Donor Specific Tolerance Of Renal Allografts Following Haploidentical In Utero Hematopoietic Cell Transplantation In The Canine Model

In utero hematopoietic cell transplantation (IUHCT) can result in allogeneic mixed hematopoietic chimerism and associated donor specific tolerance (DST). We have reported a 1-2% donor chimerism threshold for consistent DST in the murine model as defined by the ability to enhance engraftment postnatally with a same donor minimal conditioning BMT, and have confirmed this finding in the canine model of IUHCT. Recently, we have optimized the canine model and achieved higher levels of chimerism (average>10%). As prenatal tolerance induction for postnatal organ transplantation is one of the clinical goals of IUHCT, we hypothesized that the presence of donor chimerism (>2.0%) after haploidentical IUHCT in the canine model would be sufficient to allow same donor renal transplants without immunosuppression.

Stable mixed hematopoietic macrochimerism was documented by VNTR after haploidentical IUHCT performed at 40 days gestation using maternal donor BM cells in 4 pups (chimerism levels 3-38%). One positive control canine with no detectable chimerism following IUHCT also underwent haploidentical renal transplantation. Renal transplantation was performed from the maternal donor at ages between 12 and 18 months, and the pups were serially followed by ultrasound of the graft, blood chemistry and urinalysis post transplant. At 60 days an open biopsy of the allograft was taken and at 6 months a graft nephrectomy was performed for histologic analysis.

Following transplantation, all recipients demonstrated blood flow to the renal cortex and all laboratory values were within normal ranges. At 60 days and 6 months 3 of the 4 recipients demonstrated a graft without evidence of acute or chronic rejection. The recipient with the lowest level of chimerism (3%) demonstrated evidence of mild interstitial nephritis (Banff class 1 rejection) following transplantation at the time of renal biopsy which increased in severity to severe interstitial fibrosis and moderate tubular atrophy (Banff class 3 rejection) at the time of graft nephrectomy. The positive control canine without detectable chimerism demonstrated clinical and histologic evidence of acute rejection within one week of transplantation.

Our results support the ability of IUHCT to induce DST for haploidentical organ transplantation, in a large animal model, without the need for immunosuppression. In agreement with previous studies in the murine model there appears to be a threshold level of donor chimerism required for associated DST. Although our numbers are not adequate to establish absolute thresholds of chimerism predictive of DST for organ transplantation, it appears to be slightly higher than the 1-2% threshold established for cellular transplantation.

No relevant conflicts of interest to declare.