Of note, the single KEX1-vaccinated animal that developed Pneumocystis co-infection, 74-15 (Cohort 1 VAX) experienced a more rapid progression of SIV infection compared to other animals within the same group (CD4+ T cell count <200 cell/μl by 14 weeks post-infection, Supplemental Figure 1; chronic CD4+ T cell count of 84 cells/μl, Extended Data Table 1) and developed evidence of Pneumocystis co-infection by 32 weeks post-infection. Here, CD4 is linked to infection.