Adenosine DeAminase (ADA) as an adjuvant molecule for human HIV-1 vaccine

Follicular helper T cells (Tfh) play critical role in shaping, instructing, and initiating T-cell dependent antibody responses. Understanding the underlying mechanisms that enhance their function is therefore critical for vaccine development. Using a unique gene array analysis, we have identified adenosine deaminase (ADA), as a novel key molecule that drives Tfh helper program in proliferating Germinal Centers Tfh (GC Tfh) and circulatory Tfh (cTfh) cells following their interactions with B cells. In fact, our gene array analysis showed that CD26 and ADA were exclusively up-regulated within the less efficient cTfh1 (CD4+CD45RA−CXCR5+CXCR3+) and cTfh2-17 (CD4+CD45RA−CXCR5+CXCR3+CCR6+/−) subsets, respectively. ADA enzymatic activity is significantly higher, as well, in cTfh2-17 than in the less-efficient cTfh1 cells. Exogenous ADA enhances the ability of Tfh cells to provide B cell help while inhibition of ADA activity by specific inhibitors impeded Tfh function and blunted antibody response. Our results further demonstrated that enhancement of Tfh function by ADA pathway could be due to increase in IL-6 and decrease in IL-2 production in the co-culture, and maintenance of low extracellular expression of CD26. Moreover, blocking IL-2 in cTfh2-17 co-culture from virally suppressed HIV subjects (ST) showed a significant decrease of CD26 expression associated with a rescued helper capacity. Finally, in vivo use of recombinant ADA as an adjuvant in a DNA based HIV vaccine enhanced Tfh cells differentiation and enhanced anti-Env humoral response and isotype class-switch. Thus, ADA activity fine-tunes Tfh helper program and deciphering how ADA regulate the function of Tfh subsets would benefit future vaccine adjuvant design.