Introduction: Type 1 Diabetes (T1D) is an autoimmune disorder characterized by the loss of pancreatic beta cells, causing chronic hyperglycemia. While whole pancreas and islet transplantation can restore normoglycemia, the shortage of donors and the recurrent autoimmunity present challenges for the application of this therapy. Multiple research groups have developed different protocols to generate islet cells from human pluripotent stem cells (hPSCs), but unless transplanted, these cells only recapitulate some features of their mature counterpart. This highlights the importance of the microenvironment in shaping endocrine cell maturation. While perturbations of mesenchymal, endothelial, and neuronal cells have been shown to impact endocrine function, the contribution of hematopoietic cells during pancreas development is still poorly understood. 

Methods: To gain insights into the role of the hematopoietic cells during pancreas development, we performed snRNAseq analysis of human fetal pancreatic samples and identified 12 hematopoietic clusters. By focusing on the myeloid cells, we identified two subpopulations reflecting their developmental heterogeneity and functional competence. Using hPSC-derived cell populations, we bench-marked cellular composition and molecular profiles and established a co-culture system to study myeloid-endocrine organoid development in-vitro. 

Results: We determined that hPSC-derived myeloid cells promoted the maturation and viability of developing endocrine cells, beyond the maturation state observed under standard growth conditions. Finally, we found that transplantation of myeloid-endocrine organoids enhanced engraftment, vascularization, and maturation of hPSC-derived endocrine cells in the subcutaneous space. This comprehensive interrogation of the hematopoietic cells within the pancreatic niche and its applications might revolutionize stem cell-based transplantation modalities and tissue engineering strategies for diabetes.