Fetoscopic versus Ultrasound-Guided Intravascular Delivery of Maternal Bone Marrow Cells in Fetal Macaques: A Technical Model for Intrauterine Haemopoietic Cell Transplantation

Regenerative medicine: prenatal approaches

This two-paper Series focuses on recent advances and applications of regenerative medicine that could benefit paediatric patients. Innovations in genomic, stem-cell, and tissue-based technologies have created progress in disease modelling and new therapies for congenital and incurable paediatric diseases. Prenatal approaches present unique opportunities associated with substantial biotechnical, medical, and ethical obstacles. Maternal plasma fetal DNA analysis is increasingly adopted as a noninvasive prenatal screening or diagnostic test for chromosomal and monogenic disorders. The molecular basis for cell-free DNA detection stimulated the development of circulating tumour DNA testing for adult cancers. In-utero stem-cell, gene, gene-modified cell (and to a lesser extent, tissue-based) therapies have shown early clinical promise in a wide range of paediatric disorders. Fetal cells for postnatal treatment and artificial placenta for ex-utero fetal therapies are new frontiers in this exciting field.

Maternal microchimerism and cell-mediated immune-modulation enhance engraftment following semi-allogenic intrauterine transplantation

Successful intrauterine hematopoietic cell transplantation (IUT) for congenital hemoglobinopathies is hampered by maternal alloresponsiveness. We investigate these interactions in semi-allogenic murine IUT. E14 fetuses (B6 females × BALB/c males) were each treated with 5E+6 maternal (B6) or paternal (BALB/c) bone marrow cells and serially monitored for chimerism (>1% engraftment), trafficked maternal immune cells, and immune responsiveness to donor cells. A total of 41.0% of maternal IUT recipients (mIUT) were chimeras (mean donor chimerism 3.0 ± 1.3%) versus 75.0% of paternal IUT recipients (pIUT, 3.6 ± 1.1%). Chimeras showed higher maternal microchimerism of CD4, CD8, and CD19 than non-chimeras. These maternal cells showed minimal responsiveness to B6 or BALB/c stimulation. To interrogate tolerance, mIUT were injected postnatally with 5E+6 B6 cells/pup; pIUT received BALB/c cells. IUT-treated pups showed no changes in trafficked maternal or fetal immune cell levels compared to controls. Donor-specific IgM and IgG were expressed by 1%-3% of recipients. mIUT splenocytes showed greater proliferation of regulatory T cells (Treg) upon BALB/c stimulation, while B6 stimulation upregulated the pro-inflammatory cytokines more than BALB/c. pIUT splenocytes produced identical Treg and cytokine responses to BALB/c and B6 cells, with higher Treg activity and lower pro-inflammatory cytokine expression upon exposure to BALB/c. In contrast, naïve fetal splenocytes demonstrated greater alloresponsiveness to BALB/c compared to B6 cells. Thus pIUT, associated with increased maternal cell trafficking, modulates fetal Treg, and cytokine responsiveness to donor cells more efficiently than mIUT, resulting in improved engraftment. Paternal donor cells may be considered alternatively to maternal donor cells for intrauterine and postnatal transplantation to induce tolerance and maintain engraftment.