Objective  To systematically evaluate the similarities between six-gene-modified pig red blood cells and human red blood cells in multiple dimensions, including cell morphology, hematological parameters, microbial safety and serological compatibility, and to verify the feasibility of using six-gene-modified pig red blood cells as an alternative for blood transfusion in cases of traumatic hemorrhage.

Methods  Blood samples from O-type human donor, six-gene-modified O-type pig and wild-type O-type pig were collected. The pig gene-modified phenotype was identified by flow cytometry. The morphology was observed using field emission scanning electron microscopy and the diameter was measured. Hematological tests, including blood routine, osmotic fragility test, adenosine triphosphate (ATP) and 2,3-diphosphoglycerate (2,3-DPG) content and partial pressure of oxygen at 50% hemoglobin saturation (P50), were conducted to assess the deformability of red blood cells. Real-time fluorescent quantitative polymerase chain reaction was used to screen for zoonotic viruses, and cross-matching was performed using column gel method, condensation amine method and saline tube method.

Results  The six-gene-modified pig red blood cells successfully knocked out the α-Gal, Neu5Gc and Sda antigens and expressed hCD55. Wild-type pig red blood cells expressed these three antigens but did not express human complement regulatory proteins. All three types of red blood cells presented a biconcave discoid morphology. The diameter of O-type human red blood cells was larger than that of the six-gene-modified porcine red blood cells and wild-type pig red blood cells (all P < 0.05). The average red blood cell volume and average red blood cell hemoglobin of O-type humans were higher than those of the six-gene-modified pig red blood cells, and the distribution width-variable coefficient of O-type human red blood cells was lower than that of the six-gene-modified pig red blood cells (all P < 0.05). There were no statistically significant differences in the permeability fragility, ATP content, 2,3-DPG content, P50 and red blood cell deformability indicators of the three types of red blood cells (all P > 0.05). The screening for zoonotic viruses in human and animal cells of the six-gene-modified pigs and wild-type pigs was negative. The cross-matching results showed that in the column gel method and condensation amine method, the primary and secondary sides of the six-gene-modified pig red blood cells did not agglutinate with human red blood cells, while the wild-type pig red blood cells agglutinated with human red blood cells in all cross-matching methods.

Conclusions  The six-gene-modified pig red blood cells are highly similar to human red blood cells in terms of morphology, key hematological parameters, energy metabolism, oxygen-carrying capacity, mechanical properties, microbial safety and serological compatibility, providing an experimental basis for the clinical transformation of xenotransfusion.