Although the use of CD19-CAR T-cell therapy has revolutionized the treatment paradigm for CAYA patients with relapsed/refractory B-cell ALL(1, 4, 28), it may be associated with risk of toxicity related morbidity and mortality. Importantly, these toxicities are associated with risk of multi-organ dysfunction and/or failure, including AKI(29, 30). While AKI post-CAR T-cell therapy has been described in several reports of adult patients, these data are lacking in the CAYA population(15). In our study of 34 CAYA patients treated with CD19-CAR T-cell therapy, we found an incidence of AKI based on creatinine of 20%, with most episodes being more severe. Additionally, all instances of AKI occurred within the initial 14 days post-infusion, and there was a relationship between the presence of CRS/NTX and the development of AKI, particularly severe CRS/NTX.
Our study found an incidence of AKI in pediatric CD19-CAR T-cell recipients similar to the limited previously published data (15). Importantly, our data highlights that the majority of CAYA patients who developed AKI had a more severe form, and that AKI is most likely to develop early after CAR T-cell therapy. While half of the patients in our cohort had a return of kidney function to baseline before day 30 post-infusion, one patient did require kidney replacement therapy, and the long-term impact on kidney function is unknown. These data highlight the significant risk of AKI in the CAYA patient population and should prompt close monitoring of kidney function in the early post-infusion period to facilitate management changes aimed at minimizing kidney injury. Given the known increased morbidity and mortality associated with AKI in the post-transplant population(35–38), strategies to mitigate the risk of AKI should be implemented in patients undergoing CAR T-cell therapy as well.
Patients treated with CAR T-cell therapy may be predisposed to the development of AKI, including due to the receipt of multiple prior treatment regimens, prior episodes of AKI, and lower pre-treatment GFR(12, 18, 31). While our study was not able to identify pre-treatment variables that were associated with risk of developing AKI post-CAR T-cell therapy, pre-treatment disease burden did show a large, estimated effect size, but with a wide variability. While our sample size may limit our power to determine such an association, this result is consistent with previous reports in CAYA patients(15). However, this differs from data of adult patients where pre-treatment factors such as prior AlloHCT and lower baseline GFR portended a higher risk of developing AKI. This difference may relate to patient age, and the expected decline in kidney function and other age-related physiologic changes(32). Post-CAR T-cell therapy, additional risk factors for the development of AKI may be present, including exposure to nephrotoxic agents, the development of tumor lysis syndrome, infection or, particularly for patients treated with CAR T-cells, the development of systemic inflammation(33). Consistent with previous reports in both adults and CAYA patients(6, 15, 16), we found a strong association between CRS and NTX and the rate of AKI. Biologically, this is a rational association given that CRS includes hypotension and vasodilatory shock, which may lead to reduced kidney perfusion and subsequent kidney injury(34).
Tools such as cystatin C and other biomarkers may assist in earlier detection of AKI, and therefore allow for improved management and reduction in prevalence of severe AKI. Serum cystatin C is a sensitive marker of AKI in a variety of patient populations(39, 40), and in an oncologic CAYA patient population, cystatin C has been described as a potential tool to detect eGFR changes earlier than sCr after an insult, with superior sensitivity for detecting minor changes in kidney function(38). Cystatin C has also been readily identified as a more sensitive marker of kidney function in the CAYA patient population, as these patients tend to have lower muscle mass, thus leading to overestimation of GFR with creatinine-based equations(17, 41). However, there have been caveats to its use in the presence of rapid cell turnover, as well as steroid use. To our knowledge, no study has looked at cystatin C based AKI in patients treated with CAR T-cell therapy. Our data on cystatin C are limited by sample size, variable monitoring patterns and, anecdotally, increased use of cystatin C testing in patients suspected to have a change in kidney function. However, our data highlight that in this CAYA patient population, cystatin C based eGFR trended lower than sCr based eGFR both pre- and post-CAR T-cell infusion. Additionally, we were able to detect AKI in 1 patient by cystatin C that was not apparent by sCr. In future prospective studies, routine monitoring of cystatin C may provide more robust data to determine the utility of using cystatin C in assessing kidney function and potentially risk stratifying for AKI in this patient population.
In conclusion, our study identified that CAYA patients undergoing CD19-CAR T-cell therapy have a high incidence of AKI post-infusion, particularly in the initial weeks after treatment. We also demonstrate a strong association between the development of AKI and presence of CRS or NTX. While many patients recovered their kidney function, the long-term effects of this injury are unknown. As the experience in CAR T-cell therapy grows for various malignancies, larger studies are needed to risk stratify patients for specific organ toxicities, including kidney injury. Furthermore, investigation into the utility of other biomarkers of kidney function such as cystatin C, may more readily identify AKI in this population, leading to earlier interventions intended to reduce morbidity and mortality.