1. Relationship between Mixed Chimerism and Clinical Tolerance after Combined Kidney and Hematopoietic Cell Transplantation using Total Lymphoid Irradiation and Antithymocyte Globulin Conditioning
Stephan Busque, John Scandling, Judith Shizuru, Robert Lowsky, Asha Shori, Kent Jensen, Edgar Engleman and Sam Strober

2. TTS 2010 Congress, Vancouver
Immune Tolerance
Definition
The specific absence of a destructive immune response to a transplanted tissue without immunosuppression
Operational Criteria
1) Complete withdrawal of immunosuppression followed by,
2) No evidence for rejection of transplanted organ for > 1 year
Specificity
1) In animals: Normal rejection of third-party graft
2) in humans: Specific in vitro non-responsiveness to donor
Strober S and Sachs D
TTS 2010 Congress, Vancouver 2

3. The host’s chimeric immune system sees the donor graft as self
Pathway to Tolerance
Immune chimerism has been thought to be the way to tolerance since the work of Medawar and colleagues in neonatal mice six decades ago*
The host’s chimeric immune system sees the donor graft as self
* Billingham RE, et al.
Nature 172: 603, 1953

4. Two Types of Chimerism Complete Mixed  Partial
Nature of replacement of recipient immune and blood-forming cells with donor cells
Partial
Used to treat cancer 
No recipient immune cells present
Both donor and recipient immune cells present
Host vs donor tolerance can be tested
Donor vs host tolerance can be tested
Significant risk of GvHD
Significant risk of infection
Goal of Stanford protocol

5. Stanford Tolerance Induction HLA-Matched and -Mismatched Protocols 2005-2016 Goals
No immune graft loss
Achieved in all 45 patients enrolled over the last 11 years
No severe or chronic infection, or GvHD
Achieved in all 45
No maintenance immunosuppressive drugs
Achieved in 80% of HLA-matched
Not yet achieved in mismatched

6. Stanford Tolerance Induction

7. Stanford Tolerance Induction Combined Kidney and Hematopoietic Cell Transplantation
rATG (1.5 mg/kg x 5)
TLI (120 cGy x 10)
CD34+ cells
CD3+ cells
Day 0
Kidney
Transplant
MMF > 1 mo
Corticosteroid
Calcineurin Inhibitor > 6 mo
Withdraw immunosuppression if:
- Mixed chimerism > 6 months
- No evidence of rejection
- No GvHD

8. HLA-Matched Protocol Immunosuppression-Independent Chimerism
Days After Kidney Transplantation

9. HLA-Matched Protocol Immunosuppression-Dependent Chimerism
Days After Kidney Transplantation
Days After Kidney Transplantation

10. HLA-Matched Protocol 2005-2016 Current Status
28 transplanted
21 mixed chimeras withdrawn from immunoRx drug
20 without subsequent rejection
Up to 8 years off drug
7 of the 21 have not lost mixed chimerism
14 of the 21 lost mixed chimerism after year 1
1 developed acute rejection at 4 years off drug
5 did not achieve mixed chimerism
2 are in drug taper

11. HLA Haplotype-Matched Protocol 2010-2016 Goals and Current Status
Step 1
T-cell dose escalation study to achieve mixed chimerism for at least 1 year
17 transplanted; 5 achieved goal
Step 2
In persistent chimeras:
Withdraw MMF during months 9-12
Taper tacrolimus to minimum effective dose (MED), 3-5 ng/mL, during months 12-15
5 achieved goal
Step 3
Withdraw tacrolimus during year 2
Return to MED if chimerism lost
In progress

12. HLA Haplotype-Matched Protocol Loss of Chimerism after Drug Withdrawal10
% Donor Cells
CNI/MMF dose (mg/day)
Serum Creatinine
Days After Kidney Transplantation

13. Stanford Tolerance Induction 2005-2016 Summary
HLA-Matched Protocol
No graft loss
80% developed mixed chimerism and came off drug
HLA Haplotype-Matched Protocol
Persistent mixed chimerism achieved
Drug withdrawal in chimeras in year 2 to determine fraction on MED tacrolimus versus off drug
No GvHD
No severe or chronic infection

14. Conclusion What of mixed chimerism as a biomarker? HLA-Matched
Loss after drug withdrawal may be a biomarker of risk of losing tolerance
HLA-Mismatched
Biomarker of host vs donor tolerance
Guide to withdrawal of immunoRx drug

15. Stanford Tolerance Induction Core Clinical and Translational Investigative Team
Medicine
Robert Lowsky, MD
John Scandling, MD
Judy Shizuru, PhD, MD
Sam Strober, MD
Radiation Therapy
Richard Hoppe, MD
Surgery
Stephan Busque, MD
Asha Shori, MD
Pathology
Ed Engleman, MD