Adverse childhood experiences (ACEs) such as childhood neglect, abuse, and exposure to violence, substance use, or mental health problems are estimated to be the root cause of 9 of the 10 leading causes of death in the US. High levels of ACEs can lead to long-term disruptions in immune function and genetic regulatory mechanisms. Sensitive parenting is essential for protecting infants and children from the impact of ACEs. Yet parenting can be particularly challenging when parents themselves have a history of ACEs, which can undermine their capacity to provide sensitive care. Nevertheless, many exposed to ACEs do not develop poor health outcomes or become less sensitive parents. Positive childhood experiences (PCEs) often co-occur with ACEs and can be an important source of resilience that buffers the deleterious effects of ACEs. However, the positive effects of PCEs and the biobehavioral mechanisms through which parents' ACEs and PCEs together shape child health remain poorly understood. The proposed K99/R00 study aims to elucidate the relationships among mothers' ACEs and PCEs, maternal sensitivity, and immune regulation in infants (3 months) and toddlers (12-36 months) of mothers who are living with opioid dependence, a high-risk group that often encounters a host of adversities. This study will build on an NICHD-funded randomized clinical trial (R01HD098525) that tests the efficacy of the Attachment and Biobehavioral Catch-up (ABC) intervention among mothers with opioid dependence and infants with perinatal opioid exposure. Assessment of child immune regulation is not currently included in the parent study. Leveraging the parent study's pre-intervention data, the K99 phase will investigate the associations between 100 mothers' ACEs and PCEs, maternal sensitivity, and their 3-month-old infants' immune regulation, indicated by salivary C-reactive protein (CRP) and secretory Immunoglobulin A (sIgA). My long-term career goal is to become an independent investigator who integrates biological and behavioral concepts and methods to promote the health and well-being of families and young children exposed to high levels of adversity. My prior work has focused on behavioral pathways by which ACEs and PCEs may transmit across generations. To date, I have had limited training in research using biological approaches and methods. I am motivated to expand my knowledge and skills in assessing immune biomarkers and intervention research through the proposed training and research during the K99 phase. This will build a strong foundation for the R00 phase and facilitate my transition to independence. Guided by the established Conserved Transcriptional Response to Adversity genomic framework, the R00 phase aims to determine how mothers' ACEs and PCEs are associated with toddlers' immune regulation as indicated by both cellular (salivary CRP and sIgA) and transcriptomic (immune cell gene expression profile) biomarkers; this will be accomplished by prospectively fol...