Acute immune-therapy toxicity

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Immune therapy includes checkpoint inhibitors, engineered cellular products such as CAR-T and T-cell-engaging bispecific antibodies. Checkpoint blockade can inflame almost any organ after immune tolerance is released. Cellular and bispecific therapies can cause cytokine-release syndrome and immune-effector-cell-associated neurotoxicity through rapid T-cell activation, cytokines and endothelial dysfunction. The relevant toxicity clock differs: CRS often begins soon after cell or step-up dosing, whereas checkpoint endocrine, lung or bowel illness can appear after treatment has stopped.

Clinical patterns are organ-specific but overlap with common cancer emergencies. Checkpoint pneumonitis causes cough, breathlessness, hypoxaemia and ground-glass or organising change; colitis causes diarrhoea, pain and blood; hepatitis may be asymptomatic until liver tests rise; myocarditis causes fatigue, chest pain, conduction disturbance or troponin elevation; myositis and myasthenic overlap can cause bulbar or respiratory weakness. Hypophysitis and adrenalitis present through fatigue, vomiting, hypotension, hyponatraemia and hypoglycaemia. Sepsis, embolism, progression and conventional drug toxicity remain active differentials.

CRS is graded from fever with preserved circulation to vasopressor and high oxygen requirement. ICANS can begin with impaired attention, handwriting or naming before aphasia, seizure, weakness or cerebral oedema. No inflammatory biomarker reliably distinguishes CRS from infection, and the two can coexist in profoundly immunocompromised patients. Cultures, empirical antibiotics and organ support therefore proceed while the treating centre grades toxicity and directs tocilizumab or corticosteroid.

Management combines withholding the trigger, severity assessment and organ-specific immune suppression or replacement. Severe checkpoint toxicity usually requires corticosteroid, with second-line agents chosen by organ: infliximab or vedolizumab for selected steroid-refractory colitis, mycophenolate for hepatitis, and specialist cardiopulmonary or neurological immunosuppression for high-risk disease. Endocrine failure is treated with hormone replacement rather than escalating immunosuppression indefinitely. Rechallenge is never an automatic consequence of recovery; the MDT weighs toxicity recurrence, residual organ damage and cancer benefit.

Key points

Immune toxicity can affect any organ and may begin during treatment or weeks to months after the last checkpoint dose; ask specifically about the exact immune product and date.
Withhold further immune therapy for clinically significant suspected toxicity and contact acute oncology or the cellular-therapy centre immediately.
First-line assessment combines ABCDE, sepsis cultures and lactate, FBC, renal, liver, glucose, cortisol and thyroid tests with organ-specific ECG, troponin, CT, stool or neurological evaluation.
Do not let an immune-toxicity label delay antibiotics, anticoagulation, drainage or other treatment for a plausible coexisting emergency.
Severe checkpoint toxicity commonly requires intravenous methylprednisolone 1 to 2 mg/kg/day or the organ-specific protocol, followed by a slow taper after objective improvement.
Give hydrocortisone 100 mg IV immediately for suspected adrenal crisis, then 200 mg over 24 hours or 50 mg every 6 hours with intravenous saline and endocrine review.
For protocol-defined significant CAR-T CRS, tocilizumab 8 mg/kg IV up to 800 mg can be repeated at intervals of at least 8 hours to a maximum four total doses; treat sepsis concurrently.
Tocilizumab does not adequately treat isolated ICANS; significant neurotoxicity uses structured scoring, corticosteroid and seizure or critical-care management through the treating centre.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Checkpoint tolerance is removed

PD-1, PD-L1 and CTLA-4 blockade releases inhibitory signals, allowing antitumour T cells and auto-reactive immune pathways to inflame normal organs.

Engineered immune-cell activation

CAR-T cells expand after antigen recognition and release cytokines, while endothelial and blood-brain-barrier activation contributes to CRS and ICANS.

Bispecific antibody engagement

Antibodies that link T cells to tumour antigen can generate rapid cytokine release and neurotoxicity, particularly during initial or step-up dosing.

Predisposition and treatment overlap

Pre-existing autoimmunity, combined checkpoint treatment, organ irradiation, infection and other anticancer toxicity can increase severity or obscure the cause.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Organ-directed T-cell inflammation
Activated lymphocytes and cytokines infiltrate lung, bowel, liver, skin, endocrine glands, kidney, heart, muscle and nervous system.
2
Cytokines produce distributive physiology
Interleukin-6 and other mediators cause fever, vasodilatation, endothelial leak, hypotension, hypoxia and multi-organ dysfunction during CRS.
3
Endothelial and barrier dysfunction
Systemic inflammation activates cerebral endothelium and disrupts the blood-brain barrier, contributing to oedema and the cognitive and motor features of ICANS.
4
Endocrine tissue may be destroyed
Pituitary, thyroid, adrenal or pancreatic inflammation can leave permanent hormone failure even after the acute immune process settles.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Checkpoint pneumonitis

New dry cough, exertional dyspnoea, hypoxaemia or bilateral inflammatory CT change during or after checkpoint exposure requires urgent assessment.

Immune colitisRed flag

Increasing stool frequency, nocturnal diarrhoea, blood, pain or fever can progress to dehydration, toxic dilatation and perforation.

Myocarditis overlapRed flag

Troponin elevation, chest pain, heart block or arrhythmia with ptosis, diplopia or proximal weakness suggests myocarditis with myositis or myasthenia.

Endocrine crisisRed flag

Vomiting, hypotension, hypoglycaemia, hyponatraemia, headache or visual change can indicate adrenal insufficiency or hypophysitis.

Cytokine-release syndrome

Fever followed by hypotension or hypoxia after CAR-T or bispecific therapy requires CRS grading and simultaneous sepsis treatment.

Early ICANSRed flag

Inattention, dysgraphia, word-finding difficulty, tremor or altered behaviour can precede seizure and reduced consciousness.

Red flags requiring action

New breathlessness, hypoxaemia or diffuse lung change during checkpoint therapy may be pneumonitis, infection or embolism and requires urgent imaging and oncology review.
Chest pain, troponin rise, conduction change, arrhythmia or heart failure can represent immune myocarditis with a high early mortality.
Hypotension, vomiting, hyponatraemia, hypoglycaemia or severe weakness can indicate immune adrenal insufficiency or hypophysitis and needs immediate hydrocortisone.
Fever with hypotension or hypoxia soon after CAR-T or a bispecific antibody is possible cytokine-release syndrome, but bacterial sepsis must be treated in parallel.
New handwriting change, word-finding difficulty, inattention, tremor, focal weakness, seizure or reduced consciousness after cellular therapy raises ICANS.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line sepsis and organ screenFirst stepFirst line
Why
Identify infection, shock and the organ systems requiring immediate support.
Interpretation and limitations
Obtain observations, lactate, cultures, FBC, renal, liver, glucose, coagulation and inflammatory markers; no single result distinguishes infection from immune toxicity.
02
ECG, troponin, CK and echocardiography
Why
Detect myocarditis, conduction injury and myositis overlap early.
Interpretation and limitations
Any compatible symptom or troponin rise requires urgent cardio-oncology review; preserved ejection fraction does not exclude dangerous myocarditis.
03
CT chest and respiratory assessment
Why
Define pneumonitis extent and distinguish infection, embolism, oedema and progression.
Interpretation and limitations
Use pulse oximetry, blood gas and CT pattern with cultures; bronchoscopy is selected when stable enough and the result changes treatment.
04
Stool and colitis assessment
Why
Exclude infection and grade bowel inflammation before advanced immunosuppression.
Interpretation and limitations
Send stool culture and C difficile testing, assess blood, frequency and pain and use CT or endoscopy for severe or refractory disease while avoiding delay in impending perforation.
05
Cortisol, ACTH, thyroid and pituitary profile
Why
Identify adrenal, pituitary and thyroid failure causing fatigue, hypotension or sodium change.
Interpretation and limitations
Draw cortisol and ACTH before steroid only when this causes no delay; suspected adrenal crisis is treated immediately and TSH alone cannot diagnose central hypothyroidism.
06
Structured CRS and ICANS grading
Why
Match tocilizumab, corticosteroid, seizure and critical-care escalation to severity.
Interpretation and limitations
Record oxygen and vasopressor requirement and repeat attention, language, writing, orientation, motor and consciousness assessment; trend outweighs one score.
07
MRI, EEG and lumbar studies
Why
Investigate severe or atypical neurological toxicity and exclude stroke, infection, seizure and metastasis.
Interpretation and limitations
Select tests with neurology and the cellular-therapy centre; normal early imaging does not exclude ICANS, and lumbar puncture requires pressure and coagulation safety.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Sepsis and opportunistic infection

Fever, shock, diarrhoea, lung change and encephalopathy can be infectious and may coexist, especially after corticosteroid or cellular therapy.

Cancer progression or obstruction

Lymphangitic disease, brain metastasis, biliary obstruction and marrow progression mimic organ immune toxicity and require imaging or tissue when appropriate.

Conventional treatment toxicity

Cytotoxic drugs, radiotherapy, targeted agents and supportive medicines cause pneumonitis, diarrhoea, hepatitis, myocardium injury and confusion through non-immune mechanisms.

Vascular and metabolic emergency

Pulmonary embolism, acute coronary syndrome, stroke, tumour lysis, calcium or sodium disturbance and adrenal crisis can resemble or complicate immune illness.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01InitialHold therapy and assess both toxicity and infectionFirst stepA patient exposed to immune therapy develops a new inflammatory, endocrine, cardiac or neurological syndrome.

1Use ABCDE and monitoring, identify exact product and dates, hold further immune treatment and contact acute oncology or the cellular-therapy centre immediately.
2Obtain sepsis and organ-directed tests and start antimicrobials and other emergency treatment when indicated without waiting for a toxicity grade.
3Assign organ and severity grade and arrange the monitoring setting, recognising myocarditis, respiratory weakness, adrenal crisis, CRS and ICANS may need critical care early.

02Checkpoint toxicityStart organ-specific immune suppressionClinically important checkpoint pneumonitis, colitis, hepatitis, nephritis, myocarditis or neurological toxicity is likely.

1Give the protocol corticosteroid route and dose matched to severity, using intravenous methylprednisolone for severe organ dysfunction and obtaining key cultures or tissue when this will not delay rescue.
2Second lineReassess objectively within the organ-specific interval and add the recommended second-line agent with the relevant specialist if steroid response is inadequate.
3Plan infection prophylaxis, glucose and gastric or bone safeguards and a slow taper after improvement to reduce rebound; document whether rechallenge is prohibited or requires MDT review.

03EndocrineReplace the missing hormone firstAdrenal, pituitary, thyroid or insulin deficiency is suspected.

1For possible adrenal crisis, draw cortisol and ACTH only if immediate, then give hydrocortisone and intravenous saline without waiting for confirmation.
2Secure cortisol replacement before levothyroxine in combined pituitary deficiency and treat diabetic ketoacidosis or severe thyrotoxicosis through the standard emergency pathway.
3Arrange endocrine follow-up, sick-day and emergency-card education and recognise that permanent replacement may be needed even if immune therapy stops.

04Cellular therapyTreat CRS and ICANS as distinct syndromesFever, hypotension, hypoxia or neurological change follows CAR-T or a T-cell-engaging product.

1Culture and treat possible infection, grade CRS from oxygen and vasopressor need and give protocol tocilizumab for significant CRS while supporting circulation and breathing.
2Repeat structured neurological scoring and give centre-directed corticosteroid for significant ICANS; treat seizure and cerebral oedema and involve neurocritical care early.
3Do not rely on tocilizumab for isolated ICANS and continue surveillance because CRS and neurotoxicity can peak and resolve on different timelines.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

Suppresses damaging T-cell and cytokine inflammation in lung, bowel, liver, kidney, heart, muscle and nervous-system toxicity.

Intravenous methylprednisolone for severe checkpoint toxicity

Give methylprednisolone 1 to 2 mg/kg intravenously once daily, or the divided organ-specific equivalent, for severe immune-mediated toxicity, with pulse dosing reserved for selected life-threatening cardiac or neurological disease under specialist protocol.

Obtain cultures and treat infection concurrently, monitor glucose, mental state, gastrointestinal and muscle effects and add Pneumocystis, bone and gastric safeguards when exposure is prolonged; taper slowly after response.

Replaces absent cortisol during immune adrenalitis or hypophysitis and restores vascular responsiveness in crisis.

Hydrocortisone for adrenal crisis

Give hydrocortisone 100 mg intravenously or intramuscularly immediately, then 200 mg over 24 hours by infusion or 50 mg intravenously every 6 hours with intravenous 0.9% sodium chloride and glucose as required.

Do not delay for cortisol results. Monitor sodium, potassium, glucose, fluid and precipitating infection and provide ongoing replacement, sick-day rules and an NHS Steroid Emergency Card after stabilisation.

Blocks interleukin-6 receptor signalling and reverses protocol-defined significant cytokine-release syndrome while organ support and sepsis care continue.

Tocilizumab for CAR-T CRS

For adults weighing at least 30 kg, give tocilizumab 8 mg/kg intravenously over 60 minutes, maximum 800 mg; if needed, give up to three additional doses at least 8 hours apart under the treating-centre protocol.

Do not delay cultures, antibiotics or vasopressors. Monitor liver tests, cytopenia and infection; isolated ICANS may not respond and requires corticosteroid and neurological management.

Blocks tumour necrosis factor when severe checkpoint colitis does not improve adequately with corticosteroid.

Infliximab for selected steroid-refractory colitis

Give infliximab 5 mg/kg intravenously as a specialist rescue dose after appropriate infection screening, with repeat dosing determined by response and the immune-colitis protocol.

Avoid bowel perforation, uncontrolled sepsis and significant immune hepatitis; screen tuberculosis and hepatitis and involve gastroenterology because vedolizumab or another strategy may be safer.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Respiratory failure

Immune pneumonitis, capillary leak or infection can progress to diffuse alveolar injury, mechanical ventilation and prolonged oxygen dependence.

Myocarditis and malignant arrhythmia

T-cell myocardial and conduction-system inflammation can cause ventricular dysfunction, heart block, ventricular arrhythmia and sudden death.

Bowel perforation or severe hepatitis

Untreated immune colitis can progress to toxic dilatation and perforation, while hepatitis can cause coagulopathy and liver failure.

Permanent endocrine and neurological disability

Adrenal, pituitary and insulin deficiency often require lifelong replacement, while severe ICANS or immune neuropathy can leave cognitive or motor impairment.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

During acute illness, trend observations, oxygen and vasopressor need, neurological score, stool output, urine, glucose and the organ-specific laboratory marker.
Repeat ECG and troponin closely in suspected myocarditis and escalate conduction change or arrhythmia even if ventricular function appears preserved.
During corticosteroid, monitor infection, glucose, delirium, proximal strength, gastrointestinal and bone risk and document the taper and prophylaxis.
For endocrine injury, follow hormone replacement, sodium and glucose and provide sick-day, emergency injection and alert-card education before discharge.
After CRS or ICANS, continue centre-defined observation because inflammatory and neurological trajectories may diverge after initial improvement.
Any immune-therapy rechallenge requires a recorded MDT decision based on organ, grade, residual damage, alternatives and expected cancer benefit.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Toxicity outlives the dose

Checkpoint effects can begin after treatment stops, so remote exposure remains relevant when a new organ syndrome appears.

Myocarditis can hide in a normal EF

Conduction disease and troponin elevation may precede systolic dysfunction, making early ECG and biomarker review essential.

Cortisol precedes thyroid

Starting levothyroxine before protecting an ACTH-deficient patient can accelerate cortisol demand and precipitate adrenal collapse.

CRS is not sepsis exclusion

Timing and cytokines can support CRS, but infection remains common and simultaneous empirical treatment is often necessary.

Writing reveals ICANS

A changed sentence or naming difficulty can expose early cortical dysfunction before a major fall in consciousness.

11Common pitfallsFrequent interpretation and management errors.

01
Assuming every fever after cellular therapy is CRS and withholding antibiotics.
02
Continuing checkpoint therapy through significant suspected organ toxicity without acute oncology discussion.
03
Calling new dyspnoea immune pneumonitis without assessing infection, embolism, cardiac disease and progression.
04
Starting levothyroxine before cortisol protection in possible hypophysitis.
05
Waiting for a cortisol result before treating adrenal crisis.
06
Using tocilizumab as sole treatment for isolated ICANS.
07
Stopping high-dose corticosteroid abruptly after improvement and triggering rebound toxicity or adrenal suppression.