Nanoparticles decorated with the iRGD homing peptide selectively delivered payloads to the placentas of pregnant primates without crossing to the fetus — a major step toward safe pregnancy treatments.
Placenta only — no fetal exposureiRGD peptide-decorated nanoparticles accumulated in the placenta of pregnant rhesus macaques but were not detected in fetal tissues, while non-targeted nanoparticles spread to both maternal and fetal organs
What the researchers found
Liposomes decorated with the iRGD homing peptide (CRGDKGPDC) selectively accumulated in the placentas of pregnant rhesus macaques — without crossing to the fetus. This is a critical proof-of-concept: a peptide-guided nanoparticle can deliver drug payloads specifically to the placenta in a primate model closely resembling human pregnancy.
The iRGD-targeted liposomes were well tolerated with no adverse clinical reactions, no abnormal placental or fetal pathology, and stable maternal blood markers. Importantly, non-targeted (ARA peptide) liposomes showed widespread distribution to both maternal and fetal tissues — demonstrating that the iRGD peptide targeting is what prevents fetal exposure. The approach worked at both early gestation (days 45-64) and mid-gestation (days 84-100).
Why it matters
Treating pregnancy complications like preeclampsia and fetal growth restriction has been nearly impossible because any drug given to the mother also reaches the developing fetus. This peptide-targeted nanoparticle approach solves that problem by delivering drugs exclusively to the placenta. Moving from mice to rhesus macaques — whose placentas closely resemble human placentas — is a major translational milestone that brings this technology significantly closer to human clinical trials.
The numbers in context
n=11 pregnant rhesus macaques (8 iRGD, 3 ARA control) · iRGD peptide: CRGDKGPDC · Early gestation: days 45-64 · Mid-gestation: days 84-100 · Term = 165 days · No fetal transfer with iRGD · No adverse reactions · 24-hour tissue collection
How the study worked
Researchers produced liposomes using the thin-film method, decorating them with either the placenta-homing peptide iRGD (CRGDKGPDC) or a non-targeting control peptide ARA (ARALPSQRSR), and loaded them with a fluorescent tracer. These were infused intravenously into pregnant rhesus macaques at two gestational timepoints. After 24 hours, maternal blood and tissues from the mother, placenta, and fetus were collected and examined for fluorescent signal, while blood markers and organ pathology were assessed for safety.
Who was studied
11 pregnant rhesus macaques at early and mid-gestation
What this study cannot tell us
Very small sample size (11 animals total, with only 1-4 per condition). The study used a fluorescent tracer rather than an actual therapeutic drug, so drug-specific effects can't be assessed. Only a 24-hour observation window was used — longer-term safety, repeated dosing, and effects on pregnancy outcomes weren't evaluated. Rhesus macaque placentas, while similar to human placentas, are not identical.
How to read the evidence
This is a well-designed in vivo study in a highly translatable primate model (rhesus macaque) published in a respected journal. The small sample size, use of fluorescent tracer rather than therapeutic payload, and single-dose design limit the evidence grade, but the primate validation is a significant advance over the prior mouse studies.
When this study was published
Published in 2026, this is very recent research at the cutting edge of peptide-guided drug delivery. It represents the latest milestone in a line of work that began with mouse studies and has now progressed to nonhuman primates.
The bigger picture
Peptide-guided drug delivery is one of the most promising applications of peptide science. This study demonstrates the technology in one of its most impactful potential uses: making it safe to treat the placenta during pregnancy. Preeclampsia, fetal growth restriction, and other placental disorders affect millions of pregnancies globally with limited treatment options. A targeted delivery platform validated in primates could transform maternal-fetal medicine.
Questions still open
- Will the iRGD-targeted liposomes maintain their placental selectivity when loaded with actual therapeutic drugs rather than fluorescent tracers?
- How would repeated dosing over the course of pregnancy affect safety and efficacy?
- Could this platform be adapted to deliver gene therapies or other advanced therapeutics specifically to the placenta?
Common questions
How does a peptide make nanoparticles go to the placenta?
Why is it so important that the nanoparticles didn't reach the fetus?
Read the original research
Targeted nanoparticles for placenta-specific drug delivery in pregnant rhesus macaques.
Theranostics, 16(5), 2118-2135
Citation
Schmidt, Jenna K; Mitzey, Ann M; Keding, Logan T; Shaw, Sarah A; Renshall, Lewis; Beards, Frances; Al-Mugotir, Mona H; Simmons, Heather A; Basu, Puja; Schotzko, Michele L; Ren, Emily; Golos, Thaddeus G; Harris, Lynda K. (2026). Targeted nanoparticles for placenta-specific drug delivery in pregnant rhesus macaques.. Theranostics, 16(5), 2118-2135. https://doi.org/10.7150/thno.115081