GI in the Immunocompromised Host: Immune Checkpoint Inhibitor Toxicity

0:00Welcome to Board Pearls. This is episode four of four of the GI in the Immunocompromised Host chapter, in the Special Populations and Acute or Supportive Care module. In this episode we cover checkpoint inhibitor toxicity: ICI colitis with grade-based corticosteroids then infliximab or vedolizumab for refractory disease, ICI hepatitis with the typical onset window and management that holds checkpoint inhibitors and starts steroids based on transaminase grade, and the irAE recognition framework across pneumonitis, endocrinopathies, dermatologic toxicity, and the other organ-specific adverse events.

0:36Checkpoint inhibitor toxicity is one entity with many organ targets. The drugs release the brakes on T cells so the immune system can recognize tumor. The same T cells, once unleashed, recognize self. The pattern of organ injury follows from where T cells run unchecked, and the severity follows from how broadly the brake was released. That is the organizing idea of the entire chapter on these toxicities, and it predicts both which organs get hit and how aggressive the rescue has to be.

1:05The drug classes target two checkpoints at two different stages of T-cell activation. CTLA-4 acts in lymph nodes at the priming stage, where naive T cells first see antigen. Ipilimumab and tremelimumab block CTLA-4. PD-1 and PD-L1 act in tissue at the effector stage, where activated T cells reach the target. Nivolumab, pembrolizumab, and cemiplimab block PD-1. Atezolizumab and durvalumab block PD-L1. That distinction predicts toxicity in two ways. Anti-CTLA-4 broadens the T-cell repertoire that gets activated, so toxicities are more frequent, more severe, and recur reliably on rechallenge. Anti-PD-1 and anti-PD-L1 release effector T cells in tissue, so toxicities are more focal and less likely to recur on monotherapy rechallenge. Combination ipilimumab plus nivolumab releases both brakes, and the toxicity rates are highest of all.

2:09Hold that mechanism in mind. It explains why grade three colitis on combination therapy permanently retires ipilimumab while anti-PD-1 may be reintroduced. It also explains why combination regimens carry the highest rate of severe colitis and severe hepatitis.

2:25Now to the colitis. The GI tract is one of the most commonly affected organ systems. Anti-CTLA-4 monotherapy produces grade three to four colitis in roughly seven to ten percent of patients. Anti-PD-1 monotherapy produces grade three to four colitis in roughly one to three percent. Combination ipilimumab plus nivolumab produces grade three to four colitis in roughly twelve percent, the highest of any regimen. Onset typically falls four to ten weeks after starting ipilimumab and three to six months into anti-PD-1 monotherapy, though late presentations beyond a year after the last dose are reported. The combination regimen tends to present early, often within weeks of the first or second cycle.

3:09Recognition is clinical context plus exclusion of mimics plus endoscopy. The dominant infectious mimic on the boards is Clostridioides difficile, and stool C. difficile testing must precede any steroid escalation in every patient. The second mimic is cytomegalovirus, particularly in patients who have already received steroids or biologics. CMV reactivation is what makes a treatment failure look like steroid-refractory colitis when it is really superinfection. So CMV polymerase chain reaction in blood and tissue is added in any steroid-pretreated patient.

3:44Endoscopy ranges from a normal-looking mucosa with inflammation only on biopsy, through erythema and granularity and friability, to deep ulceration in severe cases. Three endoscopic features predict steroid failure and biologic requirement: ulcers deeper than two millimeters, ulcers larger than one centimeter, and extensive pancolitis. Histology shows neutrophilic cryptitis, crypt abscesses, increased intraepithelial lymphocytes, and prominent crypt apoptosis. The apoptosis is more pronounced than in idiopathic inflammatory bowel disease and overlaps with the graft-versus-host disease pattern. There is also a microscopic-colitis-like pattern, more common with anti-PD-1 agents, where the endoscopic appearance is grossly normal but biopsies show a lymphocytic or collagenous infiltrate. That variant gets open-capsule budesonide nine milligrams daily and consideration of holding the checkpoint inhibitor.

4:40Grading anchors to stools per day above baseline, because severity tracks depth of T-cell-mediated mucosal injury. Grade one is fewer than four stools per day above baseline, mild and self-limited, managed with loperamide and oral hydration with the checkpoint inhibitor continued. The teaching here is that the brake-release injury at this severity does not need immunosuppression, and pulling the cancer therapy is not justified by the toxicity.

5:06Grade two is four to six stools above baseline. Hold the checkpoint inhibitor. Start oral budesonide nine milligrams daily, or oral prednisone one milligram per kilogram per day. The mechanism for the topical-acting steroid choice is that local T-cell activity has not yet produced transmural injury. A controlled-release agent with low systemic exposure suppresses the local infiltrate without committing to a long systemic taper. Reassess at seventy-two hours and escalate if there is no response.

5:38Grade three to four is seven or more stools above baseline, hospitalization, or hemodynamic instability. Permanently discontinue anti-CTLA-4. Start intravenous methylprednisolone one to two milligrams per kilogram per day for systemic suppression of the diffuse T-cell infiltrate now driving transmural injury. Reassess at seventy-two hours.

6:01The seventy-two-hour window is the key decision point. The rationale matches the kinetics of steroid-mediated lymphocyte apoptosis. By that interval, if the diffuse T-cell infiltrate is going to respond, you can see it. If it does not respond, the cells driving the colitis are escaping steroid effect and a biologic is added.

6:22The second-line choice between infliximab and vedolizumab is one of the most testable decisions in the chapter, and it splits along three considerations. Infliximab acts faster, with clinical response within days, and has the largest evidence base. Vedolizumab is gut-selective through alpha-four-beta-seven integrin blockade, which means it does not reduce systemic anti-CMV immunity the way infliximab does. Cytomegalovirus reactivation risk is therefore higher with infliximab, because systemic anti-tumor necrosis factor blockade suppresses the cellular immunity required to keep latent CMV in check. Vedolizumab acts only at gut endothelium and leaves systemic anti-CMV immunity intact.

7:03Two patient features push the choice toward vedolizumab. The first is concurrent hepatic dysfunction or any contraindication to anti-tumor necrosis factor therapy. The second is concurrent active immune-mediated hepatitis, where infliximab is outright contraindicated, and we will come back to that in the hepatitis section. Standard dosing is infliximab five to ten milligrams per kilogram, often a single dose repeated at two weeks if symptoms persist, or vedolizumab three hundred milligrams intravenously at weeks zero, two, and six.

7:37There is one clinical scenario where the steroid-refractory algorithm flips, and the boards test it directly. A patient on a prolonged prednisone taper for grade three colitis develops recurrent diarrhea, low-grade fever, and a new round of ulceration on repeat sigmoidoscopy. CMV immunohistochemistry on the ulcer base biopsies returns positive. Blood CMV polymerase chain reaction returns at a meaningful viral load. The right move is intravenous ganciclovir five milligrams per kilogram every twelve hours for at least fourteen to twenty-one days until viremia clears. Continue the existing steroid taper if clinically tolerated. Defer infliximab while CMV is active, because anti-tumor necrosis factor therapy in unsuppressed CMV reactivation precipitates fulminant viremic disease. Oral acyclovir is not the answer because CMV thymidine kinase has limited affinity for acyclovir. Foscarnet replaces ganciclovir for ganciclovir resistance or significant cytopenia.

8:44Rechallenge after recovery follows the same logic as the toxicity profile. Rechallenge with the same drug class is generally safe after grade one to two colitis once the patient returns to grade one or below. Normalized fecal calprotectin or repeat sigmoidoscopy showing mucosal healing supports the call. Rechallenge with anti-CTLA-4 after grade three to four colitis is avoided, because anti-CTLA-4 broadens the activated T-cell repertoire at the priming stage and the same broad activation recurs reliably on rechallenge. Anti-PD-1 may be considered for rechallenge after grade three colitis case-by-case. It acts at the effector stage. The broad T-cell repertoire that drove the colitis was activated by the prior CTLA-4 exposure, not by the PD-1 pathway itself. Switching from combination to anti-PD-1 monotherapy after grade three combination colitis is the typical compromise. Empiric prophylactic infliximab before rechallenge is not standard and adds infection risk without proven benefit.

9:50Now to the hepatitis. Checkpoint inhibitor hepatitis affects roughly four to nine percent of patients on anti-CTLA-4 monotherapy, one to four percent on anti-PD-1 or anti-PD-L1 monotherapy, and up to eighteen percent on combination ipilimumab plus nivolumab. The onset window is typically six to fourteen weeks after initiation, with a median around eight to twelve weeks. The presentation is most often asymptomatic transaminase elevation found on routine surveillance labs, occasionally with jaundice, and rarely with fulminant hepatitis. About one-third of patients have concurrent other-organ irAEs, one-third have fever, and one-third have rash.

10:33The injury pattern is hepatocellular more often than cholestatic, with mixed pattern occurring as well. The workup is the standard drug-induced liver injury workup with the immune-related modifications. Exclude viral hepatitis A, B, C, and E and reactivation of latent hepatitis B. Exclude concomitant drug-induced liver injury, including over-the-counter agents and herbal supplements. Exclude autoimmune hepatitis. Exclude alcohol. Imaging excludes biliary obstruction.

11:07Biopsy is not required when the clinical context is clear and other causes are excluded, but it helps in steroid-refractory or atypical presentations. Histology shows a panlobular hepatitis with mild portal lymphocytic or histiocytic inflammation. The discriminating feature from autoimmune hepatitis is the absence of plasma cells. Lymphocytic cholangitis appears in roughly half of cases. Granulomas are more common with anti-CTLA-4 than with anti-PD-1. Autoantibodies are usually negative or low-titer, and immunoglobulin G is usually normal. All of that contrasts with classical autoimmune hepatitis, where plasma cells dominate, immunoglobulin G is elevated, and autoantibodies are positive.

11:52Grading anchors to transaminase elevation and bilirubin, and the sequence mirrors the colitis sequence up to one critical contraindication. Grade one is ALT less than three times the upper limit of normal, bilirubin under one and a half times. Continue the checkpoint inhibitor with weekly liver labs. Grade two is ALT three to five times upper limit, bilirubin one and a half to three times. Hold the checkpoint inhibitor. Consider oral prednisone half to one milligram per kilogram per day if biochemistries are persistent. Grade three is ALT five to twenty times upper limit, bilirubin three to ten times. Permanently discontinue the checkpoint inhibitor. Start intravenous methylprednisolone one to two milligrams per kilogram per day. Grade four is ALT above twenty times upper limit, bilirubin above ten times, or decompensation. Permanently discontinue. Start intravenous methylprednisolone two milligrams per kilogram per day. Add mycophenolate mofetil one gram twice daily if there is no response at seventy-two hours.

13:02Steroid taper extends over four to six weeks once liver tests improve, and rapid taper drives relapse.

13:09Then the contraindication that makes the hepatitis algorithm different from the colitis algorithm. Infliximab is contraindicated in checkpoint inhibitor hepatitis. The mechanism is that infliximab can produce idiosyncratic immune-mediated drug-induced liver injury with autoimmune features and can reactivate hepatitis B. In a patient who already has active immune-mediated hepatitis from the checkpoint blockade, adding infliximab compounds the liver injury rather than resolving it. This is the critical distinction from checkpoint colitis, where infliximab is the first-line second agent because the liver-specific immune-complex toxicity is not present at the colon.

13:51Mycophenolate mofetil replaces infliximab as the second-line agent in steroid-refractory checkpoint hepatitis. The dose is one gram twice daily, sometimes escalated to one and a half grams twice daily. Mycophenolate inhibits inosine monophosphate dehydrogenase and broadly suppresses lymphocyte proliferation without the liver-specific immune-complex formation that drives infliximab hepatotoxicity. Response is typically observed within one to two weeks, slower than infliximab in colitis. Tocilizumab, an anti-interleukin-six receptor antibody, at eight milligrams per kilogram intravenously, is a third-line option. Azathioprine and tacrolimus have been used in case series for their established roles in autoimmune hepatitis. Liver transplant evaluation is reserved for patients meeting King's College Criteria for acute liver failure with synthetic dysfunction and encephalopathy not responsive to medical therapy.

14:43That swap, mycophenolate for infliximab in the hepatitis algorithm, is the single most tested distinction in the entire chapter on checkpoint toxicity. A test stem that gives a patient with checkpoint hepatitis and no biochemical improvement at seventy-two to ninety-six hours of intravenous methylprednisolone is asking for mycophenolate mofetil. The wrong answer is infliximab borrowed from the colitis algorithm, and the boards write that distractor deliberately.

15:12The sclerosing cholangitis-like variant deserves separate recognition. It is associated more with anti-PD-1 agents and presents with cholestatic liver tests, biliary strictures and beading on magnetic resonance cholangiopancreatography, and lymphocytic cholangitis on biopsy. This variant is less steroid-responsive than the parenchymal pattern, because the dominant injury is biliary obstruction and cholestatic injury from lymphocytic cholangitis. Steroids partially modulate the inflammation but do not relieve the mechanical cholestasis. Ursodeoxycholic acid is added because it enriches the bile acid pool with hydrophilic species that protect cholangiocytes from hydrophobic-bile-acid injury. That is the same mechanism that gives ursodeoxycholic acid its role in primary biliary cholangitis and primary sclerosing cholangitis. Recognition matters because the prognosis is more chronic and the response to standard checkpoint hepatitis algorithms is incomplete.

16:10Rechallenge follows the same logic as in colitis. After grade one to two hepatitis with full recovery, rechallenge with the same drug class is considered. After grade three to four hepatitis, rechallenge is generally avoided because of high recurrence rates and the risk of more severe liver injury on re-exposure.

16:29Now the rest of the organ-specific adverse events, briefly, because they sit on the same framework. Checkpoint inhibitor pancreatitis is rare at roughly one to two percent. The more common finding is asymptomatic lipase elevation without imaging changes or clinical pancreatitis. The teaching is that lipase alone is not a trigger for steroids. Symptomatic pancreatitis with an imaging correlate is what crosses into the steroid threshold. Long-term sequelae include exocrine pancreatic insufficiency and brittle diabetes from cumulative beta-cell injury. A patient with one episode of checkpoint pancreatitis has a real chance of needing pancreatic enzyme replacement and insulin afterward.

17:10Checkpoint inhibitor gastritis presents as a focal erosive or diffuse pattern that mimics Helicobacter pylori or autoimmune gastritis on endoscopy. Treatment is a proton pump inhibitor and a steroid taper. Checkpoint inhibitor esophagitis is uncommon and treated the same way.

17:28Endocrine immune-related adverse events are thyroiditis, hypophysitis, and adrenalitis. They require hormone replacement, not steroid taper, because by the time the disease is recognized the damage to the endocrine gland is usually irreversible and the patient needs lifelong replacement. Endocrinopathies frequently coexist with GI irAEs in the same patient, because the underlying T-cell activation is system-wide.

17:55The other irAEs that sit outside the GI tract follow the same logic and round out the recognition framework. Pneumonitis is dyspnea or cough with ground-glass opacities on chest imaging and is treated with holding the drug and starting steroids at a severity-driven dose, the same escalation pattern as colitis. Dermatologic toxicity ranges from mild rash and pruritus through grade three to four reactions, including rare Stevens-Johnson syndrome and toxic epidermal necrolysis. Mild rash is treated with topical steroid and antihistamines. Severe rash holds the drug and starts systemic steroid. Nephritis presents as a rising creatinine and is biopsy-confirmed when the clinical picture is atypical. Arthritis, myositis, and myocarditis are recognized rheumatic and cardiac toxicities. Myocarditis carries the highest mortality of any irAE despite being uncommon. That is why a new troponin in a patient on checkpoint inhibitors is taken seriously.

18:54The synthesis is one framework applied across organs. Drug class predicts toxicity rate: CTLA-4 broad and severe, PD-1 and PD-L1 focal and milder, combination highest. Grade drives therapy: grade one observation, grade two hold and oral steroid, grade three to four discontinue and intravenous steroid. The seventy-two-hour response window is the universal escalation trigger.

19:25Steroid-refractory colitis goes to infliximab or vedolizumab with the choice driven by hepatic comorbidity and CMV risk. Steroid-refractory hepatitis goes to mycophenolate mofetil because infliximab is contraindicated by hepatotoxicity. Endocrinopathies need replacement rather than immunosuppression because the gland is already damaged. C. difficile is excluded before steroids in every colitis patient, and CMV reactivation explains apparent steroid failure on prolonged immunosuppression.

19:58That closes the special-populations and acute-or-supportive-care module. Chapter thirty-five turns to GI in pregnancy, and the organizing question shifts. Pregnancy physiology and normal-lab shifts and imaging modality choices reframe the bedside read. Nausea and hyperemesis gravidarum, GERD, and peptic ulcer disease reframe symptom management. The intrahepatic cholestasis of pregnancy and the preeclampsia-HELLP-AFLP liver-disease spectrum drive recognition of the pregnancy-specific hepatobiliary diseases. Viral and pre-existing liver disease, IBD in pregnancy, post-bariatric pregnancy, and cholelithiasis with the procedural decisions cover the rest of the GI workload in the pregnant patient.

20:44For the full chapter, the practice vignettes, and the topic-tagged question bank, head to board pearls dot com. You'll find the rest of the series on Apple Podcasts, Spotify, or wherever you listen to podcasts. That brings us to the end of episode four of four of chapter thirty four, and I'll see you in the next one.