PlexinA4 mediates cytotoxic T cell trafficking and exclusion in cancer

Cytotoxic T cell (CTL) infiltration of the tumor carries the potential to limit cancer progression, but their exclusion by the immunosuppressive tumor microenvironment hampers the efficiency of immunotherapy. Here, we show that expression of the axon guidance molecule PlexinA4 (Plxna4) in CTLs, especially in effector/memory CD8+ T cells, is induced upon T-cell activation, sustained in the circulation, but reduced when entering the tumor bed. Therefore, we deleted Plxna4 and observed that Plxna4-deficient CTLs acquired improved homing capacity to the lymph nodes and to the tumor, as well as increased proliferation, both achieved through enhanced Rac1 activation. Mice with stromal or hematopoietic Plxna4 deletion exhibited enhanced CTL infiltration and impaired tumor growth. In a melanoma model, adoptive transfer of CTLs lacking Plxna4 prolonged survival and improved therapeutic outcome, which was even stronger when combined with anti-PD-1 treatment. PLXNA4 abundance in circulating CTLs was augmented in melanoma patients versus healthy volunteers but decreased after the first cycle of anti-PD-1, alone or in combination with anti-CTLA-4, in those patients showing complete or partial response to the treatment. Altogether, our data suggest that PlexinA4 acts as a "checkpoint", negatively regulating CTL migration and proliferation through cell autonomous mechanisms independent of the interaction with host-derived PlexinA4 ligands semaphorins. These findings pave the way towards PlexinA4-centric immunotherapies and propose PlexinA4 detection in circulating CTLs as a potential way to monitor the response to immune checkpoint blockade in metastatic melanoma patients

Steam explosion of Brewer’s spent grain improves enzymatic digestibility of carbohydrates and affects solubility and stability of proteins

Steam explosion was studied as a means to improve the enzymatic digestibility of carbohydrates in Brewer’s spent grain, a protein and lipid-rich lignocellulosic by-product of the brewing industry. Having temperature, treatment time and the presence of acid catalyst as variables, a treatment at 200 °C for 10 min without an acid catalyst was found to be the most efficient, dissolving 12.1 % of the dry matter. Mainly oligomeric non-cellulosic glucan and arabinoxylan were dissolved, and the remaining insoluble carbohydrates could be efficiently hydrolysed by an enzyme cocktail (75 % hydrolysis yield). The process also caused partial protein degradation and dissolved over a third of the total nitrogen. Meanwhile, the insoluble protein appeared to become more strongly associated with acid-insoluble lignin. Compositional changes observed in the proteins and carbohydrates were supported by the results of epifluorescence microscopy. The process yielded three chemically different fractions which could serve as biorefinery products or intermediates