Barriers to long-term follow-up in pediatric Hodgkin lymphoma survivors.

BACKGROUND/PURPOSE: Pediatric Hodgkin lymphoma (HL) survivors have an increased risk of late effects following treatment. Barriers at the patient, provider, and payor level adversely affect adherence to long-term follow-up. METHODS: We conducted a retrospective chart review of HL survivors diagnosed from 1999 to 2014 at Texas Children's Hospital. HL survivors were considered lost to follow-up if there were no documented visits to Texas Children's Cancer Center Long-Term Survivor (LTS) clinic for 2 or more years after their last LTS clinic visit. Univariate and multivariable logistic regression analyses were conducted to explore factors contributing to loss to follow-up. Reasons for not attending subsequent LTS visits were assessed by phone interviews in a subset of lost to follow-up patients. RESULTS: There were 120 HL survivors who had at least one LTS clinic visit in this timeframe; 64 (53%) were classified as lost to follow-up, and of these, 23 (36%) were interviewed. Eleven (47%) indicated that the reason for failure to follow-up was lack of or inadequate insurance, and seven (30%) stated they were unaware of the importance of continued follow-up. Loss to follow-up was associated with lack of insurance, earlier diagnosis, and lack of comorbidities in univariate analyses. Only earlier year of diagnosis (odds ratio [OR] 0.84, 95% confidence interval [CI]: 0.7-0.9, p = .01) and lack of insurance (OR 22.2, 95% CI: 4-123, p < .001) were associated with loss to follow-up in multivariable analyses. CONCLUSIONS: Insurance status and awareness of the need for long-term follow-up care are key factors associated with loss to follow-up in survivors of HL. Targeted education and low-cost options for survivorship care are potential strategies for improving adherence to long-term follow-up care in HL survivors.

Ethnic disparities in childhood leukemia survival by border residence: A Texas population-based analysis.

BACKGROUND: The US-Mexico border is a medically underserved region where survival disparities have been observed in adults diagnosed and treated for various malignancies. Studies examining survival disparities among children living in this region and diagnosed with cancer are lacking. The objective of this study was to evaluate the impact of border residence on survival among children with acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), and living near the Texas-Mexico border at the time of their diagnosis. The authors hypothesized that this group experiences inferior survival compared with patients with childhood leukemia living in nonborder areas. METHODS: The authors conducted a retrospective survival analysis leveraging data from the Texas Cancer Registry. The study included patients aged birth to 19 years who were diagnosed with ALL or AML between 1995 and 2017. Cox proportional hazards models were used to evaluate the factors associated with the risk of death. Overall survival estimates were calculated using Kaplan-Meier methods. RESULTS: During the study period, there were 6002 children diagnosed with ALL and 1279 diagnosed with AML. Inferior 5-year overall survival was observed among children with ALL living along the border region compared with those living in nonborder areas (77.5% vs. 85.8%). In adjusted models, children with ALL living along the border experienced a 30% increased hazard of death versus children living in nonborder areas. In contrast, for children with AML, survival estimates did not vary by border versus nonborder residence. CONCLUSIONS: Living along the border was associated with inferior survival among children with ALL, but not among children with AML. Additional studies are urgently needed to identify the factors driving these disparities to effectively design multilevel interventions and influence state and national cancer control programs.

Ethnic-specific predictors of neurotoxicity among patients with pediatric acute lymphoblastic leukemia after high-dose methotrexate.

BACKGROUND: High-dose methotrexate (HD-MTX; 5000 mg/m2 ) is an important component of curative therapy in many treatment regimens for high-risk pediatric acute lymphoblastic leukemia (ALL). However, methotrexate therapy can result in dose-limiting neurotoxicity, which may disproportionately affect Latino children. This study evaluated risk factors for neurotoxicity after HD-MTX in an ethnically diverse population of patients with ALL. METHODS: The authors retrospectively reviewed the medical records of patients who were diagnosed with ALL and treated with HD-MTX at Texas Children's Cancer Center (2010-2017). Methotrexate neurotoxicity was defined as a neurologic episode (e.g., seizures or stroke-like symptoms) occurring within 21 days of HD-MTX that resulted in methotrexate treatment modifications. Mixed effects multivariable logistic regression was used to estimate the odds ratio (OR) and corresponding 95% confidence interval (CI) for the association between clinical factors and neurotoxicity. RESULTS: Overall, 351 patients (58.1% Latino) who received 1183 HD-MTX infusions were evaluated. Thirty-five patients (10%) experienced neurotoxicity, 71% of whom were Latino. After adjusting for clinical risk factors, the authors observed that serum creatinine elevations ≥50% of baseline were associated with a three-fold increased odds (OR, 3.32; 95% CI, 0.98-11.21; p = .05) for neurotoxicity compared with creatinine elevation <25%. Notably, predictors of neurotoxicity differed by ethnicity. Specifically, Latino children experienced a nearly six-fold increase in neurotoxicity odds (OR, 5.80; 95% CI, 1.39-24.17; p = .02) with serum creatinine elevation ≥50% compared with creatinine elevation <25%. CONCLUSIONS: The current findings indicate that serum creatinine elevations ≥50% may be associated with an increased risk for neurotoxicity among Latino children with ALL and may identify potential candidates for therapeutic or supportive care interventions.

Acute and chronic kidney injury during therapy for pediatric acute leukemia: A report from the Leukemia Electronic Abstraction of Records Network (LEARN).

Children with acute leukemia are at increased risk of kidney injury. Using electronic health record data from three centers between 2010 and 2018, this study retrospectively described acute kidney injury (AKI) and chronic kidney disease (CKD) prevalence in children with acute lymphoblastic or myeloid leukemia (ALL, AML) using Common Terminology Criteria for Adverse Events (CTCAE) and Kidney Disease Improving Global Outcomes (KDIGO) definitions. AKI during therapy was 25% (ALL) and 32% (AML) using CTCAE, versus 84% (ALL) and 74% (AML) using KDIGO. CKD prevalence was low and Grade 1/Stage 2. Further investigation is needed to optimally define kidney injury in acute leukemia.

Child and family perceptions of satisfaction with neutropenia management in pediatric acute myeloid leukemia.

PURPOSE: Chemotherapy for pediatric acute myeloid leukemia (AML) is very intensive and many, but not all centers, require extended hospitalization until neutrophil recovery. Child and family preferences, beliefs, and experiences around hospitalization have not been systematically assessed. PATIENTS AND METHODS: We recruited children with AML and their parents from nine pediatric cancer centers across the United States for a qualitative interview about their experiences of neutropenia management. Interviews were analyzed using a conventional content analysis approach. RESULTS: Of 116 eligible individuals, 86 (74.1%) agreed to participate. Interviews were conducted with 32 children and 54 parents from 57 families. Of these 57 families, 39 were cared for as inpatients and 18 were managed as outpatients. A very high proportion of respondents in both groups reported satisfaction with the discharge management strategy recommended by the treating institution: 86% (57 individuals) of respondents who experienced inpatient management and 85% (17 individuals) of respondents who experienced outpatient management expressed satisfaction. Respondent perceptions associated with satisfaction related to safety (access to emergency interventions, infection risk, close monitoring) and psychosocial concerns (family separation, low morale, social support). Respondents believed it could not be assumed that all children would have the same experience due to varied life circumstances. CONCLUSION: Children with AML and their parents express a very high degree of satisfaction with the discharge strategy recommended by their treating institution. Respondents saw a nuanced tradeoff between patient safety and psychosocial concerns that was mediated by a child's life circumstances.

Clinician perceptions of Passport for Care, a web-based clinical decision support tool for survivorship care plan delivery.

BACKGROUND: The Children's Oncology Group Long-Term Follow-Up Guidelines provide exposure-based risks and recommendations for late effects screening of survivors of childhood cancer. Passport for Care (PFC) is a web-based clinical decision support tool for generating a personalized survivorship care plan (SCP) derived from the Guidelines and user-entered exposures. We assessed PFC clinician user practices and perceptions of PFC impact on clinic workflow, guidelines application, and survivor shared decision-making. PROCEDURE: A 35-item REDCap survey was emailed to all PFC users (n = 936) in 146 current and former PFC user clinics. Anonymous responses were permitted. Results were summarized and compared with a 2012 survey. RESULTS: Data were available from 148 respondents representing 64 out of 146 PFC user clinics (minimum clinic response rate 44%, excluding 49 anonymous responses). Generation of a personalized SCP was the most common application of PFC, followed by determination of surveillance recommendations and use as a survivor database. Twenty-five respondents (17%) felt data entry was a significant or insurmountable barrier to PFC application. Sixty-nine percent of respondents attributed PFC with a very high/high impact on guidelines adherence in their clinical practice, compared with 40% who attributed PFC with having a significant impact on adherence in 2012 (p < .001). CONCLUSION: The survey results provide valuable insights on patterns of SCP delivery and Survivor Clinic workflow. User-perceived benefits to PFC included facilitating clinician ability to follow guidelines recommendations in clinical practice. Importantly, some barriers to resource utilization were also identified, suggesting a need for user-informed adaptations to further improve uptake.

Epigenetic age acceleration among survivors of pediatric medulloblastoma and primitive neuroectodermal tumor.

Survivors of childhood central nervous system (CNS) tumors experience early-onset aging-related phenotypes. DNA methylation (DNAm) age is an emerging epigenetic biomarker of physiologic age and may be predictive of chronic health conditions in long-term survivors. This report describes the course of epigenetic age acceleration using post-diagnosis blood samples (median: 3.9 years post-diagnosis; range: 0.04-15.96) from 83 survivors of pediatric CNS tumors. Epigenetic age acceleration was detected in 72% of patients, with an average difference between chronologic and DNAm age of 2.58 years (95% CI: 1.75-3.41, p < 0.001). Time from diagnosis to sample collection correlated with the magnitude of epigenetic age acceleration.

Distribution and frequency of tyrosine kinase inhibitor-associated long-term complications in children with chronic myeloid leukemia.

BACKGROUND: Tyrosine kinase inhibitors (TKIs) improve outcomes for pediatric malignancies characterized by specific gene rearrangements and mutations; however, little is known about the long-term impact of TKI exposure. Our objective was to assess the incidence and type of late-onset TKI-related toxicities in children with chronic myeloid leukemia (CML). METHODS: We reviewed medical records from patients diagnosed with CML between 2006 and 2019 at <21 years of age and prescribed one or more TKIs. Patients treated with stem cell transplant were excluded. Outcomes were captured beginning at 1 year after CML diagnosis. Outcome incidence was described overall and stratified by TKI exposure during the data-capture period. RESULTS: Twenty-two eligible TKI-exposed patients with CML were identified. The median follow-up was 6.0 years (range: 2.2-14.3). All pericardial (n = 3) or pleural (n = 3) effusion outcomes occurred in patients treated with TKIs during the data-capture period. Other outcomes included hypertension (n = 2), ectopy on electrocardiogram (n = 2), and gastrointestinal bleed (n = 1). All outcomes were graded as mild to moderate: some resulted in a temporary discontinuation of TKI, but none led to a change in TKI. No differences were noted in outcome incidence by type of TKI exposure. CONCLUSIONS: TKIs have substantially improved prognosis for subsets of childhood leukemia, but there are limited long-term data to inform exposure-based risk for late-onset complications and screening. Our results suggest that TKI-exposed survivors may be at risk for long-term outcomes that extend well into survivorship.

Implementation of a provider-focused intervention for maximizing human papillomavirus (HPV) vaccine uptake in young cancer survivors receiving follow-up care in pediatric oncology practices: protocol for a cluster-randomized trial of the HPV PROTECT intervention.

BACKGROUND: Childhood cancer survivors are at high risk for developing new cancers (such as cervical and anal cancer) caused by persistent infection with the human papillomavirus (HPV). HPV vaccination is effective in preventing the infections that lead to these cancers, but HPV vaccine uptake is low among young cancer survivors. Lack of a healthcare provider recommendation is the most common reason that cancer survivors fail to initiate the HPV vaccine. Strategies that are most successful in increasing HPV vaccine uptake in the general population focus on enhancing healthcare provider skills to effectively recommend the vaccine, and reducing barriers faced by the young people and their parents in receiving the vaccine. This study will evaluate the effectiveness and implementation of an evidence-based healthcare provider-focused intervention (HPV PROTECT) adapted for use in pediatric oncology clinics, to increase HPV vaccine uptake among cancer survivors 9 to 17 years of age. METHODS: This study uses a hybrid type 1 effectiveness-implementation approach. We will test the effectiveness of the HPV PROTECT intervention using a stepped-wedge cluster-randomized trial across a multi-state sample of pediatric oncology clinics. We will evaluate implementation (provider perspectives regarding intervention feasibility, acceptability and appropriateness in the pediatric oncology setting, provider fidelity to intervention components and change in provider HPV vaccine-related knowledge and practices [e.g., providing vaccine recommendations, identifying and reducing barriers to vaccination]) using a mixed methods approach. DISCUSSION: This multisite trial will address important gaps in knowledge relevant to the prevention of HPV-related malignancies in young cancer survivors by testing the effectiveness of an evidence-based provider-directed intervention, adapted for the pediatric oncology setting, to increase HPV vaccine initiation in young cancer survivors receiving care in pediatric oncology clinics, and by procuring information regarding intervention delivery to inform future implementation efforts. If proven effective, HPV PROTECT will be readily disseminable for testing in the larger pediatric oncology community to increase HPV vaccine uptake in cancer survivors, facilitating protection against HPV-related morbidities for this vulnerable population. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04469569, prospectively registered on July 14, 2020.

An evidence-based, risk-adapted algorithm for antifungal prophylaxis reduces risk for invasive mold infections in children with hematologic malignancies.

BACKGROUND: Children with hematologic malignancies, especially those who receive intensive chemotherapy, are at high risk for invasive mold infections (IMI) that confer substantial mortality. Randomized controlled trials support the use of antifungal prophylaxis with antimold activity as an optimal strategy for risk reduction in this population, but studies outlining the practical application of evidence-based recommendations are lacking. PROCEDURE: We conducted a 15-year, single-institution retrospective review in a diverse cohort of children with hematologic malignancies treated with chemotherapy to determine the incidence of proven or probable IMI diagnosed between 2006 and 2020. Multivariable logistic regression was used to identify host and disease factors associated with IMI risk. We then compared the incidence and type of IMI and related factors before and after 2016 implementation of an evidence-based, risk-adapted antifungal prophylaxis algorithm that broadened coverage to include molds in patients at highest risk for IMI. RESULTS: We identified 61 cases of proven or probable IMI in 1456 patients diagnosed with hematologic malignancies during the study period (4.2%). Implementation of an antifungal prophylaxis algorithm reduced the IMI incidence in this population from 4.8% to 2.9%. Both Hispanic ethnicity and cancer diagnosis prior to 2016 were associated with risk for IMI. CONCLUSION: An evidence-based, risk-adapted approach to antifungal prophylaxis for children with hematologic malignancies is an effective strategy to reduce incidence of IMI.

Evidence for Genetic Risk Contributing to Long-Term Adverse Treatment Effects in Childhood Cancer Survivors.

Survivors of childhood cancer are at increased risk for therapy-related morbidities and mortality. Although the demographic and clinical factors predicting the risk for long-term effects of cancer therapy are well known, the impact of genetic risk for specific late effects is less clearly defined. Here, we review the extant literature and recent research describing genetic modifiers to risk for the more common late effects of childhood cancer therapy. Results of this research support the need for clinical trials that attempt to further refine risk prediction by incorporating genetic testing into existing algorithms that are primarily based on clinical and demographic factors. Confirmation of genetic predisposition, as defined by reproducibility and prospective validation, would permit therapeutic modification and discussion of individualized survivor care plans even at initial cancer diagnosis.

Incidence and predictors of treatment-related conjugated hyperbilirubinemia during early treatment phases for children with acute lymphoblastic leukemia.

Conjugated hyperbilirubinemia (CHB) and liver transaminase elevation are known complications of acute lymphoblastic leukemia (ALL) therapy, but host risk factors are poorly understood. Among 373 children diagnosed with ALL between 2011 and 2016, clinically significant CHB and transaminase elevation were observed in 15 (4.0%) and 12 (3.2%) children, respectively, during induction and consolidation. Body mass index ≥95th percentile (odds ratio 9.20, 95% confidence interval 2.56-32.96) was the only host factor independently associated with CHB, and no host factors were associated with transaminase elevation. Obese patients warrant closer monitoring of hepatic function to facilitate early intervention prior to the development of severe, adverse hepatic events.

Identifying patient- and family-centered outcomes relevant to inpatient versus at-home management of neutropenia in children with acute myeloid leukemia.

Efficacy of therapeutic strategies relative to patient- and family-centered outcomes in pediatric oncology must be assessed. We sought to identify outcomes important to children with acute myeloid leukemia and their families related to inpatient versus at-home management of neutropenia. We conducted qualitative interviews with 32 children ≥8 years old and 54 parents. Analysis revealed the impact of neutropenia management strategy on siblings, parent anxiety, and child sleep quality as being outcomes of concern across respondents. These themes were used to inform the design of a questionnaire that is currently being used in a prospective, multiinstitutional comparative effectiveness trial.

A homozygous telomerase T-motif variant resulting in markedly reduced repeat addition processivity in siblings with Hoyeraal Hreidarsson syndrome.

Hoyeraal Hreidarsson syndrome (HHS) is a form of dyskeratosis congenita (DC) characterized by bone marrow failure, intrauterine growth retardation, developmental delay, microcephaly, cerebellar hypoplasia, immunodeficiency, and extremely short telomeres. As with DC, mutations in genes encoding factors required for telomere maintenance, such as telomerase reverse transcriptase (TERT), have been found in patients with HHS. We describe 2 sibling HHS cases caused by a homozygous mutation (p.T567M) within the TERT T motif. This mutation resulted in a marked reduction in the capacity of telomerase to processively synthesize telomeric repeats, indicating a role for the T motif in this unique aspect of telomerase function. We support this finding by demonstrating defective processivity in the previously reported p.K570N T-motif mutation. The consanguineous, heterozygous p.T567M parents exhibited telomere lengths around the first percentile and no evidence of a DC phenotype. Although heterozygous processivity defects have been associated with familial, adult-onset pulmonary fibrosis, these cases demonstrate the severe clinical and functional impact of biallelic processivity mutations. Thus, despite retaining the capacity to add short stretches of telomeric repeats onto the shortest telomeres, sole expression of telomerase processivity mutants can lead to a profound failure of telomere maintenance and early-onset multisystem disease.

Invasive Candidiasis in Pediatric Hematologic Malignancy: Increased Risk of Dissemination With Candida tropicalis.

BACKGROUND: Candida species are the most common cause of invasive fungal disease, and children with hematologic malignancy are at increased risk. Non-albicans Candida (NAC) now account for more than half of all invasive candidiasis (IC) and carry a worse prognosis. We aimed to compare the epidemiology, risk factors, organ dissemination, biomarkers and outcomes in IC based on the species implicated and evaluate trends in antifungal resistance over time. METHODS: Patients 0-18 years of age with hematologic malignancy and IC at 2 centers were included. Fifty-three patients from 2011 to 2022 were identified. Information related to demographics, host and risk factors, Candida species and antifungal susceptibilities, treatment and outcomes was collected via retrospective chart review. Data were analyzed at the species level. RESULTS: The incidence rate of IC was 29 per 1000 patients with leukemia and lymphoma. The median time to infection from diagnosis of malignancy was 38 days. Candida tropicalis (n = 17; 30%) was the most identified species followed by Candida albicans (n = 14; 25%). Patients with C. tropicalis infection were more likely to have dissemination to the eyes (P = 0.035), spleen (P = 0.001) and skin (P = 0.003) than patients with C. albicans or other NAC. Of the 34 patients who underwent dilated retinal examination, 24% (n = 8) had evidence of intraocular candidiasis. Seven of the 8 patients with intraocular disease had prolonged candidemia (3 or more days; P = 0.003). The 12-week crude mortality rate was 16.9%. CONCLUSIONS: NAC, specifically C. tropicalis, accounted for most of the IC in children with hematological malignancies. Screening for intraocular candidiasis continues to play an important role in patients with IC, and future studies are needed to determine if screening can be limited to patients with select risk factors.

Preferences for survivorship education and delivery among Latino and non-Latino childhood cancer survivors and caregivers.

PURPOSE: To assess survivor and parent perceptions of the long-term survivor visit and preferences regarding accessing health information, survivorship education, and support networks in rural and metropolitan regions of Texas. METHODS: Leveraging the multi-institutional Survivorship and Access to Care for Latinos to Understand Disparities (SALUD) cohort, we administered a 26-item bilingual survey to adult survivors of childhood cancer and parents of younger survivors. Characteristics and responses were compared between survivors vs. parents and Latinos vs. non-Latinos using a t test or Fisher exact test. Odds ratios for the outcomes of interest were calculated with 95% confidence intervals. RESULTS: We received 138 responses from 59 survivors and 79 parents of survivors treated at three Texas pediatric cancer hospitals/clinics. Parents were more likely than survivors to seek survivorship information from other survivors or parents of survivors (OR=6.32, 95% CI 1.78, 22.47), and non-Latinos preferred social media as an educational resource (OR=3.70, CI 1.58, 8.68). Survivors, particularly Latino survivors, preferred short videos as a mode of survivorship education delivery. Highest topic priorities for survivorship education were 'risk for second cancers' and 'diet, nutrition, and exercise.' All parents and survivors who rated survivor physical and mental health as 'fair' or 'poor' identified as Latino. CONCLUSIONS: These results highlight differences in perceived health status between Latino and non-Latino survivors and support the development of adapted survivorship education content to address the specific needs of Latino survivors. Implications for Cancer Survivors Results of this study suggest a need for survivorship educational materials in multiple formats and that are tailored to the style, content, language preferences, and health literacy status of the target population.

Short NK- and Naïve T-Cell Telomere Length Is Associated with Thyroid Cancer in Childhood Cancer Survivors: A Report from the Childhood Cancer Survivor Study.

BACKGROUND: Survivors of childhood cancer are at risk for therapy-related subsequent malignant neoplasms (SMN), including thyroid SMN. Telomere length (TL) is associated with cancer risk, but the relationship between TL and SMN risk among survivors is less clear. METHODS: We conducted a nested, matched case-control study of radiation-exposed 15-year+ adult survivors of childhood cancer with thyroid SMN (cases) and without SMN (controls). Forty-six cases were matched to 46 controls by primary diagnosis, chemotherapy (yes/no), radiation field, and follow-up duration. Lymphocyte TL (LTL) was measured by telomere flow-FISH cytometry using blood samples banked at a mean of 38.9 years (cases), 39.2 years (controls). Genetic variation in telomere genes was assessed by whole genome sequencing. Point estimates for LTL <10th percentile were determined for cases and controls. RESULTS: Cases had shorter median LTL than controls in three out of four leukocyte subsets. Cases were more likely to have NK cell LTL <10th percentile (P = 0.01), and 2.8-fold more likely to have naïve T-cell LTL <10th percentile than controls (CI, 1.07-8.78). Five out of 15 cases with a rare indel or missense variant had naïve T-cell LTL <10th percentile, compared with one out of eight controls. CONCLUSIONS: Long-term survivors have shorter than expected LTL, a finding that is more pronounced among survivors with thyroid SMN. IMPACT: The long-term impact of childhood cancer treatment on immune function is poorly understood. Our findings support immune function studies in larger survivor cohorts to assess long-term deficits in adaptive and innate immunity that may underlie SMN risk.

T cells expressing constitutively active Akt resist multiple tumor-associated inhibitory mechanisms.

Adoptive transfer of antigen-specific cytotoxic T lymphocytes has shown promise for the therapy of cancer. However, tumor-specific T cells are susceptible to diverse inhibitory signals from the tumor microenvironment. The Akt/protein kinase B plays a central role in T-cell proliferation, function, and survival and we hypothesized that expression of constitutively active Akt (caAkt) in T cells could provide resistance to many of these tumor-associated inhibitory mechanisms. caAkt expression in activated human T cells increased proliferation and cytokine production, a likely result of their sustained expression of nuclear factor-κB (NF-κB) and provided resistance to apoptosis by upregulating antiapoptotic molecules. caAkt expressing T cells (caAkt-T-cells) were also relatively resistant to suppression by and conversion into regulatory T cells (Tregs). These characteristics provided a survival advantage to T cells cocultured with tumor cells in vitro; CD3/28-stimulated T cells expressing a chimeric antigen receptor (CAR) specific for disialoganglioside (GD2) that redirected their activity to the immunosuppressive, GD2-expressing neuroblastoma cell line, LAN-1, resisted tumor-induced apoptosis when co-expressing transgenic caAkt. In conclusion, caAkt-transduced T cells showed resistance to several evasion strategies employed by tumors and may therefore enhance the antitumor activity of adoptively transferred T lymphocytes.