Hypothesis: Tregulator/Teffector cell balance toward donor antigens will predict long term outcome in drug minimization trials.
Methods: Recipients of a 1 HLA haplotype mismatched kidney from living related donor [n=9] or a HLA 0MM deceased donor kidney[n=1] were induced with a single dose of Alemtuzumab, tacrolimus, and sirolimus. Tacrolimus was withdrawn at 3 mos. Fresh PBMC were sampled and tested for donor-specific regulation [DSR] at 6 mo intervals. DSR was measured by % bystander suppression of recall antigen [EBV or TT]-induced footpad swelling in the trans-vivo DTH assay. Suppression was triggered via indirect pathway, using a crude cell sonicate of donor Ags [dAg]. Patients were also monitored for humoral anti-donor immunity using Luminex single antigen beads, quantitated by MFI values for identified immunodominant donor class I and class II specificities.
Results: Median follow-up time was 4 yrs. All patients except 2 [see Table 1] have been successfully maintained on sirolimus monotherapy. Patients were classified according to regulation status over multiple timepoints: 1) Regulators= bystander suppression values were consistently [6/7,7/7 timepoints] >50%; 2) Non-regulators= no regulation at any time, or only a single timepoint of >50% regulation ; and 3) Intermediate= 2-3 timepoints of DSR >50%.
| Regulator | Non-Regulator | Intermediate | |
| No. of Patients | n=2 | n=4 | n=4 |
| Creatinine (mg/dL) | 1.1 | 2 | 1.6 |
| Estimated GFR* | 60 | 36.5 | 53 |
| Sirolimus dose (mg/24h) | 1 | 4** | 1 |
| Sirolimus level (ng/mL) | 4 | 10 | 6 |
| Protein/creatinine (g/g) | 0.0995 | 0.79 | 0.13 |
| MFI Class I *** | 100 | 500 | 111 |
| MFI Class II*** | 0 | 5344 | 0 |
*ml/min/1.73m2
**No other immunosuppressants except for:
1 pt on Tacrolimus 6 mg daily, MPA 540 mg bid and pred
1 pt on MPA 540 mg bid and pred
***Immunodominant donorspecific antibody measured by single bead Luminex assay
Conclusions: Sirolimus monotherapy after Alemtuzumab induction and CNI withdrawal was associated with better clinical outcomes in regulators (intermediate or total) compared to non-regulators. Regulators had lower DSA levels to donor HLA antigens. The tolerance signature in PBMC was dynamic, and thus may require longitudinal f/u to establish its stability for use in IS minimization trials.