1. VIRTUAL PRA AND CROSSMATCHING
Dolly B. Tyan, PhD
Cedars-Sinai Medical Center
Los Angeles, CA
Dolly B. Tyan, PhD UNOS Strategic Planning 10/05

2. PURPOSE OF PRA TO INFORM THE CLINICIAN/SURGEON OF THE:
LIKELIHOOD OF A TRANSPLANT
ANTIBODY SPECIFICITY

3. PRA Panel Reactive Antibody – (%)
Relatively uninformative
No specificity
Population dependent
Can vary widely by panel tested

4. PRA VARIABILITY 50 cell panel
A2+ CELLS
ON PANEL
PRA
(%) 5 10 20 25 50

5. PRA ANALYSIS BY DIFFERING METHODLOGIES
POSITIVE NEGATIVE
CDC
AHG-CDC 116 (+13%)
ELISA 127 (+10%)
FLOW (+10%)
Gebel and Bray, Transplantation 69: , 2000.

6. Virtual PRA Calculated PRA value Based on:
ABSOLUTE antibody specificity and
ACTUAL HLA antigen frequencies
in donor population
INDEPENDENT of the method
Virtual PRA
Dolly B. Tyan, PhD UNOS Strategic Planning 10/05

7. of all donors ever typed
NATIONAL PRA
Calculate
the antigen frequency
of all donors ever typed
in UNET database

8. CALCULATED PRA – STANDARDIZED
Antibody Specificity
PRA (%) A1 21 B8 17
A1 + B8 28
DR3 24
A1 + B8 + DR3 45

9. Conclusions Results in National PRA Equivalence
Virtual PRA antibody detection must:
Be Sensitive and HLA-Specific
Be able to Predict the final crossmatch
Be able to identify ALL unacceptable (avoid) antigens
(A-, B-, Cw, DRB1, DQB1, DP??)
Requires accurate typing of deceased donors
Incorporate Both Class I and Class II specificities
Current definition of PRA must change:
Need local/national donor pool antigen frequencies
Incorporate both Class I and II antigens
Results in National PRA Equivalence

10. PURPOSE OF CROSSMATCH
TO INFORM THE CLINICIAN/SURGEON OF THE RISK* FOR:
PRESENCE OF DSA (DONOR SPECIFIC ANTIBODIES)
HYPERACUTE REJECTION
HUMORAL REJECTION
* (not contraindication)

11. CAN WE DO A VIRTUAL CROSSMATCH??? WE ARE DOING IT NOW! (BUT NOT WELL…)

12. WHAT IS A VIRTUAL CROSSMATCH?
Recipient antibodies fully characterized, known, and computerized (i.e., UNOS “unacceptable/avoid” algorithm)
Recipients with antibody to donor antigens are eliminated without crossmatch
parameters for which antibodies important determined at local level
Not a substitute for final crossmatch for remaining potential recipients

13. FINAL XM WORKLOAD CURRENT PRACTICE
Regional trays by ABO blood group
(First phase XMs – 100s of samples)
Final XMs
Negative patients from first phase with highest number of points (may be up to 25)
Highly sensitized patients often positive in final XM done by more sensitive technique (e.g., Flow) – i.e., wasted effort

14. CALCULATED PRA – STANDARDIZED
Antibody Specificity
PRA (%) A1 21 B8 17
A1 + B8 28
DR3 24
A1 + B8 + DR3 45

15. VIRTUAL XM PROPOSED PRACTICE
No first phase testing
Final XMs
Incompatible recipients excluded by computer
Select top 5 – 10 patients on match run for final XM
Highly sensitized patients likely to be transplanted

16. Crossmatch Comparison
First phase XMs
3-4 hrs
Final XMs – >25
Repeat CDC
Flow
Highly sensitized patients eliminated at final – wasted effort
First phase XMs
3-4 hrs
Final XMs - 5
Repeat CDC
Flow
Highly sensitized patients transplanted

17. VIRTUAL CROSSMATCH CHALLENGES
Requires complete and accurate knowledge of historical and current antibody specificity/isotype by most sensitive methods
Requires real time updating of “unacceptables” in UNET
Requires regular screening (not less than quarterly) – More for desensitization protocols

18. VIRTUAL CROSSMATCH CHALLENGES cont’d
Antibody profiles can change over time (e.g., become weaker)
Desensitization protocols can cause real time variation in antibody profile
May eliminate an eligible recipient depending on local preference (e.g., patient with antibody to 50% of the A2+ cells on panel)

19. Accelerates organ placement
VIRTUAL CROSSMATCH
BENEFITS
Decreases number of patients needing actual final crossmatch
(No regional screen trays)
Decreases time required for final crossmatching
Minimizes wasted time crossmatching highly sensitized patients with known incompatibilities
Decrease in CIT in some regions
Accelerates organ placement

20. CONCLUSIONS VIRTUAL PRA Results in National PRA Equivalence
VIRTUAL CROSSMATCH
Accelerates organ placement

21. CAVEAT A variant system is required for patients undergoing desensitization
Dolly B. Tyan, PhD UNOS Strategic Planning 10/05