[Delayed response with peripheral blood CD8+ T cell expansion during elranatamab therapy in relapsed/refractory multiple myeloma].

We report the case of an 81-year-old woman with relapsed/triple-class refractory multiple myeloma (IgA-λ type) complicated by acute kidney injury, who received elranatamab as seventh-line therapy. Serum free light chain (sFLC) levels decreased and renal function improved shortly after treatment initiation, and IgA declined after 4.9 months, ultimately resulting in a deep response. Notably, marked peripheral CD8+ T cell expansion was observed at the onset of response, and counts remained elevated during sustained remission. This case suggests that early sFLC reduction is a useful indicator for treatment continuation, and that peripheral CD8+ T-cell dynamics may serve as an on-treatment response biomarker for elranatamab therapy.