PDCD1 and infection: Other recent studies using non-lethal Plasmodium yoelii 17XNL (Py17XNL) infection focused on co-stimulatory markers on CD4+ T-cells, and demonstrated that Programmed cell Death 1 (PD-1) and LAG-3 blockade, or stimulation via OX40 boosted Tfh and GC B-cell responses, with positive effects on parasite control [4,17].