CAR-T and Engager Toxicity

Approved cellular and engager products (high-yield)

• CD19 CAR-T (B-cell malignancies)
  • Tisagenlecleucel (Kymriah) — r/r B-ALL ≤25 yo (ELIANA), r/r DLBCL (JULIET), r/r FL (ELARA).
  • Axicabtagene ciloleucel (Yescarta) — r/r LBCL (ZUMA-1), 2L LBCL (ZUMA-7), r/r FL (ZUMA-5).
  • Brexucabtagene autoleucel (Tecartus) — r/r MCL (ZUMA-2), adult B-ALL (ZUMA-3).
  • Lisocabtagene maraleucel (Breyanzi) — r/r LBCL (TRANSCEND-NHL-001), 2L LBCL (TRANSFORM/PILOT), CLL/SLL (TRANSCEND CLL-004), MCL, FL.
  • Obecabtagene autoleucel (obe-cel, Aucatzyl) — adult r/r B-ALL (FELIX). Lower CRS/ICANS rates due to fast off-rate ("kinetically optimized") design.
• BCMA CAR-T (multiple myeloma)
  • Idecabtagene vicleucel (Abecma) — r/r MM ≥2 prior lines (KARMMA, KARMMA-3).
  • Ciltacabtagene autoleucel (Carvykti) — r/r MM ≥1 prior line including IMiD + PI, and lenalidomide-refractory (CARTITUDE-1, CARTITUDE-4).
• CD3 bispecific T-cell engagers (BiTEs / TCEs)
  • Blinatumomab (CD19×CD3) — B-ALL.
  • Mosunetuzumab, glofitamab, epcoritamab (CD20×CD3) — B-NHL (FL, DLBCL).
  • Teclistamab, elranatamab, linvoseltamab (BCMA×CD3), talquetamab (GPRC5D×CD3) — MM.
  • Tarlatamab (DLL3×CD3) — SCLC.
• FDA boxed warnings: CRS, ICANS, and second malignancy for all CAR-T products; HLH/MAS and prolonged cytopenias additionally for BCMA products (ide-cel, cilta-cel) (T-cell malignancy class warning added April 2024 after post-marketing reports). CAR-T REMS eliminated by FDA in June 2025.

Cytokine release syndrome (CRS) — ASTCT 2019 grading

• Grade 1. Fever ≥38°C only. No hypotension, no hypoxia.
• Grade 2. Fever ≥38°C plus hypotension not requiring vasopressors AND/OR hypoxia requiring low-flow O2 (≤6 L/min nasal cannula or blow-by).
• Grade 3. Fever ≥38°C plus hypotension requiring one vasopressor ± vasopressin AND/OR hypoxia requiring high-flow O2 (>6 L/min high-flow nasal cannula, facemask, nonrebreather, or Venturi mask).
• Grade 4. Fever ≥38°C plus hypotension requiring multiple vasopressors (excluding vasopressin) AND/OR hypoxia requiring positive pressure (CPAP, BiPAP, or intubation and mechanical ventilation).
• Grade 5. Death attributable to CRS.
• Once fever is masked by tocilizumab/steroids/antipyretics, grade CRS by hypotension and hypoxia (the worse of the two); other organ toxicities are graded separately and do not change the CRS grade.

CRS pathophysiology and risk factors

• Engaged T cells release IFN-γ → activate macrophages → IL-6, IL-1, TNF-α surge → vascular leak, hypotension, hypoxia, capillary leak, end-organ dysfunction.
• Risk factors: high tumor burden (bulky disease, high LDH, BM blasts), high-intensity lymphodepletion (fludarabine + cyclophosphamide), product type (axi-cel CRS ~93%, tisa-cel ~58%, liso-cel ~42%; ide-cel ~85%; cilta-cel ~95%; obe-cel ~75% but mostly grade 1 to 2).
• Timing: onset typically day 1–7 (CD19) or product-specific for BCMA (ide-cel median day 1; cilta-cel median day 7, range 1 to 23), peak ~day 3–7, resolution by 2 weeks.
• BiTEs/TCEs: CRS clusters around the step-up doses and first full dose (product-specific; epcoritamab peaks at the first full dose); risk drops sharply by cycle 2.

CRS management

• All grades: supportive care — antipyretics (avoid scheduled APAP if febrile pattern is needed for grading), IV fluids, sepsis workup and empiric broad-spectrum antibiotics for any fever.
• Grade 1. Supportive ± single-dose tocilizumab if persistent or in high-risk patient.
• Grade 2. Tocilizumab 8 mg/kg IV if ≥30 kg, 12 mg/kg IV if <30 kg (max 800 mg per dose; may repeat q8h, max 3 doses in 24 h and 4 doses total); add dexamethasone 10 mg IV q6h if not improving in 24 h.
• Grade 3. Tocilizumab + dexamethasone 10 mg IV q6h (or methylprednisolone 1 mg/kg IV BID); ICU; pressors as needed.
• Grade 4. Tocilizumab + methylprednisolone 1 g IV daily × 3 d (pulse); ICU, mechanical ventilation, multiple pressors.
• Tocilizumab refractory: add anakinra 100–200 mg SC/IV daily (or higher in severe), or siltuximab 11 mg/kg IV.
• Tocilizumab dose limit: max 3 doses in 24 h and 4 doses total per label; doses ≥8 h apart.
• Steroid use was historically restricted out of concern for impairing CAR-T expansion, but ZUMA-1 cohort 4 and prophylactic steroid studies showed efficacy is preserved — modern practice uses steroids early and aggressively for grade ≥2.

CRS prophylaxis

• Prophylactic tocilizumab (ZUMA-1 cohort 3 with axi-cel) reduced grade ≥3 CRS (3%) but increased grade ≥3 neurologic events (42%), so it is not recommended for CAR-T; prophylactic dexamethasone (cohort 6) gave no grade ≥3 CRS without compromising efficacy.
• Bispecifics use mandated step-up dosing, premedication with dexamethasone, antihistamine, and APAP for first 1–2 cycles to reduce CRS.

Immune effector cell-associated neurotoxicity syndrome (ICANS)

ICE score (10 points)

• Orientation — year, month, city, hospital (4 pts).
• Naming — 3 objects (3 pts).
• Following commands — simple command (1 pt).
• Writing — standard sentence (1 pt).
• Attention — count backward from 100 by 10 (1 pt).
• Score 10 = no impairment, 7–9 = grade 1, 3–6 = grade 2, 0–2 = grade 3, unarousable = grade 4.

ICANS grading (ASTCT 2019)

• Grade 1. ICE 7–9, awake spontaneously.
• Grade 2. ICE 3–6, awakens to voice.
• Grade 3. ICE 0–2, awakens to tactile stim only, ANY clinical seizure that resolves rapidly with intervention OR non-convulsive seizures that resolve with intervention, focal/local edema on imaging.
• Grade 4. Unarousable or requires vigorous stimulation, life-threatening prolonged seizure (>5 min) or repetitive without return to baseline, deep focal motor weakness (hemiparesis, paraparesis), diffuse cerebral edema on imaging, decorticate/decerebrate posturing, cranial nerve VI palsy, papilledema, Cushing triad.
• Grade 5. Death from ICANS.

ICANS management

• Workup: non-contrast head CT, MRI brain, EEG (continuous if grade ≥2), LP if concern for infection or to assess CSF cytokines, neurology consult.
• Grade 1. Supportive; aspiration precautions; consider dexamethasone 10 mg IV × 1 if persistent or concurrent CRS.
• Grade 2. Dexamethasone 10 mg IV q6h (or methylprednisolone 1 mg/kg IV BID); concurrent tocilizumab only if active CRS (tocilizumab does NOT cross BBB so it does not treat isolated ICANS).
• Grade 3. Dexamethasone 10–20 mg IV q6h OR methylprednisolone 1 g IV daily; ICU monitoring; anti-epileptic prophylaxis (levetiracetam) if seizure activity.
• Grade 4. Methylprednisolone 1 g IV q12h; ICU, intubation as needed; anakinra (crosses BBB) for steroid-refractory disease; consider intrathecal chemotherapy (methotrexate ± hydrocortisone) in select refractory cases; manage elevated ICP (HOB elevation, hyperventilation, hypertonic saline).
• Seizure prophylaxis: levetiracetam 750 mg BID is given prophylactically at many centers from day of infusion through day 30.

Why tocilizumab does not work for isolated ICANS

• Tocilizumab is a large monoclonal antibody — does not cross the blood-brain barrier.
• Use is reserved for concurrent CRS only.
• Anakinra (IL-1Rα antagonist) does cross BBB, has CNS activity, and is the preferred adjunct for steroid-refractory ICANS. Dose 100–200 mg SC daily, can be higher in severe cases.

Hemophagocytic lymphohistiocytosis (HLH/MAS) after CAR-T (carHLH)

• Usually recognized as CRS resolves, but timing is variable and onset is often early (ide-cel median HLH/MAS onset ~7 d, cilta-cel ~10 d); can overlap active CRS.
• Diagnostic clues: persistent fevers, hyperferritinemia (often >10,000 ng/mL), hypertriglyceridemia, hypofibrinogenemia, cytopenias, hepatosplenomegaly, transaminitis, low NK function, soluble IL-2R elevation, hemophagocytosis on BM biopsy.
• Distinguish from CRS: often persists or worsens as CRS resolves (but can overlap), more profound cytopenias, organomegaly, ferritin out of proportion to clinical picture.
• Treatment: high-dose steroids (methylprednisolone pulse), anakinra (dose escalation often needed), etoposide for refractory disease, ruxolitinib in select cases. IVIG for hypogammaglobulinemia.

Prolonged hematologic toxicity

• Prolonged cytopenias (≥30 d after infusion) in 30–60% of patients; can persist for months. Mechanism not fully defined — likely lymphodepletion, marrow inflammation, and bystander CAR effects.
• Workup: CBC at least weekly through day 28, then per institutional schedule; BM biopsy if cytopenias persist >day 60 or worsen to rule out relapse, MDS, secondary malignancy, viral cause (CMV, parvovirus, HHV-6).
• Management: G-CSF (avoid early in CRS — can worsen), thrombopoietin receptor agonists (eltrombopag) for thrombocytopenia, transfusion support, autologous stem cell boost in select prolonged cases.
• B-cell aplasia and hypogammaglobulinemia are on-target/off-tumor for CD19 products. IgG <400 mg/dL or recurrent sinopulmonary infections → IVIG replacement (typically 400 mg/kg q4wk).
• BCMA products → less B-cell aplasia, but profound hypogammaglobulinemia from plasma cell depletion. Same IVIG approach.

Infection prophylaxis

• PJP prophylaxis (TMP-SMX, dapsone, atovaquone, or pentamidine) from day of infusion through CD4 recovery (typically 6–12 mo).
• HSV/VZV prophylaxis (acyclovir or valacyclovir) for 6–12 mo.
• Antifungal prophylaxis (fluconazole) until neutrophil recovery; expand to mold coverage if prolonged neutropenia.
• HBV reactivation prevention — entecavir or tenofovir if HBcAb+ (regardless of HBsAg status).
• Vaccinations — avoid live vaccines for at least 1 year. Inactivated vaccines (flu, COVID, pneumococcal) can be given but response is blunted.
• Re-vaccination after B-cell recovery using a post-HSCT-style schedule.

Tumor lysis syndrome

• Risk highest in high-burden ALL and aggressive lymphoma. Standard TLS prophylaxis (allopurinol, hydration; rasburicase if high-risk or uric acid elevated) around infusion.

Secondary malignancy — boxed warning April 2024

• FDA added class-wide boxed warning for T-cell malignancy after CAR-T (Apr 2024) following post-marketing reports of T-cell lymphomas (including CAR-positive T-cell lymphomas in a subset).
• Mechanism: insertional mutagenesis from lentiviral/retroviral vector integration is one proposed pathway; lymphodepletion-induced immune dysfunction also contributes.
• Lifetime monitoring recommended for any new lymphoma; biopsy specimens should be tested for CAR transgene if relevant.

Lymphocyte engager-specific toxicity considerations

• CRS dynamics are product-specific: for teclistamab most CRS occurs during step-up (step-up 1 ~37%, step-up 2 ~32%) rather than the first full dose (~20%); some agents (epcoritamab) peak at first full dose; risk falls after cycle 1 to 2. Premedication (corticosteroid, antihistamine, antipyretic) during step-up; inpatient admission is product-specific and not universal (e.g., mosunetuzumab outpatient; epcoritamab outpatient in FL but 24 h hospitalization after the first full dose (C1D15) in LBCL).
• ICANS: less common than with CAR-T but reported.
• Infection risk: profound and prolonged hypogammaglobulinemia (BCMA bispecifics in particular). PJP prophylaxis, IVIG, monitoring for opportunistic infections (PCP, CMV, fungal). Higher infection-related mortality reported with teclistamab and elranatamab vs CAR-T.
• Anaphylaxis/infusion reactions with first doses; mitigated by premedication.
• Talquetamab (GPRC5D): unique on-target/off-tumor — dysgeusia, nail changes, weight loss, skin rash from GPRC5D expression on keratinized tissues.
• Tarlatamab (DLL3, SCLC): CRS in ~50% (mostly grade 1–2), ICANS reported, requires 6 to 8 h monitoring in a healthcare setting after cycle 1 day 1 and day 8 (reduced from 22 to 24 h; FDA Sept 2026), then stay within 1 h of care for 48 h with a caregiver, then shorter observation.

Other important considerations

• Fertility: lymphodepletion regimens (flu/cy) carry gonadotoxic risk — offer fertility preservation pre-treatment.
• Cardiac: CRS-related hypotension and high-output state can precipitate decompensation in patients with baseline LV dysfunction; baseline echo recommended.
• GVHD (allogeneic CAR-T only): emerging "off-the-shelf" allo products carry GVHD risk; manage per allo-HSCT principles.
• REMS programs: FDA eliminated the REMS for all autologous CD19/BCMA CAR-T products (June 2025); labels now advise staying near a healthcare facility and not driving for 2 weeks (previously 4 and 8 weeks). REMS still applies to some bispecifics (e.g., teclistamab/talquetamab).

2024-2026 CAR-T & engager toxicity updates

• FDA T-cell malignancy class warning (Apr 2024, expanded 2025): 33+ post-marketing T-cell malignancies reported across ~30,000+ CAR-T recipients (through mid-2025); only a minority tested positive for the CAR transgene (EMA 2024: 38 cases, ~19 tested, 7 CAR-positive); transgene detection alone does not establish insertional oncogenesis. All approved CD19/BCMA products affected. Lifetime hematologic surveillance; biopsy any new lymphoma for CAR transgene.
• Prophylactic tocilizumab for T-cell engagers: TALQUETIST (Rodriguez-Otero ASH 2024) — prophylactic tocilizumab with talquetamab step-up markedly reduced grade >=2 CRS (11% vs 35%) without impact on efficacy; similar signals with teclistamab (MajesTEC-1 substudy) and elranatamab.
• Step-up dose optimization: shorter, outpatient-eligible schedules under evaluation across BCMA and GPRC5D bispecifics (teclistamab 2-step + prophy toci, talquetamab weekly-to-Q2W transition Ph3).
• Cilta-cel delayed neurotoxicity: parkinsonism, cranial-nerve palsy (CN VII most common), Guillain-Barre-like syndrome; per label, cranial nerve palsy ~7% (median onset ~3 weeks) and parkinsonism ~3% (median onset ~8 weeks, can occur months later); steroids +/- IVIG +/- plasmapheresis. Baseline neuro assessment + prolonged monitoring recommended.
• Anakinra prophylaxis: early single-arm data suggested less high-grade ICANS in high-risk CD19 CAR-T recipients, but a 2026 real-world IPTW analysis (Easton TCT 2026) found no reduction in grade ≥3 ICANS and more grade ≥3 infections; not standard outside trials.
• CD3xCD20 bispecific ICANS: glofitamab/epcoritamab ICANS rates ~3-9% (mostly grade 1-2); vast majority resolve; step-up dosing + premedication mitigates.
• Prolonged cytopenia grading: CAR-HEMATOTOX score (Rejeski Blood 2021) and EHA/EBMT ICAHT grading (Rejeski Blood 2023) validated for predicting infections and non-relapse mortality; guides G-CSF, TPO-RA, and prophylaxis intensity.
• Infection risk with bispecifics vs CAR-T: pooled analysis (Mazahreh, Blood Adv 2023): grade >=3 infection ~30% with BCMA bispecifics vs ~12% non-BCMA (incl GPRC5D/talquetamab; TALVEY label ~17%); PJP, CMV, hypogammaglobulinemia-related. IVIG replacement (target IgG >400) increasingly standard.
• Obe-cel (Aucatzyl) approval (FDA Nov 2024) — adult r/r B-ALL — CRS ~75% but almost entirely grade 1-2 (grade ≥3 3%), ICANS ~24% (grade ≥3 7%); kinetically-optimized design reduces toxicity vs conventional CD19 CAR-T.

References (open-access or freely citable)

• Lee DW et al. ASTCT consensus grading for CRS and neurologic toxicity associated with immune effector cells. Biol Blood Marrow Transplant 2019;25:625-638. PMID 30592986.
• Maus MV et al. SITC consensus on the management of toxicities of immune effector cell therapy. J Immunother Cancer 2020;8:e001511.
• Neelapu SS et al. Chimeric antigen receptor T-cell therapy — assessment and management of toxicities. Nat Rev Clin Oncol 2018;15:47-62. PMID 28925994.
• Hayden PJ et al. Management of adults and children receiving CAR T-cell therapy: 2021 best practice recommendations of EBMT/EHA/JACIE. Ann Oncol 2022;33:259-275.
• FDA package inserts: tisagenlecleucel, axicabtagene ciloleucel, brexucabtagene autoleucel, lisocabtagene maraleucel, idecabtagene vicleucel, ciltacabtagene autoleucel, obecabtagene autoleucel.