GI in the Immunocompromised Host: Hematopoietic Cell Transplant Gut GVHD

0:00Welcome to Board Pearls. This is episode two 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 hematopoietic cell transplant gut graft-versus-host disease: the post-transplant timeline that decides which diagnosis is even allowed, gut GVHD graded by stool volume with skin and liver involvement, the crypt-apoptosis histology and its differential, and treatment with corticosteroids first and ruxolitinib for steroid-refractory disease.

0:31The last episode covered solid organ transplant, where the differential is a five-drug list. Now to the hematopoietic cell transplant side, where the same word, transplant, hides a very different disease. About twenty thousand allogeneic hematopoietic cell transplants happen in the United States each year, and the post-transplant timeline organizes everything. The first twenty-one days belong to conditioning regimen toxicity. Mucositis, nausea, vomiting, and diarrhea from the cytotoxic preparative regimen that can mimic graft-versus-host disease but is not graft-versus-host disease and does not need graft-versus-host therapy. Engraftment syndrome appears around neutrophil recovery, roughly day seven to thirty, with fever, rash, non-cardiogenic pulmonary edema, and diarrhea, and it responds to a short course of corticosteroids. Classical acute graft-versus-host disease presents days fifteen to one hundred. Late-onset acute disease beyond day one hundred is formally recognized in newer frameworks. Sinusoidal obstruction syndrome, also called hepatic veno-occlusive disease, presents within twenty-one days of myeloablative conditioning with weight gain, painful hepatomegaly, and hyperbilirubinemia, often with ascites and reversed portal flow on Doppler. Defibrotide is the only FDA-approved therapy. The deep vascular liver disease lives elsewhere but the timeline cue belongs here.

1:58Acute graft-versus-host disease occurs in roughly forty percent of allogeneic transplants despite prophylaxis with calcineurin inhibitor plus methotrexate or post-transplant cyclophosphamide. Three target organs are involved. Skin, with a maculopapular rash. Liver, with cholestatic hyperbilirubinemia. Gut, with anorexia, nausea, vomiting, diarrhea, hematochezia, ileus, and abdominal pain. Gut involvement carries the worst prognosis of the three, and steroid-refractory gut graft-versus-host disease has mortality above fifty percent. The skin and liver involvement do not stand apart from gut disease in the typical patient. They coexist, and the rash plus the cholestatic hyperbilirubinemia plus the diarrhea is the recognition pattern. Risk modifiers include HLA mismatch, peripheral blood stem cell graft source over bone marrow over umbilical cord blood for acute disease specifically, and myeloablative conditioning over reduced-intensity.

3:00Gut staging is testable directly and uses the Glucksberg-Seattle thresholds anchored to daily stool volume. Stage one is diarrhea five hundred to nine hundred ninety-nine milliliters per day, or persistent nausea with histologic upper-gut graft-versus-host disease on biopsy. Stage two is one thousand to fourteen hundred ninety-nine milliliters per day. Stage three is fifteen hundred to two thousand. Stage four is greater than two thousand milliliters per day, or severe abdominal pain, or ileus, or hematochezia. Overall acute graft-versus-host disease grade combines gut stage with skin and liver stages, and grade three to four is the steroid-refractory mortality stratum. The MAGIC criteria refine the framework using two serum biomarkers, REG3-alpha and ST2, combined into Ann Arbor scores at diagnosis that predict non-relapse mortality. TIM3 has emerged as a third biomarker in late presentations.

3:58The histologic anchor is crypt apoptosis. Apoptotic bodies appear as bright eosinophilic dots within crypt epithelium, sometimes called popcorn lesions. The Lerner grading system parses biopsy severity, grade one with scattered apoptotic bodies, grade two with crypt destruction, grade three with crypt dropout, and grade four with total mucosal denudation. Endoscopic biopsy from the rectosigmoid is preferred because it offers high diagnostic yield with low procedural risk in a thrombocytopenic patient.

4:29The differential at the biopsy bench is where the careful reasoning happens, because crypt apoptosis is not pathognomonic. CMV colitis can produce crypt apoptosis that mimics graft-versus-host disease. The clinical reality is that CMV reactivation and graft-versus-host disease coexist often enough that every suspected gut graft-versus-host workup includes CMV polymerase chain reaction and tissue immunohistochemistry. Mycophenolate, conditioning regimen toxicity within day twenty-one, cord colitis after umbilical cord blood transplant, Clostridioides difficile, and viral enteritis are the other exclusions before treatment escalation. The post-HCT viral enteritis differential is broader than in immunocompetent hosts and includes rotavirus, norovirus, adenovirus, and BK virus. Adenovirus produces hemorrhagic colitis with mucosal ulceration in the heavily immunosuppressed HCT host, because absent T-cell control of adenovirus latency in the gut allows reactivation and tissue invasion. Cidofovir or brincidofovir is the antiviral when systemic adenovirus disease is documented.

5:43The treatment sequence is anchored by one mechanism and one trial. First-line therapy is intravenous methylprednisolone at two milligrams per kilogram per day with the calcineurin inhibitor continued. High-dose systemic glucocorticoid suppresses the donor-T-cell-mediated effector response across all involved tissues, which is why a topical agent like budesonide is not enough for multi-organ disease. Budesonide can be added or substituted for upper-gut-only mild disease because it has high first-pass hepatic metabolism that delivers high local concentration to upper GI mucosa with minimal systemic exposure. Roughly half of patients respond to first-line steroids. The remainder are classified as steroid-refractory at day five to seven, or sooner with frank progression.

6:30A board stem can lay this out plainly. Seven days of methylprednisolone two milligrams per kilogram per day. The patient's stool output has climbed from two liters to over three. The rash has progressed and the bilirubin keeps rising. That is steroid-refractory disease by definition. The wrong reading is to push steroids higher. Increasing methylprednisolone to four milligrams per kilogram per day is not the answer. Total colectomy is not the answer. The right answer is the next agent in the sequence, and a randomized trial put it there.

7:06That trial compared ruxolitinib against best available therapy in steroid-refractory acute graft-versus-host disease. Ruxolitinib is a JAK1 and JAK2 inhibitor, dosed at five to ten milligrams orally twice daily, and it produced a substantially higher day-twenty-eight response than the comparator and earned FDA approval in twenty nineteen for steroid-refractory acute graft-versus-host disease. The mechanism is the teaching. JAK1 and JAK2 blockade interrupts the Th1 and Th17 cytokine signaling that drives effector T-cell-mediated tissue injury. That is why ruxolitinib is the first-line second therapy. It works across skin, liver, and gut rather than at one tissue alone.

7:55Beyond ruxolitinib, the subsequent options each target a different effector pathway, and the choice depends on tissue distribution and dominant cytokine. Extracorporeal photopheresis induces regulatory T cells and is most active in skin-predominant disease. Anti-tumor necrosis factor agents, etanercept and infliximab, block the donor-T-cell-derived TNF that mediates gut epithelial apoptosis. Mycophenolate mofetil broadly suppresses lymphocyte proliferation. Vedolizumab blocks alpha-four beta-seven integrin binding to MAdCAM-one and prevents donor T-cell trafficking specifically into gut mucosa, which is why it is gut-selective and has growing data in gut graft-versus-host disease. Tocilizumab blocks interleukin-six, the dominant cytokine in late or refractory phenotypes. Mesenchymal stromal cells, in clinical-trial settings, exert broad immunomodulatory effects through paracrine signaling. The selection logic is mechanism-matched to the tissue and the cytokine, not a fixed sequence.

8:57One more stem belongs in this episode. A patient on prednisone for recurrent graft-versus-host disease returns with worsening diarrhea. Biopsy shows crypt apoptosis but also enlarged cells with intranuclear inclusions and positive CMV immunohistochemistry. Blood CMV PCR is twenty-two thousand. This is not progressive graft-versus-host disease driving the symptoms. This is CMV reactivation provoked by the steroid course itself. The answer is intravenous ganciclovir at five milligrams per kilogram every twelve hours, continuing prednisone at the current dose without escalation while CMV is active, and reassessing graft-versus-host therapy after viremia clears. Letermovir is for prophylaxis, not treatment. Pushing more steroid into active CMV makes the wrong problem worse. The teaching is that every escalation of immunosuppression in a transplant host has to be paired with infectious workup, because the iatrogenic infection often presents as treatment failure.

9:56Chronic graft-versus-host disease beyond day one hundred has a different phenotype. Esophageal strictures and webs, sicca syndrome, obstructive lung disease. It lives on a separate algorithm anchored by long-term immunosuppression with corticosteroids and steroid-sparing agents. The acute episode you just heard ends at the day-one-hundred mark, and the chronic disease that follows is its own teaching.

10:20Pull the hematopoietic cell transplant half together. The differential at every GI symptom is the donor immune system attacking the host, and time since transplant tells you whether the diagnosis is even allowed yet, with the first twenty-one days belonging to conditioning toxicity. Staging runs by stool volume on the Glucksberg-Seattle thresholds, the histology anchors on crypt apoptosis, and the biopsy-bench differential always includes CMV because apoptosis is not pathognomonic. Treatment is steroids first and ruxolitinib second on the strength of the randomized trial, with the later agents mechanism-matched to tissue and cytokine. And the shared move across both host states is to pair immunosuppression escalation with infectious workup, because CMV will exploit any opening you give it.

11:07The next episode moves to the HIV host. The CD4 count becomes the recognition anchor that converts a long pathogen list into a tiered differential. AIDS cholangiopathy, gut Kaposi sarcoma, and immune reconstitution inflammatory syndrome are the post-antiretroviral-era entities that still appear in late presenters. We also pick up typhlitis as the neutropenic enterocolitis recognition cue, with conservative management for the stable patient and surgery reserved for perforation.

11:37For 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 two of four of chapter thirty four, and I'll see you in the next one.