What Are CAR-T Cells?

CAR-T cells are genetically engineered autologous T lymphocytes that express a synthetic receptor (chimeric antigen receptor) combining:

1. Extracellular domain: Single-chain variable fragment (scFv) — antibody-like structure recognizing tumor antigen
2. Transmembrane domain: Bridges cell surface to intracellular
3. Intracellular signaling domains:
   • CD3ζ (primary): T-cell receptor signaling
   • Costimulatory domains: CD28 or 4-1BB (second signal for T-cell activation)

Generation: 1. Autologous T-cell collection (leukapheresis) 2. Ex vivo transduction with CAR construct (viral or non-viral) 3. Ex vivo expansion (2–4 weeks in cell therapy facility) 4. Single infusion into patient

Approved CAR-T Products (2026)

CAR-T Kinetics & Renal Relevance

CAR-T infusion (day 0)
    ↓
Days 0–3: CAR-T proliferation begins; limited cytokine release
    ↓
Days 3–7: PEAK CAR-T expansion & tumor engagement
    └─ Maximum cytokine release (IL-6, IFN-γ, TNF-α)
    └─ CRS symptoms typically peak days 3–5
    └─ Kidney injury onset days 3–7
    ↓
Days 7–14: CAR-T expansion plateaus; cytokines begin to decline
    └─ ICANS may emerge (days 5–10)
    └─ Renal function nadir often day 7–10
    ↓
Days 14+: Steady-state; monitoring for late complications
    └─ Most AKI resolves by day 14–21 if mild-moderate
    └─ Severe AKI may require dialysis >2 weeks

Definition & Pathophysiology [1]

CRS is a systemic inflammatory response caused by massive CAR-T proliferation and consequent immune activation.

Cytokine cascade:

CAR-T cells recognize antigen on tumor/normal B-cells
    ↓
T-cell receptor + CD28/4-1BB signaling → T-cell activation
    ↓
CAR-T secretion of:
├─ IL-2, IL-7 (T-cell growth factors)
├─ IL-6 (pro-inflammatory; acts on IL-6R)
├─ TNF-α, IFN-γ (macrophage activation)
├─ GM-CSF (hematopoietic cell activation)
└─ Other: MCP-1, IP-10, IL-10
    ↓
Activation of:
├─ Macrophages → more IL-6, TNF-α
├─ Endothelial cells → loss of barrier function
├─ Mast cells, neutrophils → further cytokine release
└─ Systemic inflammatory cascade
    ↓
SYSTEMIC CONSEQUENCES:

CRS Grading (Lee Criteria, 2014) [1]

Kidney involvement in CRS grading: - Grade 2: Cr elevation 1.5–3× baseline - Grade 3: Cr elevation >3× baseline OR eGFR <30 mL/min - Grade 4: Requiring dialysis

Mechanisms of CRS-Related AKI [1]

Clinical Presentation of CRS-Related AKI [1]

Definition & Incidence

ICANS (formerly “CAR-T related encephalopathy syndrome”) is a neurologic syndrome distinct from CRS, though often concurrent.

• Incidence: 20–50% depending on CAR-T product and patient population
• Grades: Using Common Terminology Criteria for Adverse Events (CTCAE)
• Timing: Usually days 5–10 post-infusion (slightly later than CRS peak)

Renal Involvement in ICANS

Kidney complications from ICANS: 1. Syndrome of inappropriate antidiuresis (SIADH) - Hypothalamic dysfunction from cerebral edema - Results in hyponatremia - Can worsen renal perfusion if severe (seizure risk)

2. Acute neurologic complications complicating fluid management
   • Cerebral edema → fluid restriction needed
   • But prerenal AKI requires aggressive hydration
   • Conflict: Restricted fluids for ICANS worsen renal perfusion
   • Solution: Balance with vasopressors, monitoring
3. Rhabdomyolysis (rare)
   • Severe ICANS (seizures, status epilepticus) → muscle breakdown
   • Myoglobin + AKI → acute uric acid nephropathy-like picture

Hypophosphatemia & Phosphate Wasting

Incidence: 20–30% of CAR-T recipients

Mechanism: B-cell aplasia (intentional) → loss of FGF23-producing cells → low FGF23 → increased phosphate reabsorption paradoxically BUT concurrent electrolyte wasting from capillary leak + cytokine effects → net hypophosphatemia

Clinical presentation: - Profound hypophosphatemia (PO4 <2.0 mg/dL in severe cases) - Can contribute to myopathy, rhabdomyolysis (rare) - Usually asymptomatic if mild

Management: Phosphate supplementation (IV if severe, PO if mild); self-limited, improves over weeks

Hypokalemia & Potassium Wasting

Incidence: 10–20%

Mechanism: - B-cell aplasia → loss of cells producing intracellular K stores - Capillary leak + diuresis → urinary K losses - Shift of K into cells from high catecholamine state

Management: K supplementation (IV if symptomatic, PO if mild)

Hypomagnesemia

Incidence: 10–15%

Mechanism: Similar to hypokalemia (B-cell loss, urinary wasting)

Management: Mg supplementation; usually mild

Hyponatremia (From ICANS-Related SIADH)

Mechanism: ICANS → hypothalamic dysfunction → ADH release → water retention → hyponatremia

Management: Fluid restriction (typically) + underlying ICANS treatment; may need hypertonic saline if symptomatic seizure risk

Baseline Workup

Patient scheduled for CAR-T therapy
    ↓
BASELINE (within 2 weeks of infusion):
├─ Serum creatinine, eGFR (KDIGO 2021 formula)
├─ BMP: K, Na, Mg, PO4, Ca, glucose
├─ CBC: baseline platelets (for monitoring)
├─ LDH, uric acid (assess tumor burden)
├─ Urine: UA, UPCR or 24-hr protein (assess baseline proteinuria)
├─ Cardiac: Echo or BNP (assess baseline cardiac function) — *important for CRS risk*
└─ BP: multiple readings; assess HTN baseline

Pre-CAR-T Optimization

eGFR ≥45: Standard CAR-T proceeding; baseline renal assessment only

eGFR 30–44: - Proceed with CAR-T if safe (product dependent) - Optimize fluid status (correct dehydration) - Avoid nephrotoxic agents (NSAIDs, ACE-I/ARB temporarily) - Plan for close renal monitoring (see below)

eGFR <30 or on dialysis: - CAR-T still possible but high-risk - Discuss with oncology + nephrology - May proceed with enhanced monitoring - Coordinate with dialysis schedule (hold dialysis day of CAR-T infusion, resume day after if clinically stable)

Inpatient Monitoring Schedule (Days 0–14)

Renal Function Monitoring Details

Daily labs should include: - Serum Cr (watch for rise ≥30% from baseline) - eGFR (calculate daily; trends more important than absolute value) - BMP: K, Na, Mg, PO4 (electrolyte emergencies common) - CBC: Platelets (TLS screening; thrombocytopenia may indicate worsening CRS) - LDH (days 3–7: marker of hemolysis, tumor lysis, cell death) - Urine: UA, UPCR (monitor proteinuria; new proteinuria suggests kidney injury)

CRS Grade 1–2 (Mild-Moderate)

CRS symptoms: Low-grade fever, mild tachycardia, preserved BP, no hypoxia

Renal status: Cr ≤1.5× baseline OR Cr 1.5–3× baseline with preserved urine output

Management:

Supportive care:
├─ Hydration: IV NS titrated to UOP 100–200 mL/hr (no forced diuresis)
├─ Fever management: Acetaminophen (NSAIDs contraindicated in AKI setting)
├─ Observation: Daily labs, vital signs BID
└─ Tocilizumab: Consider if worsening trend OR approaching grade 3

Monitor for progression:
├─ Recheck labs in 24 hr
├─ If stable: Continue monitoring
└─ If worsening: Escalate to grade 3 management (below)

CRS Grade 3–4 (Severe) with AKI [1]

CRS symptoms: High fever, hypotension requiring vasopressors, hypoxia requiring supplemental O2/intubation

Renal status: Cr >3× baseline OR eGFR <30 OR oliguria (<500 mL/day) OR dialysis requirement

Management:

IV tocilizumab: 8 mg/kg (max 800 mg) IV over 60 minutes
└─ Can repeat every 8–12 hours × up to 3 doses if CRS persists
Timing: Give at first sign of grade 3 CRS; don't delay

Dexamethasone 10 mg IV q6h (or equivalent)
└─ Alternative: Methylprednisolone 1 g IV q24h
└─ Taper after CRS resolves (over 2–3 days typically)

Goal: MAP >65 mmHg (minimum renal perfusion)

First-line:
├─ Norepinephrine: Start 0.01–0.05 mcg/kg/min IV, titrate to BP goal
└─ Preferred because: Maintains renal perfusion better than dopamine alone

Consider adding:
├─ Low-dose vasopressin (0.03–0.04 units/min) — synergistic with NE
└─ Stress-dose hydrocortisone (50 mg IV q6h) if severe refractory shock

AVOID: Pure dopamine as monotherapy (splanchnic vasoconstriction)

Approach:
├─ Judicious hydration: 500–1000 mL/hr NS (NOT 2–3 L/hr like TLS)
├─ Goal: Maintain UOP 50–100 mL/hr (not 200 mL/hr)
├─ Use vasopressors instead of more fluids for hypotension
├─ Monitor: Daily weights, JVD, lung sounds (assess volume status)
└─ Diuretics: Use cautiously; only if frank fluid overload (pulmonary edema)

CAR-T in Pre-Existing CKD (eGFR 30–45)

Considerations: - Higher baseline risk for severe AKI - Reduced urinary clearance of cytokines, inflammatory mediators - Lower margin for error with fluid, electrolyte management

Management modifications: - More frequent monitoring (labs q12h instead of daily) - Earlier tocilizumab consideration (grade 2.5 instead of waiting for grade 3) - Avoid aminoglycosides, amphotericin B if possible (synergistic nephrotoxicity) - Earlier CRRT discussion if Cr rises >30% from baseline

CAR-T in Dialysis Patients

Feasibility: CAR-T is possible; not contraindicated

Modifications: - Dialysis schedule: Hold HD day of infusion; resume next day if hemodynamically stable - Electrolytes: Monitor more frequently (q12h) given interdialytic interval constraints - Fluid management: More restricted due to anuric state; rely on vasopressors for hypotension - Hypokalemia risk: Higher (B-cell loss + ongoing dialytic K removal); supplement carefully - Prognosis: Similar AKI incidence but slower recovery post-CAR-T (longer clearance time for cytokines)

CAR-T in Cardiac Dysfunction

Challenge: CAR-T → CRS → myocardial injury → cardiorenal syndrome. Patients with baseline reduced EF at higher risk.

Management: - Baseline BNP/NT-proBNP + echocardiography - Close cardiology co-management - Conservative fluid approach (prioritize vasopressors) - Lower threshold for tocilizumab - Monitor troponin, BNP during CRS phase

Post-CAR-T Kidney Recovery

Prognosis: 80–90% of CAR-T recipients with AKI achieve complete renal recovery within 30 days [1]

Recovery pattern: - Mild AKI (Cr 1.5–2×): Recovery within 1 week - Moderate AKI (Cr 2–3×): Recovery within 2 weeks - Severe AKI (Cr >3×, dialysis-dependent): Recovery within 3–4 weeks in most cases

Predictors of delayed recovery: - Severe CRS (grade 4) at onset - Cardiomyopathy (reduced EF) - Concurrent ICANS - Baseline CKD

Chronic Renal Function Post-CAR-T

Incidence of lasting CKD: <5% of CAR-T recipients without pre-existing renal disease

Mechanism of chronic injury (rare): - Severe acute tubular necrosis → tubular atrophy, interstitial fibrosis - Repeated episodes of AKI (if rechallenge with second CAR-T)

Long-term monitoring: Annual Cr/eGFR assessment in survivors with prior severe AKI