutants. The severity of the endocytic defect correlates with changes in sterol structure and with the abundance of specific sterols in the ergDelta mutants. Desaturation of the B ring of the sterol molecules is important for the internalization step. A single desaturation at C-8,9 was not sufficient to support internalization at 37 degrees C whereas two double bonds, either at C-5,6 and C-7,8 or at C-5,6 and C-8,9, allowed internalization.

The WASp homologue Las17p functions with the WIP homologue End5p/verprolin and is essential for endocytosis in yeast

Several end mutations that block the internalisation step of endocytosis in Saccharomyces cerevisiae also affect the cortical actin cytoskeleton [1]. END5 encodes a proline-rich protein (End5p or verprolin) required for a polarised cortical actin cytoskeleton and endocytosis [2,3]. End5p interacts with actin [4], but its exact function is not yet known. To help elucidate End5p function, we sought other End5p-interacting proteins and identified the LAS17/BEE1 gene (encoding the yeast homologue of the human Wiskott-Aldrich Syndrome protein, WASp) as a high-copy-number suppressor of the temperature-sensitive growth and endocytic defects of end5-1 cells (carrying a frameshift mutation affecting the last 213 residues of End5p). LAS17 is unable to suppress a full deletion of END5 (end5 delta), however, suggesting that the defective End5-1p in end5-1 mutants may be stabilised by Las17p. The amino terminus of Las17p interacts with the carboxyl terminus of End5p in the yeast two-hybrid system and similar interactions have been shown between WASp and a mammalian End5p homologue, WASp-interacting protein (WIP) [5]. As las17 delta deletion mutants are blocked in endocytosis, we conclude that Las17p and End5p interact and are essential for endocytosis.

Inclusion of cholesterol in DOTAP transfection complexes increases the delivery of DNA to cells in vitro in the presence of serum

The contrast between the relative efficiency of transfection by cationic lipid reagents in vitro and that in vivo is well recognised. One suggested reason for this is the presence of competing polyanionic surfaces in blood and other biological fluids, and even in vitro transfections have to be performed in low-serum medium. In this study we have shown that by preparing cationic lipid reagents based on DOTAP with cholesterol as a second constituent of the bilayer we can achieve significant levels of in vitro transfection in serum concentrations of up to 80% (DOTAP alone did not transfect at all in these conditions). In an effort to explain the behaviour of DOTAP/cholesterol mixes under these conditions, we examined the effect of serum on the transfection complex. We could detect protein bound to each type of cationic lipid complex, but there was no difference in the amount nor in the type of protein bound. DNA within either type of complex which were incubated with increasing amounts of serum remained resistant to digestion with DNase I, and there was no reduction in the condensation of the DNA as measured by ethidium bromide fluorescence. Finally, we measured the attachment and uptake into cells by the different complexes in the presence of serum and showed that more DOTAP-cholesterol than DOTAP complexes attach to and are taken up by cells in the presence of serum. We suggest that improved cell binding and uptake may be the main mechanism by which cholesterol acts to maintain transfection in the presence of serum.

Evidence for safety and efficacy of DOTAP cationic liposome mediated CFTR gene transfer to the nasal epithelium of patients with cystic fibrosis

In cystic fibrosis (CF), mutation of the cystic fibrosis transmembrane conductance regulator (CFTR) gene results in defective transepithelial ion transport, leading to life shortening inflammatory lung disease. Before lung studies, we tested the safety and efficacy of gene delivery to the nasal epithelium of CF patients using pCMV-CFTR-DOTAP cationic liposome complex. A single dose of 400 micrograms pCMV-CFTR:2.4 mg DOTAP was administered in a randomised, double-blinded fashion to the nasal epithelium of eight CF patients, with a further eight receiving buffer only. Patients were monitored for signs and symptoms for 2 weeks before treatment and 4 weeks after treatment. Inflammatory cells were quantified in a nasal biopsy taken 3 days after treatment. There was no evidence for excess nasal inflammation, circulating inflammatory markers or other adverse events ascribable to active treatment. Gene transfer and expression were assayed by the polymerase chain reaction. Transgene DNA was detected in seven of the eight treated patients up to 28 days after treatment and vector derived CFTR mRNA in two of the seven patients at +3 and +7 days. Transepithelial ion transport was assayed before and after treatment by nasal potential difference during drug perfusion and by SPQ fluorescence halide ion conductance. Partial, sustained correction of CFTR-related functional changes toward normal values were detected in two treated patients. The level of gene transfer and functional correction were comparable to those reported previously using adenoviral vectors or another DNA-liposome complex, but here were sustained and uncompromised by false positives. These results justify further studies with pCMV-CFTR-DOTAP aimed at treating CF lung disease.

Laboratory and clinical studies in support of cystic fibrosis gene therapy using pCMV-CFTR-DOTAP

The first phase I study of cystic fibrosis gene therapy using cationic liposomes to deliver the cystic fibrosis conductance regulator gene to the nose reported partial and transient correction of the nasal transepithelial ion transport defect, While encouraging, further improvements will be required if this form of treatment is to be of therapeutic value. We tested a new formulation, pCMV-CFTR-DOTAP. The complex is stable for 10 days and effective at correcting the electrophysiological deficit in the trachea of CF mutant mice at 8 or 9 days after intratracheal instillation. Reliable protocols for consistent detection of as few as 10 molecules of CFTR mRNA and DNA in nasal brushing samples are described, Both vector and DNA have been produced to Good Manufacturing Practice standard, Nasal potential difference measurements developed at the National Heart and Lung Institute to assess the CFTR ion channel activity in CF patients replicated well at the Scottish Adult Cystic Fibrosis Service. The SPO fluorescence assay for halide ion conductance in nasal brushings has also been tested. These establish baseline conditions in the Scottish CF cohort from which evidence for correction can be judged under clinical trial conditions. These studies formed the basis for regulatory approval of a randomised, placebo controlled double-blind phase I research study.

Plasmid DNA molecules complexed with cationic liposomes are protected from degradation by nucleases and shearing by aerosolisation

The cationic liposome DOTAP was complexed with plasmid DNA encoding beta-galactosidase in various ratios. As the concentration of DOTAP increased, the DNA became increasingly refractory to staining with ethidium bromide, presumably because the DNA was becoming condensed and being encapsulated by the liposomes. Transfection by DNA-DOTAP complexes at all ratios tested was unaffected by treatment of the complexes with DNase I. This finding has relevance to clinical trials for gene therapy of cystic fibrosis, in which patients are normally removed from treatment with DNase before receiving administration of DNA. We additionally tested the effect of aerosolisation of the liposome-DNA complex and of the DNA alone on the efficiency of in vitro transfection. Aerosolised DNA complexed with fresh DOTAP led to much lower reporter gene expression in Cos 7 cells than non-aerosolised complex, since aerosolisation appeared to destroy almost all of the plasmid. However, complexing the plasmid before passage through the nebuliser did protect most of the DNA from degradation, as reflected in the levels of transfection obtained. These findings contribute towards an overall understanding of both how DNA-cationic liposome complexes are formed and their fate following administration in vivo.

Mutation of RGA1, which encodes a putative GTPase-activating protein for the polarity-establishment protein Cdc42p, activates the pheromone-response pathway in the yeast Saccharomyces cerevisiae

We have selected yeast mutants that exhibit a constitutively active pheromone-response pathway in the absence of the beta subunit of the trimeric G protein. Genetic analysis of one such mutant revealed that it contained recessive mutations in two distinct genes, both of which contributed to the constitutive phenotype. One mutation identifies the RGA1 locus (Rho GTPase activating protein), which encodes a protein with homology to GAP domains and to LIM domains. Deletion of RGA1 is sufficient to activate the pathway in strains lacking the G beta subunit. Moreover, in wild-type strains, deletion of RGA1 increases signaling in the pheromone pathway, whereas over-expression of RGA1 dampens signaling, demonstrating that Rga1p functions as a negative regulator of the pheromone response pathway. The second mutation present in the original mutant proved to be an allele of a known gene, PBS2, which encodes a putative protein kinase that functions in the high osmolarity stress pathway. The pbs2 mutation enhanced the rga1 mutant phenotype, but by itself did not activate the pheromone pathway. Genetic and two-hybrid analyses indicate that an important target of Rga1p is Cdc42p, a p21 GTPase required for polarity establishment and bud emergence. This finding coupled with recent experiments with mammalian and yeast cells indicating that Cdc42p can interact with and activate Ste20p, a protein kinase that operates in the pheromone pathway, leads us to suggest that Rga1p controls the activity of Cdc42p, which in turn controls the magnitude of signaling in the pheromone pathway via Ste20p.

end5, end6, and end7: mutations that cause actin delocalization and block the internalization step of endocytosis in Saccharomyces cerevisiae

Four mutants defective in endocytosis were isolated by screening a collection of temperature-sensitive yeast mutants. Three mutations define new END genes: end5-1, end6-1, and end7-1. The fourth mutation is in END4, a gene identified previously. The end5-1, end6-1, and end7-1 mutations do not affect vacuolar protein localization, indicating that the defect in each mutant is specific for internalization at the plasma membrane. Interestingly, localization of actin patches on the plasma membrane is affected in each of the mutants. end5-1, end6-1, and end7-1 are allelic to VRP1, RVS161, and ACT1, respectively. VRP1 and RVS161 are required for correct actin localization and ACT1 encodes actin. To our surprise, the end6-1 mutation fails to complement the act1-1 mutation. Disruption of the RVS167 gene, which is homologous to END6/RVS161 and which is also required for correct actin localization, also blocks endocytosis. The end7-1 mutant allele has a glycine 48 to aspartic acid substitution in the DNase I-binding loop of actin. We propose that Vrp1p, Rvs161p, and Rvs167p are components of a cytoskeletal structure that contains actin and fimbrin and that is required for formation of endocytic vesicles at the plasma membrane.

Yeast MEK-dependent signal transduction: response thresholds and parameters affecting fidelity

Ste7p and Mkk1p are MEK (MAPK/ERK kinase) family members that function in the mating and cell integrity signal transduction pathways in Saccharomyces cerevisiae. We selected STE7 and MKK1 mutations that stimulated their respective pathways in the absence of an inductive signal. Strikingly, serine-to-proline substitutions at analogous positions in Ste7p (position 368) and Mkk1p (position 386) were recovered by independent genetic screens. Such an outcome suggests that this substitution in other MEKs would exhibit similar properties. The Ste7p-P368 variant has higher basal enzymatic activity than Ste7p but still requires induction to reach full activation. The higher activity associated with Ste7p-P368 allows it to compensate for defects in the cell integrity pathway, but it does so only when it is overproduced or when Ste5p is missing. This behavior suggests that Ste5p, which has been proposed to be a tether for the kinases in the mating pathway, contributes to Ste7p specificity.

Evaluation in vitro and in vivo of cationic liposome-expression construct complexes for cystic fibrosis gene therapy

We have tested the cationic liposome N-(1-(2,3-dioleoyloxy)propyl)-N,N,N-trimethyl-ammoniummethylsul phate, (DOTAP), for gene delivery in vitro and in vivo with a view to clinical use in gene therapy for cystic fibrosis. Delivery of lacZ cDNA-DOTAP complexes via aerosol showed promoter-dependent differences in the pattern and longevity of expression. Repeated administration was well tolerated. The potential for the transfer of foreign genes into reproductive tissue was investigated by intravenous injection of DNA-DOTAP into female mice. Foreign DNA was undetectable in the ovaries by Southern blot analysis at 1 and 7 days after injection. Our results suggest that DOTAP merits testing in cystic fibrosis patients for delivery of the cystic fibrosis transmembrane conductance regulator (CFTR) gene to the respiratory tract and that substitution of the cytomegalovirus (CMV) promoter for the simian virus (SV) promoter may improve on the transitory response reported previously.

Liposome-mediated CFTR gene transfer to the nasal epithelium of patients with cystic fibrosis

We report the results of a double-blind, placebo-controlled trial in nine cystic fibrosis (CF) subjects receiving cationic liposome complexed with a complementary DNA encoding the CF transmembrane conductance regulator (CFTR), and six CF subjects receiving only liposome to the nasal epithelium. No adverse clinical effects were seen and nasal biopsies showed no histological or immuno-histological changes. A partial restoration of the deficit between CF and non-CF subjects of 20% was seen for the response to low Cl- perfusion following CFTR cDNA administration. This was maximal around day three and had reverted to pretreatment values by day seven. In some cases the response to low Cl- was within the range for non-CF subjects. Plasmid DNA and transgene-derived RNA were detected in the majority of treated subjects. Although these data are encouraging, it is likely that transfection efficiency and the duration of expression will need to be increased for therapeutic benefit.

Long-term survival of the exon 10 insertional cystic fibrosis mutant mouse is a consequence of low level residual wild-type Cftr gene expression

Recently we have created a mouse model of cystic fibrosis (CF) by insertional gene targeting to exon 10. In common with CF subjects, this model displays a low incidence of meconium ileus. This contrasts strikingly with the very high level of fatal intestinal obstruction in the three other CF mouse models so far described. We investigate here the molecular basis of this difference in phenotype. We show that the partial duplication consequent upon insertional gene targeting allows exon skipping and aberrant splicing to produce normal Cftr mRNA, but at levels greatly reduced compared with wild-type mice. Furthermore, instead of the predicted mutant Cftr transcript, a novel mRNA is produced that utilizes cryptic splice sites in the disrupting plasmid sequence. However, we have previously shown that these mice display the ion transport defect characteristic of CF, and mutant animals can be distinguished from their normal littermates on this basis. Consistent with this, residual CFTR function has recently been observed for several "mild" mutations in CF individuals who display pancreatic sufficiency but still develop lung disease. We conclude that (i) residual wild-type mRNA in the exon 10 insertional mutant mouse ameliorates the severity of the intestinal phenotype observed in the absolute "null" CF mice, (ii) the presence of low-level residual wild-type Cftr mRNA does not correct the CF ion transport defect, and (iii) the long-term survival of this insertional mutant mouse provides the opportunity to address the factors important in development of lung disease.

A series of vectors that simplify mammalian gene targeting

In order to facilitate the procedure of mammalian gene targeting, we have produced and functionally tested a series of generic vectors. Homologous recombination has been achieved with each vector. The vectors are designed for both replacement and insertional recombination, are suitable for 'hit and run' strategies and contain all necessary genetic elements for both positive-negative and promoterless/gene fusion enrichment of homologous integrations. Multiple unique restriction sites are included to simplify the incorporation of genomic targeting sequences.

Functional homology of protein kinases required for sexual differentiation in Schizosaccharomyces pombe and Saccharomyces cerevisiae suggests a conserved signal transduction module in eukaryotic organisms

We present genetic evidence that three presumptive protein kinases of Schizosaccharomyces pombe, byr2, byr1, and spk1 that are structurally related to protein kinases of Saccharomyces cerevisiae, STE11, STE7, and FUS3, respectively, are also functionally related. In some cases, introduction of the heterologous protein kinase into a mutant was sufficient for complementation. In other cases (as in a ste11- mutant of S. cerevisiae), expression of two S. pombe protein kinases (byr2 and byr1) was required to observe complementation, suggesting that byr2 and byr1 act cooperatively. Complementation in S. pombe mutants is observed as restoration of sporulation and conjugation and in S. cerevisiae as restoration of conjugation, pheromone-induced cell cycle arrest, and pheromone-induced transcription of the FUS1 gene. We also show that the S. pombe kinases bear a similar relationship to the mating pheromone receptor apparatus as do their S. cerevisiae counterparts. Our results indicate that pheromone-induced signal transduction employs a conserved set of kinases in these two evolutionarily distant yeasts despite an apparently significant difference in function of the heterotrimeric G proteins. We suggest that the STE11/byr2, STE7/byr1, and FUS3/spk1 kinases comprise a signal transduction module that may be conserved in higher eukaryotes. Consistent with this hypothesis, we show that a mammalian mitogen-activated protein (MAP) kinase, ERK2, can partially replace spk1 function in S. pombe.

Cystic fibrosis in the mouse by targeted insertional mutagenesis

Cystic fibrosis is a fatal genetic disorder which afflicts 50,000 people worldwide. A viable animal model would be invaluable for investigating and combating this disease. The mouse cystic fibrosis transmembrane conductance regulator gene was disrupted in embryonal stem cells using an insertional gene targeting vector. Germ-line chimaeras were derived and the offspring of heterozygous crosses studied. These homozygous mutant mice survive beyond weaning. In vivo electrophysiology demonstrates the predicted defect in chloride ion transport in these mice and can distinguish between each genotype. Histological analysis detects important hallmarks of human disease pathology, including abnormalities of the colon, lung and vas deferens. This insertional mouse mutation provides a valid model system for the development and testing of therapies for cystic fibrosis patients.

Constitutive mutants of the protein kinase STE11 activate the yeast pheromone response pathway in the absence of the G protein

STE4 encodes the beta-subunit of a heterotrimeric guanine nucleotide-binding protein (G protein) that is an early and essential component of the pheromone signal transduction pathway. From a ste4 deletion strain we have isolated both dominant and recessive suppressors that show increased transcription of pheromone responsive genes and have regained the ability to mate, albeit at a low level. Each of these suppressor mutations suppresses ste4 and ste5 deletions but not deletions in STE7, STE11, or STE12. Among the dominant mutations, we have identified two alleles of STE11, a gene that encodes a protein kinase activity essential for mating. One allele contains an alteration in the putative regulatory domain of the protein kinase; the second allele has an alteration in the catalytic site. In strains carrying these mutations, a second protein kinase required for mating, STE7, becomes hyperphosphorylated, just as it does in wild-type cells treated with pheromone. Thus, a protein kinase cascade appears to be an essential feature of the response pathway and probably connects the receptor/G protein to an identified transcription factor, STE12.

Identification of a cell-specific DNA-binding activity that interacts with a transcriptional activator of genes expressed in the acinar pancreas

Footprint analysis of the 5'-flanking regions of the alpha-amylase 2, elastase 2, and trypsina genes, which are expressed in the acinar pancreas, showed multiple sites of protein-DNA interaction for each gene. Competition experiments demonstrated that a region from each 5'-flanking region interacted with the same cell-specific DNA-binding activity. We show by in vitro binding assays that this DNA-binding activity also recognizes a sequence within the 5'-flanking regions of elastase 1, chymotrypsinogen B, carboxypeptidase A, and trypsind genes. Methylation interference and protection studies showed that the DNA-binding activity recognized a bipartite motif, the subelements of which were separated by integral helical turns of DNA. The alpha-amylase 2 cognate sequence was found to enhance in vivo transcription of its own promoter in a cell-specific manner, which identified the DNA-binding activity as a transcription factor (PTF 1). The observation that PTF 1 bound to DNA sequences that have been defined as transcriptional enhancers by others suggests that this factor is involved in the coordinate expression of genes transcribed in the acinar pancreas.

Thromboembolic meningoencephalitis caused byHaemophilus somnusinfection in a bull calf — A new disease in New Zealand

Thromboembolic meningoencephalitis (TEME) caused by Huemophilus somnus infection was diagnosed for the first time in New Zealand in an eight month old bull calf. Clinical signs included pyrexia, excessive salivation, recumbency, opisthotonus and rigidity of the front legs. Multiple red, malacic foci (1-10 mm in diameter) were visible grossly on the surface of the cerebrum and cerebellum, and were scattered throughout the brain parenchyma. Histologically these lesions consisted of focal haemorrhage, necrosis and neutrophilic infiltration. Fibrin thrombi and colonies of gram negative bacteria were present in many small blood vessels within necrotic foci. An organism with the morphological and biochemical characteristics of Haemophilus somnus was cultured from the brain. Although TEME is an important disease of feedlot cattle in North America and Europe it is relatively uncommon in cattle grazing pasture and is therefore unlikely to become a major problem in New Zealand.

Sequence organisation and transcriptional regulation of the mouse elastase II and trypsin genes

Elastase II and trypsin mRNAs were cloned in form of their cDNAs from pancreas of strain A/J mice, and their complete nucleotide sequences were determined. The elastase II mRNA is 912 nucleotides long and encodes a protein of 271 amino acids. The cloned trypsin mRNA species is 814 nucleotides long and encodes a protein of 246 amino acids. The elastase II gene, which exists as a single copy in the haploid mouse genome, measures 11.2 kb from cap to poly(A) site and is interrupted by at least seven introns. Between 5 and 10 trypsin genes exist in the mouse genome. Five different trypsin genes, two of which are closely linked in a tail-to-tail manner, were studied in detail. They vary in size between 3.4 and 4.0kb, and all are interrupted by four introns. DNA sequence comparison of the elastase II, trypsin and Amy-2a alpha-amylase genes reveals a conserved 13 nucleotide motif in their 5'-flanking regions. The differential accumulation of the elastase II and trypsin mRNAs in the cytoplasm of the acinar pancreatic cell is regulated predominantly at the transcriptional level.

The Yorkshire antenatal anti-D immunoglobulin trial in primigravidae

2069 Rh(D)-negative women in their first pregnancy received 100 micrograms doses of anti-D immunoglobulin at 28 and 34 weeks' gestation and a further dose at delivery if the infant was Rh(D)-positive. The antibody status was determined at 28 weeks, 34 weeks, at delivery, and 6 months after delivery. The findings were compared with those in a control group of 2000 Rh(D)-negative primigravidae who gave birth to Rh(D)-positive infants and received the standard post-delivery injection of anti-D immunoglobulin. 2 women in the trial group and 18 in the control group became actively immunised during the first pregnancy. 325 women in the trial group have had a further Rh(D)-positive pregnancy and in 2 anti-D antibodies were detected for the first time. 528 control women have had a further Rh(D)-positive pregnancy and anti-D was demonstrable in 29-18 in whom antibodies developed during the first pregnancy and 11 in whom antibodies first appeared during the second. The reduction in the incidence of sensitisation was significant. It is estimated that the extra cost in anti-D immunoglobulin was approximately pounds 1600 for each woman sensitised.