Pre-Transplant Marrow CD3+ T cell Status and Outcomes in Newly Diagnosed Multiple Myeloma Undergoing Autologous Hematopoietic Cell Transplantation

T cells are key components of the adaptive immune system and play a critical role in tumor control and long-term cure. They can recognize and eliminate tumor cells directly or indirectly through cytokine release and Fas/FasL-mediated apoptosis. Recent advances in multiple myeloma (MM) treatment involving T cell–redirecting therapies such as bispecific antibodies and CAR-T cells have greatly improved outcomes, highlighting the importance of T-cell functionality. Given this, it remains unclear whether the baseline T-cell repertoire, particularly marrow CD3+ T-cell content, influences outcomes in newly diagnosed MM (NDMM) patients undergoing autologous hematopoietic cell transplantation (Auto-HCT). To evaluate whether pre-transplant marrow CD3⁺ T-cell levels are associated with post-transplant outcomes, including progression-free survival (PFS) and overall survival (OS), in NDMM patients undergoing Auto-HCT. We performed a retrospective single-institution study of 180 NDMM patients who underwent Auto-HCT between 2019–2024. Disease stage, cytogenetic risk, and depth of response before transplant (PR, VGPR, CR) were recorded, with post-transplant responses assessed at day +100. Flow cytometry of pre-transplant marrow quantified CD3+ T cells, using the median count of 440 as the cutoff for CD3-high (>440) and CD3-low (440 (HR 0.67; 95% CI 0.40–1.13; log-rank p =0.13). Pre-transplant marrow CD3+ T-cell levels did not significantly affect PFS or OS following Auto-HCT, though an early survival signal was observed among CD3-high patients. Further prospective studies exploring additional T-cell subsets (CD4, CD8) and their relationship with CD3 levels are warranted to clarify how immune repertoire diversity impacts post-transplant outcomes in NDMM.