Immune Checkpoint Inhibitor Adverse Event Management — Part 1: Overview of Checkpoint Inhibitors and General Principles of irAE Management

Classes of Immune Checkpoint Inhibitors

Immune checkpoint inhibitors (ICIs) are monoclonal antibodies that block inhibitory receptors on T cells or their ligands on tumor cells and antigen-presenting cells. By releasing these “brakes” on the adaptive immune system, ICIs restore T-cell-mediated antitumor immunity. The currently approved classes and agents are summarized below.^{1 2}

Anti-PD-1 (Programmed Death-1) Inhibitors

PD-1 is an inhibitory receptor expressed on activated T cells. Engagement of PD-1 by its ligands PD-L1 and PD-L2 on tumor cells leads to T-cell exhaustion and immune evasion. Anti-PD-1 antibodies block this interaction, restoring T-cell effector function.

Anti-PD-L1 (Programmed Death-Ligand 1) Inhibitors

PD-L1 inhibitors block the ligand PD-L1 on tumor cells and antigen-presenting cells, preventing its engagement with PD-1 (and also B7-1/CD80) on T cells.

Anti-CTLA-4 (Cytotoxic T-Lymphocyte-Associated Protein 4) Inhibitors

CTLA-4 is an inhibitory receptor that competes with the co-stimulatory receptor CD28 for binding to B7 ligands (CD80/CD86) on antigen-presenting cells. CTLA-4 blockade enhances T-cell activation and proliferation, particularly in the priming phase of the immune response.

Anti-LAG-3 (Lymphocyte-Activation Gene 3) Inhibitor

Combination Immunotherapy

Combination regimens using anti-CTLA-4 plus anti-PD-1 (e.g., ipilimumab plus nivolumab) or anti-CTLA-4 plus anti-PD-L1 (e.g., tremelimumab plus durvalumab) produce higher response rates in several tumor types but are associated with significantly higher rates and severity of irAEs. Toxicity profiles of combination regimens are discussed in detail in Part 5.³

Mechanism of Immune-Related Adverse Events

The precise pathophysiology of irAEs is incompletely understood but involves several interrelated mechanisms:^{2 4}

1. Loss of peripheral self-tolerance. Checkpoint receptors normally function to maintain peripheral tolerance by dampening T-cell responses to self-antigens. Blocking these receptors unleashes autoreactive T cells that can attack normal tissues.

2. Cross-reactivity between tumor neoantigens and self-antigens. T cells primed against tumor-associated antigens may cross-react with homologous antigens expressed in normal tissues (molecular mimicry).

3. Enhanced T-cell priming and expansion. Particularly relevant for anti-CTLA-4 agents, which augment T-cell activation in lymph nodes, leading to broader and more polyclonal T-cell responses including autoreactive clones.

4. Alteration of humoral immunity. ICIs can increase autoantibody production and disrupt B-cell tolerance.

5. Enhanced cytokine production. Increased levels of pro-inflammatory cytokines (IL-17, IFN-gamma, TNF-alpha) contribute to tissue inflammation and damage.

6. Complement activation and direct antibody-mediated effects. Some irAEs may involve complement deposition or antibody-dependent cell-mediated cytotoxicity, particularly in the case of anti-CTLA-4 agents (IgG1 isotype).

Epidemiology, Timing, and Risk Factors

Incidence by Agent Class

Typical Timing of irAE Onset

While irAEs can occur at any time – including weeks to months after treatment discontinuation – the following general patterns are observed:^{1 4}

Delayed irAEs: irAEs can present months to over a year after treatment discontinuation. Clinicians should maintain a high index of suspicion for irAEs in any patient with a history of ICI exposure, even if treatment was completed or discontinued long prior.⁵

Risk Factors for irAEs

• Combination immunotherapy (anti-CTLA-4 + anti-PD-1) is the strongest risk factor for severe irAEs
• Higher doses of ipilimumab (3 mg/kg vs 1 mg/kg) are associated with increased toxicity
• Preexisting autoimmune disease (see Part 5)
• Prior irAE with rechallenge (see Part 5)
• Certain tumor types may have higher rates of specific irAEs (e.g., melanoma patients may have higher rates of colitis)
• Concurrent radiation therapy may increase risk of pneumonitis in irradiated fields
• Genetic factors (certain HLA alleles) are under investigation

CTCAE Grading: General Framework

All irAEs are graded using the Common Terminology Criteria for Adverse Events (CTCAE), currently version 5.0. The general grading framework is:^{1 3}

Organ-specific grading criteria are detailed in the respective sections of Parts 2 through 5.

General Principles for Holding, Resuming, and Discontinuing Immunotherapy

When to Hold Immunotherapy

• Grade 2 irAEs (most organ systems): Hold ICI until toxicity resolves to grade 1 or lower. Endocrine irAEs that are well controlled on hormone replacement are an exception and typically do not require holding therapy.¹
• Grade 3 irAEs: Hold ICI. May resume once toxicity resolves to grade 1 or lower and corticosteroids are tapered to prednisone equivalent of 10 mg/day or less, but only after careful risk-benefit discussion.
• Any irAE requiring hospitalization should prompt ICI hold pending workup and stabilization.

When to Permanently Discontinue Immunotherapy

Permanent discontinuation is recommended for:^{1 3 5}

• Any grade 4 irAE (with exceptions for endocrine irAEs manageable with hormone replacement)
• Grade 3 irAEs that do not improve to grade 1 within 12 weeks of corticosteroid initiation
• Inability to taper corticosteroids to prednisone 10 mg/day or equivalent within 12 weeks
• Recurrence of grade 3 irAE upon rechallenge
• Specific organ toxicities regardless of grade:
  • Myocarditis (any grade – given high mortality)
  • Grade 3–4 pneumonitis
  • Grade 4 colitis
  • Grade 4 hepatitis (AST/ALT > 20x ULN or total bilirubin > 10x ULN)
  • Grade 3–4 neurologic irAEs (myasthenia gravis, Guillain-Barre, encephalitis)
  • Stevens-Johnson syndrome or toxic epidermal necrolysis
  • Grade 4 nephritis
  • Grade 3–4 myositis (particularly with cardiac or respiratory involvement)

Holding Anti-CTLA-4 vs Anti-PD-1 in Combination Regimens

In patients receiving combination anti-CTLA-4 + anti-PD-1 who develop irAEs:

• Grade 2 irAE: May hold both agents or consider discontinuing anti-CTLA-4 and continuing anti-PD-1 after resolution
• Grade 3 irAE: Hold both agents; upon resolution, may consider resuming anti-PD-1 monotherapy after careful discussion, permanently discontinuing anti-CTLA-4
• Grade 4 irAE: Permanently discontinue both agents (with endocrine exceptions as noted)

Corticosteroid Protocols

Corticosteroids are the cornerstone of irAE management. The following general dosing framework applies across most organ systems, with organ-specific modifications detailed in subsequent parts.^{1 2 3}

Corticosteroid Dosing by irAE Grade

Corticosteroid Taper Protocol

Premature tapering is one of the most common causes of irAE relapse. The following general taper schedule is recommended:^{1 3}

For Grade 2 irAEs (starting from prednisone 0.5–1 mg/kg/day):

• Once irAE improves to grade 1 or lower, begin taper
• Taper by 10 mg per week if starting dose is 40–60 mg/day
• Taper by 5 mg per week once below 20 mg/day
• Total taper duration: minimum 4–6 weeks

For Grade 3–4 irAEs (starting from prednisone 1–2 mg/kg/day or IV equivalent):

• Once irAE improves to grade 1 or lower, transition from IV to oral if applicable
• Taper by 10 mg per week if starting dose > 60 mg/day
• Taper by 5–10 mg per week once at 40–60 mg/day
• Taper by 5 mg per week once below 20 mg/day
• Total taper duration: minimum 6–8 weeks (some organ systems require longer, e.g., hepatitis, colitis)

Critical principles for corticosteroid tapering:

• Do not taper faster than the minimum recommended schedule, even if the patient feels well
• If irAE symptoms recur during taper, increase dose to the last effective dose and attempt a slower taper after at least 1 week of stabilization
• If unable to taper below prednisone 10 mg/day within 12 weeks, consider steroid-sparing immunosuppressive agents and permanent discontinuation of ICI
• Prolonged corticosteroid use (> 4 weeks at prednisone > 20 mg/day) warrants PJP prophylaxis with trimethoprim-sulfamethoxazole (single-strength tablet daily or double-strength three times weekly), stress-dose steroid education, bone health assessment, and glucose monitoring

Supportive Care During Corticosteroid Therapy

Immunosuppressive Escalation Protocols

For irAEs that are refractory to corticosteroids (no improvement within 48–72 hours of high-dose corticosteroids, or worsening despite adequate dosing), escalation to additional immunosuppressive agents is warranted. The choice of agent depends on the organ system involved.^{1 2 3 6}

Summary of Immunosuppressive Agents for Steroid-Refractory irAEs

Algorithm for Steroid-Refractory irAEs

1. Confirm adequate corticosteroid dosing (prednisone 1–2 mg/kg/day or IV equivalent) for at least 48–72 hours
2. Rule out alternative diagnoses (infection, disease progression, other drug effect)
3. Select organ-specific immunosuppressive agent (see organ-specific chapters)
4. Initiate immunosuppressive agent while continuing high-dose corticosteroids
5. Once irAE improves, taper corticosteroids first, then taper or discontinue the second-line agent
6. If inadequate response to first second-line agent within 48–72 hours, escalate to third-line agent or consider multidisciplinary consultation

Infusion Reactions vs Immune-Related Adverse Events

Infusion reactions are distinct from irAEs and must be differentiated because they require different management approaches.^{1 3}

Key Differences

Infusion Reaction Grading and Management

Avelumab-Specific Premedication

Avelumab has a higher rate of infusion reactions (approximately 25%) compared to other ICIs. Standard premedication with diphenhydramine 25–50 mg and acetaminophen 500–650 mg approximately 30 minutes before the first 4 infusions is recommended per the prescribing information.¹

Baseline Evaluation and Monitoring During ICI Therapy

Recommended Baseline Assessments Before Starting ICI

Routine Monitoring During ICI Therapy

General Approach to irAE Workup

When an irAE is suspected, a systematic workup should be performed to confirm the diagnosis and exclude other etiologies:^{1 2}

1. Grade the toxicity using CTCAE v5.0 criteria specific to the organ system involved
2. Exclude non-irAE causes: infection, disease progression, other drug toxicity, unrelated medical conditions
3. Obtain organ-specific laboratory and imaging studies as detailed in subsequent organ-system chapters
4. Consult appropriate subspecialty early for grade 3–4 toxicities or unusual presentations
5. Hold immunotherapy per grading guidelines
6. Initiate corticosteroids at the appropriate dose for the grade and organ system
7. Document the irAE including grade, onset timing, and management plan
8. Escalate immunosuppression if no improvement within 48–72 hours of adequate corticosteroid dosing
9. Plan for taper and follow-up once improvement is achieved
10. Determine ICI rechallenge eligibility (see Part 5)

References