I first read about the immune response part of the method in the book "What doesn't kill us" by Scott Carney:
https://www.amazon.com/dp/B01IIQQF2O/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1
Wim was initially tested for an immune response to a harmless form of E. Coli. that still initiates a response from the immune system in most people. He had a minimal reaction, and that led to a scientific study of his method on the response to this pathogen:
http://www.pnas.org/content/111/20/7379
In the book, the author meets with people who suffer from Rheumatoid arthritis, Parkinsons, and other autoimmune illnesses, who have taken up the method as means of treatment. In fact (according to the book) Wim's son who is running the business is focusing more on promotion of the medical treatment angle than on the other incredible achievements (marathon in the Arctic, etc.).
You'd probably really like What Doesn't Kill Us (got the title wrong above). It goes into the medical side of things quite a bit.
What Doesn't Kill Us: How Freezing Water, Extreme Altitude, and Environmental Conditioning Will Renew Our Lost Evolutionary Strength https://www.amazon.com/dp/B01IIQQF2O/ref=cm_sw_r_cp_api_i_qEHWDbRVY82B5
many good things:
extend life
improve health
increase body resiliency
prevent and cure auto-immune diseases
make you stronger
What Doesn't Kill Us: How Freezing Water, Extreme Altitude, and Environmental Conditioning Will Renew Our Lost Evolutionary Strength:
1) improves health 2) improves resilience 3) prevents and even treats auto-immune disorders (if combined with breathing) 4) helps with weight loss
This book is great resource
What Doesn't Kill Us: How Freezing Water, Extreme Altitude, and Environmental Conditioning Will Renew Our Lost Evolutionary Strength https://www.amazon.com/dp/B01IIQQF2O/ref=cm_sw_r_cp_api_i_bv1WDbCW8QYXK
many good things: 1) extend life 2) improve health 3) increase body resiliency 4) prevent and cure auto-immune diseases 5) make you stronger 6) all special forces training include lots of cold water exposure... for a reason
What Doesn't Kill Us: How Freezing Water, Extreme Altitude, and Environmental Conditioning Will Renew Our Lost Evolutionary Strength:
well, if you are personally afraid of cold water - just say so. no need to justify your insecurities with laughing at it.....
anyways, once you decide to man up a bit (if this would ever happen....) , here is a book for you: