Biomarkers of Immune Dysfunction and Vaccine Responsiveness in People with Chronic Traumatic Spinal Cord Injury

Background: Infections are the leading cause of death and re-hospitalization for persons with chronic SCI. Also, most persons with chronic SCI have elevated systemic inflammation, which may impede rehabilitation and promotes many common medical consequences of SCI, e.g., neuropathic pain, cardiovascular disease, and stroke. We do not understand the biological mechanisms underlying heightened infection risk or increased inflammation in chronic SCI. This gap in knowledge limits strategies to promote functional abilities, health, survival, and quality of life, and hampers clinical trials, for persons with chronic SCI. To bridge this gap in knowledge, here we propose to use single cell transcriptomic profiling at baseline and in response to vaccination to influenza (flu) and secondarily, to the SARS-CoV-2 virus which causes COVID-19. We will determine relationships of systemic inflammation and vaccine responses (early/innate and late/adaptive immunity), to injury severity. Our hypothesis is that persons with chronic SCI will have higher inflammatory profiles at baseline and weaker vaccine responses compared to uninjured controls, and that this will be to the greatest degree in persons with more severe injuries. We will test our hypothesis via these Specific Aims in persons with chronic SCI and in uninjured controls. Specific Aim 1: Identify baseline systemic immune profiles. We will determine: (A) transcriptional profiles in white blood cells (WBC) at baseline (day 0) using single cell RNA-Seq (scRNA-Seq), (B) relative frequencies of WBCs using flow cytometry, (C) levels of systemic inflammatory cytokines by ELISA. We expect participants with SCI to have more frequent and activated cell subsets associated with inflammation and less frequent cell subsets and reduced activation states associated with effective adaptive immune responses. Specific Aim 2: Determine systemic immune responses to vaccination. (A) After vaccination to seasonal flu, we will characterize: (1) transcriptional profiles of early/innate and late/adaptive immune responses (days 3 and 8) in WBC using scRNA- Seq, (2) relative frequencies of WBCs using flow cytometry, (3) levels of systemic inflammatory cytokines by ELISA (days 3 and 8), and (4) determine antibody titers (day 28 post vaccination). (B) After vaccination to SARS-CoV-2, we will obtain the same immune outcomes as in Aim 2A. We expect to observe weaker responses to flu and SARS-CoV-2 vaccination in persons with SCI vs. uninjured controls and to a greater degree in participants with AIS AB vs CD injuries. As at baseline, we expect participants with SCI to have more frequent and activated cell subsets associated with inflammation and less frequent cell subsets and reduced activation states associated with successful vaccine responses. We will examine potential correlations with clinical and demographic variables. Study Design: Participants will be adults (N=75): N=50 with chronic SCI, N=25 uninjured controls, who complete the study. Assuming a 20% attrition rate, we plan to enroll 60 participants with SCI and 30 participants without SCI. SCI Group: We will recruit 50% with motor complete and 50% with motor incomplete injuries (n=25 AIS AB, n=25 AIS CD). Blood will be collected at baseline, 3, 8, and 28 days after vaccination for immune analyses. Analysis of covariance will be performed for physical activity level and other clinical/demographic features, e.g., injury level. Correlation of immune outcomes with infection incidence will determined using data collected from Form II of the NIH SCI Model Systems. Participants will provide a COVID-19 history, have COVID PCR testing and antibody status determined, to enable potential stratification of analyses. Impact: There are approximately 350,000 Americans living with SCI. Despite advances in medical care, life expectancy remains significantly below uninjured persons, with infections (pneumonia and sepsis) remaining the leading causes of rehospitalization and death. Data from this study will inform future clinical trials of high dose or adjuvanted flu vaccines, both of which are recommended by the CDC for individuals with weakened immune systems such as people over the age of 65 or some people with disabilities, and/or modified anti-SARS-CoV-2 vaccine regimens, for which recommendations are rapidly evolving and for which no public data exists for this population foster targeted anti-inflammatory therapies for individuals with chronic SCI. Expansion: This proposal builds on our recently completed study, "Biomarkers of Spontaneous Recovery From Traumatic SCI (SCIMARK)." There are no validated biochemical markers of functional recovery in SCI and relatively little is known about the biological processes that influence American Spinal Injury Association grade changes and/or functional recovery in humans after SCI. The objective of the SCIMARK study was to determine circulating inflammatory profiles and functional recovery in the first year after SCI, within the same participants. We are using these data to build a predictive model of functional recovery after SCI that incorporates blood-based biomarkers. The hypothesis tested is that levels of some inflammatory markers correlate inversely with functional recovery. Data is also being used to identify molecular pathways that represent potential novel therapeutic targets. Less