Premature Immune Aging in Survivors of Childhood Hematologic Malignancies

Introduction: Survival and cure rates for childhood cancers have dramatically improved over the past decades, raising attention to potential long-term sequelae related to treatment including increased infectious risk, chronic inflammation, and other medical comorbidities contributing to frailty. While immunosenescence has been defined in the context of healthy aging, there are few published studies examining premature immune aging during cancer survivorship. We hypothesize that survivors of childhood hematologic malignancies experience long-lasting effects on immunity evidenced by alterations in immune cell subsets with increased expression of senescence-associated markers. Methods: We enrolled survivors of hematologic cancers diagnosed prior to age 18 who completed treatment and have been in remission for ≥12 months. Following informed consent, blood samples were collected, and clinical data was obtained from patient questionnaire and chart review including medical history, cancer treatment, body mass index, complete blood counts, post-treatment infections and hospitalizations, physical activity (adapted from the Global Physical Activity Questionnaire), and self-reported exhaustion and walking limitations. Frailty scores were calculated using modified Fried frailty criteria. Flow cytometry of peripheral blood mononuclear cells (PBMCs) was performed to assess markers of immune senescence, including CD28, CD27, KLRG1, CD57, CD45RA, CD45RO, and p16. PBMCs from five healthy donors (median age 24 years, range 21-29) served as controls for immunology studies, and groups were compared using Welch's unpaired t-test. Results: We enrolled 15 males and 10 females with a history of pre-B-cell acute lymphoblastic leukemia (ALL; n=14), T-cell ALL (n=4), acute myeloid leukemia (n=2), and Hodgkin lymphoma (n=5). The median age at enrollment was 19 years (range 6-30), with a median of 44 months elapsed since treatment completion (range 12-169). Subjects reported a median of 0.4 infections/year (range 0-10) post-treatment. The median calculated frailty score was 0 (range 0-3) with an average score of 0.4±0.8. Complete blood counts were available for 23 subjects and were within normal range, with mean white blood cell count 7.0±2.1 K/µL, absolute neutrophil count of 4.0±1.5 K/µL, and absolute lymphocyte count of 2.0±1.1 K/µL. By flow cytometry, childhood cancer survivors (n=15) had a significantly lower percentage of CD3+ cells (49% vs 68%; p<0.001) compared to healthy controls. Within the CD3+ compartment, survivors had less CD8+ cells (23% vs 33%; p<0.001), more cells expressing the CD45RO (memory) isoform (43% vs 34%; p=0.055), and fewer expressing the CD45RA (naïve) isoform (50% vs 60%; p=0.053). The survivors also had decreased CD45RA+ natural killer (NK) cells (89% vs 96%; p=0.02) and increased CD45RO+ NK cells (3% vs <1%; p=0.04). The overall proportion of B cells did not differ between the two groups, but survivors exhibited decreased expression of the memory B cell marker CD27 (16% vs 28%; p=0.055). No significant differences were observed in p16 expression among various immune subsets between these younger cohorts. Conclusions: Our preliminary results demonstrate that survivors of childhood hematologic cancers exhibit signs of immune aging usually appreciated in older adults, despite normal blood counts and no current evidence of significant health problems, increased infectious risk, or frailty. Ongoing work will expand the sample size of survivors and healthy controls across the life span, generate more comprehensive immunosenescence profiles, in addition to investigating how these immune alterations correlate with increased short-term and long-term risks of inflammation and other age-related comorbidities.