There are early evidence from USC medical school that fasting regenerates new immune cells from stem cells [0] and some early evidence that it can reduce the impact of some autoimmune diseases like MS [1].

[0] https://news.usc.edu/63669/fasting-triggers-stem-cell-regene...

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4899145/

edit: typo and clarity