Although quite a bit more edgy, and I haven't looked into it myself, I have been super intrigued by this 2014 PNAS paper documenting strong positive effect on the immune system of an intervention of meditation, breathing and cold therapy....Voluntary activation of the sympathetic nervous system and attenuation of the innate immune response in humans
Matthijs Koxa,b,c,1, Lucas T. van Eijka,c, Jelle Zwaaga,c, Joanne van den Wildenberga,c, Fred C. G. J. Sweepd, Johannes G. van der Hoevena,c, and Peter Pickkersa,chttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC4034215/
I seem to recall that you are skeptical re cold therapy, and I realize that even trying to do the breathing technique here could be a non-starter in your present condition, but this paper looks very solid to me and I think I would look into it more myself if facing a severe immune system challenge, so didn't want to keep to myself. That said, this response seems to propose that maybe the whole thing was just a placebo effect...http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4819555/
So just think of it as another wacky idea to consider...