Development of Onchocerca volvulus in humanized NSG mice and detection of parasite biomarkers in urine and serum

Patton, John B.; Bennuru, Sasisekhar; Eberhard, Mark L.; Hess, Jessica A.; Torigian, April; Lustigman, Sara; Nutman, Thomas B.; Abraham, David

In vitro studies on the development of filarial worms including O. volvulus [69, 70] and Brugia malayi [71] have demonstrated that host cells are needed in the culture wells to optimize parasite growth and development. Furthermore, optimal development and survival of larval T. spiralis in mice requires the presence of mouse eosinophils [33] . It was thus hypothesized that adding human cells to the NSG mice, from the tissues that the parasites are normally found juxtaposed in humans, might provide additional required nutritional or developmental elements found in humans required for parasite development and survival. Four different single cell xenografts were screened: HuSkMc, LEC, HaCaT and BESM. Of these four cell lines, HuSkMc was found to support the highest average percent survival of the implanted worms and consistent infection rates over a 12-week time period (Figs 1 and 2) As an alternative to adding single cell populations to the NSG mice, multipotential umbilical cord stem cells were transferred to the immunodeficient mice. NSG, NSG-SGM, and NRG mice, all of which lack functional immune responses, were humanized with CD34 + umbilical cord stem cells. The humanization of the various immunocompromised mouse strains resulted in the development of an immature human immune system. The developing immune system in these mice displays a T-independent response, limited antigen-specific IgM responses, and the presence of multiple innate immune cells has been noted [25] . When humanized NSG, NSG-SGM, and NRG mice were infected with O. volvulus L3, higher GM parasite recoveries were observed when compared to NSG mice without any human cells but these enhancements were not significant. Although NSG-SGM did have consistent infection rates with O. volvulus we had significant difficulties establishing reliable engraftment of human cells in this strain of mice. Extending this concept further, BLT mice which contain CD34 + stem cells in addition to fetal tissue were used. BLT mice are known to develop a more mature version of a human immune system. Limited T-dependent recognition is seen within these mice and better overall functionality of both the B and T-cells has been documented [36] . BLT mice supported the highest average parasite recoveries of any mouse model tested at 4-weeks, although the average fell to be in line with the HuNSG and HuSkMc models by 8-weeks post infection. The mean lengths of the parasites recovered from 4-and 8-week time points from the NSG mice were comparable to those recovered from BLT mice. This suggests a link between the enhanced survival, may be related to the presence of the human immune cells, but the growth of the parasites that survive may not be related to the human cell byproducts. Although cellular engraftments levels in BLT and HuNSG mice were not rechecked at the end of the experiment previously published data have shown that these animals reliably hold their engraftments for extended periods of time [72, 73] .