CD38+CD101+ T cells, which characterize a permanently dysfunctional population of T cells, previously linked to post-stem cell transplant relapse in multiple myeloma (33), were present in 22.02 ± 7.6% of late relapsed multiple myeloma CAR T cells compared with 6.39 ± 0.9% in HD products (NS; Fig. 3E). Here, CD38 is linked to plasma cell myeloma.