CXCL1: A new diagnostic biomarker for human tuberculosis discovered using Diversity Outbred mice

Abstract

More humans have died of tuberculosis (TB) than any other infectious disease and millions still die each year. Experts advocate for blood-based, serum protein biomarkers to help diagnose TB, which afflicts millions of people in high-burden countries. However, the protein biomarker pipeline is small. Here, we used the Diversity Outbred (DO) mouse population to address this gap, identifying five protein biomarker candidates. One protein biomarker, serum CXCL1, met the World Health Organization’s Targeted Product Profile for a triage test to diagnose active TB from latent M.tb infection (LTBI), non-TB lung disease, and normal sera in HIV-negative, adults from South Africa and Vietnam. To find the biomarker candidates, we quantified seven immune cytokines and four inflammatory proteins corresponding to highly expressed genes unique to progressor DO mice. Next, we applied statistical and machine learning methods to the data, i.e., 11 proteins in lungs from 453 infected and 29 non-infected mice. After searching all combinations of five algorithms and 239 protein subsets, validating, and testing the findings on independent data, two combinations accurately diagnosed progressor DO mice: Logistic Regression using MMP8; and Gradient Tree Boosting using a panel of 4: CXCL1, CXCL2, TNF, IL-10. Of those five protein biomarker candidates, two (MMP8 and CXCL1) were crucial for classifying DO mice; were above the limit of detection in most human serum samples; and had not been widely assessed for diagnostic performance in humans before. In patient sera, CXCL1 exceeded the triage diagnostic test criteria (>90% sensitivity; >70% specificity), while MMP8 did not. Using Area Under the Curve analyses, CXCL1 averaged 94.5% sensitivity and 88.8% specificity for active pulmonary TB (ATB) vs LTBI; 90.9% sensitivity and 71.4% specificity for ATB vs non-TB; and 100.0% sensitivity and 98.4% specificity for ATB vs normal sera. Our findings overall show that the DO mouse population can discover diagnostic-quality, serum protein biomarkers of human TB.

Host-pathogen genetic interactions underlie tuberculosis susceptibility in genetically diverse mice

“…Lung CFU was strongly correlated with weight loss, mediators that enhance neutrophil differentiation or migration (CXCL2 (MIP-2; r = 0.79), CCL3 (MIP-1a; r = 0.77), G-CSF ( r = 0.78), and CXCL1 (KC; r = 0.76)), and more general proinflammatory cytokines (IL-6 ( r = 0.80) and IL-1α ( r = 0.76)) ( Figure 1—figure supplement 1 ). These findings are consistent with previous work in the DO panel, that found both proinflammatory chemokines and neutrophil accumulation to be predictors of disease ( Ahmed et al, 2020 ; Gopal et al, 2013 ; Koyuncu et al, 2021 ; Niazi et al, 2015 ).…”

“…Together, these resources have been leveraged to identify host loci underlying the immune response to infectious diseases ( Noll et al, 2019 ). In the context of TB, DO mice have been used as individual, unique hosts to identify correlates of disease, which resemble those observed in non-human primates and humans ( Ahmed et al, 2020 ; Gopal et al, 2013 ; Koyuncu et al, 2021 ; Niazi et al, 2015 ). Small panels of the reproducible CC strains have been leveraged to identify host background as a determinant of the protective efficacy of BCG vaccination ( Smith et al, 2016 ) and a specific variant underlying protective immunity to tuberculosis ( Smith et al, 2019 ).…”

Potential diagnostic biomarkers for pulmonary tuberculosis in humans are not elevated in Mycobacterium tuberculosis culture–positive Asian elephants (Elephas maximus)

“…As such, this work demonstrates that while the biomarkers CXCL1, MMP8, IL-10, IFN-γ, and TNF-α can be detected in Asian elephant serum, they are unlikely to share the same utility in elephant TB that they possess in human TB given that they are not elevated in clinically healthy M.tb culture-positive elephants. This finding may differ with disease state, as experimental studies 17 using human sera have shown significantly higher concentrations of CXCL1 and MMP8 in patients with active pulmonary TB (ie, exhibiting clinical signs) compared to latent M.tb infection (ie, not clinically ill). Given their lack of clinical signs, M.tb culture-positive elephants in this study were likely asymptomatically infected, analogous to humans with latent M.tb infection.…”

“…The biomarkers chemokine (C-X-C motif) ligand 1 (CXCL1), matrix metalloproteinase 8 (MMP8), interleukin-10 (IL-10), interferon-γ (IFN-γ), and tumor necrosis factor-α (TNF-α) have been shown to be significantly elevated in the serum of Diversity Outbred mice infected with M.tb compared to noninfected mice, and this research recently showed translational relevance to humans. 17 In this study, we sought to determine (1) if these 5 biomarkers could be detected in serum from Asian elephants, and (2) if the serum concentrations of these 5 biomarkers are significantly elevated in M.tb culture-positive elephants compared to M.tb culture-negative elephants. We predicted that these biomarkers would be both detectable and significantly elevated in serum from M.tb culture-positive elephants compared to M.tb culture-negative elephants.…”

Genetic Background Matters: Population-Based Studies in Model Organisms for Translational Research

“…By applying machine learning algorithms to multidimensional data, the authors discovered CXCL1 as a putative biomarker of TB in the serum of mice. The biomarker was further validated in samples derived from human patients, discriminating active TB from latent infection and non-TB lung disease [ 45 ]. This study highlights the relevance of using population-based strategies to accelerate human biomarker discovery, validation, and testing.…”