Rejection - Professor Richard Kirk 2023

Pulmonary Transplantation
Evaluation	Listing	Candidate FU	Donor Offer	Peri Tx Issues	Transplant Week 1	Transplant FU	Rejection	Drug Interactions

Rejection

Rejection is an ever present concern in post transplant patients. It may occur if immunosuppression is inadequate. This may be due to an incidental illness preventing adequate absorption, altered metabolism e.g. prescription of a drug which increases the metabolism of calcineurin drugs by enhancing cytochrome P450 enzyme activity, an inflammatory illness causing upregulation of the immune system or nonadherence to the immunosuppression regime. Clinically there may be no symptoms, otherwise cough, breathless, low grade fever, and lethargy are common. Examination may be normal but often demonstrates tachypnoea and coarse rales throughout. Oxygen saturations may be lower than normal and FEV1 reduced by ≥ 10%. Investigations should include measuring a spot calcineurin level as well as a trough level at the appropriate time.

Spirometry is used to serial assess FEV1 and FVC following transplantation. It is generally accepted that a fall in FEV1 ≥ 10% from the previous baseline should be a trigger to consider the cause of allograft dysfunction - e.g. infection, aspiration (GERD), acute rejection or major airway stenosis. If routine tests fail to establish a cause e.g. bacterial or viral infection, then further investigation with CT scan, bronchoscopy with BAL and transbronchial biopsy is advisable. A persistent fall ≥ 20% from baseline in FEV1 and/or FVC may be due to chronic lung allograft rejection (CLAD).

Acute rejection may be due to cell mediated rejection (CMR) or antibody mediated rejection (AMR). While undoubtedly rejection may be purely one or the other, most times there is an element of both. AMR in lung transplant is more contentious than in other solid organ transplants as an immunopathological diagnosis is more difficult because the features overlap significantly with other causes of graft dysfunction e.g. infection.

Cell Mediated Rejection

Rejection with graft dysfunction should always be treated. The patient is admitted and the cause sought with a detailed history to assess if absorption (e.g. diarrhoea or vomiting illness) or compliance issues. Immunosuppression levels should be taken in addition to an assessment of DSA. A CXR may be normal or show ill-defined perihilar and lower lobe opacities, along with septal lines and pleural effusions. As infection and rejection may be difficult to separate clinically a CT scan, bronchoscopy with BAL and lung biopsy is helpful. Biopsy Grade A2 (table 1) and upwards are always treated.

Methylprednisolone 10mg/kg (maximum 1G) is given intravenously, daily for 3 days. Most will resolve with this alone
Thymoglobulin is rarely required, but if necessary 1.5 mg/kg is given intravenously with subsequent doses dependent on the CD3 count. Anti-infective prophylaxis as for thymoglobulin given for induction therapy should be given for 3 months.
Immunosuppression (calcineurin and cell cycle inhibitors) should be maximised
Steroids are weaned to a maintenance level for 3-6 months, provided the patient remains rejection free.

Table 1: Standardization of Nomenclature in the Diagnosis of Lung Rejection. Stewart et al. J Heart Lung Transplant 2007;26:1229–42
Acute Rejection			Airway Inflammation
Grade	Severity	Description	Grade	Severity	Description
A0	None	Normal parenchyma	B0	None	No evidence of bronchiolar inflammation
A1	Minimal	Scattered, infrequent perivascular mononuclear infiltrates that are 2–3 cells thick	B1R	Low grade	Mononuclear cells within the sub-mucosa of the bronchioles with occasional sub-mucosal eosinophils
A2	Mild	More frequent perivascular mononuclear infiltrates that are readily recognizable at low magnification; infiltrates may include lymphocytes, macrophages, and eosinophils	B2R	High grade	Large and activated mononuclear cells, eosinophils, and plasmacytoid cells in the submucosa; evidence of epithelial damage with necrosis, metaplasia, and intra-epithelial lymphocytic infiltration
A3	Moderate	Dense perivascular mononuclear infiltrates commonly associated with endothelialitis; extension of inflammatory cell infiltrate into alveolar septa and airspaces; eosinophils and occasional neutrophils are common	BX	Ungradable	No bronchiolar tissue available
A4	Severe	Diffuse perivascular, interstitial, and air-space infiltrates of mononuclear cells; alveolar pneumocyte damage and endothelialitis

Antibody Mediated Rejection

Antibody mediated rejection (AMR) has increasingly been implicated, allograft rejection. Activated B cells transform into plasma cells producing donor specific antibodies (DSA) against the graft. DSA interacting with the graft leads to complement activation and inflammation. Histopathologic features may show neutrophil capillaritis and arteritis and C4d deposition. In conjunction with circulating donor specific antibodies these features suggest AMR but are not conclusive as they may be seen in other forms of allograft dysfunction including infection. The ISHLT consensus document on AMR (Table 2) came to the following definitions:

Table 2. ISHLT AMR Definitions. Levine et al. J Heart Lung Transplant 2016;35:397–406
Definite clinical AMR	Allograft dysfunction in the presence of DSA plus positive histology suggestive of AMR and positive C4d staining. ACR and AMR can be concurrent, but other causes have been excluded.
Probable clinical AMR	Allograft dysfunction in the presence of 2 of the 3 following criteria: presence of DSA; positive histology suggestive of AMR; and positive C4d staining. A grading of probable AMR may be given to a recipient who has coexistent AMR with infection or ACR when all 3 diagnostic criteria are present
Possible clinical AMR	Allograft dysfunction in the presence of 1 of 3 following criteria: presence of DSA; positive histology suggestive of AMR; and positive C4d staining. A grading of possible AMR may be given to a recipient who has coexistent AMR with infection or ACR when 2 diagnostic criteria are present.

The initial treatment of AMR includes reducing antibody (DSA) levels with plasmapheresis. Immunoglobulin infusions will also reduce DSA levels. To reduce activation of the immune system and inflammation steroids are usually administered, often with thymoglobulin. Longer term strategies to reduce DSA include rituximab to destroy B cells and prevent them developing into plasma cells and targeting plasma cells (e.g. bortezomib). Plasmapheresis, photopheresis, immunoglobulin and targeting plasma cells may be utilized if ongoing therapy is necessary.

Chronic Lung Allograft Vasculopathy

Chronic Lung Allograft Vasculopathy (CLAD) is defined as a substantial and persistent decline (≥20%) in measured FEV1 value from the baseline value. The baseline value is computed as the mean of the best 2 post-operative FEV1 measurements (taken >3 weeks apart). CLAD can present either as a pre-dominantly obstructive ventilatory pattern (bronchiolitis obliterans syndrome - BOS), a restrictive pattern (Restrictive Allograft Syndrome - RAS, or a mixed obstructive and restrictive pattern that is not explained by other conditions (Table 3). If lung function parameters remain impaired on a second reading at least 3 weeks after the first ≥20% fall from baseline and after adequate treatment of secondary causes such as infection, acute cellular/antibody-mediated rejection, or airway stenosis has been implemented, then a diagnosis of “probable” CLAD can be made. If the patient is not on azithromycin then an 8 week course should be given, followed by reassessment, as a proportion of suspected CLAD patients may not have CLAD and respond with normalisation of FEV1. The severity of CLAD is graded (Table 4).

There are few treatment options for CLAD and, to date, these have mostly been reported in patients with BOS and have shown limited efficacy. Treatments include avoiding sustained administration of high-dose corticosteroids due to harmful side effects and lack of efficacy. Other options include: conversion of cyclosporine to tacrolimus; a trial of azithromycin for ≥8 weeks; and fundoplication for documented gastro-esophageal reflux in selected cases. A fall FVC after a reduction in FEV1 or a concurrent fall in both is a poor prognotic finding.

Table 3: CLAD Phenotypes
	Obstruction	Restriction	CT
	FEV1/FVC < 0.7	TLC decline > 10% baseline	Opacities
BOS	Yes	No	No
RAS	No	Yes	Yes
Mixed	Yes	Yes	Yes
Undefined*	Yes	Yes or No	Yes or No
* Undefined has 2 possible combinations, making it difficult to categorize in the upper panels (BOS, RAS, or mixed phenotype).

Table 4: CLAD Staging
CLAD Stage	Spirometry
CLAD 0	Current FEV1 >80% FEV1 baseline
CLAD 1	Current FEV1 >65‒80% FEV1 baseline
CLAD 2	Current FEV1 >50‒65% FEV1 baseline
CLAD 3	Current FEV1 >35‒50% FEV1 baseline
CLAD 4	Current FEV1 ≤35% FEV1 baseline

Resistant or Multiple Rejection Episodes

Despite adequate immunosuppression a rejection episode may prove difficult to control or there may be multiple episodes of rejection - both are concerning for the longevity of the graft. Resistant or multiple rejection episodes may occur for no apparent reason - possibly as an idiosyncratic response to standard therapy. The following may then be considered.

Switching standard immunosuppression regime

Assuming compliance is adequate, when multiple rejection episodes occur then exchanging within drug classes may be helpful e.g. one calcineurin for another, one cell cycle inhibitor for a different one.

Immunosuppression Regime

When compliance is an issue attempt to minimize the drug regime by eliminating non essential medications and reduce frequency of others e.g. use long acting tacrolimus.

Alternative Immunosuppressants

Alemtuzumab is an anti CD52 antibody and targets B and T cells, macrophages and other elements of the innate system. It is therefore a veey strong immunomodulator and the main risk is infection. Basiliximab, usually used for induction, can be given monthly. Belatacept binds to CD80 and CD86 on APCs to prevent T cell activation and proliferation. It is aslo given monthly and may be helpful in certain situations with non adherent patients.

Extracorporeal photopheresis (ECP)

ECP is a relatively unused approach to control rejection - in part because of its constraints in small infants. Approximately 10-15% of the blood volume is removed, the white cells separated, a photosensitizing agent added and then they are passed under UV light and finally returned to the circulation. Treatments are usually monthly. ECP results in apoptosis of the white cells but the effect differs among the cell lines - B & T cells and NK cells are severely affected, but Treg cells much less so. The overall effect is thus complex but appears to downregulate the immune system and reduce inflammation. In the clinical context in small studies it appears to inhibit ongoing, chronic rejection in solid organ transplants.

Total Lymphoid Irradiation (TLI)

This entails irradiating the thoracic and abdominal lymphoid tissue. It is not an easy technique, especially in smaller children, and there are considerable side effects on other tissues.