Special Immunologic Situations

The contract between this chapter and the reader.

1. 1. Identify the immunologic barriers to transplantation.
2. 2. Describe ABO-incompatible transplantation and its desensitization.
3. 3. Describe HLA desensitization of the sensitized patient.
4. 4. Explain paired kidney exchange.
5. 5. Approach re-transplantation and its immunologic risk.
6. 6. Weigh paired exchange versus desensitization versus waiting.
7. 7. Recognise the higher antibody-mediated rejection risk of incompatible transplantation.
8. 8. Distinguish effective-care from preference-sensitive decisions here.
9. 9. Counsel patients on the options and their trade-offs.

A sixty-second reading. Each bullet stands alone.

• Some candidates face an immunologic barrier: an ABO-incompatible donor or HLA sensitization.
• The options are a compatible donor through paired exchange, desensitization, an incompatible transplant, or waiting.
• ABO-incompatible transplantation removes blood-group antibodies (plasma exchange, rituximab, IVIG) to a low titre before transplant.
• After an ABO-incompatible transplant, accommodation lets the graft tolerate the return of antibody.
• HLA desensitization lowers donor-specific antibody and converts a positive crossmatch with plasma exchange, IVIG, and rituximab.
• Desensitization enables transplantation but carries a higher antibody-mediated rejection risk and cost.
• Paired kidney exchange swaps incompatible donor-recipient pairs to find compatible matches.
• Paired exchange gives a compatible transplant and is preferred when available.
• Re-transplant candidates are often sensitized by the prior graft and are at higher immunologic risk.
• For an incompatible pair, the choice between paired exchange, desensitization, and waiting is preference-sensitive.
• Even a desensitized incompatible transplant may offer a survival benefit over prolonged dialysis for some.
• A compatible transplant has better outcomes than a desensitized incompatible one.
• These decisions are made with the patient, weighing risk, urgency, and donor availability.

The medical core. An expert should agree the special immunologic situations are fully covered here.

Why it matters at the bedside

Some patients have a willing donor they cannot use, or antibodies that lock them out of almost every kidney. This chapter is about getting them transplanted anyway — by swapping donors, by stripping out the offending antibody, or by accepting a calculated immunologic risk. Each route has a price, and the hardest part is often not the protocol but the decision of which route to take.

The immunologic barriers

• Two barriers recur. An ABO-incompatible donor (the recipient has blood-group antibodies against the donor) and an HLA-sensitized recipient (donor-specific antibody, a positive crossmatch, or a high cPRA — the histocompatibility chapter). For each, the menu is the same: find a compatible donor through paired exchange, lower the antibody by desensitization and transplant incompatibly, or wait for a compatible deceased donor.

ABO-incompatible transplantation

• ABO incompatibility — anti-A or anti-B isoagglutinins against the donor's blood group — is now routinely crossed. Desensitization removes the isoagglutinins (plasma exchange or immunoadsorption) with rituximab and IVIG, bringing the titre low enough to transplant safely. Remarkably, the graft then often develops accommodation, tolerating the eventual return of antibody, and outcomes with established protocols are good.

HLA desensitization

• For the HLA-sensitized recipient with donor-specific antibody and no compatible donor, desensitization lowers the DSA and converts a positive crossmatch — using plasma exchange, IVIG, and rituximab (and sometimes more) — to permit transplantation. It is harder than ABO desensitization and the results less assured.

The cost and risk of desensitization

• Desensitization is not free: it enables transplantation but at the price of a higher antibody-mediated rejection risk, greater cost and intensity, and outcomes that, while often better than remaining on dialysis, are worse than a compatible transplant. This is the central tension — a sooner, riskier graft against a later, safer one (or none).

Paired kidney exchange

• Paired kidney exchange sidesteps the antibody altogether: two (or more, in chains) incompatible donor-recipient pairs swap donors so that each recipient receives a compatible kidney. Because it yields a compatible transplant without the risks of desensitization, it is the preferred route for an incompatible pair with a willing donor whenever a match can be found.

Re-transplantation

• Re-transplant candidates are a special immunologic group: the prior graft has usually sensitized them, generating anti-HLA antibodies and raising their immunologic risk. The strategy is to avoid the HLA antigens of the failed graft, account for the higher sensitization, and manage the failed graft itself (the closing chapter) — re-transplantation is common but immunologically demanding.

The decision: exchange versus desensitize versus wait

• For an incompatible pair, three paths compete: paired exchange (a compatible graft, if a match exists), desensitization (an incompatible graft now, with higher risk), or waiting for a compatible deceased donor (which may be a long wait, especially at high cPRA). The right path depends on donor availability, urgency, the patient's tolerance of risk, and how long the wait would be — a genuinely preference-sensitive decision.

Effective-care versus preference-sensitive

• Some of this is effective-care: defining the barrier, the desensitization protocol, the crossmatch target, avoiding the failed graft's antigens. But the choice among exchange, desensitization, and waiting is preference-sensitive — reasonable patients weigh the sooner-but-riskier incompatible transplant against the safer-but-slower compatible one differently, and the decision belongs to them.

Outcomes and counseling

• Honest counseling holds two truths together: a compatible transplant (including through exchange) outperforms a desensitized incompatible one, and yet for some patients — highly sensitized, facing years on dialysis — a desensitized incompatible transplant still beats waiting. Presenting the real risks, the real waits, and the real alternatives is what lets the patient choose well.

Five fully-built tables.

Table A — The barriers and options

Table B — ABO-incompatible transplantation

Table C — HLA desensitization

Table D — Paired kidney exchange

Table E — Re-transplantation

Visualise & Map

Numbered rules. These numbers are the cross-reference handle for the cases and flowcharts.

Clinical Reasoning

Five cases. Each stops you at a decision before it answers it.

Exhaustive. Every rule in the chapter is here.

Safety & Evidence

Panel A — Red flags

Panel B — NEVER DO

Anti-patterns clinicians fall into. Each becomes a Level 22 distractor.

The grade reflects strength of evidence, not importance.

Patient Decisions

Outcomes as natural frequencies. Figures are representative; the direction of effect is given where precise numbers are uncertain.

Decisions where the right answer depends on the patient's values and situation, not the evidence alone.

Effective-care decisions (not preference-sensitive)

• Defining the immunologic barrier (ABO titre, DSA, crossmatch) — the laboratory dictates it.
• The desensitization protocol itself — a standardised, evidence-based regimen.
• Requiring an acceptable crossmatch/titre before transplant — safety dictates it.
• Avoiding the HLA antigens of a failed graft in re-transplantation — immunology dictates it.

The conversation rehearsed as a skill. Numbers trace to Level 14.

Apply & Test

Copy-paste chart notes that map to the real decisions in this chapter.

Template 1 — Immunologic-barrier strategy note

• Barrier: ABO-incompatible (titre ___) / HLA-sensitized (DSA, cPRA ___, crossmatch ___).
• Willing donor available? yes/no; paired-exchange candidate? ___.
• Strategy: paired exchange / desensitization / wait for compatible.
• Re-transplant: failed-graft antigens to avoid ___.
• Decision type: effective-care vs preference-sensitive; patient's preference ___.

Template 2 — Desensitization plan / consent note

• Protocol: plasma exchange/immunoadsorption; rituximab; IVIG; (± others).
• Target: ABO titre / DSA / crossmatch conversion ___.
• Risks counselled: higher AMR risk; cost/intensity; worse than compatible.
• Alternative discussed: paired exchange / waiting; survival vs dialysis ___.
• Consent obtained; post-transplant AMR surveillance plan ___.

Pre-rounds compression. Rules only.

Active recall. At least one card per objective.

Micro-teaching for rounds. Two scenarios, five steps each.

Metacognition anchored to this chapter's tensions. No answers provided.

1. 1. A desensitized incompatible transplant is riskier than a compatible one but sooner than a long wait; how do you help a patient value time-on-dialysis against rejection risk?
2. 2. Paired exchange depends on a large, well-run pool; how much does a patient's access to a compatible kidney depend on factors of geography and system rather than biology?
3. 3. Desensitization is intensive and costly for an uncertain gain; who should decide when its risk and price are justified — and on what grounds?
4. 4. Counseling must convey that incompatible is worse than compatible yet possibly better than waiting; how do you hold both truths without steering the patient?
5. 5. The highly sensitized are often sensitized by prior transplants and pregnancies — events not of their choosing; what does fairness owe them in access to these options?

Nine items, each anchored in this chapter. At least one per objective.