Mitigating xenogeneic barriers to chimerism through Cas13-induced host attenuation.

Interspecies chimeras serve as valuable models for studying mammalian development and advancing strategies for organ generation. However, xenogeneic barriers-such as mismatched developmental timing, cell adhesion differences, and intercellular competition-restrict the contribution of human pluripotent stem cells (hPSCs) to non-human embryos. Here, we report that Cas13 collateral RNA cleavage can be harnessed to selectively attenuate host cell proliferation to boost donor cell chimerism. In mouse epiblast stem cells (mEpiSCs), Cas13 activation degraded target RNAs and bystander transcripts, producing a reversible decrease in cell proliferation while preserving pluripotency. In co-culture, selective attenuation of mEpiSCs enhanced the competitiveness and survival of wild-type mEpiSCs and hPSCs in both intra- and interspecies settings. In vivo, blastocysts engineered with inducible Cas13 (iCas13) showed increased donor cell integration in chimeric embryos and adult tissues. Together, these findings demonstrate a generalizable strategy to modulate donor-host dynamics and mitigate xenogeneic barriers to interspecies organogenesis.