Discussion

Many mammals are highly susceptible to infection by African trypanosome species including domestic cattle. 10 million square miles of African land is thereby left uncultivated, as farmers are unable to maintain livestock for haulage, milk, and food. Baboons and other primates are immune to infection by Trypanosoma brucei and related species due to the anti-microbial activity of Trypanosome lytic factor (TLF). We propose to combat this debilitating economic and agricultural burden by generating genetically modified cattle expressing the baboon TLF genes in order to create an indigenous breed capable of thriving in sub-Saharan Africa. TLF is a 550-kDa high-density lipoprotein (HDL) incorporating the primate specific haptoglobin-related protein (HPR), which enhances parasite uptake of TLF, which carries the pore-forming toxin apolipoprotein L-I (APOLI). We have generated baboon APOLI expressing transgenic mice via stable germline integration in a C57BL/6N background. Ubiquitin promoter driven expression of APOLI protects mice from infection by T. b. brucei, T. congolense, and T. b. rhodesiense. This protection is augmented by co-expression of baboon HPR via hydrodynamic gene delivery. The mice secrete 10-20 fold less APOLI into their serum compared to baboons. We have not detected any APOLI induced host toxicity; however, this low expression level has selected for baboon APOLI resistant trypanosomes. We are determining the source of the APOLI resistance via RNA sequencing and testing more trypanosome species in our mice. To prevent resistance from developing in cattle, we are generating mice with both APOLI (higher expression) and HPR in order to produce fully protected animals. The information obtained in these studies will be applied to the generation of genetically modified cattle in the near future.