On the morning of Day +31, we got further clarification from the doctor overseeing the treosulfan trial. She said not to worry about the B cell percentage because B cells can take 6 months or more to develop. We were more worried about the T cells which were at 76%; the doctor said that this is within the expected range for the first chimerism result for this chemo protocol, and she expects the percentage of donor T cells to increase by the next sorted chimerism test.
The NK and myeloid cells were at 100% donor, which is very good. Last year's first chimerism test in L.A. was unsorted, meaning the "78%" last year was an overall indication of engraftment and was not broken down by each type of white blood cell. The Seattle doctor overseeing the treosulfan trial said that an overall/unsorted chimerism test is heavily influenced by myeloid cells, so given last year's first test result of an overall 78%, Jacob probably had a much lower percentage of donor myeloid cells shortly after last year's transplant than he does this year.
All things considered, Jacob's initial chimerism result is better than we thought when we first got the numbers. After hearing the doctor's interpretations, we feel better about it than we did the night before.
We nevertheless remain slightly cautious about getting overly optimistic at this point. While we trust this doctor's expertise, last year's experience still haunts our memories.
Because of Jacob's history of losing his graft last year, the team will be extra cautious and will do the second sorted chimerism test on Day +56 (instead of the usual Day +80). This will allow for earlier detection if the graft starts decreasing, and it will provide more time for corrective action if necessary.