Berberine Promotes Induction of Immunological Tolerance to an Allograft via Downregulating Memory CD8+ T-Cells Through Altering the Gut Microbiota

Emerging evidence has linked the gut microbiota dysbiosis to transplant rejection while memory T-cells pose a threat to long-term transplant survival. However, it's unclear if the gut microbiome alters the formation and function of alloreactive memory T-cells. Here we studied the effects of berberine, a narrow-spectrum antibiotic that is barely absorbed when orally administered, on the gut microbiota, memory T-cells, and allograft survival. In this study, C57BL/6 mice transplanted with islets or a heart from BALB/c mice were treated orally with berberine. Allograft survival was observed, while spleen, and lymph node T-cells from recipient mice were analyzed using a flow cytometer. High-throughput sequencing and qPCR were performed to analyze the gut microbiota. CD8(+) T-cells from recipients were cultured with the bacteria to determine potential T-cell memory cross-reactivity to a specific pathogen. We found that berberine suppressed islet allograft rejection, reduced effector CD8(+)CD44(high)CD62L(low) and central memory CD8(+)CD44(high)CD62L(high) T-cells (T-CM), altered the gut microbiota composition and specifically lowered Bacillus cereus abundance. Further, berberine promoted long-term islet allograft survival induced by conventional costimulatory blockade and induced cardiac allograft tolerance as well. Re-colonization of B. cereus upregulated CD8(+) T-CM cells and reversed long-term islet allograft survival induced by berberine plus the conventional costimulatory blockade. Finally, alloantigen-experienced memory CD8(+) T-cells from transplanted recipients rapidly responded to B. cereus in vitro. Thus, berberine prolonged allograft survival by repressing CD8(+) T-CM through regulating the gut microbiota. We have provided the first evidence that donor-specific memory T-cell generation is linked to a specific microbe and uncovered a novel mechanism underlying the therapeutic effects of berberine. This study may be implicated for suppressing human transplant rejection since berberine is already used in clinic to treat intestinal infections.

Automated summary

This study demonstrates that berberine prolongs allograft survival by repressing CD8(+) central memory T-cells through regulating the gut microbiota, providing a novel mechanism underlying its therapeutic effects.