Evolution of Mitochondrial DNA Content After Planned Interruption of HAART in HIV-Infected Pediatric Patients Antoni Noguera, 1 Constanza More ´ n, 2,3 Nu ´ ria Rovira, 1 Emı ´lia Sa ` nchez, 4 Glo ` ria Garrabou, 2,3 Mireia Nicola `s, 2,3 Carmen Mun ˜ oz-Almagro, 5 Francesc Cardellach, 2,3 O ` scar Miro ´, 2,3 and Cla ` udia Fortuny 1 Abstract HAART-related long-term toxicities, many of them ascribed to mitochondrial (mt) toxicity of the nucleoside analogues, are being increasingly reported in HIV-infected children. HIV infection can also cause mt damage. Case series include 13 vertically HIV-infected pediatric patients (9 girls, median age 10.5 years) with optimal long-term response to a first-line HAART regimen who underwent planned treatment interruption (PTI). MtDNA content from peripheral blood mononuclear cells was assessed by means of a real-time PCR technique at PTI and 12 months later and expressed as an mtDNA/nuclear DNA ratio, together with lactate levels. At PTI, patients had remained a median time of 4.7 years on HAART and 4.3 years with complete suppression of viral replication. The main reason leading to PTI was treatment fatigue. One month after PTI, HIV plasmatic viral load had increased to 4.8 log copies/ml and stabilized thereafter. During the 12-month study period, all children remained free from any HIV-related clinical event. A progressive and significant decrease in median CD4 cell counts and percentages was observed 12 months after PTI. One year after PTI, the median mtDNA/ nuclear DNA ratios had increased from 0.76 to 1.08 ( p ¼ 0.002) and lactate levels had decreased (from 1.12 to 0.73 mmol/liter; p ¼ 0.019). Changes in mtDNA did not correlate with changes in lactate levels. No rela- tionship was found between the evolution in mt toxicity markers and the rest of the clinical, immunological, and virological variables. In this series, PTI led to a partial restoration of mtDNA levels and a significant decrease in lactate values. T he implementation of highly active antiretroviral (ARV) therapy (HAART) has significantly improved morbidity and mortality from HIV infection/AIDS in the pediatric population. 1 Nucleoside analogue reverse tran- scriptase inhibitors (NRTIs) remain the backbone of most HAART regimens, especially among children, for whom many of the newest drugs have not yet been licensed. NRTIs also inhibit DNA polymerase gamma, which can lead to mitochondrial (mt) DNA (mtDNA) depletion, and to mt dysfunction. HAART-related long-term toxicities are being increasingly reported in vertically HIV-infected pediatric patients. 2,3 Many of these have been ascribed to direct mt toxicity of the NRTIs. Further investigation on the patho- genesis, clinical manifestations, and therapeutics of these toxicities in children is mandatory, as these patients shall be exposed to ARV for an ever-increasing length of time throughout postnatal growth and development. We report our experience with HAART interruption in a series of HIV- infected children and its effects on biological markers of mt toxicity. This was a prospective case series of perinatally HIV- infected pediatric patients followed up in a third-level pediatric hospital in Barcelona (Spain) who underwent planned treat- ment interruption (PTI). At the time of PTI, all patients ful- filled the following requirements: to be on a first-line HAART, freedom from any active HIV-related clinical condition, undetectable plasmatic HIV-RNA (limit of <50 copies/ml; CA HIV Monitor; Roche, Basel, Switzerland), and a main- tained immune situation (flow cytometry, FACSCalibur; BD Biosciences, San Jose, CA) within CDC Category 1 (>350 cells/mm 3 for adolescents or >25% for children aged 12 years or less) for at least the past 2 years. ARV treatment 1 Unitat d’Infectologia, Servei de Pediatria, Hospital Sant Joan de De ´u, University of Barcelona, Barcelona, Spain. 2 Mitochondrial Research Laboratory, Muscle Research Unit, IDIBAPS-University of Barcelona, Internal Medicine Department-Hospital Clı ´nic of Barcelona, Barcelona, Spain. 3 CIBER de Enfermedades Raras (CIBERER), Barcelona, Spain. 4 Blanquerna School of Health Sciences, Universitat Ramon Llull, Barcelona, Spain. 5 Servei de Microbiologia, Hospital Sant Joan de De ´u, Barcelona, Spain. AIDS RESEARCH AND HUMAN RETROVIRUSES Volume 26, Number 9, 2010 ª Mary Ann Liebert, Inc. DOI: 10.1089/aid.2009.0273 1015