Hi Leung, so sorry about your niece!
According to our doctor, the only benefit from a shorter length of time between ATGs is if you can do them within a month of each other. That way you can get a cumulative effect of the two together. Any longer than that, and the benefit is lost. That's why he started pushing for a second one after not seeing any improvement in my husband within the first month. Of course one month is too soon in most cases to see a response, so we wanted to wait, and eventually he did start to improve (tx-independant at 10 weeks).
Normally it is recommended to give it at least 6 months. Some responses do occur later on, but it is less common at that point. I don't really understand how it works either, since as you say, the ATG would no longer be in the system at that point. If your niece had not shown any response yet, I would say to give it at least six months. Since she did show an early response but has since declined, however, my feeling is that this may change the equation somewhat. Has anyone here had the experience of having counts rebound after a rise and drop like that? I'm wondering if that may have been all there is, in which case a second round might be better sooner rather than later. I'm just speculating, I'd welcome any input from someone with more experience.
-Lisa, husband Ken age 60 dx SAA 7/04, dx hypo MDS 1/06 w/finding of trisomy 8; 2 ATGs, partial remission, still using cyclosporine