ENGINEERING AND PRECLINICAL EVALUATION OF DRIED FOOD-FORMULATED YEAST-SECRETED ANTIBODIES AS PERI-EXPOSURE PROPHYLAXIS AGAINST CLOSTRIDIOIDES DIFFICILE DISEASE.
Clostridioides difficile gastrointestinal infection (CDI) causes significant disease burden, often following gut dysbiosis induced by antibiotic treatment in at-risk individuals. A non-invasive, easy to use targeted prophylaxis in such cases of acute elevated CDI risk, especially in those with a history of recurrent CDI, would prevent much suffering. In this study, we envisioned a simple prophylactic intervention for CDI enabled by the oral administration of yeast-secreted dried food-formulated C. difficile toxin A (TcdA)-and B (TcdB)-neutralizing VHH-based antibodies. We engineered two antibody versions: a previously reported tetravalent VHH (VHH4) comprising dual specificities for TcdA and TcdB, and its murine IgA Fc fusion counterpart (VHH4-mIgA Fc). We explored Generally Recognized as Safe (GRAS) Komagataella phaffii yeast as a low-cost, highly scalable production platform. In a first experiment, we produced the antibodies at small scale in shake flask yeast cultivations and formulated the secreted antibody-containing growth medium into standard-composition dried mouse feed pellets. The antibody food pellet-administration intervention was tested in a C. difficile spore-challenged mouse model in which CDI leads to 50% mortality of untreated animals. We started the antibody-feed prophylaxis dosed at 10 nmol/g pellet one day prior to C. difficile challenge and continued until the infection was cleared with ad libitum feeding. We found that the VHH4 feed almost completely prevented mortality and reduced disease-related weight loss. Despite its higher in vitro potency against TcdA and equipotent potency against TcdB, the VHH4-mIgA Fc fusion did not confer additional in vivo benefit, and further work focused on the simpler VHH4 format. Scalable high-cell-density bioreactor production of VHH4 yielded equally effective prophylactic formulations at the same dose of 10 nmol/g pellet, achieving complete survival and reduced disease burden. Our findings suggest that, with further antibody- and process development, oral prophylaxis with scalable, cost-effective, yeast-produced, dried food-formulated anti-toxin VHHs could offer a simple non-invasive, non-antibiotic prophylaxis option for the high-risk (r)CDI patient population.