Though I've been on combination therapy for several years, only in recent months have I developed a noticable shrinkage of subcutaceous tissue on my cheeks. I've heard of an experimental therapy in Europe. Are collegen injections a possible treatment? Cheek implants? Any other advice?

There are a number of different therapies for facial fat loss, but unfortunately none of them work particularly well. They include discontinuation or change of the antiretrovirals that you're on, discontinuation of any androgens (e.g., testosterone), and injection of collagen/silicone/polylactic acid. The last agent is probably the experimental agent you heard about and it has achieved some success in European trials. There are plastic surgeons and dermatologists that will treat facial fat loss, but you should check on experience and long-term success before accepting any treatment, since it can be quite expensive.