My 61 Y/o Son-in-law Was Diagnosed With Severe Rheumatoid Arthritis

My 61 y/o son-in-law was diagnosed with severe rheumatoid arthritis 2 months ago. He was put on Imuran for 10 days until he had breathing problems and rushed to the ED. He has been in ICU for 2 weeks with pulmonary fibrosis as a result of the Imuran. Appparentlly, this is a fare side effect. All other Dx's have been ruled out. We have been told by the pulmonologist, internist an rheumatologist that his chances are 50/50 for survival. He is able to breathe with hospital C-pap equipment but a vent. is coming very soon. Do you have any input or have you heard of this as a side effect to the Imuran?
Thank you.