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VIRTUAL PRA AND CROSSMATCHING

Dolly B. Tyan, PhD

Cedars-Sinai Medical Center

Los Angeles, CA

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PURPOSE OF PRA

• TO INFORM THE CLINICIAN/SURGEON OF THE:

–LIKELIHOOD OF A TRANSPLANT

–ANTIBODY SPECIFICITY

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PRAPanel Reactive Antibody – (%)

•Relatively uninformative

•No specificity

•Population dependent

•Can vary widely by panel tested

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PRA VARIABILITY50 cell panel

A2+ CELLS

ON PANEL

PRA

(%)

5 10

10 20

25 50

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CDCCDC 102102 162 162CDCCDC 102102 162 162

PRA ANALYSIS BY DIFFERING PRA ANALYSIS BY DIFFERING METHODLOGIESMETHODLOGIES

PRA ANALYSIS BY DIFFERING PRA ANALYSIS BY DIFFERING METHODLOGIESMETHODLOGIES

POSITIVEPOSITIVE NEGATIVENEGATIVEPOSITIVEPOSITIVE NEGATIVENEGATIVE

AHG-CDCAHG-CDC 116 116 (+13%)(+13%) 148 148AHG-CDCAHG-CDC 116 116 (+13%)(+13%) 148 148

ELISAELISA 127 127 (+10%)(+10%) 137 137ELISAELISA 127 127 (+10%)(+10%) 137 137

FLOWFLOW 139 139 (+10%)(+10%) 125 125FLOWFLOW 139 139 (+10%)(+10%) 125 125

Gebel and Bray, Transplantation 69:1370-1374, 2000.Gebel and Bray, Transplantation 69:1370-1374, 2000.

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Calculated PRA value

Based on: ABSOLUTE antibody specificity andACTUAL HLA antigen frequencies in donor populationINDEPENDENT of the method

Calculated PRA value

Based on: ABSOLUTE antibody specificity andACTUAL HLA antigen frequencies in donor populationINDEPENDENT of the method

Virtual PRA

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NATIONAL PRA

Calculatethe antigen frequency

of all donors ever typedin UNET database

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CALCULATED PRA –STANDARDIZED

Antibody Specificity PRA (%)

A1 21

B8 17

A1 + B8 28

DR3 24

A1 + B8 + DR3 45

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ConclusionsConclusions

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

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

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PURPOSE OF CROSSMATCH

• TO INFORM THE CLINICIAN/SURGEON OF THE RISK* FOR:

–PRESENCE OF DSA (DONOR SPECIFIC ANTIBODIES)

–HYPERACUTE REJECTION–HUMORAL REJECTION

* (not contraindication)

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CAN WE DO A VIRTUAL CROSSMATCH???

WE ARE DOING IT NOW! (BUT NOT WELL…)

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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

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FINAL XM WORKLOADCURRENT 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

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CALCULATED PRA –STANDARDIZED

Antibody Specificity PRA (%)

A1 21

B8 17

A1 + B8 28

DR3 24

A1 + B8 + DR3 45

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VIRTUAL XMPROPOSED 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

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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

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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

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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)

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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

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CONCLUSIONS

VIRTUAL PRA

–Results in National PRA Equivalence

VIRTUAL CROSSMATCH- Accelerates organ placement

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CAVEAT

A variant systemis requiredfor patients

undergoing desensitization