Immune Checkpoint Inhibitor-Associated Nephrotoxicity.

CONTEXT: The clinical indications for immune checkpoint inhibitors (ICIs) are rapidly expanding. However, adverse events affecting multiple organs, including kidneys leading to ICI-associated acute kidney injury (AKI), remain a significant challenge with ICI therapy. Although AKI is considered a rare complication, it can be severe and result in treatment interruption or discontinuation of ICIs. Despite a generally favorable kidney prognosis, the possibility of re-challenging ICI therapy remains a subject of debate, particularly for patients who have exhausted other treatment options or experienced severe AKI. Subject of Review: In a recent review article, Sprangers et al. provide a comprehensive overview of the possible mechanisms and clinical manifestations of ICI-associated AKI [Nat Rev Nephrol. 2022;18(12):794-805]. The authors propose a practical strategy for diagnosing and managing suspected cases of ICI-associated AKI, which includes identifying a subset of eligible patients who may be re-exposed to ICIs following an episode of AKI. Second Opinion: The authors of the review article offer several recommendations on the diagnosis and treatment of ICI-associated nephrotoxicity. While we generally agree with the recommendations proposed by the authors, it is important to acknowledge that the available data primarily rely on small retrospective studies, as the authors have recognized. In addition, there are two key questions that need be carefully addressed in future studies: (1) the optimal dose and duration of corticosteroids and the use of alternative immunosuppressive agents in patients with ICI-associated nephrotoxicity and (2) a clear guideline for restarting ICI treatment in patients with AKI who have not fully recovered their kidney function.

Infliximab for Treatment of Immune Adverse Events and Its Impact on Tumor Response.

Background: Immune-related adverse events (irAEs) challenge the use of immune checkpoint inhibitors (ICIs). We performed a retrospective study to evaluate response to infliximab for immune-related adverse event management, and infliximab's effect on progression-free survival (PFS) and overall survival (OS) with a focus on melanoma and genitourinary cancers. Methods: We retrospectively reviewed records of all cancer patients exposed to infliximab after immune checkpoint inhibitor (ICI) treatment from 2004 to 2021 at the MD Anderson Cancer Center. Survival was assessed utilizing the Kaplan-Meier method. Univariate and multivariate logistic regression was utilized to evaluate predictors of infliximab response, OS, and PFS. Results: We identified 185 cancer patients (93 melanoma and 37 genitourinary cancers) treated with ICI and who received infliximab to treat irAEs. Within 3 months of treatment initiation, 71% of the patients responded to infliximab, 27% had no response, and 2% had unknown response. Among different irAEs, colitis was associated with increased response to infliximab at 3 months, irrespective of the type of malignancy. We evaluated best tumor response before and after infliximab in the entire cohort and again in the melanoma and genitourinary (GU); the findings were similar in the melanoma cohort and the entire cohort, where best tumor response before and after infliximab was not significantly different. In the melanoma cohort, acute kidney injury (AKI) was associated with increased risk of death, p = 0.0109, and having response to infliximab was associated with decreased risk of death, p = 0.0383. Interestingly in GU cancer patients, myositis was associated with increased risk of death, p = 0.0041, and having a response to infliximab was marginally associated with decreased risk of death, p = 0.0992. As regards PFS, in a multivariate Cox regression model, having a history of cardiovascular disease remained significantly associated with shorter PFS in the melanoma cohort. For patients with GU cancers, response to infliximab was associated with longer PFS. Conclusions: Our study is among the largest retrospective analyses of infliximab use for irAE management. Patients with colitis were the best responders to infliximab. AKI before initiation of infliximab in the melanoma subcohort and myositis in GU subcohort are associated with higher risk of death. Our results indicate no association between infliximab and cancer progression with the exception of genitourinary cancers.

Pathologic Predictors of Response to Treatment of Immune Checkpoint Inhibitor-Induced Kidney Injury.

BACKGROUND: Immune-related adverse events are a management challenge in patients receiving immune checkpoint inhibitors (ICIs). The most common renal immune-related adverse event, acute interstitial nephritis (AIN), is associated with patient morbidity and mortality. AIN, characterized by infiltration of renal tissue with immune cells, may be analogous to kidney transplant rejection. We evaluated clinical variables and pathologic findings to identify predictors of renal response and overall survival (OS) in patients with ICI-induced AIN. DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS: We reviewed the records and biopsy specimens of all 35 patients treated for ICI-induced AIN at our institution, between August 2007 and August 2020, who had biopsy specimens available. Two board-certified renal pathologists graded the severity of inflammation and chronicity using transplant rejection Banff criteria and performed immunohistochemistry analysis. Patients were categorized as renal responders if creatinine had any improvement or returned to baseline within 3 months of initiating treatment for AIN. Clinical and pathologic characteristics and OS were compared between responders and non-responders. RESULTS: Patients with high levels of interstitial fibrosis were less likely to be responders than those with less fibrosis (p = 0.02). Inflammation, tubulitis, the number of eosinophils and neutrophils, and the clustering or presence of CD8+, CD4+, CD20+, or CD68+ cells were not associated with renal response. Responders had better OS than non-responders (12-month OS rate 77% compared with 27%, p = 0.025). Responders who received concurrent ICIs had the best OS, and non-responders who did not receive concurrent ICIs had the worst OS (12-month OS rate 100% for renal response and concurrent ICIs, 72% for renal response and no concurrent ICIs, and 27% for no renal response and no concurrent ICIs; p = 0.041). CONCLUSIONS: This is the first analysis of ICI induced nephritis where a detailed pathological and clinical evaluation was performed to predict renal response. Low levels of interstitial fibrosis in kidney tissue are associated with renal response to treatment for ICI-induced AIN, and the renal response and use of concurrent ICIs are associated with better OS in these patients. Our findings highlight the importance of the early diagnosis and treatment of ICI-AIN, while continuing concurrent ICI therapy.

Electrolytes disturbances in cancer patients.

PURPOSE OF REVIEW: Hypernatremia, hyperphosphatemia, hypocalcaemia, hyperkalaemia and hypermagnesemia are electrolytes disturbances that can arise in cancer patients in relation to unique causes that are related to the cancer itself or its treatment and can lead to delay or interruption of cancer therapy. This article summarizes these main causes, the proposed pathophysiology and the recommended management for these disturbances. RECENT FINDINGS: There have been many cancer drugs approved in the field of oncology over the past several years and a subset of these drugs have been associated with electrolytes disturbances. This includes, for example, immune checkpoint inhibitor related hyperkalemia, fibroblast growth factor 23 inhibitor associated hyperphosphatemia and epidermal growth factor receptor inhibitor associated hypomagnesemia and hypocalcaemia. SUMMARY: This article provides an updated review of certain electrolytes disturbance in cancer patients and allows clinicians to have a greater awareness and knowledge of these electrolyte abnormalities in efforts to early recognition and timely management.

Hypophosphatemia in cancer patients.

Dysregulation of phosphorus homeostasis resulting in hypophosphatemia is common in cancer patients and can result in serious complications and impact outcomes. Several factors, including critical illness, nutritional status, cancer type and therapy, influence the development of hypophosphatemia. Hypophosphatemia can develop as a result of phosphaturic mesenchymal tumors or as a paraneoplastic phenomenon. The clinical presentation for hypophosphatemia varies depending on the duration and severity of the hypophosphatemia and affects several organ systems. Among other serious effects, hypophosphatemia can impair tissue oxygenation and can cause hemolysis, leukocyte and platelet dysfunction, encephalopathy, seizures, arrhythmias, cardiomyopathy, rhabdomyolysis and coma. Multiple studies have demonstrated that hypophosphatemia is an adverse prognostic marker in inpatients with increased in-hospital stay, mortality and postoperative complications. The phosphate level is homeostatically regulated and maintained in a narrow range by three main hormones: parathyroid hormone, fibroblast growth factor 23 and 1,25-dihydroxyvitaminD3. Together, these hormones regulate how the intestine, kidneys and bones traffic phosphorus. Several hematological malignancies and cancer therapies are associated with proximal tubular dysfunction (Fanconi syndrome), resulting in phosphaturia. Caution should be taken with parenteral administration of phosphate salts, because secondary complications can develop, principally due to hypocalcemia. The general approach to hypophosphatemia should target the underlying cause. Early recognition and prevention are essential and the approach to hypophosphatemia in the cancer patient, because of the nuances and complexity, should be multidisciplinary.

Acute kidney injury in patients treated with immune checkpoint inhibitors.

BACKGROUND: Immune checkpoint inhibitor-associated acute kidney injury (ICPi-AKI) has emerged as an important toxicity among patients with cancer. METHODS: We collected data on 429 patients with ICPi-AKI and 429 control patients who received ICPis contemporaneously but who did not develop ICPi-AKI from 30 sites in 10 countries. Multivariable logistic regression was used to identify predictors of ICPi-AKI and its recovery. A multivariable Cox model was used to estimate the effect of ICPi rechallenge versus no rechallenge on survival following ICPi-AKI. RESULTS: ICPi-AKI occurred at a median of 16 weeks (IQR 8-32) following ICPi initiation. Lower baseline estimated glomerular filtration rate, proton pump inhibitor (PPI) use, and extrarenal immune-related adverse events (irAEs) were each associated with a higher risk of ICPi-AKI. Acute tubulointerstitial nephritis was the most common lesion on kidney biopsy (125/151 biopsied patients [82.7%]). Renal recovery occurred in 276 patients (64.3%) at a median of 7 weeks (IQR 3-10) following ICPi-AKI. Treatment with corticosteroids within 14 days following ICPi-AKI diagnosis was associated with higher odds of renal recovery (adjusted OR 2.64; 95% CI 1.58 to 4.41). Among patients treated with corticosteroids, early initiation of corticosteroids (within 3 days of ICPi-AKI) was associated with a higher odds of renal recovery compared with later initiation (more than 3 days following ICPi-AKI) (adjusted OR 2.09; 95% CI 1.16 to 3.79). Of 121 patients rechallenged, 20 (16.5%) developed recurrent ICPi-AKI. There was no difference in survival among patients rechallenged versus those not rechallenged following ICPi-AKI. CONCLUSIONS: Patients who developed ICPi-AKI were more likely to have impaired renal function at baseline, use a PPI, and have extrarenal irAEs. Two-thirds of patients had renal recovery following ICPi-AKI. Treatment with corticosteroids was associated with improved renal recovery.

Incidence, predictors, and survival impact of acute kidney injury in patients with melanoma treated with immune checkpoint inhibitors: a 10-year single-institution analysis.

Background: The incidence of renal immune-related adverse events (irAEs) is reported to be 3.8%, with varied definitions of acute kidney injury (AKI). This study reports a 10-year experience at MD Anderson Cancer Center of patients diagnosed with melanoma and treated with immune checkpoint inhibitors (ICIs) and evaluated the incidence of AKI, associated factors, and its association with overall survival. Methods: A retrospective chart review (2010-2019) of all patients with melanoma treated with ipilimumab, nivolumab, pembrolizumab, or atezolizumab was performed. All available serum creatinine data were extracted and used to calculate the estimated GFR (eGFR) using the CKD Epi equation, and to diagnose AKI using the two KDIGO (Kidney Disease: Improving Global Outcomes) criteria for defining stage I AKI in 1664 unique patients. Cumulative incidence rates of AKI after initiation of ICIs were calculated in the presence of death as a competing risk. The effects of covariates on the cumulative incidence function of AKI were evaluated in a univariant and multivariable analysis. Overall survival was estimated by Kaplan-Meier method in accordance to the occurrence of AKI. Results: The incidence of AKI by definitions 1a and 1b were 3.49% and 3.33%, respectively. After adjudication, AKI attributable to ICI was 58% and 65% of the overall incidence of AKI in each definition respectively. Increasing age was associated with decreased risk of AKI. Asian race was associated with a higher risk of AKI. Comorbidities were not associated with increased risk of AKI while use of proton pump inhibitors (PPI), ipilimumab or ICI combinations were significantly associated with AKI. AKI was not significantly associated with overall survival. Immune-related adverse events (irAEs) occurred in 30% of patients with AKI but their incidence was not different in patients with AKI attributable to ICI versus other AKI. Conclusions: In a large population of patients with melanoma treated with ICIs, an accurate documentation of AKI in setting of ICI use and predictors associated is presented. AKI following ICI use is infrequent, not associated with mortality, and associated with the use of ipilimumab, ICI combinations and PPIs.

Lupus-Like Glomerulonephritis Associated With Regorafenib, a Multikinase Inhibitor.

Drug-induced lupus glomerular diseases have historically been associated with hydralazine, but new drugs that modify the growth, metabolism, and immunity of cells are increasingly found to cause glomerular disease. This includes anti-tumor necrotic factor and other antibody agents used in cancer treatment. Multitarget tyrosine kinases such as regorafenib are increasingly used in metastatic malignancies with good outcomes. Currently, they are not known to have kidney complications except for proteinuria, hypertension, and electrolyte disturbances such as hypophosphatemia. We report a patient who presented within months after starting regorafenib therapy for metastatic colon cancer with acute kidney injury, proteinuria, and hematuria. Biopsy revealed endocapillary proliferative glomerulonephritis with full-house staining on immunofluorescence in the absence of any systemic manifestation of systemic lupus erythematosus. The kidney injury improved with corticosteroid treatment and discontinuation of regorafenib therapy. We discuss the possible mechanisms that led to this class IV pattern of lupus nephritis and conclude that it is likely drug-induced lupus nephritis from regorafenib.

Infliximab for the treatment of patients with checkpoint inhibitor-associated acute tubular interstitial nephritis.

Acute tubular interstitial nephritis (ATIN) is the most frequently reported pathology in patients with checkpoint inhibitor (CPI) induced acute kidney injury (AKI). Glucocorticoid (GC) therapy and discontinuation of CPI are the mainstay of treatment to prevent permanent renal dysfunction and dialysis. However, less than 50% of patients have complete kidney recovery and relapse of ATIN can occur. Infliximab is effective in treating other immune-related adverse events but its use for the treatment of CPI-ATIN is not well established. We report the first retrospective study examining the steroid-sparing potential of infliximab in achieving durable and complete renal recovery for patients with CPI-ATIN. Data were collected from medical records of patients diagnosed with CPI-AKI with a kidney biopsy or clinical diagnosis of ATIN that was managed with GC and infliximab. Infliximab-containing regimens were used to treat 10 patients with CPI-ATIN. Four patients relapsing after GC therapy achieved durable and complete renal recovery, four patients experienced partial renal recovery, and two patients showed no improvement in kidney function. This is the first study evaluating clinical outcomes using an infliximab-containing regimen for treatment of relapsed CPI-ATIN in patients or patients failing to achieve complete response after primary therapy. Our data suggest that infliximab may be a treatment option for achieving durable and complete renal recovery in this patient population and represents a potential steroid-sparing strategy in challenging cases of CPI-ATIN. Rigorous clinical studies are warranted to evaluate the risk-benefit analysis for infliximab usage in CPI-ATIN patients.

Immune checkpoint inhibitor associated reactivation of primary membranous nephropathy responsive to rituximab.

The same mechanisms that mediate antitumor immunity from checkpoint inhibitors (CPIs) can also lead to unintended targeting of normal tissues, characterized as immune-related adverse events (irAEs). Those with pre-existing autoimmune disease are believed to be particularly vulnerable for exacerbating underlying autoimmunity or inducing severe irAEs. We report the first case of CPI-associated reactivation of primary membranous nephropathy (MN) in a patient with pleural mesothelioma responding to immunotherapy. Due to its specificity in targeting B-lymphocytes, rituximab was used to treat primary MN with the expectation that this would not interfere with the benefits gained from T cell-mediated antitumor immunity. Rituximab was effective in treating CPI-associated reactivation of MN, and the patient was successfully rechallenged with nivolumab and maintained stable kidney function and sustained clinical antitumor effect. While exacerbation of pre-existing autoimmune diseases from CPIs is common, therapy for autoimmune reactivation can be rationally directed by an understanding of the immunosuppressive mechanism with goals of cancer treatment.

Checkpoint inhibitor-related renal vasculitis and use of rituximab.

The percentage of patients with cancer eligible for checkpoint inhibitor (CPI) therapy has increased rapidly over the past few years and approaches 45%. As a result, more cases of CPI-related nephrotoxicity, including a rare subset with vasculitis, are being reported. To elucidate the clinical presentation of CPI-associated renal vasculitis and its possible mechanisms, treatment options and prognosis, we describe cases from a comprehensive cancer center and reviewed the literature for similar cases. We retrospectively reviewed the charts of all patients with cancer from 2014 to 2020 who were diagnosed with CPI-related nephrotoxicity and underwent a kidney biopsy. We identified five cases of renal vasculitis: three patients were diagnosed with seronegative antineutrophil cytoplasm antibody (ANCA)-associated vasculitis, one case with seropositive ANCA-associated vasculitis and one case was diagnosed with IgA vasculitis. Of these cases, four patients were receiving nivolumab, and one patient was receiving tremelimumab. All patients had microscopic hematuria, four out of five patients had negative ANCA serology, one patient had concurrent lung involvement and positive ANCA serology, and all had severe acute kidney injury with creatinine >4.50 mg/dL on diagnosis. All patients were treated by discontinuing CPI and initiating corticosteroids and rituximab. Three patients received plasmapheresis; two of these required renal replacement therapy including the patient with lung involvement. All patients after rituximab had a partial or complete renal response. Two patients died within 8 months of diagnosis due to malignancy progression. None of the patients had a relapse of vasculitis. We demonstrated that CPI can be associated with different types of renal vasculitis that are predominantly ANCA negative and manifest as severe acute kidney injury. Despite the lack of strong evidence, treatment similar to treatment of primary seropositive ANCA-associated vasculitis with corticosteroids and rituximab is well tolerated with favorable renal outcomes.

Impact of autologous stem cell transplantation on long term renal function and associated progression-free and overall survival in multiple myeloma.

The long-term impact of Autologous hematopietic stem cell transplantation (ASCT) on renal function, and the impact of renal function on progression-free survival (PFS) and overall survival (OS) in patients with multiple myeloma are not known. We retrospectively reviewed the records of 885 patients at our institution. We used linear mixed effect models to study the change in estimated glomerular filtration rate (eGFR) and a joint model approach to assess associations between the eGFR, PFS and OS. Sensitivity analyses were conducted at days 0, 100, 180, and 365 post-SCT. eGFR post-ASCT was significantly lower than at day 0 but stabilized at approximately 80 mL/min/1.73 m2. There was no association between eGFR and PFS or OS.; However, relapsed disease and ISS stage were associated with shorter PFS and OS. This data suggests that although there is a modest decline in eGFR post-ASCT, it is not associated with an adverse impact on PFS or OS. KEY POINTS Advanced MM stage at diagnosis was associated with reduced eGFR at all stages of chronic kidney disease. eGFR was not associated with PFS or OS in any of the analyses, but disease-related factors prior to ASCT were all associated with reduced eGFR, PFS and OS. ASCT did not adversely impact kidney function and mitigated the risk of CKD on outcomes in MM.

Clinical Features and Outcomes of Immune Checkpoint Inhibitor-Associated AKI: A Multicenter Study.

BACKGROUND: Despite increasing recognition of the importance of immune checkpoint inhibitor-associated AKI, data on this complication of immunotherapy are sparse. METHODS: We conducted a multicenter study of 138 patients with immune checkpoint inhibitor-associated AKI, defined as a ≥2-fold increase in serum creatinine or new dialysis requirement directly attributed to an immune checkpoint inhibitor. We also collected data on 276 control patients who received these drugs but did not develop AKI. RESULTS: Lower baseline eGFR, proton pump inhibitor use, and combination immune checkpoint inhibitor therapy were each independently associated with an increased risk of immune checkpoint inhibitor-associated AKI. Median (interquartile range) time from immune checkpoint inhibitor initiation to AKI was 14 (6-37) weeks. Most patients had subnephrotic proteinuria, and approximately half had pyuria. Extrarenal immune-related adverse events occurred in 43% of patients; 69% were concurrently receiving a potential tubulointerstitial nephritis-causing medication. Tubulointerstitial nephritis was the dominant lesion in 93% of the 60 patients biopsied. Most patients (86%) were treated with steroids. Complete, partial, or no kidney recovery occurred in 40%, 45%, and 15% of patients, respectively. Concomitant extrarenal immune-related adverse events were associated with worse renal prognosis, whereas concomitant tubulointerstitial nephritis-causing medications and treatment with steroids were each associated with improved renal prognosis. Failure to achieve kidney recovery after immune checkpoint inhibitor-associated AKI was independently associated with higher mortality. Immune checkpoint inhibitor rechallenge occurred in 22% of patients, of whom 23% developed recurrent associated AKI. CONCLUSIONS: This multicenter study identifies insights into the risk factors, clinical features, histopathologic findings, and renal and overall outcomes in patients with immune checkpoint inhibitor-associated AKI.

Nephrotoxicity of immune checkpoint inhibitors beyond tubulointerstitial nephritis: single-center experience.

RATIONALE & OBJECTIVE: The approved therapeutic indication for immune checkpoint inhibitors (CPIs) are rapidly expanding including treatment in the adjuvant setting, the immune related toxicities associated with CPI can limit the efficacy of these agents. The literature on the nephrotoxicity of CPI is limited. Here, we present cases of biopsy proven acute tubulointerstitial nephritis (ATIN) and glomerulonephritis (GN) induced by CPIs and discuss potential mechanisms of these adverse effects. STUDY DESIGN, SETTING, & PARTICIPANTS: We retrospectively reviewed all cancer patients from 2008 to 2018 who were treated with a CPI and subsequently underwent a kidney biopsy at The University of Texas MD Anderson Cancer Center. RESULTS: We identified 16 cases diagnosed with advanced solid or hematologic malignancy; 12 patients were male, and the median age was 64 (range 38 to 77 years). The median time to developing acute kidney injury (AKI) from starting CPIs was 14 weeks (range 6-56 weeks). The average time from AKI diagnosis to obtaining renal biopsy was 16 days (range from 1 to 46 days). Fifteen cases occurred post anti-PD-1based therapy. ATIN was the most common pathologic finding on biopsy (14 of 16) and presented in almost all cases as either the major microscopic finding or as a mild form of interstitial inflammation in association with other glomerular pathologies (pauci-immune glomerulonephritis, membranous glomerulonephritis, C3 glomerulonephritis, immunoglobulin A (IgA) nephropathy, or amyloid A (AA) amyloidosis). CPIs were discontinued in 15 out of 16 cases. Steroids and further immunosuppression were used in most cases as indicated for treatment of ATIN and glomerulonephritis (14 of 16), with the majority achieving complete to partial renal recovery. CONCLUSIONS: Our data demonstrate that CPI related AKI occurs relatively late after CPI therapy. Our biopsy data demonstrate that ATIN is the most common pathological finding; however it can frequently co-occur with other glomerular pathologies, which may require immune suppressive therapy beyond corticosteroids. In the lack of predictive blood or urine biomarker, we recommend obtaining kidney biopsy for CPI related AKI.

Primary Pulmonary Diffuse Large B Cell Non-Hodgkin's Lymphoma: A Case Report and Literature Review.

BACKGROUND Primary pulmonary diffuse large B cell lymphoma (DLBCL) is extremely rare neoplasm representing only 0.5-1% of primary pulmonary malignancies. These patients usually have non-specific clinical presentation and radiological findings. Therefore, it is important to increase awareness of this rare disease, as the correct characterization of the tumors will have therapeutic and prognostic implications. CASE REPORT We present the case of a middle-aged Hispanic woman with chronic cough and an abnormal chest X-ray revealing a lung mass, who was found to have primary pulmonary DLBCL. She underwent 6 cycles of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) therapy and attained complete remission. CONCLUSIONS With its non-specific presentation, the diagnosis of primary pulmonary DLBCL is very challenging and often leads to misdiagnosis or delayed diagnosis. The pathogenesis of primary pulmonary DLBCL is still poorly understood. The choice of treatment approach should be based on the biological characteristic of the tumor, stage, and performance status.

Bystander effect in tumor cells produced by Iodine-125 labeled human lymphocytes.

PURPOSE: To investigate the ability of human lymphocytes labeled with DNA-incorporated (125)I to exert an inhibitory (antiproliferative) bystander effect on co-cultured human colon adenocarcinoma LS174T cells in vitro. MATERIALS AND METHODS: Human peripheral blood lymphocytes were stimulated to synthesize DNA in the presence of phytohemagglutinin (PHA) and labeled with 5-[(125)I]iodo-2'-deoxyuridine. Human colon adenocarcinoma LS174T cells were co-cultured with the (125)I-labeled lymphocytes in various ratios for 5 days and the proliferation of the LS174T cells was assessed. Further, the supernatant media from these co-cultures were: (i) Transferred to LS174T cells and their proliferation measured after 5 days, (ii) used to assess the clonogenic survival of LS174T cells, and (iii) screened for factors that suppress growth. RESULTS: A significant reduction in the proliferation of LS174T cells was observed when co-cultured either with (125)I-labeled lymphocytes (56 ± 3.5%) or the supernatant media (52.5 ± 1.3%) obtained from these co-cultures. Clonogenic survival of LS174T cells grown in the supernatant media corroborated the decrease in tumor cell growth. CONCLUSION: The observed reduction in the proliferation of LS174T cells in presence of (125)I-labeled lymphocytes or media obtained from such co-cultures can be attributed to an inhibitory (antiproliferative) bystander effect, probably mediated by factor(s) released from the dying (125)I-labeled lymphocytes.