Passive perinatal immunotherapy via transamniotic antibody delivery

Transamniotic Fetal Immunotherapy with Secretory IgA: A Potential Novel Ancillary Strategy for the Prevention of Necrotizing Enterocolitis

INTRODUCTION

Secretory immunoglobulin-A (SIgA), which is not produced perinatally, binds bacteria enhancing mucosal immunity. Higher levels of intestinal bacteria bound by SIgA are protective against necrotizing enterocolitis. Transamniotic fetal immunotherapy (TRAFIT) has previously been used to deliver SIgA to the fetal digestive tract, however, with unclear functional impact. We sought to determine whether SIgA administered via TRAFIT could functionally bind intestinal bacteria postnatally.

METHODS

Fetuses (n = 38) from 4 dams underwent intra-amniotic injections of human SIgA on gestational day 19 (E19; term = E22-E23). After spontaneous delivery, pups were survived for 1-2 days postnatally before intestinal contents were procured and submitted to flow cytometry. Specimens were stained for bacteria (Syto-GFP) and human SIgA (PE) to prevent cross-reactivity with maternal rat SIgA.

RESULTS

Overall survival was 94.7% (36/38). SIgA-bacterial complexes were identified in all samples at all time points showing significantly higher positive PE events than unstained controls (p = 0.03-0.05). The proportion of bacteria bound by IgA decreased daily, from 45.6% to 29.9% bound at 4-6 days post-TRAFIT, respectively (overall p = 0.05).

CONCLUSIONS

TRAFIT with secretory IgA leads to functionally IgA-bound bacteria into the postnatal period and may be a novel strategy for enhancing early mucosal immunity, potentially protecting the neonate against necrotizing enterocolitis.

Fetal Secretory IgA Delivery via Transamniotic Fetal Immunotherapy (TRAFIT) in a Rodent Model

PURPOSE

We sought to determine the feasibility and routing kinetics of transamniotic fetal delivery of secretory immunoglobulin-A (SIgA), in a rodent model.

METHODS

Fetuses (n = 94) from seven time-dated pregnant dams received intra-amniotic injections on gestational day 17 (E17, term = E21-22) of either saline (n = 15) or a solution of 1 mg/mL of ≥95% homogeneous human SIgA (n = 79). Animals were euthanized daily at E18-E21 for quantification of the IgA component by ELISA at gestational membranes, placenta, and select fetal anatomical sites against saline controls procured at term. Statistical analysis was by Mann-Whitney U-test.

RESULTS

None of the saline-injected animals had detectable human IgA. SIgA-injected fetuses showed human IgA in the stomach aspirate, intestinal wall, lungs, liver, and serum at all time points. IgA levels were significantly higher in the gastric aspirate and in the intestine than in all other sites (p < 0.001 for both), with intestinal levels remaining stable through E18-E21 (p = 0.09-0.62 pairwise). Serum and placental levels were consistently low throughout, reaching near zero levels by E21.

CONCLUSIONS

The chronology of exogenous secretory-IgA kinetics after intra-amniotic injection is suggestive of fetal uptake by ingestion, leading to consistent levels in the gastrointestinal tract. Transamniotic fetal immunotherapy (TRAFIT) with secretory-IgA may become a novel strategy for enhancing early mucosal immunity.

LEVEL OF EVIDENCE

N/A (animal and laboratory study).

TYPE OF STUDY

Animal and laboratory study.

Fetal Alloimmune Hemolytic Anemia (AHA) as a Potential Target for Transamniotic Fetal Immunotherapy (TRAFIT)

PURPOSE

Fetal alloimmune hemolytic anemia (AHA) resulting from maternal antibodies against fetal erythrocytes may require fetal administration of immunoglobulin-G (IgG) via invasive methods. IgG can reach the fetal circulation after transamniotic fetal immunotherapy (TRAFIT). We sought to both develop a model of AHA and to test TRAFIT as a potential treatment.

METHODS

Sprague-Dawley fetuses (n = 113) received intra-amniotic injections on gestational-day 18 (E18, term = E21) of either saline (control; n = 40), anti-rat-erythrocyte antibodies (AHA; n = 37), or anti-rat-erythrocyte antibodies plus IgG (AHA + IgG; n = 36). At term, blood was procured for red blood count (RBC), hematocrit, or ELISA for inflammatory markers.

RESULTS

There was no difference in survival [95% (107/113)] across groups (p = 0.87). Both hematocrit and RBC were significantly lower in the AHA group than controls (p < 0.001). Although still significantly lower than controls (p < 0.001), both hematocrit and RBC significantly increased in AHA + IgG group compared to AHA alone (p < 0.001). Pro-inflammatory TNF-α and IL1-β were significantly elevated from controls in the AHA group, but not in AHA + IgG (p < 0.001-0.159).

CONCLUSIONS

Intra-amniotic injection of anti-rat-erythrocyte antibodies can reproduce manifestations of fetal AHA, constituting a practical model of this disease. Transamniotic fetal immunotherapy with IgG reduces anemia in this model and may emerge as a new minimally invasive means of treatment.

TYPE OF STUDY

Animal and laboratory study.

LEVEL OF EVIDENCE

N/A (animal and laboratory study).

Hematogenous Routing of Exogenous mRNA Delivered Into the Amniotic Fluid

INTRODUCTION

Therapies based on exogenous messenger RNA (mRNA) administration have emerged as a powerful novel strategy for the actual or potential treatment of an assortment of diseases, including congenital surgical pathologies. We sought to determine whether the minimally invasive transamniotic route could be an alternative for prenatal mRNA delivery.

METHODS

Pregnant Sprague-Dawley dams underwent laparotomy followed by volume-matched intra-amniotic injections in all their fetuses (n = 120) of either a suspension of a custom firefly luciferase mRNA encapsulated by a lipid- and synthetic cationic polymer-based composite, or of a suspension of the same encapsulation components without mRNA, on gestational day 17 (E17; term = E21-22). On E18, E19, E20, and E21, samples from 14 fetal anatomical sites and maternal serum were procured for the screening of mRNA incorporation by host cells by measurement of luciferase activity via microplate luminometry. Statistical analysis was by Mann-Whitney U-test, including Bonferroni-adjustment.

RESULTS

Overall survival was 87.5% (105/120). Controlled by the encapsulating composite without mRNA, luciferase activity was detected in the animals that received encapsulated mRNA in the following fetal annexes: amniotic fluid, amnion, chorion, umbilical cord, and placenta (P = 0.033 to <0.001), as well as in the following fetal sites: liver, stomach, intestines, and lungs (P = 0.043-0.002).

CONCLUSIONS

Packaged exogenous mRNA can be incorporated by the fetus at least at select anatomical sites after simple intra-amniotic administration in a rodent model. The pattern and chronology of mRNA incorporation are compatible with transplacental hematogenous routing, as well as with fetal swallowing/aspiration. Further study of transamniotic mRNA administration is warranted.

Routing kinetics of human immunoglobulin-G after transamniotic fetal immunotherapy (TRAFIT) in a rodent model

PURPOSE

The transamniotic route was recently discovered as a minimally invasive means of fetal immunoglobulin administration, however by unclear mechanisms. We sought to examine IgG routing after intra-amniotic delivery.

METHODS

Sprague-Dawley fetuses (n = 78) received intra-amniotic injections of 15 mg/mL of human IgG on gestational-day 18 (E18; term=21 and 22 days). Amniotic fluid, amnion, chorion, placenta, fetal serum, liver, and stomach-aspirate samples were procured on E19, E20, and E21 for IgG quantification by ELISA. Statistical analysis was by median regression with Bonferroni-adjusted significance at p < 0.017.

RESULTS

Human IgG was detected at all sampled sites across all time points, though at significantly higher levels in the gestational membranes and fetal serum than in the stomach aspirate and liver (p < 0.001 for both). Gestational membranes showed a daily decrease after injection, stabilizing by E20 and E21 (p = 0.792 to < 0.001). Placental levels were significantly lower at E21 than E19 (p = 0.010). Fetal serum showed the highest human IgG levels at term.

CONCLUSIONS

The chronology of exogenous IgG kinetics after intra-amniotic injection is suggestive of direct placental transport leading to consistently high fetal serum levels, possibly combined with some fetal ingestion. Transamniotic fetal immunotherapy (TRAFIT) may become a practicable strategy for the prenatal treatment of select alloimmune disorders and infections.

LEVEL OF EVIDENCE

N/A (Animal and Laboratory study).

TYPE OF STUDY

Animal and Laboratory Study.