As you recall, the chimerism is the percentage of donor cells vs Idan’s old immune cells. Ideally, post stem cell transplant there is no “chimerism,” but rather 100% donor cells on all four cell lines. Sadly, with Hyper IgM Syndrome, full donor engraftment seems to be hard to achieve. For Idan, the most important cell line is the T Cells or CD3, this is where his HIGM defect is. We started in the high 90’s but have watched it fall again in the last couple of months.
We’re testing Idan’s chimerism every 2-3 weeks and, for now, the chimerism still is falling at about the same rate. When Idan’s donor t-cells first dropped, they fell 6% over the course of 4 weeks, and another 6% over the next 4 weeks. Then another 5% over 3 weeks, and now another 2% over 2 weeks. If you plot these numbers on a graph, the trend is about the same with some very marginal (as in, single digit) improvement over the last two weeks, which is within the margin of error so not meaningful.
The plan we put in place last month was to taper off his immune suppressant (Tacro) in order to allow his donor cells to mature and perhaps put up a fair fight against Idan’s old T cells. There is no right or wrong approach, as we discussed in our last post. After a few weeks, we are almost off Tacro, and expect that things will continue to get worse for now since his donor cells are only starting to wake up after being suppressed since transplant. So far he has not had signs of GVHD (which is the main risk of getting of Tacro and allowing his donors cells to mature and grow), and we hope he stays clear of this complication.
Sometime in January we will have to decide on next steps. If the donor cells continue to drop, we may elect to give Idan a donor cell boost (DLI) to tip the scales in favor of the donor. Of course this DLI comes with an even higher risk of GVHD (he got acute skin GVHD last transplant after the DLI) and there is no guarantee this will work.
For now we are just hoping that we can stabilize his graft with a good high mixed chimerism, which would be enough for Idan’s cure. Hoping that 2017 turns out to be the year we finally have the cure we have been waiting for (sad thinking how many years we have been saying that).
Wishing you all a happy and healthy New Year!