GTBP ▼ -7.1% - GT Biopharma, Inc. $GTBP - GT Biopharma Announces Potential New Indication for GTB-5550, a B7-H3-Targeted Natural Killer (NK) Cell Engager, for Multiple Myeloma GT Biopharma announced a potential new indication for its GTB-5550 candidate, a B7-H3-targeted NK cell engager, in multiple myeloma—a development that would typically support a stock but did not prevent a 7.1% decline today, suggesting investors may have focused on other factors such as timing, development stage, or broader market conditions. 15-SEP-2026 09:15 AM ET