Transient acute kidney injury after chimeric antigen receptor T-cell therapy in patients with hematological malignancies

ABSTRACT Background Acute kidney injury (AKI) occurs in 30% of patients infused with chimeric antigen receptor (CAR) T-cells. The purpose of this study was to identify risk factors and long-term outcomes after AKI in patients who received CAR T-cell therapy. Methods Medical records of 115 adult patients with R/R hematological malignancies treated with CD19-targeted CAR T-cells at Vall d'Hebron University Hospital between July 2018 and May 2021. Baseline demographic data including age, gender, ethnicity, body mass index (BMI), and co-morbidities, as well as the type of hematological neoplasia and prior lines of therapy were collected. Laboratory parameters including serum creatinine and whole blood hemoglobin were retrospectively reviewed and values were gathered for days +1, +7, +14, +21, and +28 post-infusion. Results A total of 24/115 (21%) patients developed AKI related to CAR T-cell therapy; 6/24 with AKI over chronic kidney disease (CKD). Two patients had AKI in the context of lymphodepleting (LD) chemotherapy and the other 22 after CAR T-cell infusion, starting at day+1 in 3 patients, day+7 in 13 patients, day +14 in 1 patient, day+21 in 2 patients, and day+28 in 3 patients. Renal function was recovered in 19/24 (79%) patients within the first month after infusion. Male gender, CKD, cytokine release syndrome (CRS), and immune effector cell-associated neurotoxicity syndrome (ICANS) were associated with AKI. Male gender, CKD, ICANS grade ≥3 and CRS grade ≥2 were identified as independent risk factors for AKI on multivariable analysis. In terms of the most frequent CAR T-cell related complications, CRS was observed in 95 (82%) patients and ICANS in 33 (29%) patients. Steroids were required in 34 (30%) patients and tocilizumab in 37 (32%) patients. Six (5%) patients were admitted to the intensive care unit (1 for septic shock, 4 for CRS grade ≥2 associated to ICANS grade ≥2, and 1 for CRS grade ≥3). A total of 5 (4.4%) patients died in the first 30 days after CAR T-cell infusion for reasons other than disease progression, including 4 cases of infectious complications and 1 of heart failure. Conclusion Our results suggest that AKI is a frequent but mild adverse event, with fast recovery in most patients.


INTRODUCTION
Chimeric antigen receptors ( CARs) are engineered synthetic proteins that redirect the specificity of T cells [1 , 2 ].The structure of commercially available CARs includes extracellular immunoglobulin-derived heavy and light chains to recognize specific antigens, and intracellular activating and costimulatory domains to lead signal activation, cytokine release, T-cell proliferation, and immune cell response against tumor cells.[1 , 3 -5 ] CAR T-cell therapy has been a revolutionary treatment for relapsed/refractory ( R/R) hematological malignancies including adult and pediatric B-cell acute lymphoblastic leukemia, diffuse large B-cell lymphoma, follicular lymphoma and multiple myeloma [6 -21 ].Furthermore, there are promising results in selected solid tumors and autoimmune diseases [22 , 23 ].Response rates and long-term survival are variable across diseases but they outweigh the current available therapies in these indications.
CAR T-cell therapy has a well-known acute and long-term toxicity profile [24 , 25 ].The most frequent acute adverse event is cytokine release syndrome ( CRS) , occurring usually within the first week after CAR T-cell infusion [7 -20 , 22 -30 ].CRS manifests as a rapid immune reaction driven by the massive release of cytokines, including IFN-gamma and IL-6 [29 -31 ].The clinical presentation includes fever, hypotension, and/or hypoxia.Organ dysfunction can sometimes occur in this setting but does not impact CRS grading [29 -32 ].Immune effector cell-associated neurotoxicity syndrome ( ICANS) is another frequent acute side effect which usually starts around the second week post-infusion, after CRS onset in the great majority of patients.Acute kidney injury ( AKI) develops in 20-30% of infused patients, mainly associated with CRS, electrolyte disorders and tumor lysis syndrome ( TLS) [33 -35 ].Regarding late complications, after the first month post-infusion, the most common are hypogammaglobulinemia, cytopenia, and infections [24 -28 , 29 ].
There is limited literature regarding AKI after CAR-T cell therapy.Kanduri et al. described in a systematic review of 22 cohort studies, a population of 3376 pediatric and adult patients that included the incidence of AKI and clinical complications after CAR T-cell infusion.The pooled estimated incidence of AKI was 18.6%, and AKI was presented in 17% in the subgroup of adults after the treatment.The estimated CRS incidence in all included studies was 75.4% [36 ].The purpose of this study is to determine the demographics, laboratory results and clinical evolution of patients who received CAR T-cell therapy and developed AKI, as well as identifying potential risk factors.

Data collection and analysis
We conducted a retrospective review of the medical records of 115 adult patients with R/R hematological malignancies treated with CD19-targeted CAR T-cells at Vall d'Hebron University Hospital between July 2018 and May 2021 ( Fig. 1 ) .Data collection was performed with the approval of the Ethics Committee of the Vall d'Hebron University Hospital EOM( AG) 043/2021( 5853) .
Baseline demographic data including age, gender, ethnicity, body mass index ( BMI) , and co-morbidities, as well as the type of hematological neoplasia and prior lines of therapy were collected.Laboratory parameters including serum creatinine and whole blood hemoglobin were retrospectively reviewed and values were gathered for days + 1, + 7, + 14, + 21, and + 28 postinfusion.

Definition and endpoints
AKI was defined according to the Kidney Disease Improving Global Outcomes ( KDIGO) criteria: grade 1, increase in serum creatinine ( SCr) 1.5 to < 2-fold of baseline; grade 2, increase in SCr 2-to < 3-fold of baseline; grade 3, increase in SCr ≥3-fold of baseline, OR requiring renal replacement therapy, OR SCr ≥4.0 mg/dL [37 ].Chronic kidney disease ( CKD) was defined according KDIGO as kidney damage or glomerular filtration rate ( GFR) < 60 ml/min/1.73m 2 with CKD-EPI formula for 3 months or more, irrespective of cause [38 ].Recovery of renal function was established following the consensus report of the Acute Disease Quality Initiative ( ADQI) [39 ].Severe electrolyte disorders were defined according to the Common Terminology Criteria for Adverse Events ( CTCAE) [40 ].CRS and ICANS were graded according to the American Society of Transplantation and Cellular Therapy ( ASTCT) criteria.Other treatment-related adverse events such as infections intensive care unit ( ICU) admission and death were also recorded [41 , 42 ].

Lymphodepleting chemotherapy
All patients received LD chemotherapy on the week before CAR T-cell infusion.LD chemotherapy included cyclophosphamide and fludarabine for 3-4 consecutive days, according to the label recommendations for each disease.

Statistical analysis
First, patients were divided into two groups: ( i) patients who developed AKI and ( ii) patients without AKI.The distribution was calculated with the Kolmogorov Smirnov test.Quantitative variables were analysed with the Student's t test and presented with their mean and standard deviation or median and interquartile range.Qualitative variables were analysed with Chi-squared test or Fisher's exact coefficient, and presented with their frequency

CAR T-cell therapy complications and mortality
The most frequent CAR T-cell related adverse events were CRS ( 82% any grade and 30% CRS grade ≥2) and ICANS ( 29% any grade, 4% grade ≥3) ( see Table 2 ) .To manage these adverse events, 37 ( 32%) patients required tocilizumab and 34 ( 30%) patients received steroids.Six patients were admitted to the ICU ( one with the diagnosis of refractory septic shock, four for CRS grade ≥2 associated to ICANS grade ≥2, and one for CRS grade ≥3) .Median ICU stay was 8 days [range, 2-30 days].Thirty-six patients died during study follow-up, 31 due to disease progression and five related to CAR-T cell therapy, including four cases of bacterial refractory septic shock and one case of heart failure.

DISCUSSION
CAR T-cell therapy has been a revolutionary treatment for R/R hematologic malignancies but it can lead to well-known severe complications.In our study, 24 ( 21%) patients developed AKI after CAR T-cell therapy, generally in the first week after infusion.Even though AKI is a complication of which treating physicians must be aware, it presents mostly with a mild disease and a rapid recovery, demonstrating that AKI is usually transient after CAR T-cell therapy.Our results are similar to those obtained by Gutgarts et al., who described AKI in 14 ( 30%) out of 46 patients with non-Hodgkin lymphoma receiving CAR T-cell therapy in the first 100 days after infusion.The most frequent presentation of AKI in this cohort was grade 1.In addition, 3 ( 21%) of the 14 AKI-patients died and 10 ( 71%) recovered baseline kidney function in a 30-day period [34 ].Another study by Gupta et al. described 15/67 ( 22%) patients diagnosed with diffuse large B-cell lymphoma who developed AKI within 30 days of CAR T-cell infusion.The authors confirmed that AKI was usually a mild disease with fast recovery [35 ].The largest study to date, led by Hanna et al., compared the risk of AKI in 232 patients who received CAR T-cell therapy with 414 patients who underwent auto-HCT, confirming no significant differences between both groups in the first 30 days after infusion [38 ].These results are similar to our own findings, indicating that AKI associated with CAR T-cell infusion is a mild complication with a fast recovery.
Despite the lack of consensus on the optimal fludarabine dose reduction in patients with renal impairment, the incidence of AKI related to fludarabine exposure remains lower than 5% [44 ].The need for dose adjustment in CKD patients relies on the 60% of drug excreted through urine [45 ].Most studies suggest a 20-25% reduction for mild kidney impairment and up to a 50% reduction for moderate to severe impairment [46 -48 ].Wood et al. evaluated the outcomes of CAR T-cell therapy in patients with renal impairment and determined that progressionfree survival and overall survival did not differ between patients with and without renal impairment or between those who received standard-dose fludarabine and those who received reduced-dose [49 , 50 ].Wood et al. also described that baseline renal function did not affect renal or efficacy outcomes after CAR T cell therapy.In contrast, in our study we found that patients with previous CKD had higher risk of AKI development, similarly to those described by Lyu et al. [50 ].Our analysis also suggests that there were no differences in AKI development between standard and dose-reduced fludarabine after the multivariable analysis in accordance with Wood et al. [48 ].
Our study is the first that identifies male gender as an independent risk factor for AKI development.Furthermore, the most frequent complications after CAR T-cell infusion were CRS and ICANS.AKI was diagnosed in 88% of patients with CRS, and 46% in patients with ICANS.CRS grade ≥2 and ICANS grade ≥3 were adverse events identified as risk factors for AKI development.Similarly, other authors established CRS grade ≥3 as an independent risk factor for AKI [34 , 35 ].On the other hand, Ahmed et al. carried out a retrospective analysis of the impact of CKD and AKI on CAR-T outcomes in adult patients with non-Hodgkin's lymphoma, observing that CKD patients had an increased frequency of CRS and ICANS [52 ].Furthermore, Ahmed et al. defined ICANS ≥2 was an independent risk factor for AKI development [52 ].We can surmise that proinflammatory status after CAR T-cell therapy may decrease renal perfusion and subsequently favor prerenal AKI development.Despite the risk of AKI with the proinflammatory state after CAR T-cell therapy, we consider that the potential benefit of the therapy warrants that clinicians actively monitor the development of CRS and/or ICANS.
Electrolyte disorders such as hypophosphatemia, hyponatremia, and hypokalemia are common after CAR T-cell therapy [34 ].Farooqui et al. reported in their study 14/83 ( 17%) patients developing AKI within one month after CAR-T infusion.Moreover, they found that both absolute and relative from baseline to peak levels in lactate dehydrogenase were higher among AKI patients compared to non-AKI patients [53 ].We observed that lower sodium, calcium, and phosphorus blood levels were associated with AKI in the univariable analysis.However, these findings were not confirmed in the multivariate analysis.This may be in part related to the lack of some laboratory assessments during the study follow-up.
Our study has some limitations, besides its retrospective design which precludes inferences of causal associations and selection bias.All patients included in the study received the CAR T-cell infusion, potentially overestimating the survival benefit of this treatment ( immortal bias) .Fludarabine dose adjustment was established according the Cockcroft-Gault formula even though we defined CKD based on the KDIGO definition ( based on CKD-EPI formula) .Blood test results could not be systematically compared as not all data were collected in our patient population.However, one of the strongest points of this study, in comparison with previously published articles, is that we had one of the largest cohorts and carried out long-term follow-up.Further multicenter studies with extended follow-up are needed to confirm our findings.

CONCLUSION
In our study, 21% of patients developed AKI, usually in the first week after CAR-T infusion.Most of the patients ( 79%) recovered kidney function within the first month post-treatment, suggesting that AKI is frequent but mild, with a fast recovery in this setting.Male gender and a history of CKD, together with development of CRS grade ≥2 and/or ICANS grade ≥3 after CAR

Figure 1 :
Figure 1: Flow diagram for study selection.
refractory septic shock, and the last patient recovered kidney function within the first month after CAR-T cell therapy, achieving a serum creatinine of 0.4 mg/dL.In terms of the AKI cohort, 19/24 ( 79%) patients recovered their baseline kidney function within the first month after CAR T-cell infusion [median 1 week, range 1-4 weeks].The remaining five patients continued to present an impaired kidney function after two months of follow-up ( 4/5 diagnosed with new AKI onset) [median creatinine 1.4 mg/dL, range 1.3-2.4mg/dL].Regarding the CKD group, five out of the six patients who developed AKI recovered baseline kidney function within 30 days of CAR T-cell infusion, while the remaining patient developed a decreased creatinine clearance secondary to CRS grade 2 ( from 34 ml/min/1.73m 2 to 27 ml/min1.73m 2 ) and maintained it after the 30-day of follow-up period.There were no significant differences in ICU admission and/or mortality in this CKD group.

Figure 2 :
Figure 2: Clinical outcomes in patients with AKI and previous history of CKD. ( A) PFS and OS stratified by AKI development.( B) PFS and OS stratified by CKD.

Table 1 : Demographic characteristics of the full patient population.
T-cell therapy.As a second step, actuarial survival curves were estimated using the Kaplan-Meier method to identify risk factors for mortality in a 365-day follow-up.Statistical studies were analysed using the SPSS version 20 program.Odds ratio ( OR) for AKI with 95% confidence interval ( CI) was reported.Two-sided P values 0.05 were considered statistically significant.

Table 2 : Clinical outcomes after CAR T-cell infusion in the 115 patients.
CRS: cytokine release syndrome; ICANS: immune effector cell-associated neurotoxicity syndrome; ICU: intensive care unit.

Table 3 : Adjusted odds ratio for AKI development.
aOR: adjusted odds ratio; CKD: chronic kidney disease; CRS: cytokine release syndrome; ICANS: immune effector cell-associated neurotoxicity syndrome.Multivariate analysis was obtained with logistic regression.