Enzyme-mediated depletion of methylthioadenosine restores T cell function in MTAP-deficient tumors and reverses immunotherapy resistance.

Chromosomal region 9p21 containing tumor suppressors CDKN2A/B and methylthioadenosine phosphorylase (MTAP) is one of the most frequent genetic deletions in cancer. 9p21 loss is correlated with reduced tumor-infiltrating lymphocytes (TILs) and resistance to immune checkpoint inhibitor (ICI) therapy. Previously thought to be caused by CDKN2A/B loss, we now show that it is loss of MTAP that leads to poor outcomes on ICI therapy and reduced TIL density. MTAP loss causes accumulation of methylthioadenosine (MTA) both intracellularly and extracellularly and profoundly impairs T cell function via the inhibition of protein arginine methyltransferase 5 (PRMT5) and by adenosine receptor agonism. Administration of MTA-depleting enzymes reverses this immunosuppressive effect, increasing TILs and drastically impairing tumor growth and importantly, synergizes well with ICI therapy. As several studies have shown ICI resistance in 9p21/MTAP null/low patients, we propose that MTA degrading therapeutics may have substantial therapeutic benefit in these patients by enhancing ICI effectiveness.

IgG Immune Complexes Inhibit Naïve T Cell Proliferation and Suppress Effector Function in Cytotoxic T Cells.

Elevated levels of circulating immune complexes are associated with autoimmunity and with worse prognoses in cancer. Here, we examined the effects of well-defined, soluble immune complexes (ICs) on human peripheral T cells. We demonstrate that IgG-ICs inhibit the proliferation and differentiation of a subset of naïve T cells but stimulate the division of another naïve-like T cell subset. Phenotypic analysis by multi-parameter flow cytometry and RNA-Seq were used to characterize the inhibited and stimulated T cells revealing that the inhibited subset presented immature features resembling those of recent thymic emigrants and non-activated naïve T cells, whereas the stimulated subset exhibited transcriptional features indicative of a more differentiated, early memory progenitor with a naïve-like phenotype. Furthermore, we show that while IgG1-ICs do not profoundly inhibit the proliferation of memory T cells, IgG1-ICs suppress the production of granzyme-ß and perforin in cytotoxic memory T cells. Our findings reveal how ICs can link humoral immunity and T cell function.

A Novel Biomarker Panel for the Early Detection and Risk Assessment of Hepatocellular Carcinoma in Patients with Cirrhosis.

Novel biomarkers for hepatocellular carcinoma (HCC) surveillance in patients with cirrhosis are urgently needed. We previously identified osteopontin (OPN) as a promising biomarker for the early detection of HCC. This study is to further validate the performance of OPN and identify fatty acids (FA) that could improve OPN's performance in HCC risk assessment in patients with cirrhosis. To that end, we selected 103 patients with cirrhosis under surveillance. Among them, 40 patients developed HCC during follow-up. We investigated in these 103 patients, the association between HCC incidence and prediagnostic serum levels of AFP, OPN, and 46 FAs. OPN performance was higher than AFP in detecting prediagnosis HCCs and the combination with AFP further improved OPN's performance. For patients with a diagnosis of HCC within 18 months of follow-up (HCC < 18 months), AUC for OPN + AFP was 0.77. Abundance of 11 FAs [four long-chain saturated FAs (SFA), four n-3 poly-unsaturated FAs (PUFA), and three n-6 PUFAs] were statistically different between patients who developed HCC and those who did not. Abundance changes correlated with time to diagnosis for the PUFAs, but not for the SFAs. Adding arachidic acid (20:0) and n-3 docosapentaenoic acid (22:5n3) to OPN and AFP improved the discriminatory performance (AUC = 0.83). AUC for this panel reached 0.87 for HCC < 18 months (82% sensitivity at 81% specificity). In conclusion, we identified a panel of 4 markers with strong performances that could have significant utility in HCC early detection in patients with cirrhosis under surveillance. PREVENTION RELEVANCE: This study identified a panel of 4 biomarkers that identifies with high performance patients with cirrhosis at high risk for HCC. This panel could have utility in HCC early detection in patients with cirrhosis under surveillance.