Pembrolizumab-induced Acute Tubulointerstitial Nephritis Accompanying Fanconi Syndrome and Type 1 Renal Tubular Acidosis

Abstract

Pembrolizumab, an immune checkpoint inhibitor, is used to treat a variety of refractory malignancies. However, these agents are sometimes associated with immune-related adverse events. A 71-year-old woman received pembrolizumab-integrated chemotherapy to treat her recurrent mandibular gingival cancer. Five months after stopping pembrolizumab, she developed acute tubulointerstitial nephritis associated with Fanconi syndrome and type 1 renal tubular acidosis, which resolved with steroid therapy. We experienced a case of pembrolizumab-induced Fanconi syndrome and type 1 renal acidosis. We recommend follow-up of the tubular function in addition to the renal function even after discontinuation of pembrolizumab.

Introduction

Immune checkpoint inhibitors have emerged as a mainstay in the treatment of advanced malignancies. Malignant cells inhibit T-cell activation by acting on normal host regulatory immune checkpoints, such as cytotoxic T lymphocyte-associated protein 4, programmed cell death protein-1 (PD-1), and programmed death-ligand 1. Immune checkpoint inhibitors exert their antitumor effects by blocking this pathway. Pembrolizumab is a fully humanized monoclonal antibody directed against PD-1. Many patients with refractory malignancies are eligible for immune checkpoint inhibitor therapy, and a significant number achieve favorable responses.

However, it is important to note that immune checkpoint inhibitors are associated with a variety of immune-related adverse events, as they unleash T-cell activity. One of the most commonly fatal and critical immune-related adverse events is acute tubulointerstitial nephritis (1,2). Although the detailed mechanism remains uncertain, it appears to be associated with secondary Fanconi syndrome and type 1 renal tubular acidosis (3-5).

We herein report a patient with acute tubulointerstitial nephritis associated with Fanconi syndrome and type 1 renal tubular acidosis following pembrolizumab-integrated chemotherapy.

Case Report

A 71-year-old woman presented with recurrence of surgically resected mandibular gingival cancer. Four months of combination chemotherapy with pembrolizumab, cisplatin, and fluorouracil followed by one month of pembrolizumab monotherapy failed to halt malignant progression, so secondary chemotherapy with cetuximab and paclitaxel was initiated.

She was hospitalized three months before the kidney injury hospitalization for aseptic meningoencephalitis, which was considered to be an immune-related adverse event. Steroid therapy was effective, and chemotherapy was restarted. Around the same time as meningoencephalitis, urine protein (1+) developed, but the estimated glomerular filtration rate (eGFR) did not decrease. Proteinuria persisted after discharge. One week before the hospitalization, she developed acute renal impairment and hypertension and was referred to our hospital for a further evaluation (Fig. 1). She had no history of hypertension. Loxoprofen sodium hydrate, minocycline hydrochloride, sulfamethoxazole-trimethoprim, and vonoprazan fumarate were used for a short time at the onset of meningoencephalitis, but these drugs were not used after the meningoencephalitis had been cured. Bisphosphonates were not used. She was hospitalized for a further evaluation and more intensive treatment.

Figure 1.

Clinical course. 5-FU: fluorouracil, CDDP: cisplatin, Cmab: cetuximab, PTX: paclitaxel, Dex: dexamethasone, PSL: prednisolone, mPSL: methylprednisolone, NAG: N-acetyl-β-D-glucosaminidase, β2MG: β2-microglobulin, GFR: glomerular filtration rate

On admission

She was afebrile on admission. Her blood pressure was 154/86 mmHg. Laboratory data are shown in Table 1. Urine protein was 2.36 g/g creatinine, and urine glucose was noted. Urine N-acetyl-β-D-glucosaminidase was 36.6 IU/g creatinine, and urine β₂-microglobulin was 132.8 μg/mg creatinine, indicating tubular injury. Serum creatinine was 1.85 mg/dL (i.e. eGFR 21.5 mL/min/1.73 m²), indicating acute kidney injury. Serum potassium was 2.8 mEq/L, serum inorganic phosphorus was 1.4 mg/dL, and serum uric acid was 1.9 mg/dL. The difference between serum sodium and serum chloride, an indicator of metabolic acidosis, was reduced to 27 mEq/L. A blood gas analysis (analyzed using ABL 800 Flex; Radiometer Medical ApS, Copenhagen, Denmark) showed pH 7.290, pCO₂ 31.0 mmHg, and HCO₃^- 14.7 mmol/L, indicating nonanion gap metabolic acidosis.

Table 1.

Laboratory Data in Admission.

Laboratory test	Value
Urinalysis
Urine specific gravity	1.019
Urine pH	6.5
Urine protein	(2+)
Urine occult blood	(1+)
Urine glucose	(3+)
Urine sedimentation
Red blood cells, /high power field	1-4
White blood cells, /high power field	1-4
Granular casts, /low power field	<10
Urine chemistry
Urine protein, g/g of creatinine	2.36
Urine N-acetyl-β-D-glucosaminidase, IU/g of creatinine	36.6
Urine β2-microglobulin, μg/mg of creatinine	132.8
Complete blood cell counts
White blood cells, /μL	5,320
Neutrophil, %	68.4
Eosinophil, %	3.8
Red blood cells, /µL	354×104
Hemoglobin, g/dL	9.8
Platelets, /μL	34.1×104
Serum chemistry
Total protein, g/dL	7.3
Albumin, g/dL	3.8
Glucose, mg/dL	97
Lactate dehydrogenase, IU/L	272
Uric acid, mg/dL	1.9
Blood urea nitrogen, mg/dL	32.6
Creatinine, mg/dL	1.85
Estimated glomerular filtration rate, mL/min/1.73 m2	21.5
Sodium, mEq/L	138
Potassium, mEq/L	2.8
Chloride, mEq/L	111
Calcium, mg/dL	9.3
Inorganic phosphorus, mg/dL	1.4
Blood gas analysis
pH	7.290
pCO2, mmHg	31
Calculated HCO3-, mmol/L	14.7
Serum immunological test
C-reactive protein, mg/dL	0.07
Immunoglobulin G, mg/dL	1,177
Antinuclear antibody	Negative
Anti-SS-A antibody, U/mL	0.5
Anti-SS-B antibody, U/mL	<0.4

We added further urine and laboratory data (Table 2). The huge amounts of urine glucose, incremental excretion of potassium and chloride, and generalized aminoaciduria were consistent with Fanconi syndrome. The urine anion gap was 50 mEq/L, and the urine osmolality gap was 17 mOsm/kg, indicating impaired acid excretion in urine. In contrast, urine pH was 6.5. Given these findings, we diagnosed her with concomitant type 1 renal tubular acidosis.

Table 2.

Additional Urine Chemistry Test and Indices of Urinary Excretion of Potassium, Phosphate and Uric Acid.

Laboratory test	Value	Reference value
Urine glucose, mg/dL	550
Urine sodium, mEq/L	118
Urine potassium, mEq/L	44
Urine chloride, mEq/L	112
Urine anion gap, mEq/L	50
Calculated urine osmolality, mOsm/kg	418
Measured urine osmolality, mOsm/kg	435
Urine amino acid	Diffusely positive, 19/20
Fractional excretion of potassium, %	23.4	10-20
Transtubular potassium gradient	3.71	<2
Tubular reabsorption of phosphate, %	43.9	60-90
Fractional excretion of uric acid, %	46	4-14

Calculated urine osmolality=2×[urine sodium (mmol/L)+urine potassium (mmol/L)]+urine urea (mg/dL)/2.8+urine glucose (md/dL)/18.

Kidney biopsy findings

We performed a renal biopsy to further investigate the pathology of acute kidney injury and renal tubular dysfunction. Although 14% of the glomeruli showed global sclerosis, there were no other notable abnormal findings in the glomeruli. In the renal cortex, diffuse inflammatory cell infiltration was observed in approximately 70% of the interstitium (Fig. 2a). Not only lymphocytes but also eosinophils were observed (Fig. 2b). Distal tubules were characterized by tubulitis, and proximal tubules were marked by tubule injury characterized by epithelial cell edematous swelling of epithelial cells and vacuolar degeneration (Fig. 2c). Some proximal tubules also showed tubulitis (Fig. 2d).

Figure 2.

Light microscopic findings in the kidney biopsy. a: Diffuse interstitial inflammatory cell infiltration and tubular atrophy [Hematoxylin and Eosin (H&E) staining, original magnification ×40]. b: Focal eosinophil infiltration in the interstitium (yellow arrowhead) (H&E staining, original magnification ×200). c: Diffuse interstitial mononuclear cell infiltration in the renal cortex, tubulitis in the distal tubules (blue arrowhead), and proximal tubular injury characterized by edematous cell swelling (red arrowhead) (periodic acid-Schiff stain, original magnification ×100). d: Tubulitis in the distal tubules (blue arrowhead) as well as in the proximal tubules (green arrowhead) (Periodic acid-Schiff stain, original magnification ×200).

Lymphocytes focally infiltrating the subcapsular interstitium were mainly CD20-positive, while most lymphocytes infiltrating the peritubular and interstitial areas of the renal cortex were CD3-positive, with a similar distribution of CD4-positive and CD8-positive cells, and only a few CD20-positive cells were found (Fig. 3). In the collecting tubules and the distal tubules identified by epithelial membrane antigen staining, H⁺-ATPase expression was decreased in tubular epithelial cells damaged by inflammation (Fig. 4). Immunofluorescence staining showed no deposition of immunoglobulins or complements in the glomeruli or tubular basement membrane. Acute tubulointerstitial nephritis was therefore diagnosed.

Figure 3.

Inflammatory cell infiltration in the interstitium. a-d: Lymphocytes infiltrating the subcapsular interstitium were predominantly positive for CD20 rather than CD3 or CD8 (original magnification ×40). e-h: Interstitial lymphocytic infiltration in the renal cortical labyrinth. Most of the infiltrating lymphocytes were CD3-positive T cells, some of which were CD8-positive and a few that were CD20-positive (original magnification ×200).

Figure 4.

H⁺-ATPase staining in the collecting tubules. a: The distal tubules in the renal cortex (Periodic acid Schiff stain, original magnification ×200). b: The collecting tubules and the distal tubules identified by EMA positivity (immunostaining for EMA, original magnification ×200). c: H⁺-ATPase expression was observed in collecting tubules with inconspicuous tubulitis (yellow arrowhead), and it was decreased in collecting tubules with severe tubulitis (red arrowhead) (immunostaining for H⁺-ATPase, original magnification ×200). EMA: epithelial membrane antigen

Clinical course

We suspected pembrolizumab-induced kidney disease. Given the severity of nephritis, we started an intravenous pulse steroid regimen of 3-day methylprednisolone 500 mg/day, followed by oral administration of prednisolone 1.0 mg/kg/day.

The renal function improved immediately. Four weeks after the index discharge, the eGFR increased to 49.8 mL/min/1.73 m², and proteinuria became negative. Two weeks later, prednisolone and supplementation therapy were discontinued. Four weeks later, chemotherapy with cetuximab and paclitaxel was restarted and continued without any adverse events (Fig. 1).

Discussion

We encountered a patient with pembrolizumab-induced immune-related adverse events, including Fanconi syndrome and type 1 renal tubular acidosis due to tubulointerstitial nephritis. Proximal tubular injury that caused Fanconi syndrome and distal tubulitis that caused type 1 renal tubular acidosis were pathologically identified.

The cause of kidney injury

Pembrolizumab occasionally causes acute tubulointerstitial nephritis as an immune-related adverse event (1,2). Immune checkpoint inhibitors induce an inflammatory immune response when cytotoxic effector CD8-positive T cells escape the tumor, but their effects are thought to also affect other organs, not being limited to the microenvironment, thereby resulting in immune-related adverse events (6).

Inflammation at the tumor site and the inflammatory cytokines produced there are thought to promote the activation of T cells, B cells, eosinophils, and neutrophils in the systemic circulation and encourage the migration of these cells to other organs aside from just the tumor site. CD4-positive T cells in injured tissues regulate effector CD8-positive T cells, and it has been reported that the higher the binding rate of anti-PD-1 inhibitors to CD4-positive T cells, the more likely they are to cause immune-related adverse events (7).

In our patient's kidney, CD3-positive T cells were predominant, and some CD20-positive plasma cells and eosinophils were found, similar to previous reports of this disease (8). The fact that there was no significant difference in the proportion of CD4- or CD8-positive cells differs from the findings of a previous report that found a markedly higher number of CD4-positive cells than CD8-positive cells, but the significance of this difference is currently unclear due to the paucity of reports. Similarly, the cause of the clustering of CD20-positive plasma cells is also unknown, but as mentioned above, these cells may be involved in the pathogenesis of immune-related adverse events, although further knowledge is needed. Our patient developed this condition five months after the last administration of pembrolizumab. In general, immune-related adverse events sometimes occur several months later (9,10). In addition, patients often experience immune-related adverse events in other organs prior to tubulointerstitial nephritis (2). Cisplatin can cause Fanconi syndrome, and it is usually immediate in its onset (11).

Fanconi syndrome

This is the first report of a case of Fanconi syndrome as an immune-related adverse event in which we evaluated the renal pathology. The degeneration of proximal tubular epithelial cells indicates that Fanconi syndrome in our patient was caused by cell injury. We found two cases in which immune checkpoint inhibitors caused Fanconi syndrome (Table 3) (3,4): one patient had renal failure, while the other did not. Trivial functional changes in proximal tubular epithelial cells might cause Fanconi syndrome.

Table 3.

Literature Review of Clinical Characteristics of the Immune-related Adverse Events with Fanconi Syndrome.

Reference	Age	Sex	Malignancy	ICI	Duration from the last use of ICIs to the kidney injury	irAEs preceding kidney injury	Serum Cr (mg/dL)	Plasma bicarbonate (mmol/L)	Treatment	Outcome
[3]	59	Male	Hepatocellular carcinoma	Nivolumab	Continued use	None	0.74	15	No steroid therapy	Improved after 3 weeks
[4]	58	Male	Small-cell lung cancer	Nivolumab and ipilimumab	NA (probably a few months)	Hepatitis	2.31	12	mPSL 1 mg/kg/day	Improved after 4 weeks
Our case	71	Female	Mandibular gingival cancer	Pembrolizumab	5 months	Meningoencephalitis	1.85	14.7	Intravenous pulse mPSL, PSL 1 mg/kg/day	Improved after 6 weeks

ICI: immune-checkpoint inhibitor, irAE: immune-related adverse event, Cr: creatinine, mPSL: methylpredonisolone, PSL: predonisolone, NA: not applicable

Type 1 renal tubular acidosis

In our case, urine pH did not fall below 5.5 despite the severe acidemia, and we observed damage to distal tubular epithelial cells expressing proton pumps in the renal tissue, consistent with type 1 renal tubular acidosis. Although a loading test is strictly required to diagnose type 1 renal tubular acidosis, we did not perform an ammonium chloride loading test because of the risk of worsening acidemia or a bicarbonate loading test because of the risk of worsening renal dysfunction due to the time required to correct the blood bicarbonate ion concentration and the risk of worsening hypokalemia. Since the proximal tubular epithelial cells were also injured, we speculate that there was also a complication of type 2 tubular acidosis. Immune checkpoint inhibitor-induced renal tubular acidosis has been reported in 8 cases thus far (5). No studies have reported concomitant Fanconi syndrome and type 1 renal tubular acidosis as immune-related adverse events.

The H⁺-ATPase in α-intercalated cells of the collecting tubule is responsible for acid excretion, and its dysfunction is thought to cause type 1 renal tubular acidosis (12). Indeed, a decreased expression of H⁺-ATPase has been observed in cases of tubulointerstitial nephritis in patients with Sjögren's syndrome (13). We demonstrated pathologically that the expression of H⁺-ATPase was decreased in collecting tubular epithelial cells with severe inflammation, one of the main causes of impaired acid excretion (14).

Conclusion

We experienced a rare case of pembrolizumab-induced immune-related adverse events consisting of Fanconi syndrome and type 1 renal tubular acidosis five months following the termination of pembrolizumab. We highly recommend monitoring the tubular function, such as urine glucose or tubular injury markers, in addition to the renal function, even after the termination of pembrolizumab.

The authors state that they have no Conflict of Interest (COI).