Overview of Treatment Approach
Treatment of transplant rejection is guided by the type and severity of rejection as determined by biopsy (Banff classification). Acute cellular rejection (ACR) and antibody-mediated rejection (AMR) have distinct pathophysiology and therefore require different therapeutic strategies, though they frequently coexist in the same biopsy specimen.
General principles:
- Confirm rejection by biopsy before escalating immunosuppression
- Rule out infection, drug toxicity, and obstruction as confounders
- Optimize baseline immunosuppression levels (check tacrolimus/cyclosporine trough)
- Monitor response by serial serum creatinine, proteinuria, and DSA levels
- Balance immunosuppression against infection risk
First-Line ACR Pulse Methylprednisolone
High-dose intravenous corticosteroids ("pulse steroids") are the first-line treatment for acute cellular rejection. They rapidly suppress T cell activation and the inflammatory cascade.
Mechanism: Glucocorticoids bind the intracellular glucocorticoid receptor (GR). The GC-GR complex translocates to the nucleus and: (1) represses NF-kB and AP-1 transcription factors, reducing IL-1, IL-2, IL-6, TNF-alpha, and IFN-gamma production; (2) induces lymphocyte apoptosis; (3) suppresses dendritic cell maturation and antigen presentation; (4) reduces expression of adhesion molecules on endothelial cells.
Typical Protocol:
- Methylprednisolone (Solu-Medrol) 250–1000 mg IV daily for 3 consecutive days
- Administered over 30–60 minutes each dose
- Follow with oral prednisone taper returning to baseline dose
- Some centers use 3 × 500 mg; others 3 × 250 mg for borderline/mild ACR
Efficacy
70–80% of Banff grade IA/IB ACR episodes respond to pulse steroids alone. Response is defined as return of serum creatinine to near-baseline within 5–7 days. Grades IIA/IIB (arteritis) have lower response rates (~50–60%) and often require ATG.
Monitoring and Adverse Effects: Blood glucose (hyperglycemia common, requires insulin in many patients), blood pressure, infection surveillance (CMV, fungal). Avoid rapid IV infusion — risk of arrhythmia.
Second-Line ACR Anti-Thymocyte Globulin (ATG)
ATG is a polyclonal antibody preparation used for steroid-resistant ACR or as first-line therapy for severe (Banff IIA/IIB/III) rejection. Two preparations are available: rabbit ATG (Thymoglobulin, rATG) and equine ATG (ATGAM). Rabbit ATG is generally preferred due to superior efficacy.
Mechanism: rATG contains antibodies directed against multiple T cell surface antigens (CD2, CD3, CD4, CD8, CD11a, CD18, CD25, CD44, CD45, HLA-DR, TCR). It causes: (1) rapid and profound lymphocyte depletion via complement-mediated cytotoxicity, ADCC, and apoptosis; (2) T cell activation and exhaustion; (3) induction of regulatory T cells; (4) antibody-coated T cells are cleared by the reticuloendothelial system (liver, spleen).
Typical Protocol (rATG / Thymoglobulin):
- 1.0–1.5 mg/kg/day IV over 4–6 hours via central venous access
- 3–7 doses (total cumulative dose typically 3–7.5 mg/kg)
- Premedicate with acetaminophen, diphenhydramine, and methylprednisolone to reduce infusion reactions
- Monitor CBC daily — dose-reduce or delay for platelets <50,000 or WBC <2,000
Efficacy
rATG reverses 85–95% of steroid-resistant ACR episodes. After treatment, T cell counts remain suppressed for weeks to months, requiring careful infection monitoring.
Adverse Effects: Cytokine release syndrome (fever, chills, rigors — typically first dose), serum sickness (urticaria, arthralgias), leukopenia, thrombocytopenia, increased risk of CMV disease and post-transplant lymphoproliferative disorder (PTLD). Mandatory CMV prophylaxis (valganciclovir) for 3–6 months after ATG.
AMR Plasmapheresis / Therapeutic Plasma Exchange (TPE)
Plasmapheresis rapidly removes circulating donor-specific antibodies (DSAs) and complement components from the blood. It is a cornerstone of AMR treatment, typically used in combination with IVIG.
Mechanism: The patient's plasma is separated from cellular components using centrifugation or membrane filtration. The separated plasma (containing IgG antibodies, complement, and other proteins) is discarded and replaced with fresh frozen plasma (FFP) or 5% albumin. This directly reduces circulating DSA levels by 50–70% per session. However, DSAs rebound as B cells and plasma cells continue to produce antibody, necessitating concurrent B cell/plasma cell-directed therapy.
Typical Protocol:
- 5–10 sessions over 10–14 days (alternate days or daily)
- Each session processes 1–1.5 plasma volumes (~3–4 liters in adults)
- Replacement fluid: 5% albumin (most common) or FFP (if coagulopathy)
- Often followed by IVIG 100 mg/kg post-exchange to minimize immunoglobulin rebound
Adverse Effects: Hypotension, hypocalcemia (from citrate anticoagulation — tingling, tetany), coagulopathy, access-site complications, allergic reactions to replacement fluid. Albumin replacement depletes clotting factors — watch for bleeding.
AMR Intravenous Immunoglobulin (IVIG)
IVIG is a pooled preparation of human IgG antibodies used in AMR treatment both as an adjunct to plasmapheresis and as an independent immunomodulatory agent. It is also used for desensitization protocols before transplantation in highly sensitized recipients.
Mechanism (multiple):
- Fc receptor blockade: Excess IgG saturates Fc gamma receptors on macrophages and NK cells, reducing ADCC against antibody-coated graft endothelium
- Anti-idiotype antibodies: Pooled IgG contains antibodies that neutralize pathogenic DSAs through idiotype-anti-idiotype interactions
- FcRn saturation: Saturates the neonatal Fc receptor (FcRn) responsible for IgG recycling, accelerating catabolism of all IgG (including DSAs) and reducing half-life
- Complement inhibition: Blocks complement activation and SC5b-9 formation
- B cell and plasma cell modulation
Typical Dosing:
- AMR treatment: 100–200 mg/kg IV after each plasmapheresis session, OR
- High-dose IVIG: 2 g/kg total (given over 2–4 days) as monotherapy for milder AMR
- Desensitization: 2 g/kg monthly × 4 doses pre-transplant
- Infuse over 2–4 hours; rate-escalate per manufacturer guidelines
Adverse Effects: Headache, aseptic meningitis, hemolytic anemia (blood group A/B antigens in donor pool), renal impairment (sucrose-containing formulations — avoid in renal dysfunction), thromboembolic events, anaphylaxis (rare, monitor for IgA deficiency). Expensive and product supply may be limited.
AMR / B cell depletion Rituximab (Anti-CD20)
Rituximab is a chimeric anti-CD20 monoclonal antibody that depletes CD20-expressing B cells. It is used as adjunctive therapy for AMR to target the B cell compartment responsible for DSA production.
Mechanism: CD20 is expressed on pre-B cells, naive B cells, and mature B cells, but not on plasma cells. Rituximab depletes B cells via: (1) complement-dependent cytotoxicity (CDC), (2) antibody-dependent cellular cytotoxicity (ADCC), and (3) direct induction of apoptosis. By eliminating B cell precursors and memory B cells, rituximab prevents regeneration of DSA-producing plasma cells after plasmapheresis. Importantly, it does not target existing long-lived plasma cells (hence why plasmapheresis is still needed for immediate DSA reduction).
Typical Dosing in Transplantation:
- 375 mg/m² IV as single dose, OR
- 200 mg flat dose (some centers use lower doses in transplant setting)
- Administered after completion of plasmapheresis/IVIG course
- Some protocols use 2 doses (days 1 and 15)
Adverse Effects: Infusion reactions (hypotension, bronchospasm — premedicate with antipyretics, antihistamines, steroids), PML (progressive multifocal leukoencephalopathy — rare but serious), hepatitis B reactivation (screen all patients before use), prolonged hypogammaglobulinemia. B cell depletion lasts 6–12 months.
Evidence Base
Randomized data for rituximab in AMR are limited. The RITUX ERAH trial (Sautenet et al., JASN 2016) found rituximab added to steroids + PE + IVIG did not significantly improve graft outcomes at 12 months compared to placebo. Despite this, rituximab remains widely used clinically, particularly in recurrent or severe AMR.
AMR / Plasma cell depletion Bortezomib (Velcade)
Bortezomib is a proteasome inhibitor originally developed for multiple myeloma. In transplantation, it is used to target long-lived plasma cells that are resistant to rituximab, making it a unique component of AMR therapy.
Mechanism: Bortezomib reversibly inhibits the 26S proteasome chymotrypsin-like activity, preventing degradation of pro-apoptotic regulatory factors. Plasma cells have exceptionally high rates of immunoglobulin synthesis and depend heavily on proteasome function for protein homeostasis. Proteasome inhibition triggers unfolded protein response (UPR) and endoplasmic reticulum (ER) stress, causing plasma cell apoptosis. Since plasma cells are CD20-negative, they are not targeted by rituximab — making bortezomib a complementary approach.
Typical Transplant Dosing:
- 1.3 mg/m² subcutaneous (SC preferred over IV — less peripheral neuropathy) or IV
- 4 doses: days 1, 4, 8, 11 (standard multiple myeloma-derived schedule)
- Often combined with plasmapheresis, IVIG, ± rituximab
Adverse Effects: Peripheral neuropathy (dose-limiting, significantly reduced with SC administration), thrombocytopenia, neutropenia, GI effects (nausea, diarrhea, constipation), herpes zoster reactivation (give prophylactic acyclovir), orthostatic hypotension. SC administration reduces grade 3+ peripheral neuropathy from ~17% to ~6%.
Clinical Evidence
Small prospective and retrospective series have shown bortezomib can reduce DSA levels and improve graft function in refractory AMR. It has been used both for treatment and in desensitization protocols. Large randomized trials are lacking, but it remains part of many expert center AMR protocols for refractory cases.
Treatment Algorithm Summary
| Scenario | First Line | Second Line / Adjunct |
|---|
| ACR Banff IA/IB | Pulse methylprednisolone ×3 days | Reassess; if no response → rATG |
| ACR Banff IIA/IIB | rATG + pulse steroids | Optimize CNI levels; consider IVIG if DSA+ |
| ACR Banff III | rATG + pulse steroids | Discuss graft loss risk; consider re-biopsy |
| Acute AMR (mild-moderate) | Plasmapheresis + low-dose IVIG × 5–10 sessions | Rituximab; optimize maintenance IS |
| Acute AMR (severe / arteritis) | Plasmapheresis + IVIG + pulse steroids | Rituximab + bortezomib; re-biopsy at 3 months |
| Refractory AMR | Bortezomib + plasmapheresis | Eculizumab (C5 inhibitor); clinical trial enrollment |
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