In MS organoids, particularly in PPMS, a decrease in the proliferation marker Ki67 and a reduction in the SOX2+ stem cell pool are associated with an increased expression of neuronal markers COUP-TF-interacting protein 2 (CTIP2) and T-box brain Transcription Factor 1 (TBR1), as well as a strong decrease in oligodendrocyte differentiation. Here, TBR1 is linked to myeloid sarcoma.