A major objective will be to measure the effect probiotics have on the development of tolerance to milk antigen over time. By following these infants during the first year of life, and repeatedly collecting blood and stool samples from them, we will be poised to analyze their stool microbiome signatures, and we will estimate the frequency, phenotype and TCR diversity of milk-specific T cells over time. By repeatedly challenging them with more immunologically intact milk protein, we will better define the kinetics of CMA resolution and its association to these variables. This information is likely to further elucidate CMA disease mechanisms and identify possible biomarkers of disease resolution versus persistence. It will be directly useful for evaluating the efficacy of probiotics and hydrolyzed formula for promoting milk tolerance.