Clonal Hematopoiesis in Oil Well Fire and Pesticide Exposed Gulf War Veterans

Background: U.S. service members who deployed to the 1990-1991 Gulf War (GW) were potentially exposed to oil well fires and pesticides. In 2016, the National Academies of Science, Engineering and Medicine (NASEM) reported there were insufficient data to associate deployment to the GW with cancer, cardiovascular or hematologic disease. Owing to latency, follow up is needed to determine whether an association exists with cancer. Biomarkers may predict the future risk of adverse health outcomes could bridge gaps in understanding and enhance healthcare for veterans. Clonal hematopoiesis (CH) is such a potential biomarker. We hypothesized that combat EXPOSED GW veterans will have higher rates of CH than combat UNEXPOSED GW veterans.

Methods: A discovery pilot study was performed using the U.S. Veterans Affairs (VA) Gulf War Era Cohort and Biorepository (GWECB), a cohort of 1,275 U.S. veterans who served in the GW era. From 2014-2016, GWECB collected survey detailing deployment, exposures, and medical history and a blood sample. The EXPOSED cohort included 30 GW male veterans who reported highest levels of oil well fire and pesticide exposure. An age and smoking history matched cohort of 30 men who did not deploy made up the UNEXPOSED cohort. Targeted sequencing was performed using 1,250 ng of genomic DNA obtained from archived samples and analyzed using Archer Analysis Software. Germline variants and low-quality false positives were removed with filtering. CH and CHIP were defined as the presence of a somatic mutation in a candidate gene with a VAF > 0.5% and ≥ 2%, respectively. Descriptive statistics were used to characterize rates of CH and CHIP between EXPOSED and UNEXPOSED cohorts.

Results: Median age was 59 years (range 54-64) in both cohorts. Later deployment to Afghanistan and Iraq occurred in 21 EXPOSED and 5 UNEXPOSED veterans. Median filtered depth of coverage was 7,283.5x (range 3,937-14,101x). CH was detected in 26 (43.3%) veterans, including 10 EXPOSED and 16 UNEXPOSED veterans. Median VAF for the entire group was 0.795% (range 0.52-10.73), for the EXPOSED cohort 0.775% (range 0.53-10.73), and for the UNEXPOSED cohort 0.825% (range 0.52-5.54), p= 0.9764. CHIP occurred in 2 EXPOSED and 2 UNEXPOSED veterans (6.7%). DNMT3A and TET2 were the most frequently mutated genes, and missense mutations were the most common type of mutation followed by frameshift, stop gain, and splice donor mutations. Mutations in high-risk genes were present in 2 EXPOSED and 3 UNEXPOSED veterans: DNMT3A (R882, VAF 10.73%) and TP53 (VAF 0.53%) in the EXPOSED group, and DNMT3A (R882, VAF 0.6%), JAK2 (VAF 1.92%) and PPM1D (VAF 0.53%) in the UNEXPOSED group. Compared with the EXPOSED cohort, the UNEXPOSED cohort had more mutated genes, 10 vs. 4, and more veterans with ≥ 2 mutations, 8 vs. 2. As of December 2021, among those with CHIP there was one report of skin cancer and one report of thromboembolism, both in a veteran from the EXPOSED cohort harboring a single mutation in DNMT3A. There were no reports of hematologic malignancy or ischemic cardiovascular disease among the 4 veterans with CHIP.

Conclusions: This pilot study is the first to assess CH in a military population, demonstrating GW veterans have higher rates of CHIP (6.7%) than the reported 5.6% for age matched historical controls (Jaiswal, NEJM, 2014). The UNEXPOSED cohort had higher burdens of CH, likely due to multiple factors. Because somatic mutations do not accumulate in a predictable fashion after exposure, and because the understanding of the interplay between multiple somatic mutations and clonal dynamics are evolving, further investigations are needed to confirm and expand upon the implications of our results.

Disclaimer: The contents herein are the sole responsibility of the authors and do not reflect the views, opinions or policies of Uniformed Services University of the Health Sciences, the Department of Defense (DoD) or the Departments of the Army, Navy, or Air Force.

No relevant conflicts of interest to declare.